Detecting capacitive faults and sensitivity faults in capacitive sensors

Patent metadata

Field	Value
Publication number	US-11953533-B2
Application number	US-202117347776-A
Country	US
Kind code	B2
Filing date	Jun 15, 2021
Priority date	Jun 15, 2021
Publication date	Apr 9, 2024
Grant date	Apr 9, 2024

Abstract

A capacitive sensor includes a first conductive structure; a second conductive structure that is counter to the first conductive structure, wherein the second conductive structure is movable relative to the first conductive structure in response to an external force acting thereon, wherein the second conductive structure is capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and second conductive structure; a signal generator configured to apply a first electrical signal step at an input or at an output of the first capacitor to induce a first voltage transient response at the output of first capacitor; and a diagnostic circuit configured to detect a fault in the capacitive sensor by measuring a first time constant of the first voltage transient response and detecting the fault based on the first time constant.

First claim

What is claimed is:

1. A capacitive sensor, comprising:
a first conductive structure;
a second conductive structure that is counter to the first conductive structure, wherein the second conductive structure is movable relative to the first conductive structure in response to an external force acting thereon, wherein the second conductive structure is capacitively coupled to the first conductive structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first conductive structure and second conductive structure, wherein the first capacitance is representative of the external force;
a signal generator configured to apply a first electrical signal step at an input or at an output of the first capacitor to induce a first voltage transient response at the output of the first capacitor; and
a diagnostic circuit configured to detect a fault in the capacitive sensor by calculating a first time constant of the first voltage transient response and detecting the fault based on the first time constant,
wherein the first time constant is calculated based on a time the first electrical signal step is triggered by the signal generator to a time a measured signal reaches a predefined threshold value.

2. The capacitive sensor of claim 1 , wherein the first electrical signal step causes the first capacitor to charge to a maximum voltage or to discharge to a minimum voltage.

3. The capacitive sensor of claim 1 , wherein the first electrical signal step is a step-up or a step-down signal step.

4. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit comprises a comparator, a counter, and a fault detector,
the comparator is configured to receive an output voltage representative of the first voltage transient response and compare the output voltage to a reference threshold in order to generate a comparison result having one of two comparator values,
the counter is configured to stop counting when the comparison result changes from a first comparator value to a second comparator value and output a stopped counter value representative of the first time constant, and
the fault detector is configured to compare the stopped counter value to a predetermined threshold range and generate an error signal in response to the stopped counter value being outside the predetermined threshold range.

5. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit comprises a comparator and a fault detector,
the comparator is configured to receive an output voltage representative of the first voltage transient response, and compare the output voltage to a reference threshold in order to detect the first time constant, and
the fault detector is configured to compare the first time constant to a predetermined threshold range and generate an error signal in response to the first time constant being outside the predetermined threshold range.

6. The capacitive sensor of claim 5 , wherein the diagnostic circuit comprises a counter configured to output a first counter value representative of the detected first time constant and the fault detector is configured to compare the first counter value to the predetermined threshold range and generate the error signal in response to the first counter value being outside the predetermined threshold range.

7. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit is configured to compare the first time constant to a predetermined threshold range and generate an error signal in response to the first time constant being outside the predetermined threshold range.

8. The capacitive sensor of claim 7 , wherein the predetermined threshold range comprises a minimum threshold value and a maximum threshold value, and the first time constant is outside the predetermined threshold range if it is less than the minimum threshold value or greater than the maximum threshold value.

9. The capacitive sensor of claim 1 , wherein:
the signal generator is configured to apply a second electrical signal step at the input or at the output of the first capacitor to induce a second voltage transient response at the output of the first capacitor, wherein the second voltage transient response is in a direction opposite to the first voltage transient response, and
the diagnostic circuit is configured to detect the fault in the capacitive sensor by measuring a second time constant of the second voltage transient response and detecting the fault based on the first time constant and the second time constant.

10. The capacitive sensor of claim 9 , wherein the diagnostic circuit is configured to calculate a difference between the first time constant and the second time constant, compare a magnitude of the difference to a predetermined threshold range, and generate an error signal in response to the magnitude of the difference being outside the predetermined threshold range.

11. The capacitive sensor of claim 9 , wherein:
the diagnostic circuit comprises a comparator, at least one counter, and a fault detector,
the comparator is configured to receive an output voltage representative of the first voltage transient response and the second voltage transient response, compare the output voltage to a first reference threshold in order to detect the first time constant, and compare the output voltage to a second reference threshold in order to detect the second time constant,
the at least one counter is configured to output a first counter value representative of the detected first time constant and output a second counter value representative of the detected second time constant, and
the fault detector is configured to calculate a difference between the first counter value and the second counter value, compare a magnitude of the difference to a predetermined threshold range, and generate an error signal in response to the magnitude of the difference being outside the predetermined threshold range.

12. The capacitive sensor of claim 1 , further comprising;
a third conductive structure that is counter to the first conductive structure, wherein the third conductive structure is movable relative to the first conductive structure, wherein the third conductive structure is capacitively coupled to the first conductive structure to form a second capacitor having a second capacitance that changes with a change in a distance between the first conductive structure and third conductive structure,
wherein the signal generator is configured to apply the first electrical signal step at an input or at an output of the second capacitor to induce a second voltage transient response at the output of the second capacitor; and
a diagnostic circuit configured to detect the fault in the capacitive sensor by measuring a second time constant of the second voltage transient response and detecting the fault based on the first time constant and the second time constant.

13. The capacitive sensor of claim 12 , wherein the signal generator is configured to apply the first electrical signal step simultaneously to the first capacitor and the second capacitor such that the first voltage transient response and the second voltage transient response are induced by the same electrical signal step.

14. The capacitive sensor of claim 12 , wherein:
the diagnostic circuit is configured to compare the first time constant and the second time constant to a predetermined threshold range and generate an error signal in response to either the first time constant being outside the predetermined threshold range or the second time constant being outside the predetermined threshold range.

15. The capa

Assignees

• Infineon Technologies Ag
• Capital One Services Llc

Inventors

• Stoica Dan-Ioan-Dumitru
• Buffa Cesare
• Crisu Constantin
• Tudose Mihai-Liviu
• Winkler Bernhard

Classifications

• G01R27/2605 Primary

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title

• G01R27/28

  Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response (in line transmission systems H04B3/46) · CPC title

• G01R31/2843

  In-circuit-testing · CPC title

• G01D18/00 Primary

  Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00 · CPC title

• G01R31/64 Primary

  Testing of capacitors · CPC title