JP2520120Y2 - Strain / temperature sensor abnormality detection device - Google Patents

Description

[Detailed description of the device]

[0001]

[Industrial application] The present invention relates to a strain / temperature sensor capable of performing strain measurement and temperature measurement with a single sensor, especially when an abnormality such as a disconnection or short circuit occurs in each resistance for detecting strain and temperature. The present invention relates to a strain / temperature sensor abnormality detection device capable of accurately detecting abnormality occurrence.

[0002]

2. Description of the Related Art As one of the most simple methods for measuring an applied force, a strain gauge is attached to the surface of the object to which the external force is applied so that the surface strain generated by the application of the external force is strained. The change in resistance of the gauge is detected and the change in resistance is converted into an external force.

However, the resistance value R of the strain gauge attached to the surface of the object to be measured changes substantially in proportion to the strain ε of the surface of the object to be measured, and also changes due to the change in the ambient temperature T. Therefore, in order to prevent the factor of temperature change from being mixed in the measurement result of strain, four strain gates are attached to the surface of the object to be measured, and the Wheatstone brushy circuit is constituted by these.

For example, as shown in FIG. 5, four strain gauges 1a, 1b, 1c, 1d constitute a Wheatstone bridge circuit. Then, the power supply terminals 2a, 2
When the DC voltage E is applied from b, a voltage Ve proportional to the strain ε is output between the output terminals 3a and 3b. The resistance values of the strain gauges 1a to 1d are set to be equal to each other in the state where no strain ε is generated.

Then, as shown in FIG. 6 (a), when tension is applied to the object to be measured 4 in one direction, strain ε is generated in the direction of the arrow. Therefore, for example, strain gauges 1a, 1
c is attached to the surface 4a of the object to be measured in the strain generating direction, and the other strain gauges 1b and 1d are attached in the direction orthogonal to the strain generating direction.

Further, as shown in FIG. 6B, when the object 4 to be measured is a cantilever, bending stress is generated in the direction of the arrow, so that, for example, the strain gauges 1a and 1c are tensile strains of the cantilever. Is attached to the front surface where the strain occurs, and the other strain gauges 1b and 1d are attached to the back surface where the compression strain occurs.

In the strain sensor having such a configuration, when a DC voltage E is applied between the power supply terminals 2a and 2, when the strain ε does not occur, the terminal voltage of each output terminal 3a, 3b (the midpoint voltage ) Are equal to each other, the distortion detection voltage Ve is 0
V. When the strain ε is generated, the strain gauges 1a, 1
Since the resistance value of c changes, the strain detection voltage Ve has a value corresponding to the strain ε.

[0008]

In such a strain sensor, the strain gauges 1a to 1d forming the Wheatstone bridge circuit are broken or short-circuited, or the leads connecting the strain gauges 1a to 1d are connected to each other. When the line is broken, the output voltage Ve between the output terminals 3a and 3b changes to an extreme value, so that the observer changes the output voltage Ve or the distortion amount calculated from the output voltage Ve to an abnormal value. By confirming that, it is possible to detect that an abnormality has occurred.

However, for example, when two strain gauges are damaged at the same time, or when the DC voltage E is not correctly applied to the Wheatstone bridge circuit due to disconnection of lead wires, the output voltage Ve changes greatly. Therefore, it may not be possible to distinguish whether the change in the output voltage Ve is caused by the change in the strain ε or the change in the output voltage Ve. As a result, there is a concern that strain measurement will be continued without noticing the occurrence of an abnormality.

Further, a part of the strain gauge of the Wheatstone bridge circuit for strain measurement may be used as a temperature detection gauge (Japanese Patent Laid-Open No. 1-206113), or a temperature gauge dedicated to temperature detection may be provided outside the strain measurement Wheatstone bridge circuit. A strain / temperature sensor has been proposed which is capable of simultaneously measuring not only strain but also ambient temperature by connecting a temperature detecting resistor (Japanese Patent Laid-Open No. 58-134394).

However, even in these strain / temperature sensors, when the two resistors forming the Wheatstone bridge circuit are disconnected or short-circuited, the output signal Ve does not change significantly. As a result, the same problem as the above-described strain sensor dedicated to strain measurement occurs.

The present invention has been made in view of such circumstances, and by monitoring the mutual relation of the midpoint voltages of the series circuits constituting the Wheatstone bridge circuits, even if a plurality of resistors are simultaneously provided. It is an object of the present invention to provide an abnormality detecting device for a strain / temperature sensor that can reliably detect the abnormality even if an abnormality occurs in the strain / temperature sensor and further improve the reliability of the strain / temperature sensor.

[0013]

In order to solve the above-mentioned problems, the present invention provides a first resistor whose strain detecting direction coincides with a strain generating direction and a second resistor whose strain detecting direction is orthogonal to the first resistance. , A third series, a fourth series, a fifth series, and a sixth series, and a first series circuit formed by connecting first and second resistances in series, and a second series series formed by connecting the third and fourth resistances in series. Connected in parallel with each other, and connecting the first Wheatstone bridge circuit, which outputs a distortion detection signal from the middle points of the series circuits, the second series circuit, and the fifth and sixth resistors in series. And a second Wheatstone bridge circuit in which a temperature detection signal is output from between the midpoints of the series circuits, and each of the first, third, and sixth The resistance gauge ratio and temperature coefficient are larger than the gauge ratio and temperature coefficient of each of the second, fourth and fifth resistance. An abnormality detecting device for a fixed strain / temperature sensor, wherein the difference between the DC components of the midpoint voltages of the first and second series circuits exceeds an allowable value, and in the third series circuit. The added voltage value of the DC component of the point voltage and the DC component of the midpoint voltage of the series circuit of either one of the first and second series circuits is within a certain allowable range determined by the applied voltage to each Wheatstone bridge circuit. It is provided with a data processing unit which outputs an abnormality detection signal when it comes off.

[0014]

First, the reason why the strain ε and the temperature T can be independently detected in the strain / temperature sensor to which the abnormality detecting device is connected will be described.

That is, the first
6th through 6th resistors are incorporated. Then, the first and second resistors are connected in series to form a first series circuit. Similarly, the third and fourth resistors form a second series circuit, and the fifth and sixth resistors form a third series circuit. Next, the first and second series circuits are connected in parallel to form a first Wheatstone bridge circuit, and the second and third series circuits are connected in parallel to form a second Wheatstone bridge circuit. That is, the second series circuit is also used as the first and second Wheatstone bridge circuits.

Further, the gauge rate and temperature coefficient of each of the first, third and sixth resistances are set to be larger than the gauge rate and temperature coefficient of each of the second, fourth and fifth resistances.

Therefore, when strain occurs on the surface of the body to be measured to which the strain / temperature sensor is attached, only the resistance value of the first resistor changes greatly, so the output signal of the first Wheatstone bridge circuit corresponds to the strain. The distortion detection signal has the above value. The resistance value of the first resistor is greatly influenced by the ambient temperature, and the influence is included in the strain detection signal, but the third resistor is also influenced by the ambient temperature under the same condition. As a result, the temperature variation of the first resistor included in the strain detection signal is canceled by the temperature variation of the third resistor. Therefore, the temperature fluctuation component is removed from the strain detection signal.

When the ambient temperature of the strain / temperature sensor changes, the resistance values of the third and sixth resistors change greatly, so that the output signal of the second Wheatstone bridge circuit has a value corresponding to the temperature. It becomes a temperature detection signal. Even if the strain is generated on the surface of the measured object and the third resistance has the same high gauge factor as the first resistance, the strain detection direction is orthogonal to the strain generation direction. , The change in resistance is small. As a result, the distortion component is not mixed in the temperature detection signal.

Next, the reason why the abnormality can be detected will be described.

The midpoint voltage Va of the first series circuit forming one side of the first Wheatstone bridge circuit is the applied voltage E of each Wheatstone bridge circuit, the current strain ε, the current temperature T, and the bridge balance. Temperature Ts, the temperature coefficient K of the first resistance (= third resistance = sixth resistance), the temperature coefficient k of the second resistance (= fourth resistance = fifth resistance), It is expressed by the equation (1) using the gauge factor K of the first (= third resistance = sixth resistance) resistance.

Va = E {0.5+ (K−k) (T−Ts) + Gε} (1) The second resistor is arranged in the direction orthogonal to the strain generation direction and has the first gauge factor. It is assumed that there is no resistance change due to strain, since it is much smaller than the gauge factor G of the resistance.

Similarly, the midpoint voltage Vb of the second series circuit is
It becomes formula (2).

Vb = E {0.5+ (K−k) (T−Ts)} (2) Although the gauge factor G of the third resistor of the second series circuit is large, it is orthogonal to the strain generation direction. The strain term is negligible because it is arranged in the direction.

Further, in the third series circuit, the sixth resistor having a large temperature coefficient K is connected on the opposite side with respect to the first and second series circuits with the midpoint interposed therebetween. The midpoint voltage Vc of the series circuit is given by equation (3).

Vb = E {0.5− (K−k) (T−Ts)} (3) Although the gauge ratio K of the sixth resistor is large, it is arranged in a direction orthogonal to the strain generation direction. Therefore, the distortion term can be ignored.

In general, the resistance change amount [εG] with respect to the resistance strain ε is orders of magnitude smaller than the change amount KΔT with respect to the temperature change ΔT (= T-Ts). Therefore, the third term in the equation (1) is used. Is a value that can be ignored in comparison with the second term.

(Kk) (T-Ts) >> Gε Since the temperature changes slowly, by extracting the DC component of each midpoint voltage with a low-pass filter or the like,
Only the voltage value due to the temperature change can be reliably detected.

Therefore, the equation (1) can be approximated to the equation (4).

Va = E {0.5+ (K−k) (T−Ts)} (4) Therefore, the relation between (4) and (2), and the equation (2) (= (4)
The following conditional expressions (5) and (6) are established by subtracting the expression (3) from the expression).

Va = Vb (5) Vb + Vc = E (6) Therefore, each midpoint voltage V of the first, second and third series circuits
By measuring a, Vb, and Vc, it is constantly monitored that the equations (5) and (6) are satisfied, and one of the two conditional equations (5) and (6) is satisfied. If not, it can be considered that an abnormality has occurred.

Actually, as described above, the distortion term [G
Since there is an error in [ε] and there is a voltage drop in the lead wire, a constant allowable value Vmax and an allowable range (E ± ΔE) are provided as shown in equations (7) and (8), and When it comes off, an abnormality detection signal is output.

| Va−Vb | <Vmax (7) E−ΔE <Vb + Vc <E + ΔE (8) If the conditions for the occurrence of abnormality are set in this way, the four resistors that form the first Wheatstone bridge circuit are set. When two of the resistors have abnormalities at the same time, Va and Vb may change greatly at the same time, and the condition of the expression (7) may be continuously satisfied. However, if the third midpoint voltage Vc is normal, the condition of equation (8) cannot be maintained. Therefore, the abnormality detection signal is output.

When an abnormality occurs in only one resistor forming each Wheatstone bridge circuit, naturally
Since the conditions of equations (7) and (8) cannot be maintained, the abnormality detection signal is output immediately.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a top view showing a state in which the strain / temperature sensor 5 to which the abnormality detecting device of the embodiment is applied is attached to the surface 6a of the object 6 to be measured. A tensile stress is applied to the DUT 6 in the arrow direction.

In the strain / temperature sensor 5, the first to the third thin film film resistors are formed on the insulating thin film substrate 7 having a rectangular shape.
Sixth resistors R1 to R6 have been deposited using the CVD technique. Only the first resistor R1 is formed in the lengthwise direction of the insulating thin film substrate 7, that is, in the strain generating direction of the measured object surface 6a. And the other second to sixth resistors R2 to R
6 is formed in a direction orthogonal to the first resistor R1.
The longitudinal direction of each of the resistors R1 to R6 is the strain detection direction.

Of the six resistors R1 to R6, the first resistor R1, the third resistor R3 and the sixth resistor R6 are amorphous silicon semiconductor thin films. The gauge factors G of the first, third and sixth resistors R1, R3, R6 formed of this amorphous silicon semiconductor thin film are very high values of 20-30. Also, the first, third and sixth resistors R1, R3 formed of the amorphous silicon semiconductor thin film,
The temperature-resistance value characteristic of R6 is a negative characteristic as shown in FIG. 3, and the temperature coefficient K is a very high value of -500 to -3000 ppm.

On the other hand, for the other second, fourth and fifth resistors R2, R4 and R5, for example, a metal such as [Ta ₂ N] is deposited on the thin film insulating substrate 7 as described above. Is configured. The gauge factor of each of the thin film resistors R2, R4 and R5 is a value of almost 0, and the temperature coefficient k is a value of about -100 ppm.

Therefore, the first, third and sixth resistors R1
, R3, R6 have a gauge ratio G and a temperature coefficient K that are orders of magnitude higher than the gauge ratios and temperature coefficients k of the other second, fourth and fifth thin film resistors R2, R4, R5. is there.

Then, the first resistor R1 and the second resistor R2
Is connected in series to the output terminal 9a, the middle point of the series circuit 8b in which the third resistor R3 and the fourth resistor R4 are connected in series is connected to the output terminal 9b,
Further, the midpoint of the series circuit 8c in which the fifth resistor R5 and the sixth resistor R6 are connected in series is connected to the output terminal 9c.

Further, one end of each series circuit 8a, 8b, 8c is commonly connected to the ground terminal 10a, and the other end is commonly connected to the power supply terminal 10b.

FIG. 1 is a block diagram showing a schematic configuration of an equivalent circuit of the strain / temperature sensor 5 shown in FIG. 2 and the abnormality detecting device 12.

In the strain / temperature sensor 5, the first series circuit 8a and the second series circuit 8b are connected in parallel to form a first Wheatstone bridge circuit 11a.
Further, the second series circuit 8b and the third series circuit 8c are connected in parallel, and the second Wheatstone bridge circuit 11
b is configured.

The output terminals 9a, 9b, 9c, the ground terminal 10a, and the power supply terminal 10b connected to the respective midpoints of the series circuits 8a, 8b, 8c are combined into one flat cable 13 to detect the abnormality. 12 is connected.

In the abnormality detecting device 12, the ground terminal 1
The DC voltage E is applied between 0a and the power supply terminal 10b. In addition, the first Wheatstone bridge circuit 11a
The difference voltage between the midpoint voltages Vb and Va input from the is input to the next multiplexer 15 as the distortion detection signal a after being amplified by the amplifier 14a. Furthermore, the midpoint voltages Vc and Vb input from the second Wheatstone bridge circuit 11b.
The difference voltage between the two is amplified by the amplifier 14a and the temperature detection signal b
Is input to the multiplexer 15. Each series circuit 8
The midpoint voltages Va, Vb, and Vc of a, 8b, and 8c are input to the amplifiers 14a and 14b and directly to the multiplexer 15.

The multiplexer 15 inputs the distortion detection signal a, the temperature detection signal b and the respective midpoint voltages Va, Vb, V.
c is sampled at a constant sampling cycle and sent to the A / D converter 16 as a time division multiplexed signal. A / D
The converter 16 receives the input time-division multiplexed signals a,
b and each of the voltages Va to Vc are converted into digital data and sent to the data processing unit 17 including a microcomputer or the like.

The data processing unit 17 separates each digital distortion detection signal a, temperature detection signal b and each midpoint voltage Va, Vb, Vc contained in the input time division multiplexed signal. Then, from the strain detection signal a to the applied voltage E and the gauge factor G
Etc. is used to calculate the strain ε and output to the outside through the input / output port 18. Similarly, the amount of change from the reference temperature Ts is obtained from the temperature detection signal b using the applied voltage E, the temperature coefficient K, etc., and the current temperature T is calculated, and the input / output port 1
Output to the outside via 8.

Further, the data processing unit 17 has a built-in digital filter, and each input midpoint voltage V
AC components included in a, Vb, and Vc are removed, and only DC components are extracted. That is, the ambient temperature T of the DUT 6
Does not change rapidly, so the noise is removed.
Further, when the object 6 to be measured is subjected to repetitive vibration stress such as a bearing, it is expressed by the above-mentioned formula (1) at the midpoint voltage Va of the first series circuit 8a of the first Wheatstone bridge circuit 11a. The second term [εG] is an AC component having a frequency component corresponding to vibration. Therefore,
By removing this AC component with a digital filter, equation (1) can be approximated more completely to equation (4).

With the digital midpoint voltages Va, Vb, and Vc from which the AC component has been removed by the digital filter, the above-mentioned (│Va-Vb│) and (Vb + Vc) are obtained.
Is calculated. Then, it is determined whether or not these satisfy the conditional expressions (7) and (8) at the same time.

| Va−Vb | <Vmax (7) E−ΔE <Vb + Vc <E + ΔE (8) If either one of the conditional expressions (7) and (8) is not satisfied, the input / output port 18 is The abnormality detection signal c is output to the outside.

The allowable value Vmax and the allowable range (E ±
.DELTA.E) is the first, third and sixth resistors R1. The optimum value is set in consideration of the relationship between the temperature coefficient K and the gauge factor G at R3 and R6, the magnitude of the strain ε generated on the surface 6a of the object to be measured, and the probability of erroneous judgment regarding abnormality detection. It

The operation of the abnormality detecting device 12 of the strain / temperature sensor 5 thus constructed will be described.

First, in a state where the strain ε is not generated in the DUT 6 and the ambient temperature T is the reference temperature Ts (= 20 ° C.) such as room temperature which is set in advance, each midpoint voltage Va to
Both Vc are equal to E / 2. Therefore, the signal values of the strain detection signal a and the temperature detection signal b are 0V. Therefore, from the data processing unit 17, the strain ε = 0 and the temperature T = T
s is output. Naturally, since the conditional expressions (7) and (8) are simultaneously satisfied, the abnormality detection signal c is not output.

Next, when strain .epsilon. Occurs in the device under test 6 and the ambient temperature T deviates from the reference temperature Ts, the strain .epsilon. Changes only in the resistance value of the first resistor R1. And
With respect to the temperature change, the resistance values of all the resistors R1 to R6 change according to the respective temperature coefficients K and k. As a result, the midpoint voltages Va, V of the series circuits 8a, 8b, 8c, respectively.
b and Vc are respectively expressed by the equations (1), (2) and (3) described above.

As a result, the value of the distortion detection signal a represented by (Vb-Va) becomes (-0.5 EGε), and the data processor 17 outputs the strain ε. The value of the temperature detection signal b represented by (Vc-Vb) is {-E (K-k) (T-T).
s)}, and the temperature T is output from the data processing unit 17.

Also in this case, the respective midpoint voltages Va, Vb, Vc obtained by extracting only the DC component are the above-mentioned conditional expressions.
Since (7) and (8) are satisfied at the same time, the abnormality detection signal c is not output.

Next, consider a case where one of the six resistors R1 to R6 constituting the strain / temperature sensor 5 is disconnected in this state. In this case, three series circuits 8a, 8
Among the middle-point voltages Va, Vb, and Cc of b and 8c, only the middle-point voltage of the series circuit including the resistance in which the disconnection has occurred changes greatly and becomes 0V or EV. For example, the midpoint voltages Va and V
Conditional expression (7) does not hold when either of b changes significantly, and conditional expression (8) does not hold when only the midpoint voltage Vc changes significantly. As a result, the data processing unit 17 outputs the abnormality detection signal c.

Further, for example, when the first resistor R1 and the third resistor R3 constituting the first Wheatstone bridge circuit 11a are disconnected at the same time, the respective midpoint voltages Va, Vb.
Are both 0V. Therefore, conditional expression (7) maintains the established condition. However, if the other midpoint voltage Vc maintains a normal value, the condition of the other conditional expression (8) cannot be maintained and the condition is not satisfied. As a result, the data processing unit 17
Outputs an abnormality detection signal c.

Further, the DC applied voltage E applied between the power supply terminal 10b and the ground terminal 10a is caused by the breakage of the lead wire, etc.
If the voltage is not normally applied to 11b, the conditional expression (8) is not satisfied, so that the data processing unit 17 outputs the abnormality detection signal c
Is output.

As described above, the abnormality detection signal c is always output even if an abnormality such as a disconnection or a short circuit occurs in a plurality of resistors at the same time, or the applied voltage E is not normally applied. Therefore, the reliability of the strain detection signal a and the temperature detection signal b obtained from the strain / temperature sensor 5 attached to the surface 6a of the object to be measured can be significantly improved.

FIG. 4 is a block diagram showing the schematic arrangement of a strain / temperature sensor abnormality detecting apparatus according to another embodiment of the present invention. The same parts as those in the embodiment shown in FIG. 1 are designated by the same reference numerals. Therefore, detailed description of the overlapping portions will be omitted.

