JP3117769B2 - Fault diagnosis device for force or load detection sensor and self-recovery device thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, for example, a fault diagnosis apparatus for a force or load detection sensor using a strain gauge, such as an electric resistance wire type strain gauge or a semiconductor strain gauge to diagnose whether a failure, the failure And a device for performing a self-return when the diagnosis is made.

[0002]

2. Description of the Related Art A sensor using a strain gauge as described above is widely used in the field of industrial measurement of load, pressure, etc., and has a high accuracy and a relatively low failure rate. Used as a sensor. FIG. 5 shows a sensor using such a strain gauge. FIG. 5 (a) shows a sensor used for a compression type load cell, and FIG. 5 (b) shows a sensor used for a double beam type load cell. .

In the compression-type load cell, a strain-generating portion 12 is provided on a support portion 10, and a force receiving portion 14 is provided above the strain-generating portion 12. 14 is compressed when subjected to force. Strain gauges 16 and 18 are attached to the strain generating section 12 in parallel with the axial direction of the strain generating section 12 to detect a compressive force.
Reference numerals 0 and 22 are attached at right angles to the axial direction of the strain-flexing portion 12 to detect a tensile force. Further, in the double beam load cell, a strain generating portion 28 is formed so as to form two beams (beams) 24 and 26, and a load is applied to the strain generating portion 28, for example. This is carried out by placing an article on a mounting table 37 connected to the apparatus. When a load is applied on the mounting table 37, the strain gauges 32 and 34 receive bending stress in the direction in which the gauge bonding surface extends, and the strain gauges 30 and 36 receive bending stress in the direction in which the gauge bonding surface contracts.

The strain gauges 16, 18, 2
The 0, 22, 30, 32, 34, 36 are connected to each other to form a bridge circuit 38 as shown in FIG. However, the strain gages forming the opposite sides of the bridge circuit 38 are connected so as to receive the same type of force, such as a tensile force if a tensile force and a compressive force if a compressive force. A DC voltage for excitation is applied to two opposing connection points 40, 40 of the bridge circuit, and a connection point 4 located at a right angle to these connection points 40, 40
A detection voltage of a force or a load is extracted from 2 and 42, is converted into a digital signal by an A / D converter 44, and is supplied to a measurement data output unit 46, where the processing is performed, and the measurement value is calculated. Display and printing are performed.

[0005]

However, a sensor using such a strain gauge is a highly reliable sensor as described above, but the failure is not zero, and the shock load or the rated load exceeding the rated value is not obtained. In some cases, performance degradation or failure may occur due to adverse environmental influences (temperature, humidity, gas, static electricity, etc.). If it can no longer be used due to breakage or disconnection, it will be impossible to measure due to failure,
Erroneous measurement does not occur. However, if the performance is gradually degraded but no noticeable failure has occurred yet, there is a risk that despite the fact that the measurement value has an error, it is difficult to notice that the error is included. In particular, in the field of measurement and control for industrial use, there is a serious problem in a compounding equipment for raw materials, which is directly linked to a life-threatening accident such as generation of inferior products due to measurement errors and explosion due to poor mixing. In addition, if the above-mentioned failure occurs in the sensor used for the scale used for commercial transactions, the error increases without notice, and fair transactions cannot be performed,
Losing social confidence is a big problem.

[0006]

A failure diagnosis apparatus according to the present invention for solving the above problems has a sensor. The sensor includes first and second series circuits in which at least two resistance elements are connected in series, and the resistance elements include a detection element whose resistance value changes by a force or a load;
A dummy series circuit in which at least two dummy resistors are connected in series is connected in parallel to a power supply. A full bridge circuit in which a signal between a connection point of the resistance element of the first series circuit and a connection point of the resistance element of the second series circuit is taken out as an output, connection of the resistance element of the first series circuit A signal between a point and a connection point of the dummy resistor of the dummy series circuit is taken out as an output. A connection point of the resistance element of the first half bridge circuit and the second series circuit and the connection point of the dummy series circuit Switching means switches the sensor to one of the second half-bridge circuits from which a signal between the dummy resistor and the connection point is taken out as an output. The first operation in a normal operation state of the sensor and a specific application state of a force or load to the sensor.
The storage means stores an allowable value determined based on the output of the second half bridge circuit. The comparing means determines whether or not one of the outputs of the first and second half-bridge circuits in the specific application state exceeds the corresponding allowable value. Further, in the fault diagnosis device according to the present invention, an alarm that is activated when the comparing means determines that one of the outputs of the first and second half-bridge circuits exceeds the allowable value corresponding to each of them. Means can also be provided. The specific application state may be, for example, a state where no force or load is applied. Also, instead of comparing the outputs of the first and second half-bridge circuits in the specific application state and the corresponding allowable values, the output of the first and second half-bridge circuits is related to the force or load. An expression may be obtained and compared with the allowable value of the relational expression.

