Title of Invention

"AN IMPROVED HYDRAULIC COUPLING DEVICE FOR USE WITH IN WATER PRESSURE TRANSDUCERS"

Abstract An improved hydraulic coupling device for use within water pressure transducers, wherein the said device comprising a plurality of oil-filled metallic multiple U-shaped bends formed from a capillary tube [12] to prevent escape of oil during the movements of the transducer and one end of the said capillary tube being attached to the hydraulic pressure inlet through attachment means of the transducer [9] while the other end of the said capillary tube terminating on a metallic disk [14] being fixed on the end cap [15] of the transducer housing [17] for the transfer of the sea water pressure to the transducer, to prevent direct physical contact of the transducer [18] to sea water, preventing thereby marine corrosion of the said transducer.
Full Text The present invention relates to an improved hydraulic coupling device for use with in-water pressure based systems.
More particularly, this invention relates to a hydraulic coupling device for preventing marine corrosion, and to be used with in-water pressure transducers for the measurements of sea level; water levels in lakes, estuaries and fjords; sea surface waves; Conductivity -Temperature - Depth (CTD) profiler; Acoustic Doppler Current Profiler (ADCP); other moored Eulerian water current meter systems; and in several other oceanographic instruments and under-water vehicles where seawater pressure is to be measured.
In-water pressure transducers are devices, which convert water pressure into an equivalent electrical signal; for example A. Joseph [in "Modern techniques of sea level measurement", Encyclopaedia of Microcomputers, Vol. 23 (Supplement 2), pp.319- 344, (1999)], describes one form of a strain gauge pressure transducer, which consists of a photo-etched grid of electrical resistance foil, which is bonded on to one side of a thin metallic diaphragm using an adhesive. Strain-gauge-based pressure transducers convert water pressure to electrical signal utilizing four strain gauges, configured in the form of a full Wheatstone bridge network. A pressure change acting on the pressure sensing diaphragm leads to a corresponding electrical resistance variation in the resistance foil, which is then converted into an equivalent voltage change in the output signal.
In an alternate form of resistance strain gauge (C. Cox, T. Deaton and S. Webb, in "A deep-sea differential pressure gauge", J. Atmos. Oceanic Technol. Vol.1, pp.237-246, 1984), the sensing transducer is a thin
diaphragm made up of a single crystal silicon on which a resistance strain gauge has been created, and isolated from the bulk silicon by PN junctions (PN junction made from P-type and N-type silicon).
In a quartz pressure transducer, the key sensing element is a quartz crystal oscillating beam, which forms an integral part of a crystal oscillator, whose resonant frequency of vibration varies with the water-pressure induced axial loads.
For oceanographic applications, a hydraulic coupling device needs to be attached to the water-pressure port of the transducer in order to prevent corrosive destruction of the pressure-sensing element as a result of its physical contact with seawater. The said hydraulic coupling device consists of a jacket, which is filled with a viscous fluid such as silicone oil whose viscosity is approximately 500 centi-Stokes.
Hitherto known hydraulic coupling devices incorporated in the in-water pressure transducers have been used in deep-sea tide gauges. For example J.H. Filloux ["Deep sea tide gauge with optical readout of Bourdon tube rotations", Nature, Vol. 226, pp. 935-937, (1970)] describes a gauge where the seawater pressure intake front-end consists of a flexible membrane stretched across the pressure case of the instrument. A compartment behind the membrane is filled with oil, which connects to the pressure inlet of a free-hanging Bourdon helix attached to an optical arrangement, which measures changes in seawater pressure. The membrane is exposed to seawater pressure through an insulating fluid, devoid of air bubbles or other hollow closed spaces, which can be acted upon by the ambient seawater pressure.
The drawback of this hydraulic coupler is that the large exposed area of the membrane, though suitable for deep sea applications, is unsuitable in shallow or euphotic waters where bio-fouling affects the sensitivity response function of the gauge to pressure changes.
The hydraulic coupling device of the Harvard deep sea gauge by D.J. Baker. Jr [Rep. Meteorol. Oceanogr., No.4, Cambridge , (1971)]; also by G. Dietrich, K. Kalle, W. Kraus and G. Siedler [in "Measurement of water level variations", General Oceanography: An Introduction, pp.128-131, (1980)] is an oil - filled bag in a separate enclosure. The oil in the bag is routed through a capillary tube to the pressure port of quartz Bourdon tube, which senses seawater pressure variations relative to a reference pressure. The drawback here is the use of a separate oil bag in a separate sealed enclosure, thereby resulting in an unwieldy arrangement.
The quartz pressure transducer has gained prominence in accurate sea level measurements. The said transducer (Fig.1), produced by Paroscientific Inc. (U.S.A), comprises of a hydraulic coupling device [1] with one end attached to the pressure inlet [2] of the casing [3], and whose other end connected to the pressure port [4] of the pressure sensing device [5], where the hydraulic coupling device is a silicone oil-filled flexible plastic capillary tube of diameter 1mm, and approximate length 20 cm. Here, one end of the capillary is mounted on the end-cap of the transducer case, and the other end is connected to its pressure inlet. The device lacks compactness, and results in a slow leakage of oil over time, as we have observed in field studies.
Strain gauge pressure transducers made by Macurex Sensors Ltd. (Bangalore, India) have found applications in Indian space technology, and the front-end of this device has been converted by us for oceanographic measurements with the addition of a hydraulic coupling device, which is the subject matter of this invention. A cross sectional view of the transducer is given in Fig. 2. The said device comprises of a strain gauge foil [6], bonded on a steel diaphragm [7], which is exposed to a pressure connector [8] having a pressure inlet [9]. The strain gauge foil is electrically connected to a temperature-compensating resistor wire, which is wound on a bobin [10], and sealed in a housing [11].
The main object of the present invention is to provide an improved hydraulic coupling device for preventing marine corrosion of the pressure-sensing element of in-water pressure transducers.
Another object of the present invention is to provide a compact flat-faced hydraulic coupling device, which minimizes dynamically-induced errors in pressure measurement.
Yet another object of the present invention is to provide a hydraulic coupling device useful for integration on an in-water instrument's end-cap and in close proximity to the pressure-sensing diaphragm of the transducer.
Still another object of the present invention is to provide a hydraulic
coupling device, which allows for easy replacement of oil in the capillary tube.
The novelty and inventive steps of the present invention provide for a
compact flat-faced hydraulic coupling device, which is suitable for integration
to any in-water devices such as the end-cap of in-water instruments, remotely
operated underwater vehicles (ROVs), autonomous underwater vehicles (AUVs) and so forth for preventing marine corrosion of the pressure-sensing element of in-water pressure transducers. The device of the present invention allows for easy replacement of oil in the capillary tube by merely unplugging the device from its slot, pouring oil into the pressure port, and then plugging it back again, and locking it, thereby preventing trapping of air bubbles or other hollow closed spaces in the capillary.
In the drawings accompanying this specification:
Fig.1 illustrates the geometry of Paroscientific pressure transducer, which comprises a silicone oil filled capillary tube [1] with one end attached to
the pressure inlet [2] of the casing [3], and whose other end connected to the pressure port [4] of the sensor [5] (prior art).
