RELATING TO DIAGNOSTICS OF A CAPACITIVE SENSOR

• US 20100043531A1
• Filed: 04/06/2007
• Published: 02/25/2010
• Est. Priority Date: 04/06/2007
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Pietri, Stefano, Marshall, Ray, Garrard, Mike
• Granted Patent: US 8,629,682 B2
• Time in Patent Office: Days
• US Class Current: 73/35.70
• CPC Class Codes: G01L 23/225 circuit arrangements therefor
• CPC Class Codes: G01L 27/007 Malfunction diagnosis, i.e. diagnosing a sensor defect

Abstract

A detector circuit for detecting the presence of a remote capacitive sensor having at least two terminals connected via a protection circuit that includes one or more capacitors, the detector circuit comprising: a current supply for changing the charge on the sensor and the protection circuit, a detector for measuring the voltage on one or more of the terminals; wherein the presence of the sensor is determined by changing the charge on the capacitive sensor and the one or more capacitors of the protection circuit in a predetermined manner such that the voltage measurement on the one or more terminals when the sensor is present is significantly different than when the sensor is absent.

Claims

1. A detector circuit for detecting the presence of a remote capacitive sensor having at least two terminals connected via a protection circuit that includes one or more capacitors, the detector circuit comprising:

a voltage supply for changing the charge on the sensor and the protection circuit;

a detector for measuring the voltage on one or more of the terminals;

wherein the presence of the sensor is determined by causing the terminals to ground and then by causing a change of charge on one terminal in a predetermined manner such that the detector can detect the presence of the sensor by measuring a voltage variation of one or more terminals where the voltage variation is larger when the sensor is present than when the sensor is absent.

2. A detector circuit according to claim 1, further comprising at least one of a current source and a current sink as the current supply

3. A detector circuit according to claim 2, wherein the charge is changed by sinking or sourcing current into one sensor terminal.

4. A detector circuit according to claim 2, wherein the sourcing of current into the sensor is achieved by pulling one sensor terminal to a predetermined voltage.

5. A detector circuit according to claims 2, wherein the sourcing of current into the sensor is effected by a capacitor.

6. A detector circuit according to claims 1, further comprising a switch to switch the load on one or both terminals to an impedance level having a predetermined value to allow the detection of the voltage variation.

7. A detector circuit according to claims 1, wherein one terminal of the sensor is connected to ground.

8. A detector circuit according to claims 1, wherein the means to measure voltage is an Analogue to Digital Converter (ADC)

9. A detector circuit according to claim 1, in the form of a single silicon device.

10. A detector circuit according to claim 1, further comprising a means for providing a bias voltage on the sensor.

11. A detector circuit according to claim 1, further comprising one or more switches to change the state of the detector circuit such that the sensor and interface components can be charged or discharged;

a first sensor terminal can be pulled up to a predetermined voltage; and

a second terminal can be switched to an impedance level having a predetermined valued to allow the detection of the voltage variation.

12. A detector circuit according to claim 1, for detecting the presence of a knock sensor in an engine control system.

13. A detector circuit according to claim 1, for detecting the presence of a pressure sensor in an engine control system.

14. An electronic control unit for an engine including a detector circuit according to claim 1.

16. A detector circuit according to claim 3, wherein the sourcing of current into the sensor is achieved by pulling one sensor terminal to a predetermined voltage.

17. A detector circuit according to claim 3, wherein the sourcing of current into the sensor is effected by a capacitor.

18. A detector circuit according to claim 2, further comprising a switch to switch the load on one or both terminals to an impedance level having a predetermined value to allow the detection of the voltage variation.

19. A detector circuit according to claim 2, wherein one terminal of the sensor is connected to ground.

20. A detector circuit according to claim 2, further comprising one or more switches to change the state of the detector circuit such that the sensor and interface components can be charged or discharged;

a first sensor terminal can be pulled up to a predetermined voltage; and

a second terminal can be switched to an impedance level having a predetermined valued to allow the detection of the voltage variation.

15. A method for detecting the presence of a remote capacitive sensor having at least two terminals connected via a protection circuit that includes one or more capacitors, the method comprising:

changing the charge on the sensor and the protection circuit, measuring the voltage on one or more of the terminals;

wherein the presence of the sensor is determined by causing the terminals to ground and then by causing a change of charge on one terminal in a predetermined manner such that the detector can detect the presence of the sensor by measuring a voltage variation of one or more terminals where the voltage variation is larger when the sensor is present than when the sensor is absent.