The self-recovery device according to the present invention is configured such that when the output of one of the first and second half-bridge circuits is determined to exceed the permissible value corresponding thereto, The conversion means for converting the output of the half-bridge circuit into the output corresponding to the sensor is provided.

[0008]

In the fault diagnosis device according to the present invention, the sensor is connected to the first sensor.
And in the second half-bridge circuit, and in a specific applied state, for example, in a state where no force or load is applied,
The outputs of the first and second half-bridge circuits at that time are compared with corresponding permissible values by comparing means. If any one of the outputs of the first and second half-bridge circuits exceeds the corresponding allowable value, it can be determined that the deterioration has progressed. Therefore, for example, the notification device is operated to notify that deterioration has progressed.

In the self-recovery device according to the present invention, when it is determined that one of the first and second half-bridge circuits has deteriorated as described above, the output of the remaining half-bridge circuit is converted by the conversion means. Convert to an output equivalent to that obtained by a full bridge circuit.

[0010]

This embodiment has a bridge circuit 50 as shown in FIG. The bridge circuit 50 includes, for example, an electric resistance wire type strain gauge 52 on each side,
54, 56, 58, and these strain gauges 52
Nos. 58 through 58 are attached to the strain generating portion to receive a compressive force or a tensile force, similarly to the strain gauge shown in FIG. 5A or 5B. This bridge circuit 5
0, the connection point 60 of the strain gauges 52, 58
And a connection point 61 between the strain gauges 54 and 56, a DC power supply 62 applies a DC voltage for excitation.

Dummy resistors 64 and 66 connected in series are connected to these connection points 60 and 61, and a connection point 68 of the strain gauges 52 and 54 is connected to a changeover switch 70.
Are connected to the contacts 70a and 70b. The other contact 70c of the changeover switch 70 is connected to the dummy resistor 6
4 and 66 are connected to a connection point 72. This connection point 7
2 is also connected to the contact 74a of the changeover switch 74, and the other contacts 74b and 74c are connected to the strain gauges 56 and 58.
Is connected to the connection point 76 of

The changeover switches 70 and 74 have contacts 70d and 74d, respectively, which are linked with each other.
When the contacts d and 74d are in contact with the contacts 70a and 74a, a signal between the connection points of the strain gauges 52 and 54 and the connection points of the dummy resistors 64 and 66 is provided between the contacts 70d and 74d. Is output. These contacts 70d, 74
The output produced at d is not affected by the signals flowing through the strain gauges 56,58. Therefore, as shown in FIG. 1B, the strain gauges 52, 54 and the dummy resistors 64, 6
The output of a bridge (hereinafter, referred to as a half-bridge circuit) circuit 50a formed by the contact 70d is a contact 70d,
It is supplied during 74d.

The contacts 70d and 74d are
b, 74b, the contacts 70d, 74d
Between them, as shown in FIG.
An output of a bridge circuit (hereinafter, referred to as a full bridge circuit) 50 constituted by 2, 54, 56, and 58 is supplied.

Further, the contacts 70d and 74d are
0c, 74c, the contacts 70d, 74
Between d, a signal between the connection point of the strain gauges 56 and 58 and the connection point of the dummy resistors 64 and 66 is output. The outputs generated at the contacts 70d and 74d are not affected by the signals flowing through the strain gauges 52 and 54.
As shown in FIG. 1C, the strain gauges 56, 5
8. The output of a bridge circuit (hereinafter, referred to as a half bridge circuit) 50c constituted by the dummy resistors 64 and 66 is supplied to the contacts 70d and 74d.

That is, the full bridge circuit 50 is separated by the separating means constituted by the dummy resistors 64 and 66 and the changeover switches 70 and 74, respectively, as shown in FIG.
Half bridge circuits 50a and 50c as shown in FIG.
Can be separated. The changeover switches 70 and 7
The switching control of the fourth contacts 70d and 74d will be described later.