Fig. 2 illustrates the Macurex pressure transducer, which comprises of a strain gauge foil [6], bonded on a steel diaphragm [7], which is exposed to a pressure connector [8] having a pressure inlet [9]. The strain gauge foil is electrically connected to a temperature-compensating resistor wire, which is wound on a bobin [10], and sealed in a housing [11] (prior art).
Fig. 3 illustrates the improved hydraulic coupling device, of the present invention, which comprises of an oil-filled multiple-U-shaped capillary tube [12] sandwiched between two halves of a plug [13]. One end of the capillary terminates on a copper disc [14] fixed on the end-cap [15], with brass or copper screws [16], of the transducer housing [17]; the other end dips to the pressure port [9] of the transducer [18].
Accordingly, the present invention provides an improved hydraulic coupling device for preventing marine corrosion of in-water pressure transducers, wherein the said device comprising a plurality of oil-filled metallic multiple U-shaped bends formed from a capillary tube [12] to prevent escape of oil during the movements of the transducer and one end of the said capillary tube being attached to the hydraulic pressure inlet through attachment means of the transducer [9] while the other end of the said capillary tube terminating on a metallic disk [14] being fixed on the end cap [15] of the transducer housing [17] for the transfer of the sea water pressure to the transducer, to prevent direct physical contact of the transducer [18] to
sea water, preventing thereby marine corrosion of the said transducer.
In an embodiment of the present invention, the improved hydraulic coupling device consists of an oil-filled multiple-U-shaped capillary tube [12], wherein a multiplicity of "U" shapes offers resistance to the outflow of oil from the capillary tube.
In another embodiment of the present invention, the multiple-U-shaped capillary tube [12] is selected from copper or copper alloy to inhibit bio-fouling of the said capillary tube.
In yet another embodiment of the present invention, the multiple-U-shaped capillary tube [12] is sandwiched between two halves of a plug [13], to permit its easy fixture.
In still another embodiment of the present invention, the plug [13] is fabricated from a non-metal or from a similar metal as that of the capillary
tube [12] and the end-cap [15], thereby preventing corrosive damage arising from contact between dissimilar metals.
In a further embodiment of the present invention, the exterior end of the capillary tube terminates on a disc [14] made of copper or copper alloy to inhibit marine growth in the vicinity of the pressure inlet, thereby preventing partial or full closure of the pressure inlet during long-term deployments in euphotic zones.
The procedure of attachment of the hydraulic coupling device of the present invention to a pressure transducer shown in Fig. 2, which is used in the present case for sea level measurements, and the functioning of the present invention with reference to a typical case of sea level gauge (Fig. 3), are discussed in detail with reference to the following example, and should not be construed to limit the scope of the present invention.
With reference to Fig. 3, the transducer [18] is attached to the end-cap [15], with suitable neoprene rubber "O"-rings to prevent entry of seawater into the transducer housing [17]. The said end-cap [15] is rigidly attached to the said transducer housing [17] through a suitable attachment means. Holding the end-cap [15] in an up-right position, viscous oil (silicone oil in the present case) is then slowly poured into the pressure inlet [9] of the pressure transducer [18] through the axial slot on the end-cap [15]. Subsequently, the oil is carefully shaken to ensure that air bubbles, if any, trapped within the pressure inlet have completely escaped from the pressure inlet. A visual inspection is also carried out to confirm the total absence of air bubbles within the pressure inlet. Subsequently, the multiple-U-shaped capillary tube [12],
which is sandwiched between two halves of a plug [13], is carefully inserted into its designated slot on the end-cap [15]. The excess oil present at the pressure inlet of the transducer naturally oozes out through the multiple-U-shaped capillary tube [12], which is the only escape route for the excess oil, thereby completely pushing out the air within the capillary tube. This procedure ensures that the said capillary tube [12] has been completely filled with the viscous oil, without the presence of air bubbles or other hollow closed spaces. The axial hole on the disc [14], fabricated from copper or copper-alloy, is then inserted into the exterior end of the capillary tube. The said exterior end of the capillary tube thus terminates on the copper disc [14]. The said disc [14] is then fixed on the end-cap [15], with brass or copper screw [16]. Presence of this copper disc in close contact with the pressure inlet helps to inhibit marine growth in the vicinity of the pressure inlet, thereby preventing partial or full closure of the pressure inlet during long-term deployments in euphotic zones.
The functioning of the present invention with reference to a typical case of sea level gauge can be summarized as follows:
The hydraulic coupling device of the present invention is attached to a pressure transducer as detailed above. The pressure transducer detects sea level and its temporal variations based on the hydrostatic pressure head above its pressure inlet. Accordingly, the pressure inlet of the transducer is to be located at a known fixed datum level under water. In practice, the transducer can be (1) mounted on a platform — which can be made to rest on the sea floor
(2) mounted on a staff driven into the seabed, or
(3) attached to an existing structure.
The pressure inlet is attached to a suitable hydro-mechanical front-end to abate dynamically induced measurement inaccuracies arising from the influence of flows, waves, or a combination of flows and waves [A. Joseph, J.A.E. Desa, P. Foden, K. Taylor, J. McKeown, and E. Desa., "Evaluation and performance enhancement of a pressure transducer under flows, waves, and a combination of flows and waves", J. Atmos. Oceanic Technol., Vol. 17, No.3, pp. 357-365 (2000)]. The hydraulic coupling device of the present invention transfers the hydrostatic pressure, corresponding to the water head above the pressure inlet, to the pressure transducer. The oil present in the said hydraulic coupling device prevents direct contact of the pressure transducer with the seawater, thereby abating corrosive damage to the pressure transducer. The time-constant of the multiple-U-shaped capillary tube [12] provides a certain level of mechanical filtering of the high-frequency oscillations present in pressure measurements, caused primarily by wind-induced gravity waves and secondly by the movements of ships and boats. An active band-pass filter in the hardware circuitry does further filtering of the signal for removal of high frequency noise. Subsequent averaging of the pressure samples acquired over a sufficiently long time-period (45 s or more in usual practice) during data acquisition, under software control, recovers the tide-induced slow oscillations of water pressure. The filtered fluid pressure is translated to water level above the pressure inlet with the use of depth-mean water density.
The improved hydraulic coupling device of the present invention has been used in extensive field trials, in coastal seas and fjords, over two years, with sea level gauges incorporating the Macurex pressure transducer of Fig. 2 without any detectable corrosive effects on the transducer, thereby validating the effectiveness of this device. The main advantages of the present invention are:
1. It prevents direct physical contact of the pressure transducer to seawater,
preventing thereby marine corrossive damage of the said in-water
pressure transducer.
2. It prevents the escape of oil out of the oil-chamber during the movements
of the transducer (e.g., transportation and deployments). This feature has
been achieved through a plurality of multiple U-shaped bends formed from
the capillary tube.
3. It permits easy fixture.
4. It inhibits marine growth in the vicinity of the pressure inlet, thereby
preventing partial or full closure of the pressure inlet during long-term
deployments in euphotic zones.
5. It provides a miniature flat-faced embedded oil-chamber, which is confined
within a cylindrical plug, which forms an integral component of the end-
cap of the pressure transducer housing.





