Method and system to compensate for temperature and pressure in piezo resistive devices

• US 8,701,460 B2
• Filed: 03/31/2011
• Issued: 04/22/2014
• 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: Krishna, Siddhartha Gopal, Dawson, Chad S., Varma, Vikram
• Primary Examiner(s): Williams, Hezron E
• Assistant Examiner(s): Shabman, Mark A
• Application Number:
  US13/077,963
• Publication Number:
  US 20120247175A1
• Time in Patent Office: 1,118 Days
• Field of Search: 73/15.7
• 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 system of calibrating a piezo resistive device, comprising:

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

a processor, coupled to the piezo resistive element, for receiving signals representative of temperature and pressure readings of the piezo resistive element, calculating a first temperature as a function of the signal representative of the temperature reading, calculating an actual pressure as a function of the first temperature and the signal representative of the pressure reading, and calculating an actual temperature as a function of the first temperature, and the actual pressure times a constant (k).

2. The system of claim 1, wherein a value of the constant of the actual pressure is determined empirically.

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

4. The system of claim 3, wherein the first temperature is an actual temperature.

5. The system of claim 4, wherein calculating the actual pressure is a function of the actual temperature and the signal representative of the pressure reading of the piezo resistive device.

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

7. The system of claim 1, further comprising an analogue to digital converter (ADC), connected between the piezo resistive element and the processor, for converting the signals representative of temperature and pressure from analog signals to digital signals read by the processor.

8. The system of claim 1, wherein the piezo resistive device is a piezo resistive transducer comprising at least four piezo resistive elements and each piezo resistive element has a fluctuating resistivity.

9. The system of claim 1, wherein the piezo resistive device is a non-linear sensor and has at least two variables that have cross-dependency.