Sensor device with a self adjustor for eliminating abnormal sensitivity

• US 5,965,807 A
• Filed: 06/04/1996
• Issued: 10/12/1999
• Est. Priority Date: 06/05/1995
• Status: Expired due to Term

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Inventors: Yamashita, Yasuhiro, Ootake, Seiichirou
• Primary Examiner(s): MCCALL, ERIC SCOTT
• Application Number:
  US08/657,536
• Time in Patent Office: 1,225 Days
• Field of Search: 73/121, 73/129, 324/71.1, 324/537, 324/725, 701/70, 701/71, 701/76
• US Class Current: 73/129
• CPC Class Codes: G01D 18/004 Continuous recalibration
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown

Abstract

A brake hydraulic pressure detector includes a bridge circuit made up of a semiconductor sensor which generates a detection voltage in accordance with hydraulic pressure and resistors for setting the detection voltage during nonbraking to a nonzero predetermined voltage, an adder circuit for amplifying and generating the detection voltage from the bridge circuit by a predetermined gain, and an output circuit. Here, if the sensitivity of an output voltage with respect to the hydraulic pressure varies, i.e., if the gain varies for some reason, the output voltage during nonbraking also changes because the offset voltage is set to a nonzero voltage. Thus, abnormality in the sensitivity of the brake hydraulic pressure detector can be detected by monitoring the output voltage during nonbraking.

Claims

1. A sensor device comprising:

a bridge circuit, which includes an output terminal and detection elements whose impedances change with respect to an external condition, for generating a detection voltage across said output terminal, which corresponds to changes in said impedances of said detection elements;

a constant current circuit for driving said bridge circuit by supplying a constant current to said bridge circuit;

an amplifier unit for amplifying said detection voltage from said bridge circuit to derive and externally generate an amplifier signal so that sensitivity of said sensor device to said external condition is at a predetermined level and said amplifier signal increases in response to an increase in said detection voltage;

an adjustment circuit for setting an offset voltage that appears at said output terminal of said bridge circuit to a predetermined nonzero positive value in a reference state in which said external condition is not applied to said detection elements, whereby a zero value of said detection voltage represents absence of said external condition; and

determination means for storing a reference output from said amplifier unit when said offset voltage is set to said predetermined nonzero positive value by said adjustment circuit during an initial occurrence of said reference state, and for determining a sensor device abnormality by comparing said reference output to an output from said amplifier unit during a subsequent occurrence of said reference state while said detection elements are in a state in which said impedances change with respect to said external condition;

wherein, a characteristics line corresponding to said amplifier signal pivots around a point corresponding to said zero value of said detection voltage, when said sensitivity of said sensor device to said external condition deviates from said predetermined level.

2. A sensor device according to claim 1, wherein said detection elements are diffused resistors.

3. A sensor device according to claim 1, wherein said bridge circuit is further for generating said detection voltage which corresponds to change in impedances of said detection elements due to external pressure applied on said detection elements.

4. A sensor device according to claim 1, wherein said adjustment circuit includes trimming resistors that are connected in parallel with said detection elements of said bridge circuit.

5. A sensor device according to claim 1, wherein said adjustment circuit includes trimming resistors that are connected in series with said detection elements of said bridge circuit.

6. A sensor device according to claim 1, wherein said adjustment circuit includes a pair of trimming resistors that are connected in series with respective ones of a pair of said detection elements of said bridge circuit and another pair of trimming resistors that are connected in parallel with respective ones of another pair of detection elements of said bridge circuit.

7. A sensor device according to claim 1, wherein said bridge circuit includes a resistor for adjusting sensitivity characteristics of said bridge circuit.

8. A sensor device according to claim 1, said sensor device further comprising a compensation circuit for compensating temperature characteristics of said detection voltage generated by said bridge circuit by generating a compensation signal, wherein said amplifier unit includes:

adding means for adding said compensation signal from said compensation circuit and said detection voltage from said bridge circuit to derive a compensated signal; and

output means for externally generating said compensated signal.

9. A sensor device according to claim 1, wherein said reference state is a state in which temperature is at a predetermined reference temperature.

10. A sensor device according to claim 1, wherein:

said determination means further determines said sensor device abnormality when said output from said amplifier unit during said reference state differs from said reference output by no less than a predetermined amount.

11. A sensor device comprising:

a bridge circuit, which includes an output terminal and detection elements whose impedances change with respect to an external condition, for generating a detection voltage across said output terminal, which corresponds to changes in said impedances of said detection elements;

a constant current circuit for driving said bridge circuit by supplying a constant current to said bridge circuit;

an amplifier unit for amplifying said detection voltage from said bridge circuit to derive and externally generate an amplifier signal so that sensitivity of said sensor device to said external condition is at a predetermined level;

an adjustment circuit for setting an offset voltage that appears at said output terminal of said bridge circuit to a predetermined nonzero value in a state in which said external condition is not applied to said detection elements;

detecting means for detecting a reference state in which said external condition is not applied to said detection elements after said detection elements are placed in a state where they are sensitive to application of external conditions; and

determination means for storing a reference output from said amplifier unit when said offset voltage is set to said predetermined nonzero value by said adjustment circuit, and for determining a sensor device abnormality by comparing said reference output to an output from said amplifier unit when said detecting means detects said reference state.

12. A sensor device comprising:

a bridge circuit, which includes an output terminal and detection elements whose impedances change with respect to an external condition, for generating a detection voltage across the output terminal, which corresponds to changes in the impedances of the detection elements;

a constant current circuit for driving the bridge circuit by supplying a constant current to the bridge circuit;

an amplifier unit for amplifying the detection voltage from the bridge circuit to derive and externally generate an amplifier signal so that sensitivity of the sensor device to the external condition is at a predetermined level;

an adjustment circuit for setting an offset voltage that appears at the output terminal of the bridge circuit to a predetermined nonzero value during a reference state in which the external condition is not present; and

determination means for (i) storing an output from the amplifier unit when the offset voltage is set to the predetermined nonzero value by the adjustment circuit during an initial occurrence of the reference state, and (ii) determining deviations from a predetermined sensitivity level by comparing the stored output to an output from the amplifier unit during a subsequent occurrence of the reference state.