We claim:
1. An improved hydraulic coupling device for preventing marine corrosion of in-water pressure transducers, wherein the said device comprising a plurality of oil-filled metallic multiple U-shaped bends formed from a capillary tube [12] to prevent escape of oil during the movements of the transducer and one end of the said capillary tube being attached to the hydraulic pressure inlet through attachment means of the transducer [9] while the other end of the said capillary tube terminating on a metallic disk [14] being fixed on the end cap [15] of the transducer housing [17] for the transfer of the sea water pressure to the transducer, to prevent direct physical contact of the transducer [18] to sea water, preventing thereby marine corrosion of the said transducer.
2. An improved hydraulic coupling device as claimed in claim 1 wherein the
metal used for the said capillary tube [12] is selected from copper or its
alloys, wherein the pressure based system is selected from pressure
transducers.
3. An improved hydraulic coupling device as claimed in claims 1-2 wherein
the multiple-U-shaped capillary tube [12] is sandwiched between two
halves of a plug [13].
4. An improved hydraulic coupling device as claimed in claims 1-3 wherein
the plug [13] is selected from a non-metal or of a similar metal as that of
the capillary tube [12] and the end-cap [15].
5. An improved hydraulic coupling device as claimed in claims 1-4 wherein
the exterior end of the capillary tube terminates on a disc [14].
6. An improved hydraulic coupling device as claimed in claims 1-5 wherein the disc claimed in claim 6 is selected from copper or copper alloy so as to inhibit marine growth in the vicinity of the pressure inlet.

