METHOD AND SYSTEM TO COMPENSATE FOR TEMPERATURE AND PRESSURE IN PIEZO RESISTIVE DEVICES

• US 20120247175A1
• Filed: 03/31/2011
• Published: 10/04/2012
• Est. Priority Date: 03/31/2011
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Dawson, Chad S., Krishna, Siddhartha Gopal, Varma, Vikram
• Granted Patent: US 8,701,460 B2
• Time in Patent Office: Days
• US Class Current: 73/1.59
• CPC Class Codes: G01L 27/002 Calibrating, i.e. establishing true relation between transducer output value and value to be measured, zeroing, linearising or span error determination
• CPC Class Codes: G01L 27/005 Apparatus for calibrating pressure sensors
• CPC Class Codes: G01L 9/065 with temperature compensating means non electric temperature compensating means G01L19/04

Abstract

A method and system to calibrate temperature and pressure in piezo resistive devices for non-linear sensors having two variables, where a piezo resistive device such as a piezo resistive transducer (PRT) used for example in a pressure sensor system is calibrated to calculate actual/ambient temperature and pressure even though the PRT impedance is unbalanced relative to pressure.

Claims

1. A method of calibrating a piezo resistive device, comprising:

providing a piezo resistive element having a fluctuating resistivity in the piezo resistive device;

receiving signals representative of the temperature and pressure readings of the piezo resistive device;

calculating a first temperature as a function of the signal representative of temperature reading of the piezo resistive device; and

calculating an actual pressure as a function of the first temperature and the signal representative of pressure reading of the piezo resistive device.

2. The method of claim 1, further comprising calculating an actual temperature as a function of the first temperature and the actual pressure.

3. The method of claim 2, wherein calculating the actual temperature with a constant of the actual pressure calculated for calibrating the piezo resistive device.

4. The method of claim 1, further comprising empirically determining a value of the constant of the actual pressure.

5. The method of claim 1, wherein calculating the signal representative of first temperature is a function of the temperature reading and the signal representative of pressure reading.

6. The method of claim 5, wherein the first temperature is an actual temperature.

7. The method of claim 6, wherein calculating the actual pressure as a function of the actual temperature and the signal representative of pressure reading of the piezo resistive device.

8. The method of claim 1, wherein the piezo resistive device is arranged within a pressure sensor.

9. The method of claim 1, further comprising providing at least four piezo resistive elements forming the piezo resistive device and each piezo resistive element having a fluctuating resistivity.

10. A system of calibrating a piezo resistive device, comprising:

a piezo resistive element having a fluctuating resistivity in the piezo resistive device; and

a processor for receiving signals representative of the temperature and pressure readings of the piezo resistive device;

calculating a first temperature as a function of the signal representative of temperature reading of the piezo resistive device; and

calculating an actual pressure as a function of the first temperature and the signal representative of pressure reading of the piezo resistive device.

11. The system of claim 10, further comprising calculating an actual temperature as a function of the first temperature and the actual pressure.

12. The system of claim 11, wherein calculating the actual temperature with a constant of the actual pressure calculated for calibrating the piezo resistive device.

13. The system of claim 10, further comprising empirically determining a value of the constant of the actual pressure.

14. The system of claim 10, wherein calculating the first temperature is a function of the signal representative of temperature reading and the signal representative of pressure reading.

15. The system of claim 14, wherein the first temperature is an actual temperature.

16. The system of claim 15, wherein calculating the actual pressure as a function of the actual temperature and the signal representative of pressure reading of the piezo resistive device.

17. The method of claim 10, wherein the piezo resistive device is arranged within a pressure sensor.

18. The system of claim 10, further comprising an analogue to digital converter (ADC) for converting the signals representative of temperature and pressure from the piezo resistive device and coupled to the processor.

19. The apparatus of claim 10, wherein the piezo resistive device is a piezo resistive transducer comprising at least four piezo resistive elements forming the piezo resistive device and each piezo resistive element having a fluctuating resistivity.

20. The system of claim 10, wherein the piezo resistive device is a non-linear sensor and has at least two variables that have cross-dependency.