Title of Invention

AN INTEGRAL DIAPHRAGM ABSOLUTE PRESSURE TRANSDUCER

Abstract

The invention relates to an integral diaphragm absolute pressure transducer. It comprises of a diaphragm fixed to a pressure port having a pressure inlet tube for exposing the diaphragm to the pressure to be measured. One or more strain gauge is attached to the said diaphragm on the side opposite to the said pressure inlet and enclosed in an evacuated hermetically sealed chamber leads of the strain gauge being taken out through an insulated sealing to an upper cover.

Full Text

The invention relates to an integral diaphragm absolute pressure transducer with built-in regulator which provides relatively high output. Pressure transducers generally available provide an output voltage of the order of millivolts. They do not have input/output protection and are bulky, heavy and are of non-hermat ic types. The invention provides an integral diaphragm absolute pressure transducer which provides relatively high output of the order of few volts and low power consumption of the order of 200 milliwatts. The transducer according to the invention is light and can be made with a weight of less than 200 grams. It has a linearity of better than 0.2% at full scale output and a hysteresis better than 0.2 % at full scale output. The transducer according to the invention has high reliability and measures absolute pressure. Thus the invention provides an integral diaphragm absolute pressure transducer comprising a diaphragm fixed to a pressure port having a pressure inlet tube for exposing the diaphragm to the pressure to be measured, at least one strain gauge attached the said diaphragm on the side opposite to the said pressure inlet and enlosed in an evacuated hermetically sealed chamber, leads of the strain guage being taken out through an insulated sealing to an upper cover. In a prefered embodiment the output from the strain gauge is fed to an electronic circuit for providing higher output with output protection. The invention will now be described with reference to the accompanying drawing, in which : Fig. 1 shows the integral diaphragm absolute pressure transducer according to the invention; Fig. 2 shows the various parts of the transducer in an exploded view; Fig, 3 shows the electronic circuit provided with the transducer in a prefered embodiment. Refering to figures 1 and 2, a diaphragm (9) integral with a pressure port (10) connected to a pressure tube (11) for exposing the diaphragm (9) to the pressure to be measured. One or more strain guages (8) are bonded on the diaphragm (9) on the side opposite to the pressure port (10). The output wires from the strain gauges (8) are taken out through a glass to metal seal (7) providing an evacuated chamber (13) between the diaphragm (9) and the glass to metal seal (7). The output from the strain gauges (8) are fed to the input of the electronic circuit shown in fig, 3 through a temperature compensating network wound on a bobbin (5) provided in an upper housing (6). A printed circuit board (4) is used for connecting the temperature compensated output from strain gauges to the electronic circuit (3). A ring (12) encloses the assembly of diaphragm with strain gauges, the evacuated chamber and glass to metal seal. The ring (12) is welded to an upper cover (2), which house the electronic circuit (3). An electrical connector (1) is attached to the upper cover (2) for taking out the output from the electronic circuit. The electron beam welded joints are shown with reference letters A, B, C, D, E, F and G. These are the welded joints between the pressure inlet tube (11) and pressure port (10), between the pressure port (10) and the diaphragm (9), between the diaphragm (9) and the ring (12), between the diaphragm (9) and the upper housing (6), between the upperhousing (6) and glass to metal seal (7), between the ring (12) and the upper cover (2) and between the upper cover (2) and electrical connector (1) respectively. The evacuated chamber (13) is hermetically sealed from outside. The electronic circuit (3) is shown in detail in fig. 3. Reference numerals 101, 102 and 104 indicate the output terminals and 103, 105 and 106 indicate the input terminals. The input terminals 103, 105 and 106 are connected through a filter (Li) to a voltage regulating circuit consisting of diode Di resistor R1, Zenerdiode Z1, transorb T and a voltage regulator integrated circuit (Ui). The regulated output is fed to a bridge circuit (WB) provided with temperature stabilising resistors RTI, RT2 and RT3 and filter capacitors C3 and C4. The temperature compensated output from the bridge circuit (WB) is fed to the output terminals (101, 102 and 104) through instrumentation amplifiers U2 and U3. R2, R3 and R4 are resistors and C1, C2 and C5 are capacitors used in the circuit shown in fig. 3 as discrete components. The integral diaphragm absolute pressure transducer according to the invention has improved linearity, low hysteresis, higher reliability, large output voltage range, better signal to noise ratio and excellent repeatability. The transducer according to the invention also withstands vibration, pyro-shock and pressures upto 800 bars thus reducing the tendency to burst in use. This transducer is suitable for space application. WE CLAIM : 1. An integral diaphragm absolute pressure transducer comprising a diaphragm (9) fixed to a pressure port (10) having a pressure inlet tube (11) for exposing the diaphragm to the pressure to be measured, at least one strain gauge (8) attached the said diaphragm (9) on the side opposite to the said pressure inlet and enclosed in an evacuated hermetically sealed chamber (13) leads of the strain guage being taken out through an insulated sealing (7) to an upper cover (2). 2. The transducer as claimed in claim 1, wherein the output from the strain gauge (8) is connected through a temperature compensating network (5) to an electronic circuit (3) for providing a stable amplified output. 3, The transducer as claimed in claim 1, wherein the assembly of the strain gauge (8), the evacuated chamber (13) and glass metal seal (7) are enclosed together. 4. The transducer as claimed in claim 2, wherein the electronic circuit (3) is connected to the output from strain gauges (8) through a printed board (4). 5. The transducer as claimed in claim 3, wherein the said ring (12) is welded to an upper cover (2) and the electronic circuit (3) is housed in the said upper cover (2). 6. The transducer as claimed in claim 5, wherein an electrical connector (1) is attached to the said upper cover (2) through which the output from the electronic circuit (3) is taken out for external connection. 7. The transducer as claimed in any one of the previous claims, wherein the electronic circuit is provided with input/output protection. 8. The transducer as claimed in any one of the previous claims, wherein the joints (A, B, C, D, E, F and G) between the pressure inlet tube (11) and the pressure tube (10), between the pressure port (10) and the diaphragm (9), between the diaphragm (9) and the ring (12), between the diaphragm (9) and the upper housing (6), between the ring (12) and the uper cover (2) and between the upper cover (2) and electrical connector (1) respectively are welded joints. 9. An integral diaphragm absolute pressure transducer, substantially as hereinabove described and illustrated with reference to the accompanying drawings.

Documents:

mas-1998-2025-abstract.pdf

mas-1998-2025-claims dublicate.pdf

mas-1998-2025-claims original.pdf

mas-1998-2025-correspondance others.pdf

mas-1998-2025-correspondance po.pdf

mas-1998-2025-description complete dublicate.pdf

mas-1998-2025-description complete original.pdf

mas-1998-2025-drawings.pdf

mas-1998-2025-form 1.pdf

mas-1998-2025-form 19.pdf

mas-1998-2025-form 26.pdf