Documents:

487-del-1999-abstract.pdf

487-del-1999-claims.pdf

487-del-1999-correspondence-others.pdf

487-del-1999-correspondence-po.pdf

487-del-1999-description (complete).pdf

487-del-1999-drawings.pdf

487-del-1999-form-1.pdf

487-del-1999-form-19.pdf

487-del-1999-form-2.pdf

487-del-1999-form-4.pdf

487-del-1999-form-5.pdf


Patent Number 215625
Indian Patent Application Number 487/DEL/1999
PG Journal Number 11/2008
Publication Date 14-Mar-2008
Grant Date 28-Feb-2008
Date of Filing 31-Mar-1999
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 ELGAR DESA, NATIONAL INSTITUTE OF OCEANOGRAPHY, DONA PAULA, GOA-403004, INDIA.
2 ANTONY JOSEPH, NATIONAL INSTITUTE OF OCEANOGRAPHY, DONA PAULA, GOA-403004, INDIA.
3 DENNIS RODRIGUES, NATIONAL INSTITUTE OF OCEANOGRAPHY, DONA PAULA, GOA-403004, INDIA.
4 VISHWAMBER CHODANKAR NATIONAL INSTITUTE OF OCEANOGRAPHY, DONA PAULA, GOA-403004, INDIA.
5 SURYAKANT TENGALI NATIONAL INSTITUTE OF OCEANOGRAPHY, DONA PAULA, GOA-403004, INDIA.
PCT International Classification Number F16D 43/28
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA