Temperature compensation of strain gauge output
An apparatus includes a casing defining a fluid flow channel, the casing including one or more diaphragms each defining a portion of the fluid flow channel, a strain gauge disposed on one of the one or more diaphragms, the strain gauge having a characteristic responsive to a pressure of fluid in the fluid flow channel, a temperature-sensitive circuit element disposed on one of the one or more diaphragms, the temperature-sensitive circuit element having a characteristic responsive to a temperature of the fluid in the fluid flow channel, and temperature compensation circuitry electrically coupled to the strain gauge and to the temperature-sensitive circuit element.
1. An apparatus comprising:
a casing defining a fluid flow channel, the casing comprising one or more diaphragms each defining a portion of the fluid flow channel,
a strain gauge disposed on one of the one or more diaphragms, the strain gauge having a characteristic responsive to a pressure of fluid in the fluid flow channel,
a temperature-sensitive circuit element disposed on one of the one or more diaphragms, the temperature-sensitive circuit element having a characteristic responsive to a temperature of the fluid in the fluid flow channel,
wherein the strain gauge and the temperature-sensitive circuit element are both disposed on the same particular diaphragm,
wherein the strain gauge is disposed on a flat surface of a first portion of the particular diaphragm, and
wherein the temperature-sensitive circuit element is disposed on a flat surface of a second portion of the particular diaphragm, and
temperature compensation circuitry electrically coupled to the strain gauge and to the temperature-sensitive circuit element.
2. The apparatus of claim 1 , wherein the temperature compensation circuitry is configured to modify an output of the strain gauge based on the characteristic of the temperature-sensitive circuit element to compensate for temperature variation.
3. The apparatus of claim 1 , wherein the one or more diaphragms are configured to deform in response to the pressure of the fluid.
4. The apparatus of claim 1 , wherein an output of the strain gauge is indicative of a pressure of the fluid.
5. The apparatus of claim 1 , in which
a thickness of the second portion is greater than a thickness of the first portion.
6. The apparatus of claim 1 , wherein the first portion and the second portion are configured to deform in response to the pressure of the fluid, and wherein, at a given fluid pressure, a degree of deformation of the first portion is greater than a degree of deformation of the second portion.
7. The apparatus of claim 1 , wherein the strain gauge is mounted on a backing, the backing providing a thermal time constant for heat transfer between the fluid and the strain gauge that is substantially equal to a thermal time constant for heat transfer between the fluid and the temperature-sensitive circuit element.
8. The apparatus of claim 1 , wherein the temperature-sensitive circuit element comprises a resistor.
9. The apparatus of claim 8 , wherein the resistor has a resistance value sufficient to compensate for temperature-induced pressure span error in an output of the strain gauge.
10. The apparatus of claim 8 , wherein the resistor has a resistance value sufficient to compensate for temperature-induced zero balance pressure error in an output of the strain gauge.
11. The apparatus of claim 1 , wherein the temperature-sensitive circuit element comprises a diode.
12. The apparatus of claim 1 , wherein the temperature compensation circuitry comprises an adjustable circuit element adjustable to calibrate the temperature compensation circuitry.
13. The apparatus of claim 12 , wherein the adjustable circuit element comprises a potentiometer.
14. The apparatus of claim 12 , wherein the adjustable circuit element is automatically adjustable.
15. The apparatus of claim 1 , wherein the temperature compensation circuitry comprises a microcontroller configured to calibrate the temperature compensation circuitry.
16. The apparatus of claim 1 , wherein the strain gauge comprises one or more resistors of a set of multiple resistors forming a Wheatstone bridge.
17. The apparatus of claim 16 , wherein the Wheatstone bridge is configured in a full-bridge arrangement.
18. The apparatus of claim 1 , wherein a groove is defined in the casing.
19. The apparatus of claim 1 , wherein the casing has a diameter of less than 0.06 inches.
20. The apparatus of claim 1 , wherein at least one of the one or more diaphragms has a thickness of less than 0.008 inches.