The contacts 7 of these changeover switches 70 and 74
The outputs of the full-bridge circuit 50 or the half-bridge circuits 50a and 50c supplied between 0d and 74d are A /
The signal is converted into a digital signal by the D converter 76 and supplied to the failure diagnosis alarm and self-recovery circuit 78. The circuit 78 is constituted by, for example, a microcomputer together with a measurement data output circuit 80 described later, and includes a storage unit 78a, a comparison unit 78b, an alarm unit 78c, and a conversion unit 78d.

The storage means 78a stores allowable values of the half bridge circuits 50a and 50c. These allowable values are determined, for example, as follows.

As shown by the straight line B in FIG. 2, the full-bridge circuit 50 can measure from 0 kg to 3 kg. In a normal state, a voltage of 0 mV at 0 kg is applied to 3 kg.
Generates a voltage of 10 mV, and the output voltage Y is (10) with respect to a force or load X between 0 kg and 3 kg.
/ 3) Suppose there is a linear relationship of X.

In such a case, for example, the changeover switch 7
0, 74 contacts 70d, 74d to the contacts 70a, 74a
When the half-bridge circuit 50a as shown in FIG. 1B is constructed by switching to the above, the output is 3 mV at 0 Kg and 7.8 mV at 3 Kg as shown by the straight line A in FIG.
It is assumed that the output voltage Y1 has a linear relationship of 3 + [(7.8-3) / 3] X with respect to a force or load X between 0 kg and 3 kg.

Similarly, when the contacts 70d and 74d of the changeover switches 70 and 74 are switched to the contacts 70c and 74c to form a half bridge circuit 50c as shown in FIG. As shown, the output shows -3 mV at 0 Kg and 2.2 mV at 3 Kg,
The output voltage Y2 for a force or load X up to
Has a linear relationship of -3 + [(2.2 + 3) / 3] X.

The half bridge circuit 50a or 5b
If 0c is configured, 3mV or -3 at 0Kg
The output of mV is caused by the strain gauges 52, 54 and 64, 66 or 56, 5
8 and 64, 66 based on the non-uniformity of the resistance value,
It is not based on force or load. And the output Y
By adding 1, Y2, an output Y is obtained.

By the way, such a strain gauge 5
In 2, 54, 56, and 58, the degradation occurs as described above, but the degradation does not occur evenly so as not to affect the output of the full bridge circuit 50. As the mechanism of deterioration, first, strain gauges 52, 5
4, 56, or 58, the resistance value changes, the balance is greatly lost, a zero point (output in the state where a force or load of 0 Kg is applied) changes, and when the deterioration further progresses, the span (see FIG. 2).

FIG. 3 shows, for example, strain gauges 56, 5
8 when a deterioration occurs in any one of the circuits 8
0, the output of the half-bridge circuits 50a, 50c. The output Y11 of the half bridge circuit 50a as shown in FIG. 1B is the output Y indicated by a straight line A in FIG.
Same as 1 with no change. However, the output Y21 of the half bridge circuit 50c shown in FIG. 1C has a zero point of 2 m in the positive direction, as is clear from comparison with Y2 shown by the dotted line.
The output when V moved and a force or load of 3 Kg was applied changed to 3.5 mV. Therefore, the output sensitivity (straight line C
Slope) was (2.2 + 3) / 3,
(3.5 + 1) / 3. As a result, the output sensitivity of the full bridge circuit 50 has been reduced from 10/3 to 9.3 mV / 3.

As described above, since the deterioration causes the shift of the zero point and the decrease in the sensitivity, the deterioration can be detected by checking any of them. However, the simplest method for detecting this deterioration is to detect the movement of the zero point. Generally, the zero point of the sensor does not change so much. For example, if it changes by 10% of the full scale (10 mV in the above example) after adjustment under normal conditions, it can be determined that something is abnormal. Therefore, in this embodiment, in the normal state, the straight line A in FIG.
Assuming that the full-bridge circuit 50 and the half-bridge circuits 5a and 50b show the characteristics shown in B and C, respectively, the allowable value of the half-bridge circuit 50a is 3 mV ±
1 mV as an allowable value of the half-bridge circuit 50 c −
3 mV ± 1 mV is stored in the storage means 78a.

