Title of Invention	A CORIOLIS MASS FLOW SENSOR
Abstract	A Coriolis mass flow sensor (1) is disclosed. The Coriolis mass flow sensor comprises a flow sensor tube (16) having first and second ends, and first and second piezoelectric stacks (42) positioned on the respective first and second ends of the flow sensor tube (16), wherein the piezoelectric and reverse piezoelectric effects cause the flow sensor tube (16) to vibrate and sense the twist in the flow sensor tube (16) due to Coriolis force.

Title of Invention

A CORIOLIS MASS FLOW SENSOR

Abstract

A Coriolis mass flow sensor (1) is disclosed. The Coriolis mass flow sensor comprises a flow sensor tube (16) having first and second ends, and first and second piezoelectric stacks (42) positioned on the respective first and second ends of the flow sensor tube (16), wherein the piezoelectric and reverse piezoelectric effects cause the flow sensor tube (16) to vibrate and sense the twist in the flow sensor tube (16) due to Coriolis force.

Full Text	1. FIELD OF THE INVENTION The invention relates generally to a mass flow measurement and control and more particularly, to a mass flow measurement, a Coriolis mass flow sensor and controller based on the Coriolis force effect and having an integrated flow control valve with associated sense, control and communication electronics. This invention also relates to a device and a method for determining mass flow from a Coriolis force induced phase shift. The present invention has been divided out of Indian Patent Application No. IN/PCT/2001/00505. 2. DESCRIPTION OF RELATED ART Mass flow measurement based on the Coriolis force effect is achieved in the following manner. The Coriolis force results in the effect of a mass moving in an established direction and then being forced to change direction with a vector component normal to the establshed direction of flow. This can be expressed by the following equation : Fc = M x Ω Where Fc (the Coriolis force vector) is the result of the cross product of M (the mass flow vector) and ω (the angular velocity vector). In a rotating system, the angular velocity vector is aligned along the axis of rotation. Using the "Right Hand Rule", the fingers define the direction of rotation and the thumb, extended, defines the angular velocity vector direction. In the case of the typical Coriolis force flow sensor, a tube, through which fluid flow is to be established, is vibrated. Often the tube is in the shape of one or more loops. The loop shape is such that the mass flow vector is directed in opposite directions at different parts of the loop. The tube loops may, for example, be "U" shaped, rectangular, triangular or "delta" shaped or coiled. In the special case of a straight tube, there are two simultaneous angu ar velocity vectors that are coincident to the anchor points of the tube while the mass flow vector is in a single direction. The angular velocity vector changes directions since, in a vibrating system, the direction of rotation changes. The result is that, at any given time, the Coriolis force is acting in opposite directions where the mass flow vectors or the angular velocity vectors are directed in opposite directions. Since the angular velocity vector is constantly changing due to the vibrating system, the Coriolis force is also constantly changing. The result is a dynamic twisting motion being imposed on top of the oscillating motion of the tube. The magnitude of twist is proportional to the mass flow for a given angular velocity. DE 19,605,923, GB 2,221,302, WO 92/14123 and US Patent No. 4747312 disclose examples of flowmeters. Ir Coriolis flowmeters, flow measurement is achieved by measuring the twist in the sensor tube due to the Coriolis force generated by a fluid moving through the sensor tube. Typical known devices use pick off sensors comprising magnet and coil pairs located on the flow tube where the Coriolis force's induced displacement is expected to be greatest. The coil and magnet are mounted on opposing structures, for example, the magnet is mounted on the tube and the coil is mounted on the stationary package wall. The magnet will move in and out of the coil, inducing a current in the coil. This current is proportional to the velocity of the magnet relative to the coil. Since this is a ve ocity measurement, the velocity, and thus the signal, is at the maximum when the flow tube crosses its rest point (zero crossing). The Coriolis force induced twist causes a phase shift in the velocity signal. The phase is detected by measuring the difference in the zero crossing times between the two velocity sensors. In practice this places a large accuracy burden on the time measurement circuitry. This may limit the ultimate sensitivity of mass flow measurement by this technique. Further, the flow rate capabilities of known devices based on Coriolis technology often are limited to flow rates that are higher than desired for many applications. Moreover, existing Coriolis mass flow measuring devices only provide for mass flow sensing with no integral flow control capabilities. It has been left to the user to provide any means for controlling flow. The present invention addresses shortcomings associated with the prior art. SUMMARY OF THE INVENTION Indian patent application No. IN/PCT/2001/00505 discloses a capacitive pick off sensor for a mass flow measurement device comprising a flow sensor tube and a drive device for vibrating the flow sensor tube, the capacitive pick off sensor being characterized by : at least one conductive plate connectable to a first voltage potential and adapted to be situated adjacent a flow sensor tube connected to a second voltage potential, so as to define a gap between the flow sensor tube and the conductive plate ; such that the capacitance between the conductive plate and the flow sensor tube varies due to the relative motion of the conductive plate and the flow sensor tube when the flow sensor tube is vibrated. The present invention provides a Coriolis mass flow sensor, comprising : a flow sensor tube having first and second ends ; and first and second piezoelectric stacks positioned on the respective first and second ends of the flow sensor tube ; wherein the piezoelectric and reverse piezoelectric effects cause the flow sensor tube to vibrate and sense the twist in the flow sensor tube due to Coriolis force. The present invention also discloses a Coriolis mass flow controller, comprising : a flow sensor tube ; a drive device situated relative to the flow sensor tube so as to cause the flow sensor tube to vibrate ; a position sensing device situated relative to the flow sensor tube so as to measure the twist in the flow sensor tube due to Coriolis force ; and a flow control portion adapted to receive fluid from the flow sensor tube. The present invention further provides a device for determining mass flow from a Coriolis force-induced phase shift between first and second input signals detected by first and second displacement gauges, comprising : a first phase sensitive detector coupled to receive the first and second input signals, the first phase sensitive cetector operable to mix the first and second input signals and pro/ide an output representing the mixed first and second input signals ; a first phase shifter coupled to receive the first input signal and operable to output a signal representing the first input signal phase shifted 90°; a second phase sensitive detector coupled to receive the first phase shifter output and the second hput signal, the second phase sensitive detector operable to mix the phase shifted first input signal and the second input signal and provide an output representing the mixed signals ; and a processor coupled to the first and second phase sensitive detectors to receive the mixed signals and operable to calculate the vector magnitude and phase of the mixed signals relative to each other, wherein the vector phase is proportional to mass flow. The present invention in addition provides a method of determining mass flow from a Coriolis force-induced phase shift between first and second input signals detected by first and second displacement gauges, comprising : mixing the first input signed with the second input signal to produce a first output signal ; phase shifting the first input signal 90° ; mixing the second input signal with the phase shifted first input signal to produce a second output signal; and calculating the vector magnitude and phase of the first and second output signals relative to each other, wherein the vector phase is proportional to mass flow. Lastly, the present invention provides a device for determining mass flow from a Coriolis force-induced phase shift between first and second input signals detected by first and second disolacement gauges, comprising : a differential amplifier coupled to receive the first and second input signals, the differential amplifier operable to output a signal representing the difference between the first and second input signals ; a first phase sensitive detector coupled to receive the output of the differential amplifier and the first input signal and provide an output representing the mixed differential amplifier signal and the first input signal; a phase shifter coupled to receive the first input signal and operable to output a signal representing the first input signal phase shifted 90° ; a second phase sensitive detector coupled to receive the phase shifter output and the differential ampl fier signal and provide an output representing the mixed phase shifted first input signal and the differential amplifier signal, and provide an output representing the mixed signals ; and a processor coupled to he first and second phase sensitive detectors to receive the mixed signals and operable to calculate the vector magnitude and phase of the mixed signals relative to each other, wherein the vector phase is proportional to mass flow In one aspect of the present invention, a capacitive pick off sensor for a mass flow measurement devce is disclosed. The mass flow measurement device includes a flow sensor tube and a drive device for vibrating the flow sensor tube. The capacitive picK off sensor includes at least one conductive plate connectable to a first voltage potential and adapted to be situated adjacent the flow sensor tube which is connected to a second voltage potential. The conductive plate is positioned relative to the flow sensor tube so as to define a gap therebetween. The capacitance between the conductive plate and the flow sensor tube varies due to the relative motion of the conductive plate and the flow sensor tube when the flow sensor tube is vibrated. In another aspect of the present invention, a Coriolis mass flow sensor includes a flow sensor tube, a drive device situated relative to the flow sensor tube so as to cause the flow sensor tube to vibrate, and capacitance displacement gauges situated relative to the flow sensor tube so as to measure the twist in the flow sensor tube due to Coriolis force. In specific embodiments, electromagnetic, electrostatic, acoustic, and/or piezoelectric drives are used to vibrate the flow sensor tube. In still further embodiments, piezoelectric devices are used both to vibrate the flow sensor tube and measure the twist in the flow sensor tube. In yet another aspect of the present invention, a Coriolis mass flow controller includes a flow sensor tube, a drive device situated relative to the flow sensor tube so as to cause the flow sensor tube to vibrate and a position sensing device situated relative to the flow sensor tube so as to measure the twist in the flow sensor tube due to Coriolis force. The Coriolis mass flow controller further includes an integrated flow control device adapted to receive fluid from the flow sensor tube. Such an integrated flow control device and associated sensing electronics provide a more compact package that is easier to use and provides significant improvement in dynamic performance. In a further aspect of the present invention, a Coriolis mass flow sensor includes a flow sensor tube, a housing having the flow sensor tube situated therein, a drive device positioned outside the housing for vibrating the flow sensor tube, and at least one pick off sensor situated relative to the flow sensor tube so as to measure the twist in the flow sensor tube due to Corioiis force. In exemplary embodiments, the pick off sensors are situated in the housing. In further embodiments, a magnet is coupled to the flow sensor tube, and the drive device comprises an electromagnetic coil. The magnet may be a non-rare earth magnet, and more specifically, a nickel plated samarium cobalt magnet. The electromagnetic coil may comprise a power inductor. In accordance with still further aspects of the present invention, a mass flow measurement device includes an enclosure having first and second ends, a flow body, and a first sealing member situated relative to the enclosure first end and the flow body such that the flow body and the first end are connected in a sealed manner. A user interface assembly and a second sealing member are situated relative to the enclosure second end such that the user interface assembly and the second end are connected in a sealed manner. The sealing members allow interchanging among multiple types of user interface assemblies, including a user interface assembly that is IP-65/NEMA 4X compliant, and provide additional fluid containment. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon, reference to the accompanying drawings whereir : Figure 1 is a block diagram conceptually illustrating a Coriolis mass flow sensor in accordance with aspects of the present invention ; Figures 2A and 2B illustrate a Coriolis mass flow sensor employing an electromagnetic drive in accordance with an embodiment of the present invention ; Figures 3A and 3B illustrate a Coriolis mass flow sensor employing an electrostatic drive in accordance with an embodiment of the present invention ; Figures 4A and 4B illustrate a Coriolis mass flow sensor employing an acoustic drive in accordance with an embodiment of the present invention ; Figures 5A, 5B and 5C illustrate a Coriolis mass flow sensor employing a piezoelectric drive in accordance with an embodiment of the present invention ; Figure 6 is a schematic of a lock-in amplifier for measuring the Coriolis force induced phase shift in accordance with the present invention ; Figure 7 is a schematic of a dual channel lock-in amplifier for measuring the Coriolis force induced phase shift in accordance with the present invention ; Figure 8 is a graph illustrating the relationship between the amplitudes of input signals from sensor tube position sensors using signal processing methods in accordance with the present application Figure 9 is a schemalic of a dual lock-in amplifier for measuring the Coriolis force induced phase snift in accordance with the present invention ; Figure 10 is a schematic of a dual lock-in amplifier including reference frequency adjustment for measuring the Coriolis force induced phase shift in accordance with the present invention ; Figure 11 illustrates a first embodiment of a capacitive displacement probe in accordance with the present invention ; Figure 12 illustrates a second embodiment of a capacitive displacement probe in accordance with the present invention ; Figure 13 illustrates a third embodiment of a capacitive displacement probe in accordance with the present invention ; Figure 14 is a perspective view of a Coriolis mass flow controller in accordance with an embodiment of the present invention ; Figure 15 is a sectional view of the Coriolis mass flow controller shown in Figure 14 ; Figure 16 is an exploded view of the Coriolis mass flow controller shown in Figure 15 ; Figures 17 A and 17B i lustrate aspects of a prior art threaded valve connection and a sealed threaded valve connection in accordance with the present invention, respectively ; and Figure 18 is a perspective view of an embodiment of a Coriolis mass flow controller in accordance further aspects of the present invention. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as hereinafter claimed. DETAILED DESCRIPTION OF THE INVENTION Illustrative embodiments; of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system- related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. Figure 1 is a block diagram conceptually illustrating a Coriolis mass flow sensor in accordance with aspects of the present invention. The Coriolis mass flow sensor 1 includes a flow sensor tube 2, with a drive device 3 situated relative thereto so as to vibrate the tube 2. Displacement gauges 4 are positioned relative to the tube 2 so as to measure the twist in the tube 2 due to Coriolis force. A typical material for the sensor tube 2 is 316L stainless steel. Reasons for using 316L stainless steel include that it is resistant to chemical attack from many substances, it is resistan' to rupture from normal process pressures, it is typically noncontaminating and can be readily formed to the desired shape of a Coriolis sensor tube. However, 316L. stainless steel is not suitable for all applications. Therefore, it is necessary that other tube materials be available to cover applications not suitable for 316L stainless steel. Known devices use silicon as an alternative materia to 316L. stainless steel. The advantage of silicon over 316L stainless steel is that sensor tubes can be made in a smaller form than can be realized by 316L stainless steel. Another consideration far material selection for the sensor tube 2 is the resistance to stress induced or enhanced corrosion. Stress is generated at the base of the bending arm where the tubes are mounted. In polycrystalline materials stress will cause impurities in the material to diffuse and concentrate at grain boundaries between the microcrystalline granular regions. This will, in many cases, weaken the bonds between the microcrystalline grains making the material to be more susceptible! to chemical attack. Single crystal materials like silicon or sapphire are less likely to be affected in this manner. Metals, like 316L stainless steel are usually polycrystalline and therefore more susceptible to this type of chemical attack to varying degrees. Amorphous materials like silica glass and several plastics also are more resistant to stress induced chemical attack, since they do not have a grain structure like polycrystalline materials. Tube materials that are susceptible to chemical attack may have their surfaces modified or coated in such a way as to minimize corrosion or attack at the surfaces if the use of the underlying material is otherwise attractive. Surface modification may be accomplished by ion implantation, thermal diffusion, and chemical or electrochemical reaction. The intent; here, is to remove, redistribute, or introduce elemental or molecular species that leave a chemically resistant layer at the surface. Surface coating may be accomplished by thermally activated deposition from a vapor, liquid or powder impinging on the surface at elevated temperaures. Lower temperatures may be used if the chemically reactive species is also excited or ionized by plasma or an intense photon flux as from a laser. Other materials resistant to chemical attack may be deposited by nonreactive, physical vapor deposition as accomplished by thermal or electron beam evaporation or by ion sputtering. If sputtering is accomplished using a highly energetic ion beam so that the sputtered species is chemically excited or ionized, then a chemical reaction with the surface is also accomplished, which may be desirable for certain deposited materials. Also, chemical reactions at the surface may be accomplished by accelerating the chemical species so that the kinetic energy can be used to activate or enhance the chemical reaction. Tube materials used for the Coriolis flow sensing tube 2 in particular embodiments of the present irvention are Austenitic and Martensitic stainless steels, high nickel alloys, Titanium and Zirconium and their alloys, particularly Titanium-Vanadium-Aluminum alloys and Zircalloy (for their high yield strength and low Young's modulus), silcon, sapphire, silicon carbide, silica glass and plastics. Tube coating materials employed in accordance with the present invention include silicon carbide, nickel, chrome, diamond, refractory carbides, refractory metal nitrides, and refractory metal oxides. Figures 2A and 2B illustrate a Coriolis mass flow sensor 1 in accordance with particular embodiments of the present invention. The Coriolis mass flow sensor 1 employs an electromagnetic drive 10 that includes an electromagnet 12 driven by a signal source (not shown), which, in the embodiment illustrated, comprises a sinusoidal signal source. The electromagnet 12 is situated near a small permanent magnet 14 mounted on a sensor tube 16. The sensor tube 16 is connected to a base 18 that includes first and second ports 19, so as to define a flow path from one port 19 through the flow tube 16 to the other port 19. The exemplary sensor tube 16 shown in the embodiments disclosed herein is generally "U" shaped, though o:her shapes, such as delta shaped, rectangular, coiled, or straight tubes may also be used. Figures 3A and 3B illustrate an embodiment similar to that shown in Figure 2, using an electrostatc drive. The electrostatic drive 20 includes a charge plate 22 positioned near a small dielectric plate 24 mounted on the sensor tube 16. If the tube 13 is made of dielectric material, then the charge plate 22 is positioned near the tube 16 and the dielectric plate 24 may be eliminated. Again, the charge plate is driven by a signal source (not shown), such as a sinusoidal signal SOL rce. A voltage applied to the charge plate 22 will produce an electric field between it and the dielectric plate 24. This will produce a surface charge on the dielectric plate 24. As the voltage polarity is rapidly changed on the charge plate 22, the resultant electric field between it and the dielectric plate 24 will alternately be attractive or repulsive causing the flow tube 16 to vibrate. Figures 4A and 4B illustrate another embodiment of the Coriolis mass flow sensor 1 that employs a novel acoustic drive 30. The acoustic drive 30 includes a small speaker 32 placed nea'the tube 16. The pressure waves generated by the speaker 32 cause the tube 16 to vibrate. In Figures 5A, 5B and 5C, yet another embodiment of the Coriolis mass flow sensor 1 is illustrated. The Coriolis mass flow sensor 1 of Figures 5A, 5B and 5C uses a piezoelectric drive 40, wherein two piezoelectric stacks 42 are positioned on opposite sides of each leg of the flow tube 16, in effect creating two bimorphs on each leg 16 as shown in Figure 5. The piezoelectric and reverse piezoelectric effects would be used to either drive and/or sense the deflection of the tube 16. Mass flow measurement s achieved by measuring the twist in the sensor tube 16 due to the Coriolis force generated by a fluid moving through the sensor tube 16. For example, pick cff sensors comprising magnet and coil pairs are typically located on the flew tube 16 where the Coriolis forces induced displacement is expected to be greatest. The coil and magnet are mounted on opposing structures, for example, the magnet is mounted on the tube 16 and the coil is mounted on the stationary package wall. The magnet will move in and out of the coil, inducing a current in the coil. This current is proportional to the velocity of the magnet relative to the coil. Since this is a velocity measurement, the velocity, and thus the signal, is at the maximum when the flow tube 16 crosses its rest point (zero crossing). The Coriolis force induced twist causes a phase shift in the velocity signal that is detected by measuring the difference in the zero crossing times between the two velocity sensors. In practice this places a large accuracy burden on the time measurement circuitry. This may limit the ultimate sensitivity of mass flow measurement by this technique. Aspects of the present nvention provide a flow measurement technique that provides for a lower flow capability, is more direct and requires less accuracy in the circuitry than typical time' based signal conditioning techniques. Referring to the embodiments illustrated in Figures 2-4, displacement of the vibrating sensor tube is measured usirg capacitive pick off sensors. Two capacitance displacement gauges 50 are positioned near the tube 16 at positions symmetric to the shape of the tube 16 so as to measure the twist in the sensor tube 16 due to the Coriolis force generated by a fluid moving through the sensor tube 16. In specific embodiments of the present invention, the capacitance displacement gauges 50 are miniaturized and surface mounted on the sensor package wall or on a sensor block inserted inside the loop of the flow sensor tube. The twist in the sensor tube 16 due to the Coriolis force results in a phase shift between the two signals from the capacitance displacement gauges 50. Since this is a displacement measurement, the signal is directly proportional to the displacement. The relative displacement of each side of the tube is measured as a phase shift. The gauge driver and signal conditioning electronics translate the relative displacement of the tube 16 into a high level signal which is a function of the phase shift that can be used to measure the Coriolis effect when flow is established through the tube 16. A first signal processing technique uses a lock-in amplifier with a reference signal supplied by one of the displacement gauges 50, and an input signal supplied by the other displacement gauge 50. Either gauge 50 may supply the reference or the input signal. The phase output from the lock-in amplifier is proportional to flow. Figure 6 is a functional schematic of a lock-in amplifier 52, with which such a method for measuring the Coriolis force induced phase shift in accordance with the present nvention may be implemented. The signals are moving left to right as illustrated in Figure 6. The Left input 100 and Right input 102 signals are from the Left and Right displacement gauges 50 respectively. For example, the Left input 100 may be used as the reference signal. The sine out 103 is the drive signal, phase locked to the Left input 100 signal. This will drive the flow sensor tube 16 at resonance. The Right Input 102 signal is mixed with the Left/Reference Input 100 signal and its 90° phased shifted signal 104 in the two Phase Sensitive Detectors (PSDs) 106. Functionally, the PSDs 106 multiply the two signals, producing a high frequency component and a DC component. The low pass filters 108 remove the high frequency component producing a DC voltage at the X and Y outputs 110, 112. The X output 110 is called the "in-phase" component and the Y output 112 is called the "quadrature" component of the vector signal relative to the reference signal. Each of these components is phase sensitive; however, the vector magnitude and phase components can be separated by the following relationships : The relationship between the outputs from the lock-in amplifier 52 and the inputs from the displacement gauges 50 is derived as follows : Consider the two signas as sine waves with arbitrary amplitudes and arbitrary phase difference. Each signal can be represented as below : At the bottom PSD 106 the following operation occurs : This signal has a DC vo tage component and an AC component at twice the frequency. The Low Pass Filter (L.PF) 108 removes the AC component leaving At the top PSD 106 the folowing operation occurs : We have a cosine multiplier since cos ωt = sin(ωt + 90°). Again, we have a signal with AC and DC components, which after passing through the LPF 108, results in the following : Calculating the magnitude, R, and the phase angle, 8, from equations 1 and 2 we have : and These calculations may be executed by any suitable digital or analog processing device 120. The vector phase is proportional to mass flow. Another method in accordance with embodiments of the invention requires a dual channel lock-in amplifier with the reference signal and one input signal supplied by one of the displacement gauges 50 and a second input signal supplied by the other displacement gauge 50. The difference between the two input signals is then measured against the reference signal. The resultant phase output from the lock-in amplifier is proportional to flow. Figure 7 is a functional schematic of a dual channel lock-in amplifier 54. The signals are moving in the same manner and have the same definitions as in Figure 6. The Left input 100 is also used as the reference signal. As before, the sine out 103 is the drive signal, phase locked to the Left input 100 signal. in this case, the Left Input 100 signal is subtracted from the Right Input 102 signal and mixed with the Left/Reference Input 100 signal and its 90° phased shifted signal 104 in the two Phase Sensitive Detectors (PSDs) 106. The internal functions are the same as in the lock-in amplifier 52 of Figure 6. The following derivation may be used to determine the relationship between the outputs from the lock-in amplifier 54 and the inputs from the displacement gauges 52. Any suitable digital or analog processing device 120 may be used to perform the calculations. Consider the two signals as sine waves with arbitrary amplitudes and arbitrary phase difference. Each signal can be represented as below : Vleft= Vref= A Sin at VrigM™B sin (ot + $) The output of the Low No se Differential Amplifier 114 in this case will be At the bottom PSD 106 the following operation occurs : This signal has a DC voltage component and an AC component at twice the frequency. The Low Pass Filter (LPF) 108 removes the AC component leaving At the top PSD 106 the following operation occurs : We have a cosine multiplier since cos ωt = sin (ωt + 90°). Again, we have a signal with AC and DC components, which after passing through the LPF, results in the following ; Calculating the magnitude, R, and the phase angle, θ, from equations 1 and 2 we have : and θ is no longer the phase angle, but is the arctangent, a function of the phase angle and the amplitudes of the Left and Right input signals. Analysis of this equation shows that θ is a strong function of Φ. In fact, the relative amplitudes of the input signals can control the strength of this function. This can be illustrated in graph shown in Figure 8, in which A and B are the amplitudes of the Left and Right signals respectively. As the amplitudes are more closely matched, the sensitivity is higher for the lock-in amplifier output, 6. Even for amplitudes that are matched within 2%, the sensitivity of θ to Φ is nearly 100 times that of the standard lock-in amplifier configuration. Figure 9 is a functional schematic of a dual lock-in amplifier 56 with which another exemplary method for measuring the Coriolis force induced phase shift in accordance with the present nvention is implemented. The signals are moving in the same manner and have the same definitions as disclosed above. The Left input 100 is also used as the reference signal. As before, the sine out 103 is the drive signal, phase locked to the Left input 100 signal. In this case, the Left Input 100 signal is mixed with itself and its 90° phased-shifted signal in the two Phase Sensitive Detectors (PSDs) 106 in the top lock-in amplifier 58. In the bottom lock- in amplifier 60, the Right Input ' 02 signal is mixed with the Left Input 100 signal and its 90° phased-shifted signal in the two Phase Sensitive Detectors (PSDs) 106. The paired outputs from the non-phase shifted PSDs 106 and phase shifted PSDs 106 are differentiated in the two Low Noise Differential Amplifiers 114. The DC components of the signals are passed by the Low Pass Filters 108 to give the usual lock-in amplifier outpu:s. The mathematics, which may be executed by any suitable digital or analog processing device 120, are the same as in the method outlined above in conjunction with Figure 7, though the order in which the operations occur is different. In the Dual Channel Lock-in technique of Figure 7, two high level signals, with very small differences are subtracted. The low-level signal is then multiplied with a high level signal, which can introduce noise in analog circuits or round off errors in digital circuits. In the Dual Lock-in technique of Figure 9, the high level signals are first multiplied and the resulting signals, which are close in amplitude, are then subtracted resulting in an output with lower noise. A lock-in amplifier's use is most notable with respect to measuring a low- level signal that is buried in noise of a much higher amplitude. The lock-in amplifier accomplishes this by acting as an extremely narrow bandpass filter. The signal and noise is multiplied by a reference sine and cosine wave, and then passed through a low-pass filter to remove the reference frequency. The result of the multiply/filter operations are DC signals that represent a complex vector (x + iy). The phase difference between the reference frequency and the signal of interest can be determined by atan(y/x). In terms of measuring Coriolis force, the phase difference between two signals of the same frequency is of interest. This can be accomplished using dual lock-in amplifiers, each driven with the same reference frequency as shown in Figure 10. In the functional schematic illustrated in Figure 10, Left and Right input signals 100, 102 are multiplied by reference sine and cosine waves provided by a reference frequency generator 144. The input signals 100, 102 are mixed with the sine and cosine signals in PSDs 106, then passed through fifth- order bessel IIR low pass filters 148 as described in conjunction with Figure 6, Figure 7 and Figure 9. The multiply/filter process described above is performed on the Left and Right input signals 100, 102 with a resulting phase difference output X, Y of each signal with respect to the reference frequency. The difference between the two output signals X, Y represents the phase difference between the two input signals 100, 102. In the case of Coriolis mass flow, this phase difference represents an indication of mass flow 152. When using lock-in amplifiers to measure the extremely small phase differences associated with Coriolis mass flow, it is necessary to adjust the reference frequency to match the signal of interest. If the reference signal is not very close to the signal of interest, a very low frequency AC signal will appear at the outputs of the low-pass fiters 148. The frequency of the Coriolis sensor changes with mass flow, temperature, density and pressure, further complicating the measurement process. The reference frequency can be adjusted accurately by processing the output vector from one of the input signals 100, 102. First, the derivative of the output vector is calculated. This may be accomplished by calculating the complex difference between two consecutive output vectors. Then, the original output vector is rotated 90 degrees and the dot product of this vector and the derivative is calculated, resulting in an error signal 150 that is provided to the reference frequency generator 144. The error signal 150 is negative, positive, or zero, if the reference frequency needs to be adjusted down, up or unchanged, respectively. The amount of reference frequency adjustment is dependent on the accuracy of the phase measurement, but generally, the finer the adjustment, the better the accuracy as determhed by calculating the standard deviation over a number of output samples. However, the finer adjustment (small step changes) of reference frequency will be detrimental if there are step changes in the signal frequency, as the reference frequency generator 144 will take too long reaching the intended frequency. If the signal frequency experiences frequent step changes, a PID or adaptive algorithm can be used to adjust the reference frequency in a more responsive manner. In alternative embodiments, the capacitance displacement probes 50 may be mounted on piezoelectric actuators that would, first, align the capacitance displacement probes 50 in three dimensions. Further, when used with the dual channel lock-in amplifier or dual lock-in amplifier methods disclosed herein, the piezoelectric actuators can dynamically adjust the sensitivity of the flow sensor, thereby providing an extended range of operation. Such dynamic positioning provides compensation for manufacturing variability, particularly the positioning of the flow sensor tube relative to the capacitance displacement probe. Dynamic positioning also provides compensation for dimensional shifts due to relative thermal expansion of the various components. Used in combination with the dual channel lock-in amplifier or dual lock-in amplifier, dynamic positioning allows the two displacement signals to be closely matched to provide an adjustable sensitivity to flow. A low sensitivity would be used for high flow conditions while high sensitivity would be used for extended low flow conditions thereby increasing the dynamic range of flow measurement. Embodiments of the present invention additionally provide improved capacitance measurement techniques, specifically, a novel geometry of the capacitance displacement probe. Normally, the displacement of an object is measured as a distance normal to the capacitance displacement probe. The displacement may also be measured as a distance tangential to the capacitance displacement probe. Referring o Figure 11, this can be accomplished by placing two plates 130 side by side with a uniform gap 132 between the plates 130 and placed near a sensor tube 134 in the plane tangential to the motion (indicated by the arrow 136) as shown in Figure 11. In one embodiment, the plates 130 will be at the same potential and the sensor tube 134 will be at ground potential. The sensor tube 134 is positioned directly over the gap 132 between the plates 130 with the expected motion 136 normal to the gap so that cyclic motion of the sensing tube 134 will position the tube 134 more closely to one plate 130 than the other 130. The relative capacitance is measured between each of the plates 130 and the sensor tube 134. As the sensor tube 134 moves over one plate 130 or the other, the amount of area contributing to the capacitance will change and thus the relative capacitance measured. An alternative configuration has the gap 132 running diagonally across the sensor tube 134 as shown in Figure 12. This allows a less precise placement of the sensor tube 134 over the plane of the plates 130. Misalignment of the sensor tube 134 will cause a smaller mismatch in the signal as compared to the parallel gap 132. A further embodiment has the gap 132 in a "saw tooth" pattern as shown in Figure 13. This is an improvement over the diagonal gap 132 in that an angular misalignment of the .sensor tube 134 with respect to the gap 132, whether parallel or diagonal, will cause a difference in the rate of change of capacitance between the two plates 130. This will introduce an unwanted change in phase between the two signals. The "saw tooth" pattern will average out any angular misalignment of the sensor tube 134, providing more symmetrical signals. Figure 14, Figure 15 and Figure 16 illustrate an exemplary low flow Coriolis mass flow controller 200 in accordance with an embodiment of the present invention. The Coriolis mass flow controller 200 includes a flow sensor portion 202 and a flow control portion 204. A processor either internal or external to the mass flow controller 200 receives an indication of a set point, or desired mass flow. The set point value is compared to the actual mass flow as indicated by flow sensor portion 202 to generate an error value. The flow control portion 204 includes a valve that is manipulated to adjust the flow rate and minimize the error. The implementation of particular control schemes would be a routine undertaking for one skilled in the art having the benefit of this disclosure, and thus, the specifics of such an implementation are not addressed in detail herein. The flow sensor portion 202, which is surrounded by an enclosure 205, includes a sensor tube 206 that is bent into a loop shape, a drive device 208 and two pick off sensors 210 positioned at opposite sides of the sensor tube 206 that measure the displacement of the sides of the sensor tube 206. In existing Coriolis devices, the sensor is typically enclosed in a welded metal housing. The sensor tube within the housing also has attached to it displacement or velocity sensors with wires connecting through feedthroughs to electronics outside the housing The sensor tube in such devices is relatively large and has a resonant frequency that is about 100 Hz. For smaller sensor tubes, as in embodiments of he present invention, the resonant frequency is somewhat higher, on the order of 200 Hz and greater. As the frequency increases, there will be an increased viscous damping effect due to the atmospheric conditions inside the sensor enclosure. By evacuating the enclosure and utilizing vacuum compatibe materials inside the enclosure, the viscous damping can be reduced or' even eliminated. Thus, in the exemplary embodiment illustrated, the sensor tube 206 is situated within a vacuum sensor housing 207. The sensor tube 206 is designed 1:o allow elastic bending orthogonal to a line connecting the legs of the tube's loop. The loop is wide enough to allow elastic twisting about the center ine of the loop. In order to measure the Coriolis force at low flows, the sensor tube 206 mass needs to be minimized. Tube sizing is critical since the tube needs to be small, yet still capable of retaining the fluids at extended pressures. It is a so preferable for the pick off sensors 210 to be non-contact since any contact with the tube 206 or mass loading on the tube 206 may suppress the Coriolis force. Pick off sensor technologies may include capacitive, magnetic, piezoresistive and optical. Piezoresistive, strain gauge displacement sensors do contact the tube but at the base of the loop where the displacement is minimum and the strain is the highest. This would have minimal effect on the tube's vibration. Optical technologies include various laser and white light interferometric displacement techniques, triangulation techniques, multiple internal reflection and beam occultation techniques. Magnetic displacement technologies include Hall effect, eddy current, variable reluctance and magnetoresistive techniques. Capacitive pick off sensor technology is used in the illustrated embodiment because it has the sensitivity required to measure the tube displacement, it is noncontact, and would not be affected by a magnetic drive device. The capacitive pick off sensors 210 each include at least one conductive plate 300, which is connected to a given voltage potential and situated adjacent the flow sensor tube 206 so as to define a gap therebetween. The flow sensor tube 206 is connected to a voltage potential different than the conductive plate 300. The capacitance between the conductive plate 300 and the flow sensor tube 206 varies due to the relative motion of the conductive plate 300 and the flow sensor tube 206 when the flow sensor tube is vibrated 206. In the illustrated embodiment, the conductive plates comprise first and second plates as disclosed above in conjunction with Figures 11-13. In the particular embodiment illustrated, saw-tooth shaped plates, as illustrated in Figure 13, are employed. The capacitive pick off sensors 210 are assembled into an integrated sensor block 301 sized to fit into the sensor enclosure 207, dimensionally referenced to the back wall of the enclosure 207 by press pins 302. The conductive plates 300 of the capacitive pick off sensors 210 are manufactured on a multilayer printed circuit board so as to provide a guard layer to minimize parasitic capacitance and a back contact layer for soldering to the sensor block 301. Since the capacitive pick off sensors 210 are required to operate in a vacuum, low outgassing materials are used in the illustrated embodiment. Standard fiberglass materials are not vacuum compatible. Desired material characteristics include that it be vacuum compatible, solderable, bondable into multilayers with a low outgassing bond and that it have a low dielectric constant for simple guard layer design. In a specific embodiment, commercially available DRUOID is used. The sensor block 301 containing the capacitive pick off sensors 210 can be adjusted to optimize the spacing to the sensor tube 206. This is accomplished using electron discharge machined hinge plates. Tapered set screws spread gaps to effect linear and angular movement of the capacitive pick off sensors. Further, the conductive plates 300 of the capacitive pick off sensors include contact pads that allow wires to be soldered or wire bonded to a printed circuit board 303 on the front of the sensor block interconnecting the capacitive pick off sensors 210 with a hermeticaly sealec electrical connector that interfaces with capacitance displacement electronics outside the sensor enclosure 207. The drive device 208 drives the tube 206 into a bending mode, vibration, causing it to vibrate. In the illustrated embodiment, the drive device 208 consists of a small magnet 304 soldered on the sensor tube 206 and a small electromagnetic coil 306 to al ernately push and pull on the magnet 304. In the embodiment shown in Figure '6, a non-rare earth magnet, and more particularly, a nickel plated samarium cobalt magnet is used. The samarium cobalt magnet has a good magnetic strength to weight ratio. !n this embodiment, the magnet weighs approximately 20 mg The magnet 304 is positioned at the top, center of the sensor tube 206 so that the magnetic poles are directed parallel to the tube's preferred displacement direction. The coil 306 is located outside the sensor enclosure 207, coupled to a circuit board 209. The sensor enclosure 207 is nonmagnetic and thus transparent to the magnetic fields. The coil 306 is an open coil type as opposed to a toroid design. In this embodiment the coil 306 is a commercially available power inductor rated at least 1 mH. The center axis of the coil 306 is aligned perpendicular to the face of the magnet 304. The sensor tube 206 is driven to resonance using the signal from one of the capacitive pick off sensors as feedback to the coil drive circuit through a phase locked loop (PLL) function. The function may be implemented as an electrical circuit or in software. The sensor tube 206 is mounted to a base portion 212, which defines a flow inlet 214 and a flow outlet 216, such that a flow passage is provided from the inlet, through the flow sensor tube 206, through the flow control portion 204, and through the sensor flow outlet 216. The flow control portion 202 includes a meter body 222 with a valve coil 228 and coil cover 230 situated therein. A valve stem 232 and plunger 234 are situated within the valve coil 228, and a valve body 236 is connected to the meter body 222 with a seal 238 therebetween. A valve seat 240, a spring 242 and an orifice 244 are positioned within the valve body 236. End blocks 224, 225 are situated on either end of the flow control portion 204 with seals 226 provided between the meter body 222 and end block 224, and between the valve body 236 and end block 225. In one embodiment, the seals 226 comprise electroformed nickel seals. In an exemplary embodiment, the Coriolis mass flow controller 200 is assembled in the following manner. The meter body 222 and sensor enclosure 207, as well as a base plate 310, a center post 312 and the sensor tube 206 are assembled and held in place by a fixture that dimensionally references the sensor tube 206 to the walls of the sensor enclosure 207. The remaining parts are indexed by press pins 330. These parts are then brazed as a single unit. The magnet 304 is soldered orto the sensor tube 206. The sensor block 301 is assembled and installed into the sensor enclosure 207 using press pins 302. The press pins 302 exteng through the back of the sensor enclosure 207 by approximately 0.5 mm. A hermetically sealed connector 320 is pressed into the back opening 322 of the sensor enclosure 207. The sensor block press pins 302 and hermetically sealed connector 320 are laser welded to provide a leak tight seal. A cover 324 is placed over the front side of the sensor enclosure 207 in a vacuum environment and e-beam welded into place, providing a vacuum tight environment. The remaining valve components and end blocks 224, 225 are then assembled with the meter body 222. The electroformed nickel seals 226 may be used, or elastomeric o-rings may be used for calibration purposes, then replaced with the nickel seals. The electronics are assembled and installed on the completed assembly. An o-ring 332 is installed on the base plate 310 and the enclosure 205 is pressed down over the o-ring seal 332. Cam locks on the base plate 310 are rotated to lock down the enclosure 205. An o-ring 334 is installed on an electronics cover cap 336. The electronics cap 336 is positioned over a user interface connector 338. The electronics cap 336 is pressed into place on the enclosure 205 affecting the o-ring seal. The assembled mass flow controller 200 is then tested and calibrated. The exemplary Coriolis mass flow controller 200 has a modular design that provides several benefits;. As discussed above, the electronics packaging is designed to effect o-ring seals at the flow body (between the lower end of the enclosure 205 and base plate 310) and at the top to a user interface cap (between the upper end of the enclosure 205 and electronics cap 336). The electronics cap 336 is connected to a user interface board 340 internal to the Coriolis mass flow controller 200, which is also connected, to the sense and control electronics. The electronics cap 336 and user interface board 340 together define the interface to tne user's electronics. This allows the flexibility to configure the interface according to the user's requirements without the need to design different sense and control electronics and enclosure for each user configuration. A variant of the user interface cap, for example, will have seals and electrical conduit to provide a device that is IP-65/NEMA 4X compliant. An example of such a device 400 is shown in Figure 18. In comparison, the embodiment illustrated in Figures 14-16 includes a connector 342 coupled to the user interface board 340. As shown n Figure 18, an electronics cap 337 is extended to provide space, for the additional components required for a particular application. Another feature of an o-ring sealed enclosure 205 is that it provides a tertiary fluid containment, the sensor tube 206 being the primary fluid containment and the sensor enclosure 207 providing the secondary containment. In the event that the-e are bubbles in the fluid being controlled, the annular opening around the plunger in a conventional valve restricts the passage of bubbles to the outlet of the valve. Bubbles will collect at the entrance of the annular opening to the point that the liquid flow will be restricted and flow control will be lost. If the annular opening is enlarged, the increased spacing of the plunger from the valve coil will reduce the field strength in the magnetic circuit and thus reduce the effective force that can be achieved in order to open or close the valve against hydraulic forces created by the fluid. Thus, in the illustrated Coriolis mass flow controller 200, a circular hole 246 is provided through the plunger 234. The crcular hole 246 is compatible with the shape and size of the bubbles, allowing bubbles to pass more freely through the valve. This minimizes the possibility of flow restriction caused by the bubbles. The hole 246 through the center of the plunger 234 minimizes any effects on the magnetic circuit so that the force to open and close the valve against hydraulic forces is maintained. With typical existing valves, the valve plunger has a captive seat that is made from some deformable material that, when pressed against the land of the orifice, will form a seal against flow. In the case of a normally closed, solenoid type valve, the force against the seat may be generated by a spring balanced so that the solenoid action lifts he seat from the orifice land. In the case of a normally open, solenoid type valve, the force against the seat is generated by the solenoid action and is balanced so that the spring lifts the seat from the orifice when the magnetic field is removed. The seat material may be elastomeric, plastic, or a ductile metal. It is usually preferable to have elastic deformation over plastic deformation so that the seal is repeatable. Alternatively, hard materials may be used for the seat and land, but fabricated to very tight tolerances including highly matched, surfaces between the seat ana land. This is a high cost approach. The spacing between the seat and land is critical to valve operation since the magnetic force on the plunger is not linear with displacement. In the case of a normally open valve, the normal position of the plunger and thus the seat relative to the land needs to be optimized in order to, provide the maximum force when the seat is moved against the land, while al owing the maximum flow in the open position. In a normally closed valve, the force of the seat against the land is generated by the spring. The spring force needs to be sufficient to close against hydraulic forces, yet minimized to allow he magnetic force to lift the seat from the land sufficient distance to allow maximum flow. Existing devices may use a variety of means to adjust the spacing between the seat and land, including placing shims under the land or seat, or having a threaded adjustmen: screw n the orifice component. As shown in Figure 17 A, however, a typical threaded adjustment in the orifice does not seal between the orifice body 250 and the valve body 252, leaving a leak path 254 between threads 256. Such a threaded adjustment requires that the threads 256 be sealed against fluid leakage. A separate seal, such as an o-ring or gasket provides this seal. In accordance with aspects of the present invention, the orifice 244 and/or land are made of a plastic material, such as VESPEL®, which is machinable into a threaded component with a precision orifice. As shown in the exemplary embodiment illustrated in Figure 17B, the threads 256 are machined oversized so that there is an interference fit 258 between the orifice body 250 and valve body 252, thus sealing, eliminating the need for a separate seal (o-ring or gasket). The orifice land now is the deformable member simplifying the design and manufacture of the valve seat 240 and plunger 234 (referring to Figures 15 and 16). The present invention, however, is not necessarily limited to any specific valve plunger configuration. In alternative embodiments, a pump is used in place of the valve. A metering pump for example, may be used for fluid control purpose. In particular, a piezoelectric pump may be employed that includes a plurality of piezoelectric tube portions. The piezoelectric tube portions are controlled in a manner to cause different tube portions to constrict or expand, thus allowing the fluid flow to be controlled as desired. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as claimed hereinafter. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention as claimed. WE CLAIM: 1. A Coriolis mass flow senser (1), comprising: a flow sensor tube (16) having first and second ends; and first and second piezoelectric stacks (42) positioned on the respective first and second ends of the flow sensor tubs (16); wherein the piezoelectric and reverse piezoelectric effects cause the flow sensor tube (16) to vibrate and sense the twist in the flow sensor tube (16) due to Coriolis force. A Coriolis mass flow sensor (1) is disclosed. The Coriolis mass flow sensor comprises a flow sensor tube (16) having first and second ends, and first and second piezoelectric stacks (42) positioned on the respective first and second ends of the flow sensor tube (16), wherein the piezoelectric and reverse piezoelectric effects cause the flow sensor tube (16) to vibrate and sense the twist in the flow sensor tube (16) due to Coriolis force.

Full Text

1. FIELD OF THE INVENTION
The invention relates generally to a mass flow measurement and control
and more particularly, to a mass flow measurement, a Coriolis mass flow sensor
and controller based on the Coriolis force effect and having an integrated flow
control valve with associated sense, control and communication electronics.
This invention also relates to a device and a method for determining mass flow
from a Coriolis force induced phase shift.
The present invention has been divided out of Indian Patent Application
No. IN/PCT/2001/00505.
2. DESCRIPTION OF RELATED ART
Mass flow measurement based on the Coriolis force effect is achieved in
the following manner. The Coriolis force results in the effect of a mass moving in
an established direction and then being forced to change direction with a vector
component normal to the establshed direction of flow. This can be expressed by
the following equation :
Fc = M x Ω
Where Fc (the Coriolis force vector) is the result of the cross product of M (the
mass flow vector) and ω (the angular velocity vector).
In a rotating system, the angular velocity vector is aligned along the axis of
rotation. Using the "Right Hand Rule", the fingers define the direction of rotation
and the thumb, extended, defines the angular velocity vector direction. In the
case of the typical Coriolis force flow sensor, a tube, through which fluid flow is to
be established, is vibrated. Often the tube is in the shape of one or more loops.

The loop shape is such that the mass flow vector is directed in opposite directions at
different parts of the loop. The tube loops may, for example, be "U" shaped,
rectangular, triangular or "delta" shaped or coiled. In the special case of a straight tube,
there are two simultaneous angu ar velocity vectors that are coincident to the anchor
points of the tube while the mass flow vector is in a single direction.
The angular velocity vector changes directions since, in a vibrating system, the
direction of rotation changes. The result is that, at any given time, the Coriolis force is
acting in opposite directions where the mass flow vectors or the angular velocity vectors
are directed in opposite directions. Since the angular velocity vector is constantly
changing due to the vibrating system, the Coriolis force is also constantly changing.
The result is a dynamic twisting motion being imposed on top of the oscillating motion
of the tube. The magnitude of twist is proportional to the mass flow for a given angular
velocity.
DE 19,605,923, GB 2,221,302, WO 92/14123 and US Patent No. 4747312
disclose examples of flowmeters. Ir Coriolis flowmeters, flow measurement is achieved
by measuring the twist in the sensor tube due to the Coriolis force generated by a fluid
moving through the sensor tube. Typical known devices use pick off sensors
comprising magnet and coil pairs located on the flow tube where the Coriolis force's
induced displacement is expected to be greatest. The coil and magnet are mounted on
opposing structures, for example, the magnet is mounted on the tube and the coil is
mounted on the stationary package wall. The magnet will move in and out of the coil,
inducing a current in the coil. This current is proportional to the velocity of the magnet
relative to the coil. Since this is a ve ocity measurement, the velocity,

and thus the signal, is at the maximum when the flow tube crosses its rest point
(zero crossing). The Coriolis force induced twist causes a phase shift in the
velocity signal. The phase is detected by measuring the difference in the zero
crossing times between the two velocity sensors. In practice this places a large
accuracy burden on the time measurement circuitry. This may limit the ultimate
sensitivity of mass flow measurement by this technique.
Further, the flow rate capabilities of known devices based on Coriolis
technology often are limited to flow rates that are higher than desired for many
applications. Moreover, existing Coriolis mass flow measuring devices only
provide for mass flow sensing with no integral flow control capabilities. It has
been left to the user to provide any means for controlling flow.
The present invention addresses shortcomings associated with the prior
art.
SUMMARY OF THE INVENTION
Indian patent application No. IN/PCT/2001/00505 discloses a capacitive
pick off sensor for a mass flow measurement device comprising a flow sensor
tube and a drive device for vibrating the flow sensor tube, the capacitive pick off
sensor being characterized by :
at least one conductive plate connectable to a first voltage potential and
adapted to be situated adjacent a flow sensor tube connected to a second
voltage potential, so as to define a gap between the flow sensor tube and the
conductive plate ;

such that the capacitance between the conductive plate and the flow
sensor tube varies due to the relative motion of the conductive plate and the flow
sensor tube when the flow sensor tube is vibrated.
The present invention provides a Coriolis mass flow sensor, comprising :
a flow sensor tube having first and second ends ; and
first and second piezoelectric stacks positioned on the respective first and
second ends of the flow sensor tube ;
wherein the piezoelectric and reverse piezoelectric effects cause the flow
sensor tube to vibrate and sense the twist in the flow sensor tube due to Coriolis
force.
The present invention also discloses a Coriolis mass flow controller, comprising :
a flow sensor tube ;
a drive device situated relative to the flow sensor tube so as to cause the
flow sensor tube to vibrate ;
a position sensing device situated relative to the flow sensor tube so as to
measure the twist in the flow sensor tube due to Coriolis force ; and
a flow control portion adapted to receive fluid from the flow sensor tube.
The present invention further provides a device for determining mass flow
from a Coriolis force-induced phase shift between first and second input signals
detected by first and second displacement gauges, comprising :
a first phase sensitive detector coupled to receive the first and second
input signals, the first phase sensitive cetector operable to mix the first and

second input signals and pro/ide an output representing the mixed first and
second input signals ;
a first phase shifter coupled to receive the first input signal and operable
to output a signal representing the first input signal phase shifted 90°;
a second phase sensitive detector coupled to receive the first phase
shifter output and the second hput signal, the second phase sensitive detector
operable to mix the phase shifted first input signal and the second input signal
and provide an output representing the mixed signals ; and a processor coupled
to the first and second phase sensitive detectors to receive the mixed signals
and operable to calculate the vector magnitude and phase of the mixed signals
relative to each other, wherein the vector phase is proportional to mass flow.
The present invention in addition provides a method of determining mass
flow from a Coriolis force-induced phase shift between first and second input
signals detected by first and second displacement gauges, comprising :
mixing the first input signed with the second input signal to produce a first
output signal ;
phase shifting the first input signal 90° ;
mixing the second input signal with the phase shifted first input signal to
produce a second output signal; and
calculating the vector magnitude and phase of the first and second output
signals relative to each other, wherein the vector phase is proportional to mass
flow.

Lastly, the present invention provides a device for determining mass flow
from a Coriolis force-induced phase shift between first and second input signals
detected by first and second disolacement gauges, comprising :
a differential amplifier coupled to receive the first and second input
signals, the differential amplifier operable to output a signal representing the
difference between the first and second input signals ;
a first phase sensitive detector coupled to receive the output of the
differential amplifier and the first input signal and provide an output representing
the mixed differential amplifier signal and the first input signal;
a phase shifter coupled to receive the first input signal and operable to
output a signal representing the first input signal phase shifted 90° ;
a second phase sensitive detector coupled to receive the phase shifter
output and the differential ampl fier signal and provide an output representing the
mixed phase shifted first input signal and the differential amplifier signal, and
provide an output representing the mixed signals ; and
a processor coupled to he first and second phase sensitive detectors to
receive the mixed signals and operable to calculate the vector magnitude and
phase of the mixed signals relative to each other, wherein the vector phase is
proportional to mass flow
In one aspect of the present invention, a capacitive pick off sensor for a
mass flow measurement devce is disclosed. The mass flow measurement
device includes a flow sensor tube and a drive device for vibrating the flow
sensor tube. The capacitive picK off sensor includes at least one conductive

plate connectable to a first voltage potential and adapted to be situated adjacent
the flow sensor tube which is connected to a second voltage potential. The
conductive plate is positioned relative to the flow sensor tube so as to define a
gap therebetween. The capacitance between the conductive plate and the flow
sensor tube varies due to the relative motion of the conductive plate and the flow
sensor tube when the flow sensor tube is vibrated.
In another aspect of the present invention, a Coriolis mass flow sensor
includes a flow sensor tube, a drive device situated relative to the flow sensor
tube so as to cause the flow sensor tube to vibrate, and capacitance
displacement gauges situated relative to the flow sensor tube so as to measure
the twist in the flow sensor tube due to Coriolis force. In specific embodiments,
electromagnetic, electrostatic, acoustic, and/or piezoelectric drives are used to
vibrate the flow sensor tube. In still further embodiments, piezoelectric devices
are used both to vibrate the flow sensor tube and measure the twist in the flow
sensor tube.
In yet another aspect of the present invention, a Coriolis mass flow
controller includes a flow sensor tube, a drive device situated relative to the flow
sensor tube so as to cause the flow sensor tube to vibrate and a position sensing
device situated relative to the flow sensor tube so as to measure the twist in the
flow sensor tube due to Coriolis force. The Coriolis mass flow controller further
includes an integrated flow control device adapted to receive fluid from the flow
sensor tube. Such an integrated flow control device and associated sensing

electronics provide a more compact package that is easier to use and provides
significant improvement in dynamic performance.
In a further aspect of the present invention, a Coriolis mass flow sensor
includes a flow sensor tube, a housing having the flow sensor tube situated
therein, a drive device positioned outside the housing for vibrating the flow
sensor tube, and at least one pick off sensor situated relative to the flow sensor
tube so as to measure the twist in the flow sensor tube due to Corioiis force. In
exemplary embodiments, the pick off sensors are situated in the housing. In
further embodiments, a magnet is coupled to the flow sensor tube, and the drive
device comprises an electromagnetic coil. The magnet may be a non-rare earth
magnet, and more specifically, a nickel plated samarium cobalt magnet. The
electromagnetic coil may comprise a power inductor.
In accordance with still further aspects of the present invention, a mass
flow measurement device includes an enclosure having first and second ends, a
flow body, and a first sealing member situated relative to the enclosure first end
and the flow body such that the flow body and the first end are connected in a
sealed manner. A user interface assembly and a second sealing member are
situated relative to the enclosure second end such that the user interface
assembly and the second end are connected in a sealed manner. The sealing
members allow interchanging among multiple types of user interface assemblies,
including a user interface assembly that is IP-65/NEMA 4X compliant, and
provide additional fluid containment.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other objects and advantages of the invention will become apparent upon
reading the following detailed description and upon, reference to the
accompanying drawings whereir :
Figure 1 is a block diagram conceptually illustrating a Coriolis mass flow
sensor in accordance with aspects of the present invention ;
Figures 2A and 2B illustrate a Coriolis mass flow sensor employing an
electromagnetic drive in accordance with an embodiment of the present
invention ;
Figures 3A and 3B illustrate a Coriolis mass flow sensor employing an
electrostatic drive in accordance with an embodiment of the present invention ;
Figures 4A and 4B illustrate a Coriolis mass flow sensor employing an
acoustic drive in accordance with an embodiment of the present invention ;
Figures 5A, 5B and 5C illustrate a Coriolis mass flow sensor employing a
piezoelectric drive in accordance with an embodiment of the present invention ;
Figure 6 is a schematic of a lock-in amplifier for measuring the Coriolis
force induced phase shift in accordance with the present invention ;
Figure 7 is a schematic of a dual channel lock-in amplifier for measuring
the Coriolis force induced phase shift in accordance with the present invention ;
Figure 8 is a graph illustrating the relationship between the amplitudes of
input signals from sensor tube position sensors using signal processing methods
in accordance with the present application

Figure 9 is a schemalic of a dual lock-in amplifier for measuring the
Coriolis force induced phase snift in accordance with the present invention ;
Figure 10 is a schematic of a dual lock-in amplifier including reference
frequency adjustment for measuring the Coriolis force induced phase shift in
accordance with the present invention ;
Figure 11 illustrates a first embodiment of a capacitive displacement
probe in accordance with the present invention ;
Figure 12 illustrates a second embodiment of a capacitive displacement
probe in accordance with the present invention ;
Figure 13 illustrates a third embodiment of a capacitive displacement
probe in accordance with the present invention ;
Figure 14 is a perspective view of a Coriolis mass flow controller in
accordance with an embodiment of the present invention ;
Figure 15 is a sectional view of the Coriolis mass flow controller shown in
Figure 14 ;
Figure 16 is an exploded view of the Coriolis mass flow controller shown in
Figure 15 ;
Figures 17 A and 17B i lustrate aspects of a prior art threaded valve
connection and a sealed threaded valve connection in accordance with the
present invention, respectively ; and
Figure 18 is a perspective view of an embodiment of a Coriolis mass flow
controller in accordance further aspects of the present invention.