21. The apparatus of claim 1 , wherein the strain gauge and the temperature-sensitive circuit element are separated along a fluid flow direction of the fluid in the fluid flow channel.
22. The apparatus of claim 1 , wherein the strain gauge and the temperature-sensitive circuit element are separated along a circumferential direction with respect to a fluid flow direction of the fluid in the fluid flow channel.
23. The apparatus of claim 1 , wherein each of the first portion of the particular diaphragm and the second portion of the particular diaphragm is a truncated annulus.
24. A method comprising:
flowing a fluid through a fluid flow channel, one or more diaphragms each defining a portion of the fluid flow channel,
wherein a characteristic of a strain gauge disposed on a flat surface of a first portion of a particular diaphragm of the one or more diaphragms is responsive to a pressure of the fluid in the fluid flow channel, and
wherein a characteristic of a temperature-sensitive circuit element disposed on a flat surface of a second portion of the particular diaphragm is responsive to a temperature, and
modifying an output of the strain gauge based on the characteristic of the temperature-sensitive circuit element to compensate for temperature variation.
25. The method of claim 24 , wherein the characteristic of the strain gauge is responsive to a deformation of the particular diaphragm.
26. The method of claim 24 , comprising determining the pressure of the fluid in the fluid flow channel based on the modified output of the strain gauge.
27. The method of claim 24 , in which modifying the output of the strain gauge comprises applying a voltage to a terminal of the strain gauge, wherein the applied voltage is based on the characteristic of the temperature-sensitive circuit element.
28. The method of claim 24 , wherein a thickness of the second portion of the particular diaphragm is greater than a thickness of the first portion of the particular diaphragm.
29. A method for fabricating a pressure gauge, comprising:
defining a fluid flow path through a casing,
thinning a portion of the casing to form a diaphragm, and
disposing a strain gauge and a temperature-sensitive circuit element on the diaphragm, the strain gauge having a characteristic responsive to a pressure of fluid in the fluid flow path, and the temperature-sensitive circuit element having a characteristic responsive to temperature.
30. The method of claim 29 , wherein the thinning comprises thinning a first portion of the casing to a first thickness and thinning a second portion of the casing to a second thickness, the second thickness being greater than the first thickness.
31. The method of claim 30 , comprising disposing the strain gauge on the first portion of the diaphragm and disposing the temperature-sensitive circuit element on the second portion of the diaphragm.
32. The method of claim 31 , wherein the first portion and the second portion are flat.
33. The method of claim 29 , comprising electrically coupling an output of the strain gauge and an output of the temperature-sensitive circuit element to temperature compensation circuitry, wherein the temperature compensation circuitry is configured to modify the output of the strain gauge based on the characteristic of the temperature-sensitive circuit element.
34. An apparatus comprising:
a casing defining a fluid flow channel, the casing comprising one or more diaphragms each defining a portion of the fluid flow channel,
a strain gauge disposed on one of the one or more diaphragms, the strain gauge having a characteristic responsive to a pressure of fluid in the fluid flow channel,
a temperature-sensitive circuit element disposed on one of the one or more diaphragms, the temperature-sensitive circuit element having a characteristic responsive to a temperature of the fluid in the fluid flow channel,
wherein the strain gauge is mounted on a backing, the backing providing a thermal time constant for heat transfer between the fluid and the strain gauge that is substantially equal to a thermal time constant for heat transfer between the fluid and the temperature-sensitive circuit element, and
temperature compensation circuitry electrically coupled to the strain gauge and to the temperature-sensitive circuit element.
35. The apparatus of claim 34 , wherein the backing is composed of a flexible material.
36. The apparatus of claim 35 , wherein the backing comprises polyimide or polyester.
37. The apparatus of claim 34 , wherein the temperature-sensitive circuit element is mounted on the backing.
38. The apparatus of claim 34 , wherein the thermal time constant for heat transfer between the fluid and the strain gauge is based on a thickness of the backing.
39. The apparatus of claim 34 , wherein the strain gauge comprises a metal film on the backing.