The comparing means 78b calculates these allowable values and A /
Half bridge circuit 50 supplied from D converter 76
a, 50c is compared with the corresponding digital signal output. That is, the contact 70 of the changeover switches 70 and 74
The digital signal from the A / D converter 76 in the state where the contacts d and 74d are switched to the contacts 70a and 74a is
mV ± 1 mV, and switches 70 and 7
The digital signal from the A / D converter 76 in a state where the contacts 70d and 74d of No. 4 are switched to the contacts 70c and 74c is compared with -3 mV ± 1 mV.

This comparison is performed when the zero point measuring means 82 indicates that the point is a zero point. As the zero point measuring means 82, for example, it is visually confirmed whether or not an article is present on the receiving unit 14 shown in FIG. 5A or the mounting table 37 shown in FIG. The zero point adjusting device may be operated manually, or as a method for automatically performing the operation, a photoelectric detector that detects the presence or absence of an article on the mounting table 37 can be used. The switches 70 and 74 are also switched by the failure diagnosis alarm and self-recovery circuit 78 based on the instruction of the zero point from the zero point measuring means 82.

The alarming means 78c notifies when the output of the half bridge circuit 50a or 50c shown in FIG. 1 (b) or (c) exceeds an allowable value as a result of the comparison by the comparing means 78a. It is for.

The conversion means 78d switches the changeover switch 70 when it is determined that one of the half bridge circuits 50a, 50c shown in FIG. 1B or FIG. , 74 so that the output from the normal half-bridge circuit is always A / D converter 7
6, and when a force or load is applied thereafter, the output of the normal half-bridge circuit is to be converted into the applied force or load.

For example, as shown by the straight line B in FIG. 2, the output Y in the normal state of the full bridge circuit 50 is
0/3) X, and the output Y1 when the half bridge circuit 50a shown in FIG. 1B is normal is 3 + [(7.8- 3) / 3]
X has a linear relationship, and as shown by a straight line C in FIG.
The output Y2 in the normal state of the half bridge circuit 50c of (c) has a linear relationship of −3 + [(2.2 + 3) / 3] X with X.

Therefore, for example, when there is an abnormality in the half-bridge circuit 50c in FIG. 1C, when trying to obtain Y from the output Y1 of the half-bridge circuit 50a in FIG. Is subtracted from Y1 at that time, and the subtraction value may be multiplied by the ratio of the inclination of the straight line B to the inclination of the straight line A. Similarly, FIG.
When there is an abnormality in the half bridge circuit 50a of (b),
When obtaining Y from the output Y2 of the half bridge circuit 50c in FIG. 1C, the difference -3 in the output at the zero point between Y2 and Y is subtracted from the output of Y2 at that time. , The ratio of the slope of the straight line B to the slope of the straight line C.

Therefore, the converting means 78d calculates the difference between the output at the zero point between Y1 and Y, the difference between the output at the zero point between Y2 and Y, the ratio of the slope of the straight line B to the slope of the straight line A, and the slope of the straight line C. The ratio of the slope of the straight line B is stored,
The half bridge circuit that is not determined to be abnormal
For example, in the case of the half-bridge circuit 50a shown in FIG.
Y1 is converted to the output of the full-bridge circuit 50 by using the difference between the output of the zero point of Y1, Y1 and Y, and the ratio of the slope of the straight line B to the slope of the straight line A. Similarly, if the half bridge circuit that is not determined to be abnormal is the half bridge circuit 50c in FIG. 1C, its output Y2 and Y2
By using the difference between the outputs at the zero point of Y and Y, and the ratio of the slope of line B to the slope of line C, Y2 is
Convert to 0 output.

If the comparing means 78a determines that there is no failure, the output of the full-bridge circuit 50 is thereafter changed to A /
The result of the digital conversion by the D converter 76 is supplied to the measurement data output circuit 80. If it is determined that there is a failure, the output of the conversion means 78d is supplied to the measurement data output circuit 80 thereafter. In the measurement data processing circuit 80, the signal from the A / D converter 76 or the conversion means 78
The signal from d is displayed on a display device or printed by a printer.

FIG. 4 shows a failure diagnosis alarm and self-healing circuit 7.
8. The operation of the measurement data output circuit 80 is shown in a flow chart. First, a normal measurement operation is performed (step S
10). That is, a signal obtained by converting the detection voltage from the full bridge circuit 50 into a digital signal by the A / D converter 76 is displayed on a display device or printed by a printer. Subsequently, it is determined whether a signal indicating the zero point is supplied from the zero point measuring means 82 (step S12). If it is not the zero point, the process returns to step S10 to perform a normal measurement operation.

If the zero point is reached (Yes in step S12), the changeover switches 70 and 74 are switched so that the detection output from the half bridge circuit 50a of FIG. 1B is supplied to the A / D converter 76. While reading the digital signal of the A / D converter 76, the changeover switches 70 and 74 are switched so that the detection output from the half bridge circuit 50c of FIG. 1C is supplied to the A / D converter 76. The digital signal of the / D converter 76 is read (step S14).

Then, it is determined whether or not the signal indicating the zero point is still supplied from the zero point measuring means 82 (step S16). If there is no signal indicating the zero point (No in step S16), step S1
During execution of step 4, a force or load is applied, and step S14 is performed.
Since it is unknown whether the value read at step (1) truly reads the output at the zero point, the process returns to step S10 to perform a normal measurement operation.

If the output at the true zero point is read (Yes at step S16), the digital signal output from the half-bridge circuit 50a of FIG. 1 (b) falls within the corresponding tolerance of 3 ± 1 mV. And the digital signal at the output of the half-bridge circuit 50c of FIG.
It is determined whether the value is within the range of the permissible value -3 ± 1 mV (step S18). If any of the outputs is within the allowable value (No in step S18), since no deterioration has occurred, the process returns to step S10 to perform a normal measurement operation.

If any of the outputs is out of the corresponding allowable value (Yes in step S18), a sensor error alarm is output, and the detection output of the normal half-bridge circuit is thereafter changed to the A / D converter 76. (Step S2).
0).

When a force or a load is applied, the conversion operation is performed as described above from the digital value of the detected output of the normal half-bridge circuit at that time, and converted to the output of the full-bridge circuit 50 (step S22). ). Therefore, until the sensor is replaced, the force or the load is detected in step S22.

In the above embodiment, the full bridge circuit 5
0, the outputs of the half-bridge circuits 50a and 50c are assumed to have a linear relationship with respect to force or load. However, the outputs do not always have a linear relationship. For example, when the output with respect to force or load is represented by a quadratic expression. There is also. In such a case, it is necessary to change the conversion formula used in the conversion means 78d.

In the above embodiment, the outputs of the half-bridge circuits 50a and 50c are compared with the allowable values at the zero point. However, the half-bridge circuits under a state in which a specific force or load other than the zero point is applied. The permissible values of the outputs of the half-bridge circuit 50a and 50c are stored in the storage means 78a, and the half-bridge circuit 50 in a state where a specific force or load is applied.
The outputs of a and 50c may be compared with an allowable value.

In the above embodiment, it is assumed that the zero point can always be detected. However, when the apparatus is used as a load sensor in an apparatus such as a hopper scale in which an article to be weighed is always stored inside. , It is impossible to detect the zero point. In such a case, the operation is performed as follows.

That is, the permissible values such as constants and gradient coefficients of the relational expressions for the output force or load of the full bridge circuit 50 and the half bridge circuits 50a and 50c are stored in the storage means 74.
And the output of the full bridge circuit 50 and the half bridge circuits 50a and 50b at that time is read.

This operation is repeated several times, and when the load is small, medium, and large, the output is read several times, and the average output when the load is small, the average output when the load is medium, The average output when the power is large is determined, and the full bridge circuit 5
0, a relational expression for the output force or load of the half bridge circuits 50a and 50b is obtained, and constants and coefficients of the relational expression are calculated.

Whether these are within the permissible values of the corresponding constants and coefficients stored in the storage means 78a,
In this case, since the zero point is not known, only the change in the proportionality constant of the equation will be observed. Therefore, it is not possible to determine which half bridge is abnormal, but it is possible to issue an alarm indicating that the half bridge is abnormal.

In the above embodiment, the full bridge circuit 50 has one strain gauge on one side. However, a full bridge circuit using a plurality of strain gauges on one side may be used. . Further, in the above-described embodiment, a strain gauge of an electric resistance wire type is used, but a strain gauge of a semiconductor strain gauge type may be used.