While the invention is susceptible to various modifications and alternative
forms, specific embodiments thereof have been shown by way of example in the
drawings and are herein described in detail. It should be understood, however,
that the description herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary, the intention is to
cover all modifications, equivalents, and alternatives falling within the spirit and
scope of the invention as hereinafter claimed.
DETAILED DESCRIPTION OF THE INVENTION
Illustrative embodiments; of the invention are described below. In the
interest of clarity, not all features of an actual implementation are described in
this specification. It will of course be appreciated that in the development of any
such actual embodiment, numerous implementation-specific decisions must be
made to achieve the developers' specific goals, such as compliance with system-
related and business-related constraints, which will vary from one
implementation to another. Moreover, it will be appreciated that such a
development effort might be complex and time-consuming, but would
nevertheless be a routine undertaking for those of ordinary skill in the art having
the benefit of this disclosure.
Figure 1 is a block diagram conceptually illustrating a Coriolis mass flow
sensor in accordance with aspects of the present invention. The Coriolis mass
flow sensor 1 includes a flow sensor tube 2, with a drive device 3 situated
relative thereto so as to vibrate the tube 2. Displacement gauges 4 are

positioned relative to the tube 2 so as to measure the twist in the tube 2 due to
Coriolis force.
A typical material for the sensor tube 2 is 316L stainless steel. Reasons
for using 316L stainless steel include that it is resistant to chemical attack from
many substances, it is resistan' to rupture from normal process pressures, it is
typically noncontaminating and can be readily formed to the desired shape of a
Coriolis sensor tube. However, 316L. stainless steel is not suitable for all
applications. Therefore, it is necessary that other tube materials be available to
cover applications not suitable for 316L stainless steel. Known devices use
silicon as an alternative materia to 316L. stainless steel. The advantage of silicon
over 316L stainless steel is that sensor tubes can be made in a smaller form
than can be realized by 316L stainless steel.
Another consideration far material selection for the sensor tube 2 is the
resistance to stress induced or enhanced corrosion. Stress is generated at the
base of the bending arm where the tubes are mounted. In polycrystalline
materials stress will cause impurities in the material to diffuse and concentrate at
grain boundaries between the microcrystalline granular regions. This will, in
many cases, weaken the bonds between the microcrystalline grains making the
material to be more susceptible! to chemical attack. Single crystal materials like
silicon or sapphire are less likely to be affected in this manner.
Metals, like 316L stainless steel are usually polycrystalline and therefore
more susceptible to this type of chemical attack to varying degrees. Amorphous
materials like silica glass and several plastics also are more resistant to stress

induced chemical attack, since they do not have a grain structure like
polycrystalline materials. Tube materials that are susceptible to chemical attack
may have their surfaces modified or coated in such a way as to minimize
corrosion or attack at the surfaces if the use of the underlying material is
otherwise attractive.
Surface modification may be accomplished by ion implantation, thermal
diffusion, and chemical or electrochemical reaction. The intent; here, is to
remove, redistribute, or introduce elemental or molecular species that leave a
chemically resistant layer at the surface. Surface coating may be accomplished
by thermally activated deposition from a vapor, liquid or powder impinging on the
surface at elevated temperaures. Lower temperatures may be used if the
chemically reactive species is also excited or ionized by plasma or an intense
photon flux as from a laser. Other materials resistant to chemical attack may be
deposited by nonreactive, physical vapor deposition as accomplished by thermal
or electron beam evaporation or by ion sputtering. If sputtering is accomplished
using a highly energetic ion beam so that the sputtered species is chemically
excited or ionized, then a chemical reaction with the surface is also
accomplished, which may be desirable for certain deposited materials. Also,
chemical reactions at the surface may be accomplished by accelerating the
chemical species so that the kinetic energy can be used to activate or enhance
the chemical reaction.

Tube materials used for the Coriolis flow sensing tube 2 in particular
embodiments of the present irvention are Austenitic and Martensitic stainless
steels, high nickel alloys, Titanium and Zirconium and their alloys, particularly
Titanium-Vanadium-Aluminum alloys and Zircalloy (for their high yield strength
and low Young's modulus), silcon, sapphire, silicon carbide, silica glass and
plastics. Tube coating materials employed in accordance with the present
invention include silicon carbide, nickel, chrome, diamond, refractory carbides,
refractory metal nitrides, and refractory metal oxides.
Figures 2A and 2B illustrate a Coriolis mass flow sensor 1 in accordance
with particular embodiments of the present invention. The Coriolis mass flow
sensor 1 employs an electromagnetic drive 10 that includes an electromagnet 12
driven by a signal source (not shown), which, in the embodiment illustrated,
comprises a sinusoidal signal source. The electromagnet 12 is situated near a
small permanent magnet 14 mounted on a sensor tube 16. The sensor tube 16
is connected to a base 18 that includes first and second ports 19, so as to define
a flow path from one port 19 through the flow tube 16 to the other port 19. The
exemplary sensor tube 16 shown in the embodiments disclosed herein is
generally "U" shaped, though o:her shapes, such as delta shaped, rectangular,
coiled, or straight tubes may also be used.
Figures 3A and 3B illustrate an embodiment similar to that shown in
Figure 2, using an electrostatc drive. The electrostatic drive 20 includes a
charge plate 22 positioned near a small dielectric plate 24 mounted on the
sensor tube 16. If the tube 13 is made of dielectric material, then the charge

plate 22 is positioned near the tube 16 and the dielectric plate 24 may be
eliminated. Again, the charge plate is driven by a signal source (not shown),
such as a sinusoidal signal SOL rce. A voltage applied to the charge plate 22 will
produce an electric field between it and the dielectric plate 24. This will produce
a surface charge on the dielectric plate 24. As the voltage polarity is rapidly
changed on the charge plate 22, the resultant electric field between it and the
dielectric plate 24 will alternately be attractive or repulsive causing the flow tube
16 to vibrate.
Figures 4A and 4B illustrate another embodiment of the Coriolis mass flow
sensor 1 that employs a novel acoustic drive 30. The acoustic drive 30 includes
a small speaker 32 placed nea'the tube 16. The pressure waves generated by
the speaker 32 cause the tube 16 to vibrate.
In Figures 5A, 5B and 5C, yet another embodiment of the Coriolis mass
flow sensor 1 is illustrated. The Coriolis mass flow sensor 1 of Figures 5A, 5B
and 5C uses a piezoelectric drive 40, wherein two piezoelectric stacks 42 are
positioned on opposite sides of each leg of the flow tube 16, in effect creating
two bimorphs on each leg 16 as shown in Figure 5. The piezoelectric and
reverse piezoelectric effects would be used to either drive and/or sense the
deflection of the tube 16.
Mass flow measurement s achieved by measuring the twist in the sensor
tube 16 due to the Coriolis force generated by a fluid moving through the sensor
tube 16. For example, pick cff sensors comprising magnet and coil pairs
are typically located on the flew tube 16 where the Coriolis forces induced

displacement is expected to be greatest. The coil and magnet are mounted on
opposing structures, for example, the magnet is mounted on the tube 16 and the
coil is mounted on the stationary package wall. The magnet will move in and out
of the coil, inducing a current in the coil. This current is proportional to the
velocity of the magnet relative to the coil. Since this is a velocity measurement,
the velocity, and thus the signal, is at the maximum when the flow tube 16
crosses its rest point (zero crossing). The Coriolis force induced twist causes a
phase shift in the velocity signal that is detected by measuring the difference in
the zero crossing times between the two velocity sensors. In practice this places
a large accuracy burden on the time measurement circuitry. This may limit the
ultimate sensitivity of mass flow measurement by this technique.
Aspects of the present nvention provide a flow measurement technique
that provides for a lower flow capability, is more direct and requires less accuracy
in the circuitry than typical time' based signal conditioning techniques. Referring
to the embodiments illustrated in Figures 2-4, displacement of the vibrating
sensor tube is measured usirg capacitive pick off sensors. Two capacitance
displacement gauges 50 are positioned near the tube 16 at positions symmetric
to the shape of the tube 16 so as to measure the twist in the sensor tube 16 due
to the Coriolis force generated by a fluid moving through the sensor tube 16. In
specific embodiments of the present invention, the capacitance displacement
gauges 50 are miniaturized and surface mounted on the sensor package wall or
on a sensor block inserted inside the loop of the flow sensor tube. The twist in
the sensor tube 16 due to the Coriolis force results in a phase shift between the

two signals from the capacitance displacement gauges 50. Since this is a
displacement measurement, the signal is directly proportional to the
displacement. The relative displacement of each side of the tube is measured as
a phase shift. The gauge driver and signal conditioning electronics translate the
relative displacement of the tube 16 into a high level signal which is a function of
the phase shift that can be used to measure the Coriolis effect when flow is
established through the tube 16.
A first signal processing technique uses a lock-in amplifier with a
reference signal supplied by one of the displacement gauges 50, and an input
signal supplied by the other displacement gauge 50. Either gauge 50 may supply
the reference or the input signal. The phase output from the lock-in amplifier is
proportional to flow. Figure 6 is a functional schematic of a lock-in amplifier 52,
with which such a method for measuring the Coriolis force induced phase shift in
accordance with the present nvention may be implemented. The signals are
moving left to right as illustrated in Figure 6. The Left input 100 and Right input
102 signals are from the Left and Right displacement gauges 50 respectively.
For example, the Left input 100 may be used as the reference signal. The sine
out 103 is the drive signal, phase locked to the Left input 100 signal. This will
drive the flow sensor tube 16 at resonance. The Right Input 102 signal is mixed
with the Left/Reference Input 100 signal and its 90° phased shifted signal 104 in
the two Phase Sensitive Detectors (PSDs) 106. Functionally, the PSDs 106
multiply the two signals, producing a high frequency component and a DC
component. The low pass filters 108 remove the high frequency component

producing a DC voltage at the X and Y outputs 110, 112. The X output 110 is
called the "in-phase" component and the Y output 112 is called the "quadrature"
component of the vector signal relative to the reference signal. Each of these
components is phase sensitive; however, the vector magnitude and phase
components can be separated by the following relationships :

The relationship between the outputs from the lock-in amplifier 52 and the
inputs from the displacement gauges 50 is derived as follows :
Consider the two signas as sine waves with arbitrary amplitudes and
arbitrary phase difference. Each signal can be represented as below :

At the bottom PSD 106 the following operation occurs :

This signal has a DC vo tage component and an AC component at twice
the frequency. The Low Pass Filter (L.PF) 108 removes the AC component
leaving

At the top PSD 106 the folowing operation occurs :
We have a cosine multiplier since cos ωt = sin(ωt + 90°).

Again, we have a signal with AC and DC components, which after passing
through the LPF 108, results in the following :

Calculating the magnitude, R, and the phase angle, 8, from equations 1
and 2 we have :
and
These calculations may be executed by any suitable digital or analog processing
device 120. The vector phase is proportional to mass flow.
Another method in accordance with embodiments of the invention
requires a dual channel lock-in amplifier with the reference signal and one input
signal supplied by one of the displacement gauges 50 and a second input signal
supplied by the other displacement gauge 50. The difference between the two
input signals is then measured against the reference signal. The resultant phase
output from the lock-in amplifier is proportional to flow. Figure 7 is a functional
schematic of a dual channel lock-in amplifier 54. The signals are moving in the

same manner and have the same definitions as in Figure 6. The Left input 100 is
also used as the reference signal. As before, the sine out 103 is the drive signal,
phase locked to the Left input 100 signal. in this case, the Left Input 100 signal
is subtracted from the Right Input 102 signal and mixed with the Left/Reference
Input 100 signal and its 90° phased shifted signal 104 in the two Phase Sensitive
Detectors (PSDs) 106. The internal functions are the same as in the lock-in
amplifier 52 of Figure 6.
The following derivation may be used to determine the relationship
between the outputs from the lock-in amplifier 54 and the inputs from the
displacement gauges 52. Any suitable digital or analog processing device 120
may be used to perform the calculations.
Consider the two signals as sine waves with arbitrary amplitudes and
arbitrary phase difference. Each signal can be represented as below :
Vleft= Vref= A Sin at
VrigM™B sin (ot + $)
The output of the Low No se Differential Amplifier 114 in this case will be

At the bottom PSD 106 the following operation occurs :

This signal has a DC voltage component and an AC component at twice
the frequency. The Low Pass Filter (LPF) 108 removes the AC component
leaving

At the top PSD 106 the following operation occurs :

We have a cosine multiplier since cos ωt = sin (ωt + 90°).

Again, we have a signal with AC and DC components, which after passing
through the LPF, results in the following ;

Calculating the magnitude, R, and the phase angle, θ, from equations 1
and 2 we have :
and
θ is no longer the phase angle, but is the arctangent, a function of the
phase angle and the amplitudes of the Left and Right input signals. Analysis
of this equation shows that θ is a strong function of Φ. In fact, the relative

amplitudes of the input signals can control the strength of this function. This can
be illustrated in graph shown in Figure 8, in which A and B are the amplitudes of
the Left and Right signals respectively. As the amplitudes are more closely
matched, the sensitivity is higher for the lock-in amplifier output, 6. Even for
amplitudes that are matched within 2%, the sensitivity of θ to Φ is nearly 100
times that of the standard lock-in amplifier configuration.
Figure 9 is a functional schematic of a dual lock-in amplifier 56 with which
another exemplary method for measuring the Coriolis force induced phase shift
in accordance with the present nvention is implemented. The signals are moving
in the same manner and have the same definitions as disclosed above. The Left
input 100 is also used as the reference signal. As before, the sine out 103 is the
drive signal, phase locked to the Left input 100 signal. In this case, the Left Input
100 signal is mixed with itself and its 90° phased-shifted signal in the two Phase
Sensitive Detectors (PSDs) 106 in the top lock-in amplifier 58. In the bottom lock-
in amplifier 60, the Right Input ' 02 signal is mixed with the Left Input 100 signal
and its 90° phased-shifted signal in the two Phase Sensitive Detectors (PSDs)
106. The paired outputs from the non-phase shifted PSDs 106 and phase shifted
PSDs 106 are differentiated in the two Low Noise Differential Amplifiers 114. The
DC components of the signals are passed by the Low Pass Filters 108 to give
the usual lock-in amplifier outpu:s. The mathematics, which may be executed by
any suitable digital or analog processing device 120, are the same as in the
method outlined above in conjunction with Figure 7, though the order in which
the operations occur is different. In the Dual Channel Lock-in technique of

Figure 7, two high level signals, with very small differences are subtracted. The
low-level signal is then multiplied with a high level signal, which can introduce
noise in analog circuits or round off errors in digital circuits. In the Dual Lock-in
technique of Figure 9, the high level signals are first multiplied and the resulting
signals, which are close in amplitude, are then subtracted resulting in an output
with lower noise.
A lock-in amplifier's use is most notable with respect to measuring a low-
level signal that is buried in noise of a much higher amplitude. The lock-in
amplifier accomplishes this by acting as an extremely narrow bandpass filter.
The signal and noise is multiplied by a reference sine and cosine wave, and then
passed through a low-pass filter to remove the reference frequency. The result of
the multiply/filter operations are DC signals that represent a complex vector (x +
iy). The phase difference between the reference frequency and the signal of
interest can be determined by atan(y/x).
In terms of measuring Coriolis force, the phase difference between two
signals of the same frequency is of interest. This can be accomplished using
dual lock-in amplifiers, each driven with the same reference frequency as shown
in Figure 10. In the functional schematic illustrated in Figure 10, Left and Right
input signals 100, 102 are multiplied by reference sine and cosine waves
provided by a reference frequency generator 144. The input signals 100, 102 are
mixed with the sine and cosine signals in PSDs 106, then passed through fifth-
order bessel IIR low pass filters 148 as described in conjunction with Figure 6,
Figure 7 and Figure 9. The multiply/filter process described above is performed

on the Left and Right input signals 100, 102 with a resulting phase difference
output X, Y of each signal with respect to the reference frequency. The
difference between the two output signals X, Y represents the phase difference
between the two input signals 100, 102. In the case of Coriolis mass flow, this
phase difference represents an indication of mass flow 152.
When using lock-in amplifiers to measure the extremely small phase
differences associated with Coriolis mass flow, it is necessary to adjust the
reference frequency to match the signal of interest. If the reference signal is not
very close to the signal of interest, a very low frequency AC signal will appear at
the outputs of the low-pass fiters 148. The frequency of the Coriolis sensor
changes with mass flow, temperature, density and pressure, further complicating
the measurement process.
The reference frequency can be adjusted accurately by processing the
output vector from one of the input signals 100, 102. First, the derivative of the
output vector is calculated. This may be accomplished by calculating the
complex difference between two consecutive output vectors. Then, the original
output vector is rotated 90 degrees and the dot product of this vector and the
derivative is calculated, resulting in an error signal 150 that is provided to the
reference frequency generator 144. The error signal 150 is negative, positive, or
zero, if the reference frequency needs to be adjusted down, up or unchanged,
respectively.

The amount of reference frequency adjustment is dependent on the
accuracy of the phase measurement, but generally, the finer the adjustment, the
better the accuracy as determhed by calculating the standard deviation over a
number of output samples. However, the finer adjustment (small step changes)
of reference frequency will be detrimental if there are step changes in the signal
frequency, as the reference frequency generator 144 will take too long reaching
the intended frequency. If the signal frequency experiences frequent step
changes, a PID or adaptive algorithm can be used to adjust the reference
frequency in a more responsive manner.
In alternative embodiments, the capacitance displacement probes 50 may
be mounted on piezoelectric actuators that would, first, align the capacitance
displacement probes 50 in three dimensions. Further, when used with the dual
channel lock-in amplifier or dual lock-in amplifier methods disclosed herein, the
piezoelectric actuators can dynamically adjust the sensitivity of the flow sensor,
thereby providing an extended range of operation.
Such dynamic positioning provides compensation for manufacturing
variability, particularly the positioning of the flow sensor tube relative to the
capacitance displacement probe. Dynamic positioning also provides
compensation for dimensional shifts due to relative thermal expansion of the
various components. Used in combination with the dual channel lock-in amplifier
or dual lock-in amplifier, dynamic positioning allows the two displacement signals
to be closely matched to provide an adjustable sensitivity to flow. A low
sensitivity would be used for high flow conditions while high sensitivity would be

used for extended low flow conditions thereby increasing the dynamic range of
flow measurement.
Embodiments of the present invention additionally provide improved
capacitance measurement techniques, specifically, a novel geometry of the
capacitance displacement probe. Normally, the displacement of an object is
measured as a distance normal to the capacitance displacement probe. The
displacement may also be measured as a distance tangential to the capacitance
displacement probe. Referring o Figure 11, this can be accomplished by placing
two plates 130 side by side with a uniform gap 132 between the plates 130 and
placed near a sensor tube 134 in the plane tangential to the motion (indicated by
the arrow 136) as shown in Figure 11. In one embodiment, the plates 130 will be
at the same potential and the sensor tube 134 will be at ground potential. The
sensor tube 134 is positioned directly over the gap 132 between the plates 130
with the expected motion 136 normal to the gap so that cyclic motion of the
sensing tube 134 will position the tube 134 more closely to one plate 130 than
the other 130. The relative capacitance is measured between each of the plates
130 and the sensor tube 134. As the sensor tube 134 moves over one plate 130
or the other, the amount of area contributing to the capacitance will change and
thus the relative capacitance measured.
An alternative configuration has the gap 132 running diagonally across the
sensor tube 134 as shown in Figure 12. This allows a less precise placement of
the sensor tube 134 over the plane of the plates 130. Misalignment of the sensor

tube 134 will cause a smaller mismatch in the signal as compared to the parallel
gap 132.
A further embodiment has the gap 132 in a "saw tooth" pattern as shown
in Figure 13. This is an improvement over the diagonal gap 132 in that an
angular misalignment of the .sensor tube 134 with respect to the gap 132,
whether parallel or diagonal, will cause a difference in the rate of change of
capacitance between the two plates 130. This will introduce an unwanted change
in phase between the two signals. The "saw tooth" pattern will average out any
angular misalignment of the sensor tube 134, providing more symmetrical
signals.
Figure 14, Figure 15 and Figure 16 illustrate an exemplary low flow
Coriolis mass flow controller 200 in accordance with an embodiment of the
present invention. The Coriolis mass flow controller 200 includes a flow sensor
portion 202 and a flow control portion 204. A processor either internal or external
to the mass flow controller 200 receives an indication of a set point, or desired
mass flow. The set point value is compared to the actual mass flow as indicated
by flow sensor portion 202 to generate an error value. The flow control portion
204 includes a valve that is manipulated to adjust the flow rate and minimize the
error. The implementation of particular control schemes would be a routine
undertaking for one skilled in the art having the benefit of this disclosure, and
thus, the specifics of such an implementation are not addressed in detail herein.

The flow sensor portion 202, which is surrounded by an enclosure 205,
includes a sensor tube 206 that is bent into a loop shape, a drive device 208 and
two pick off sensors 210 positioned at opposite sides of the sensor tube 206 that
measure the displacement of the sides of the sensor tube 206.
In existing Coriolis devices, the sensor is typically enclosed in a welded
metal housing. The sensor tube within the housing also has attached to it
displacement or velocity sensors with wires connecting through feedthroughs to
electronics outside the housing The sensor tube in such devices is relatively
large and has a resonant frequency that is about 100 Hz. For smaller sensor
tubes, as in embodiments of he present invention, the resonant frequency is
somewhat higher, on the order of 200 Hz and greater. As the frequency
increases, there will be an increased viscous damping effect due to the
atmospheric conditions inside the sensor enclosure. By evacuating the enclosure
and utilizing vacuum compatibe materials inside the enclosure, the viscous
damping can be reduced or' even eliminated. Thus, in the exemplary
embodiment illustrated, the sensor tube 206 is situated within a vacuum sensor
housing 207.
The sensor tube 206 is designed 1:o allow elastic bending orthogonal to a
line connecting the legs of the tube's loop. The loop is wide enough to allow
elastic twisting about the center ine of the loop. In order to measure the Coriolis
force at low flows, the sensor tube 206 mass needs to be minimized. Tube sizing
is critical since the tube needs to be small, yet still capable of retaining the fluids
at extended pressures. It is a so preferable for the pick off sensors 210 to be

non-contact since any contact with the tube 206 or mass loading on the tube 206
may suppress the Coriolis force.
Pick off sensor technologies may include capacitive, magnetic,
piezoresistive and optical. Piezoresistive, strain gauge displacement sensors do
contact the tube but at the base of the loop where the displacement is minimum
and the strain is the highest. This would have minimal effect on the tube's
vibration. Optical technologies include various laser and white light
interferometric displacement techniques, triangulation techniques, multiple
internal reflection and beam occultation techniques. Magnetic displacement
technologies include Hall effect, eddy current, variable reluctance and
magnetoresistive techniques.
Capacitive pick off sensor technology is used in the illustrated
embodiment because it has the sensitivity required to measure the tube
displacement, it is noncontact, and would not be affected by a magnetic drive
device. The capacitive pick off sensors 210 each include at least one conductive
plate 300, which is connected to a given voltage potential and situated adjacent
the flow sensor tube 206 so as to define a gap therebetween. The flow sensor
tube 206 is connected to a voltage potential different than the conductive plate
300. The capacitance between the conductive plate 300 and the flow sensor
tube 206 varies due to the relative motion of the conductive plate 300 and the
flow sensor tube 206 when the flow sensor tube is vibrated 206.

In the illustrated embodiment, the conductive plates comprise first and
second plates as disclosed above in conjunction with Figures 11-13. In the
particular embodiment illustrated, saw-tooth shaped plates, as illustrated in
Figure 13, are employed. The capacitive pick off sensors 210 are assembled into
an integrated sensor block 301 sized to fit into the sensor enclosure 207,
dimensionally referenced to the back wall of the enclosure 207 by press pins
302. The conductive plates 300 of the capacitive pick off sensors 210 are
manufactured on a multilayer printed circuit board so as to provide a guard layer
to minimize parasitic capacitance and a back contact layer for soldering to the
sensor block 301. Since the capacitive pick off sensors 210 are required
to operate in a vacuum, low outgassing materials are used in the illustrated
embodiment. Standard fiberglass materials are not vacuum compatible. Desired
material characteristics include that it be vacuum compatible, solderable,
bondable into multilayers with a low outgassing bond and that it have a low
dielectric constant for simple guard layer design. In a specific embodiment,
commercially available DRUOID is used.
The sensor block 301 containing the capacitive pick off sensors 210 can
be adjusted to optimize the spacing to the sensor tube 206. This is accomplished
using electron discharge machined hinge plates. Tapered set screws spread
gaps to effect linear and angular movement of the capacitive pick off sensors.
Further, the conductive plates 300 of the capacitive pick off sensors include
contact pads that allow wires to be soldered or wire bonded to a printed circuit
board 303 on the front of the sensor block interconnecting the capacitive pick off

sensors 210 with a hermeticaly sealec electrical connector that interfaces with
capacitance displacement electronics outside the sensor enclosure 207.
The drive device 208 drives the tube 206 into a bending mode, vibration,
causing it to vibrate. In the illustrated embodiment, the drive device 208 consists
of a small magnet 304 soldered on the sensor tube 206 and a small
electromagnetic coil 306 to al ernately push and pull on the magnet 304. In the
embodiment shown in Figure '6, a non-rare earth magnet, and more particularly,
a nickel plated samarium cobalt magnet is used. The samarium cobalt magnet
has a good magnetic strength to weight ratio. !n this embodiment, the magnet
weighs approximately 20 mg The magnet 304 is positioned at the top, center of
the sensor tube 206 so that the magnetic poles are directed parallel to the tube's
preferred displacement direction.
The coil 306 is located outside the sensor enclosure 207, coupled to a
circuit board 209. The sensor enclosure 207 is nonmagnetic and thus
transparent to the magnetic fields. The coil 306 is an open coil type as opposed
to a toroid design. In this embodiment the coil 306 is a commercially available
power inductor rated at least 1 mH. The center axis of the coil 306 is aligned
perpendicular to the face of the magnet 304. The sensor tube 206 is driven to
resonance using the signal from one of the capacitive pick off sensors as
feedback to the coil drive circuit through a phase locked loop (PLL) function. The
function may be implemented as an electrical circuit or in software.

The sensor tube 206 is mounted to a base portion 212, which defines a
flow inlet 214 and a flow outlet 216, such that a flow passage is provided from
the inlet, through the flow sensor tube 206, through the flow control portion 204,
and through the sensor flow outlet 216. The flow control portion 202 includes a
meter body 222 with a valve coil 228 and coil cover 230 situated therein. A valve
stem 232 and plunger 234 are situated within the valve coil 228, and a valve
body 236 is connected to the meter body 222 with a seal 238 therebetween. A
valve seat 240, a spring 242 and an orifice 244 are positioned within the valve
body 236. End blocks 224, 225 are situated on either end of the flow control
portion 204 with seals 226 provided between the meter body 222 and end block
224, and between the valve body 236 and end block 225. In one embodiment,
the seals 226 comprise electroformed nickel seals.
In an exemplary embodiment, the Coriolis mass flow controller 200 is
assembled in the following manner. The meter body 222 and sensor enclosure
207, as well as a base plate 310, a center post 312 and the sensor tube 206 are
assembled and held in place by a fixture that dimensionally references the
sensor tube 206 to the walls of the sensor enclosure 207. The remaining parts
are indexed by press pins 330. These parts are then brazed as a single unit. The
magnet 304 is soldered orto the sensor tube 206. The sensor block 301 is
assembled and installed into the sensor enclosure 207 using press pins 302.
The press pins 302 exteng through the back of the sensor enclosure 207 by
approximately 0.5 mm. A hermetically sealed connector 320 is pressed into the
back opening 322 of the sensor enclosure 207. The sensor block press pins 302

and hermetically sealed connector 320 are laser welded to provide a leak tight
seal. A cover 324 is placed over the front side of the sensor enclosure 207 in a
vacuum environment and e-beam welded into place, providing a vacuum tight
environment.
The remaining valve components and end blocks 224, 225 are then
assembled with the meter body 222. The electroformed nickel seals 226 may be
used, or elastomeric o-rings may be used for calibration purposes, then replaced
with the nickel seals. The electronics are assembled and installed on the
completed assembly. An o-ring 332 is installed on the base plate 310 and the
enclosure 205 is pressed down over the o-ring seal 332. Cam locks on the base
plate 310 are rotated to lock down the enclosure 205. An o-ring 334 is installed
on an electronics cover cap 336. The electronics cap 336 is positioned over a
user interface connector 338. The electronics cap 336 is pressed into place on
the enclosure 205 affecting the o-ring seal. The assembled mass flow controller
200 is then tested and calibrated.
The exemplary Coriolis mass flow controller 200 has a modular design
that provides several benefits;. As discussed above, the electronics packaging is
designed to effect o-ring seals at the flow body (between the lower end of the
enclosure 205 and base plate 310) and at the top to a user interface cap
(between the upper end of the enclosure 205 and electronics cap 336). The
electronics cap 336 is connected to a user interface board 340 internal to the
Coriolis mass flow controller 200, which is also connected, to the sense and
control electronics. The electronics cap 336 and user interface board 340

together define the interface to tne user's electronics. This allows the flexibility to
configure the interface according to the user's requirements without the need to
design different sense and control electronics and enclosure for each user
configuration.
A variant of the user interface cap, for example, will have seals and
electrical conduit to provide a device that is IP-65/NEMA 4X compliant. An
example of such a device 400 is shown in Figure 18. In comparison, the
embodiment illustrated in Figures 14-16 includes a connector 342 coupled to the
user interface board 340. As shown n Figure 18, an electronics cap 337 is
extended to provide space, for the additional components required for a
particular application.
Another feature of an o-ring sealed enclosure 205 is that it provides a
tertiary fluid containment, the sensor tube 206 being the primary fluid
containment and the sensor enclosure 207 providing the secondary containment.
In the event that the-e are bubbles in the fluid being controlled, the
annular opening around the plunger in a conventional valve restricts the passage
of bubbles to the outlet of the valve. Bubbles will collect at the entrance of the
annular opening to the point that the liquid flow will be restricted and flow control
will be lost. If the annular opening is enlarged, the increased spacing of the
plunger from the valve coil will reduce the field strength in the magnetic circuit
and thus reduce the effective force that can be achieved in order to open or
close the valve against hydraulic forces created by the fluid. Thus, in
the illustrated Coriolis mass flow controller 200, a circular hole 246 is provided

through the plunger 234. The crcular hole 246 is compatible with the shape and
size of the bubbles, allowing bubbles to pass more freely through the valve. This
minimizes the possibility of flow restriction caused by the bubbles. The hole 246
through the center of the plunger 234 minimizes any effects on the magnetic
circuit so that the force to open and close the valve against hydraulic forces is
maintained.
With typical existing valves, the valve plunger has a captive seat that is
made from some deformable material that, when pressed against the land of the
orifice, will form a seal against flow. In the case of a normally closed, solenoid
type valve, the force against the seat may be generated by a spring balanced so
that the solenoid action lifts he seat from the orifice land. In the case of a
normally open, solenoid type valve, the force against the seat is generated by
the solenoid action and is balanced so that the spring lifts the seat from the
orifice when the magnetic field is removed. The seat material may be
elastomeric, plastic, or a ductile metal.
It is usually preferable to have elastic deformation over plastic deformation
so that the seal is repeatable. Alternatively, hard materials may be used for the
seat and land, but fabricated to very tight tolerances including highly matched,
surfaces between the seat ana land. This is a high cost approach. The spacing
between the seat and land is critical to valve operation since the magnetic force
on the plunger is not linear with displacement. In the case of a normally open
valve, the normal position of the plunger and thus the seat relative to the land
needs to be optimized in order to, provide the maximum force when the seat is

moved against the land, while al owing the maximum flow in the open position. In
a normally closed valve, the force of the seat against the land is generated by
the spring. The spring force needs to be sufficient to close against hydraulic
forces, yet minimized to allow he magnetic force to lift the seat from the land
sufficient distance to allow maximum flow.
Existing devices may use a variety of means to adjust the spacing
between the seat and land, including placing shims under the land or seat, or
having a threaded adjustmen: screw n the orifice component. As shown in
Figure 17 A, however, a typical threaded adjustment in the orifice does not seal
between the orifice body 250 and the valve body 252, leaving a leak path 254
between threads 256. Such a threaded adjustment requires that the threads 256
be sealed against fluid leakage. A separate seal, such as an o-ring or gasket
provides this seal.
In accordance with aspects of the present invention, the orifice 244 and/or
land are made of a plastic material, such as VESPEL®, which is machinable into
a threaded component with a precision orifice. As shown in the exemplary
embodiment illustrated in Figure 17B, the threads 256 are machined oversized so
that there is an interference fit 258 between the orifice body 250 and valve body
252, thus sealing, eliminating the need for a separate seal (o-ring or gasket). The
orifice land now is the deformable member simplifying the design and
manufacture of the valve seat 240 and plunger 234 (referring to Figures 15 and
16).

The present invention, however, is not necessarily limited to any specific
valve plunger configuration. In alternative embodiments, a pump is used in place
of the valve. A metering pump for example, may be used for fluid control
purpose. In particular, a piezoelectric pump may be employed that includes a
plurality of piezoelectric tube portions. The piezoelectric tube portions are
controlled in a manner to cause different tube portions to constrict or expand,
thus allowing the fluid flow to be controlled as desired.
The particular embodiments disclosed above are illustrative only, as the
invention may be modified and practiced in different but equivalent manners
apparent to those skilled in the art having the benefit of the teachings herein.
Furthermore, no limitations are intended to the details of construction or design
herein shown, other than as claimed hereinafter. It is therefore evident that the
particular embodiments disclosed above may be altered or modified and all such
variations are considered within the scope and spirit of the invention as claimed.

WE CLAIM:
1. A Coriolis mass flow senser (1), comprising:
a flow sensor tube (16) having first and second ends; and
first and second piezoelectric stacks (42) positioned on the respective first and
second ends of the flow sensor tubs (16);
wherein the piezoelectric and reverse piezoelectric effects cause the flow sensor
tube (16) to vibrate and sense the twist in the flow sensor tube (16) due to Coriolis force.

A Coriolis mass flow sensor (1) is disclosed. The Coriolis mass flow sensor
comprises a flow sensor tube (16) having first and second ends, and first and second
piezoelectric stacks (42) positioned on the respective first and second ends of the flow
sensor tube (16), wherein the piezoelectric and reverse piezoelectric effects cause the
flow sensor tube (16) to vibrate and sense the twist in the flow sensor tube (16) due to
Coriolis force.

Documents:

904-KOL-2005-CORRESPONDENCE 1.1.pdf

904-KOL-2005-CORRESPONDENCE 1.2.pdf

904-KOL-2005-FORM 1 1.1.pdf

904-kol-2005-granted-abstract.pdf

904-kol-2005-granted-claims.pdf

904-kol-2005-granted-correspondence.pdf

904-kol-2005-granted-description (complete).pdf

904-kol-2005-granted-drawings.pdf

904-kol-2005-granted-examination report.pdf

904-kol-2005-granted-form 1.pdf

904-kol-2005-granted-form 18.pdf

904-kol-2005-granted-form 2.pdf

904-kol-2005-granted-form 3.pdf

904-kol-2005-granted-form 5.pdf

904-kol-2005-granted-gpa.pdf

904-kol-2005-granted-reply to examination report.pdf

904-kol-2005-granted-specification.pdf

904-KOL-2005-OTHERS 1.1.pdf

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Patent Number

229503

Indian Patent Application Number

904/KOL/2005

PG Journal Number

08/2009

Publication Date

20-Feb-2009

Grant Date

18-Feb-2009

Date of Filing

30-Sep-2005

Name of Patentee

EMERSON ELECTRIC CO.

Applicant Address

8100 WEST FLORISSANT, ST. LOUIS, MISSOURI 63136

Inventors:

#	Inventor's Name	Inventor's Address
1	BARGER MICHAEL J	596 BECK ROAD, SOUDERTON PA
2	DILLE JOSEPH C	623 COUPATH ROAD,TELFORD PA
3	WHITELEY JEFFERY L	369 DEERWOOD LANE, QUAKERTOWN, PA
4	SCOTT TIMOTHY W	138 WENTWORTH DRIVE, LANSDALE PA

PCT International Classification Number

G 01 F 1/84

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/111,504	1998-12-08	U.S.A.
2	09/326,949	1999-06-07	U.S.A.
3	09/430,881	1999-11-01	U.S.A.