Capacitive physical quantity sensor and method of diagnosing the same

• US 20070126432A1
• Filed: 11/14/2006
• Published: 06/07/2007
• Est. Priority Date: 11/30/2005
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Goto, Keisuke
• Granted Patent: US 7,432,724 B2
• Time in Patent Office: Days
• US Class Current: 324/658
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• CPC Class Codes: G01D 2218/10 Testing of sensors or measuring arrangements
• CPC Class Codes: G01D 5/241 by relative movement of capacitor electrodes
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

A capacitive sensor for detecting a physical quantity includes a movable electrode and a fixed electrode, and a controlling unit for applying a signal between the movable electrode and the fixed electrode. The controlling unit includes an input terminal, an output terminal, and a time measuring means for measuring a time period. The controlling unit measures the time period, for which a diagnosis instruction signal is input into the input terminal. The controlling unit performs the self-diagnosis, after the instruction signal continues for a predetermined time period.

Claims

1. A capacitive sensor for detecting a physical quantity, the sensor comprising:

a movable electrode and a fixed electrode; and

a controlling unit for applying a signal between the movable electrode and the fixed electrode, the controlling unit including

an input terminal, into which an instruction signal for instructing a self-diagnosis is input,

an output terminal, which outputs an indication signal for indicating a state of the self-diagnosis, and

a time measuring means for measuring a time period, for which the instruction signal is input into the input terminal, wherein

the controlling unit performs the self-diagnosis, after the instruction signal continues for a predetermined time period.

2. The sensor according to claim 1, further comprising:

a C-V conversion circuit, which outputs a voltage corresponding to a variation of a capacitance formed by the movable electrode and the fixed electrode; and

a signal processing circuit, which outputs a signal corresponding to a variation of the physical quantity by processing the voltage from the C-V conversion circuit, wherein

the movable electrode is displaced in accordance with the variation of the physical quantity,

the controlling unit periodically applies a detection signal for detecting the variation of the capacitance in a normal measuring mode, and

the controlling unit applies a displacement signal for displacing the movable electrode before applying the detection signal in a self-diagnostic mode.

3. The sensor according to claim 1, wherein:

the time measuring means measures the time period by using a clock for generating clock signals; and

the predetermined time period corresponds to a time longer than an assumed time, for which external noises continue.

4. The sensor according to claim 1, wherein:

the controlling unit outputs the indication signal from the output terminal, when the instruction signal is finished due to a completion of the self-diagnosis.

5. The sensor according to claim 1, wherein:

the controlling unit performs the self-diagnosis, in a case in which a plurality of instruction signals is input into the input terminal, and

the self-diagnosis is not performed, in a case in which the instruction signals are not input into the input terminal.

6. The sensor according to claim 5, wherein:

the controlling unit performs the self-diagnosis, in a case in which a first instruction signal and a second instruction signal are input into the input terminal, and

the controlling unit prohibits the self-diagnosis, in a case in which only the first instruction signal is input into the input terminal.

7. The sensor according to claim 6, wherein:

the output terminal outputs different signals between cases, in which the first instruction signal is input, and in which the second instruction signal is input.

8. The sensor according to claim 6, wherein:

the controlling unit recognizes the second instruction signal as a first instruction signal, if the second instruction signal is input into the input terminal after a predetermined time since the first instruction signal is input.

9. The sensor according to claim 8, wherein:

the predetermined time is longer than an assumed time, in which the second instruction signal is input.

10. A method of diagnosing a capacitive physical quantity sensor comprising:

inputting a preparation signal into an input terminal of the capacitive physical quantity sensor for a first predetermined time;

determining whether an output terminal of the capacitive physical quantity sensor has output a first output signal for the first predetermined time or not in response to the preparation signal;

instructing a self-diagnosis by inputting an instruction signal into the input terminal for a second predetermined time, if the output terminal is determined to have output the first output signal for the first predetermined time; and

diagnosing the capacitive physical quantity sensor to be normal, if the output terminal outputs a second output signal for the second predetermined time.

11. The method according to claim 10, wherein:

the capacitive physical quantity sensor includes a first output terminal and a second output terminal as the output terminal,

the capacitive physical quantity sensor has a first sensitivity and a second sensitivity for a single direction,

the first output terminal outputs a signal of the first sensitivity,

the second output terminal outputs a signal of the second sensitivity, which is formed by amplifying the signal of the first sensitivity, and

the diagnosing is performed based on a time, for which the signal of the second sensitivity continues.

12. The method according to claim 10, wherein:

the first predetermined time is in a range between 0.1-0.5 msec.