[0046]

As described above, according to the present invention, when the sensor is switched to the first and second half-bridge circuits, the first and second half-bridges almost always degrade at the same time. If any of the half-bridge circuits are gradually deteriorating, it informs the user that a failure is occurring. By replacing the sensor, erroneous measurement can be prevented from being performed for a long time. Further, according to the present invention, if it is determined that an abnormality has occurred in one half-bridge circuit, the output of the other normal half-bridge circuit can be converted into the output of the full-bridge circuit by the conversion means. Further, it is possible to prevent a situation in which a transaction or a production line must be stopped until the user replaces the force or load detection sensor.

[Brief description of the drawings]

FIG. 1 is a block diagram of a failure diagnosis device and a self-recovery device for a force or load detection sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a change state of an output with respect to an applied force or load in a normal state of a full bridge circuit 50 and half bridge circuits 50a and 50c in the embodiment.

FIG. 3 is a diagram showing a half bridge circuit 50a in the embodiment;
FIG. 10 is a diagram illustrating a change state of an output with respect to an applied force or a load of the full bridge circuit 50 and the half bridge circuits 50a and 50c when an abnormality occurs in any of 50c.

FIG. 4 is a flowchart of the embodiment.

FIG. 5 is a diagram showing a use state of a conventional force or load detection sensor.

FIG. 6 is a block diagram of a conventional force or load detection sensor.

[Explanation of symbols]

 Reference Signs List 50 full bridge circuit 50a 50c half bridge circuit 64 66 dummy resistor 70 74 changeover switch 78a storage means 78b comparison means 78c alarm means 78d conversion means

Claims (5)

(57) [Claims] At least two resistance elements are connected in series, and these resistance elements include first and second series circuits each including a detection element whose resistance value changes by a force or a load, and at least two dummy resistances. A sensor connected in parallel with a power supply, and a dummy series circuit in which a series of devices are connected in series, and between a connection point of the resistance element of the first series circuit and a connection point of the resistance element of the second series circuit. A full-bridge circuit from which a signal is taken out as an output, and a first signal from which a signal between a connection point of the resistor element of the first series circuit and a connection point of the dummy resistor of the dummy series circuit is taken out as an output.
And a second half-bridge circuit from which a signal between the connection point of the resistor element of the second series circuit and the connection point of the dummy resistor of the dummy series circuit is taken out as an output. Switching means for switching the sensor; and a first and a second switch in a normal operation state of the sensor and in a specific application state of a force or load to the sensor.
Storage means for storing respective allowable values based on the output of the half-bridge circuit, and one of the outputs of the first and second half-bridge circuits when the specific application state is set. And a comparing means for determining whether or not the allowable value is exceeded. 2. The failure diagnosis device for a force or load detection sensor according to claim 1, wherein said comparing means determines whether one of the outputs of said first and second half-bridge circuits corresponds to each of said outputs. A failure diagnostic device for a force or load detection sensor, comprising a notifying device that operates when it is determined that the value exceeds the value. 3. The failure diagnosis device for a force or load detection sensor according to claim 1, wherein the specific application state is a state where no force or load is applied. Diagnostic device. 4. The fault diagnosis device for a force or load detection sensor according to claim 1, wherein one output of said first and second half-bridge circuits exceeds the corresponding allowable value. When it is determined that the first and second
A self-recovery device for a force or load detection sensor, comprising a conversion means for converting the other output of the half-bridge circuit into an output corresponding to the output of the full-bridge circuit. 5. At least two resistive elements are connected in series, the resistive elements including first and second series circuits including a detecting element whose resistance value changes by a force or a load, and at least two dummy resistors. A sensor connected in parallel with a power supply, and a dummy series circuit in which a series of devices are connected in series, and between a connection point of the resistance element of the first series circuit and a connection point of the resistance element of the second series circuit. A full-bridge circuit from which a signal is taken out as an output, and a first signal from which a signal between a connection point of the resistor element of the first series circuit and a connection point of the dummy resistor of the dummy series circuit is taken out as an output.
And a second half-bridge circuit from which a signal between the connection point of the resistor element of the second series circuit and the connection point of the dummy resistor of the dummy series circuit is taken out as an output. Switching means for switching the sensor; and a force or load of the output of the first and second half-bridge circuits determined based on the output of the first and second half-bridge circuits during normal operation of the sensor. Storage means for storing an allowable value of a gradient coefficient of a relational expression; and said sensor being switched to a first and a second half-bridge circuit by said switching means, the output force of the first and second half-bridge circuits or And a comparing means for determining whether or not the gradient coefficient of the relational expression for the load exceeds the corresponding allowable value. Fault diagnosis apparatus of the sensor.