Method for self-monitoring a ceramic pressure measuring cell of a capacitive pressure sensor and evaluation circuit for carrying out said method

• US 9,316,557 B2
• Filed: 12/07/2011
• Issued: 04/19/2016
• Est. Priority Date: 12/08/2010
• Status: Active Grant

• Current Assignee: I F M Electronic GmbH
• Original Assignee: I F M Electronic GmbH
• Inventors: Walter, Heinz
• Primary Examiner(s): WILLIAMS, HEZRON
• Assistant Examiner(s): Kidanu, Gedeon M
• Application Number:
  US13/883,851
• Publication Number:
  US 20130269412A1
• Time in Patent Office: 1,595 Days
• Field of Search: 73 157- 169, 737/08, 737/18, 737/24, 361/283, 374/143, 702/98
• US Class Current: 1/1
• CPC Class Codes: G01L 25/00 Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
• CPC Class Codes: G01L 27/007 Malfunction diagnosis, i.e. diagnosing a sensor defect
• CPC Class Codes: G01L 9/003 using variations in capacitance
• CPC Class Codes: G01L 9/12 by making use of variations in capacitance , i.e. electric circuits therefor

Abstract

A method for monitoring the operation of a pressure measuring cell (10) of a capacitive pressure sensor (1), wherein the pressure measuring cell (10) has a measuring capacitor (C_M) and a reference capacitor (C_R) and the pressure measuring value (p) is obtained from the capacity values of the measuring capacitor (C_M) and the reference capacitor (C_R), characterized in that a control pressure measuring value (p′) is obtained with an auxiliary capacitor (C_Z) arranged outside the pressure measuring cell (10) and the operability of the pressure measuring cell (10) is inferred by comparing the pressure measuring value (p) to the control pressure measuring value (p′) is provided.

Claims

1. A method comprising:

monitoring an operation of a pressure measuring cell of a capacitive pressure sensor, wherein a pressure measuring cell has a measuring capacitor and a reference capacitor and the pressure measuring value is obtained from the capacity values of the measuring capacitor (C_M) and the reference capacitor;

wherein a control pressure measuring value is obtained with an auxiliary capacitor arranged outside the pressure measuring cell and the operability of the pressure measuring cell is inferred by comparing the pressure measuring value to the control pressure measuring value.

5. The method of claim 1, wherein the pressure measuring value and/or the control pressure measuring value is obtained with the aid of a quotient method.

6. The method of claim 1, wherein the control pressure measuring value is obtained from the capacity values of the measuring capacitor and the auxiliary capacitor.

7. The method of claim 1, wherein the control pressure measuring value is obtained from the capacity values of the reference capacitor and the auxiliary capacitor.

8. The method of claim 1, wherein the capacitive pressure sensor is calibrated in such a way that the control pressure measuring value and the pressure measuring value have the same functional dependence on the processing pressure and a case of malfunction is present if the difference between the pressure measuring value and the control pressure measuring value exceeds a predetermined limit value.

12. The method of claim 1, wherein the capacity of the auxiliary capacitor is independent from a pressure of a membrane of the pressure measuring cell.

2. A method comprising:

monitoring an operation of a pressure measuring cell of a capacitive pressure sensor, wherein the pressure measuring cell has a measuring capacitor and a reference capacitor and a pressure measuring value is obtained from the capacity values of the measuring capacitor and the reference capacitor;

wherein a processing unit comprising at least one converter unit and a microcontroller is provided, in which the capacity values of the measuring capacitor as well as the reference capacitor are registered, the pressure measuring value is formed from the two capacity values, and another capacity value is registered, which corresponds to an auxiliary capacitor and from which a control pressure measuring value is obtained, wherein the operability of the pressure measuring cell is inferred by comparing the pressure measuring value to the control pressure measuring value.

3. The method of claim 2, wherein the auxiliary capacitor is configured as an element outside the pressure measuring cell, whose capacity value is registered by the processing unit.

4. The method of claim 2, wherein the auxiliary capacitor is configured in the form of a capacity value stored in the processing unit, in particular in the microcontroller.

13. The method of claim 2, wherein the capacity of the auxiliary capacitor is independent from a pressure of a membrane of the pressure measuring cell.

9. An evaluation circuit for a capacitive sensor comprising:

a measuring capacitor and a reference capacitor, wherein the reference capacitor is provided in a differential branch and the measuring capacitor is provided in an integrating branch, which are connected in parallel and on which a voltage signal is applied, wherein the output signal of the integrating branch is fed to the differential branch, at whose output a first pressure-dependent output signal is applied;

wherein a control measuring branch is connected to an auxiliary capacitor in parallel with the differential branch and the output signal of the integrating branch is additionally fed to the control measuring branch, at whose output a second pressure-dependent output signal is applied, and both output signals are fed to a comparator unit, at whose output a diagnosis signal is emitted.

10. The evaluation circuit of claim 9, wherein the auxiliary capacitor is arranged outside the pressure measuring cell.

11. The evaluation circuit of claim 9, wherein the capacitive sensor is a pressure sensor.

14. The evaluation circuit of claim 9, wherein the capacity of the auxiliary capacitor is independent from a pressure of a membrane of the pressure measuring cell.