In this embodiment, the multiplexer 15 receives only the midpoint voltage Vb of the second series circuit 8b and the distortion detection signal a and the temperature detection signal b output from the amplifiers 14a and 14b. And each amplifier 1
Assuming that the gains of 4a14b are α and β, respectively, and the amplified signal levels (voltage values) of the strain detection signal a and the temperature detection signal b are Ve and Vt, the conditional expression (7) described above becomes (9)
It can be transformed like a formula.

| Va−Vb | = (Ve / α) <Vmax (9) Similarly, the conditional expression (8) described above can be transformed into the expression (10).

From Vb + Vc = (Vt / β) + 2Vb, E−ΔE <(Vt / β) + 2Vb <E + ΔE (10) That is, in this embodiment, a new conditional expression (9) (1
By using the equation (0), the number of data input to the data processing unit 17 can be limited to the midpoint voltage Vb, the strain detection signal a, and the temperature detection signal b, and the data processing unit 17, the multiplexer 15, and the A / D converter can be used. The processing load of 16 can be reduced.

[0065]

As described above, according to the abnormality detecting device for the strain / temperature sensor of the present invention, the mutual relations of the respective midpoint voltages of the series circuits constituting the Wheatstone bridge circuits satisfy the conditional expression. I am monitoring whether or not to do it. Therefore, even if an abnormality occurs in a plurality of resistors at the same time, the abnormality occurrence can be reliably detected, and the reliability of strain and temperature measured by the strain / temperature sensor can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a strain / temperature sensor abnormality detection device according to an embodiment of the present invention;

FIG. 2 is a plan view showing a strain / temperature sensor to which the device of the embodiment is applied,

FIG. 3 is a temperature-resistance characteristic diagram in each resistance of the strain / temperature sensor,

FIG. 4 is a block diagram showing a schematic configuration of a strain / temperature sensor abnormality detection device according to another embodiment of the present invention;

FIG. 5 is a Wheatstone bridge circuit diagram incorporated in a general strain sensor,

FIG. 6 is a schematic diagram showing a state in which the same general strain sensor is attached to an object to be measured.

[Explanation of symbols]

5 ... Strain / temperature sensor, 6 ... Object to be measured, 7 ... Insulating thin film substrate, 8a ... First series circuit, 8b ... Second series circuit, 8
c ... Third series circuit, 11a ... First Wheatstone bridge circuit, 11b ... Second Wheatstone bridge circuit, 12 ... Abnormality detection device, 14a, 14b ... Amplifier, 1
5 ... Multiplexer, 17 ... Data processing unit, R1 to R6
... 1st-6th resistance, Va, Vb, Vc ... Midpoint voltage.

Claims (1)

(57) [Scope of utility model registration request] 1. A first direction in which a strain detection direction coincides with a strain generation direction.
Resistance (R1) and the second, third, fourth, fifth and sixth (R2 to R6) resistances whose strain detection directions are orthogonal to the first resistance, and the first and second resistances. A first series circuit (8a) formed by connecting resistors in series and a second series circuit formed by connecting the third and fourth resistors in series.
A series circuit (8b) is connected in parallel, and a distortion detection signal (a) is output between the midpoints of the series circuits, and a first Wheatstone bridge circuit (11a) and the second series circuit. Third series circuit formed by connecting the fifth and sixth resistors in series
(8c) and the second Wheatstone bridge circuit (11b), which is connected in parallel and outputs a temperature detection signal (b) from the midpoints of the series circuits, and the first and third A strain / temperature sensor abnormality detecting device in which the gauge ratio and temperature coefficient of each of the sixth resistances are set to be larger than the gauge ratio and temperature coefficient of each of the second, fourth, and fifth resistances, Each midpoint voltage (Va, Vb) of the first and second series circuits
When the difference between the DC components exceeds the allowable value, and the DC component of the midpoint voltage (Vc) of the third series circuit and either one of the first and second series circuits. The data processing unit (17) that outputs an abnormality detection signal (c) when the added voltage value with the DC component of the midpoint voltage is out of a certain allowable range determined by the applied voltage to each Wheatstone bridge circuit Strain / temperature sensor abnormality detection device.