JP6433049B2 - Carrier type strain measuring device - Google Patents

Description

  The present invention relates to a carrier-type strain measuring device that applies a carrier power supply voltage to a measurement bridge including a strain gauge and obtains a signal corresponding to the strain resistance of the strain gauge from the output of the measurement bridge.

Conventionally, for stress measurement using a strain gauge, a carrier power supply voltage is applied to a measurement bridge formed by connecting a strain gauge and a resistor, and a signal corresponding to the strain resistance of the strain gauge is applied from the output of the measurement bridge to the carrier. 2. Description of the Related Art Carrier-type strain measurement devices that take out signals with superimposed components and obtain signals corresponding to strain resistance are often used. The reason for this is that this type of carrier-type strain measurement device is highly stable because it is less susceptible to the effects of noise such as hum generated from the power supply and the thermoelectromotive force generated at the contacts connected to the measurement bridge. This is because highly accurate strain measurement can be performed.
The present applicant applies a carrier power supply voltage such as a sine wave to a measurement bridge including a strain gauge, and obtains a signal corresponding to the strain resistance of the strain gauge from the output of the measurement bridge. A carrier-type strain measuring apparatus capable of measuring only the resistance component by automatically canceling the unbalanced component has been proposed previously, and disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2010-266408). Yes.

That is, the carrier wave type distortion measuring apparatus according to Patent Document 1 is
A measurement bridge including a strain gauge;
A carrier wave oscillation circuit for generating a carrier wave to be applied to the measurement bridge via a coupling transformer;
A carrier amplifier circuit that receives and amplifies a measurement signal superimposed on a carrier wave applied to the measurement bridge via an input transformer;
Receiving the output of the carrier wave amplifier circuit, extracting an unbalanced component corresponding to the capacitance change of the measurement bridge, and outputting a compensation phase signal corresponding to the unbalanced component;
An optical signal transmission means comprising at least one light-emitting diode and a light-receiving diode disposed to face the light-emitting diode;
A capacitance canceling drive circuit for controlling the light emission luminance of the light emitting diode according to the compensation amount signal;
The light emission from the light emitting diode is converted into an electric signal, converted into an electric signal, converted into a compensation potential having a polarity and amplitude corresponding to the compensation amount according to the current flowing through the light receiving diode, and the phase of the output waveform according to the polarity And the compensation potential is superimposed on the carrier wave and supplied to the primary side of the input transformer, and a capacitance canceling circuit for automatically canceling the unbalanced component due to the capacitance component generated in the measurement bridge;
A secondary power supply for supplying power to each circuit on the secondary side;
A primary power supply circuit that receives power from the secondary power supply via a power transformer and supplies power to each circuit on the primary side;
Comprising
For the carrier wave amplification circuit, the capacitance phase detection circuit, the capacitance cancellation drive circuit, the light emitting diode, the carrier wave oscillation circuit, and the secondary power supply,
The measurement bridge, the capacitance canceling circuit, the light receiving diode, and the primary power circuit are:
The input transformer, the optical signal transmission means, the electromagnetic means including the coupling transformer and the power transformer, and the optical signal transmission means are connected to each other and are electrically insulated. .

As described above, in the configuration shown in Patent Document 1, in order to automatically cancel the unbalanced capacity, a capacitive phase detection circuit, a capacitive cancellation driving circuit, and an optical signal transmission means are used. Many complex circuits such as cancellation circuits are required. For this reason, the configuration of Patent Document 1 complicates the circuit configuration and increases the number of components, which hinders downsizing, power saving, and cost reduction.
In general, when performing strain measurement, it is necessary to route the input cable from the measurement point to the strain measurement device. However, when using the carrier-type strain measurement device described above, the existence of distributed capacity due to the input cable must be considered. I must. The distributed capacity of the input cable appears as an initial unbalanced component for the capacity together with the initial unbalance of the resistance value of the measurement bridge. The change in the resistance value of the strain gauge is necessary for measurement, but the capacity is a factor that hinders accurate measurement. Therefore, a circuit for canceling the capacity imbalance component is required. The capacitance canceling circuit in the conventional strain measuring apparatus has a complicated circuit configuration as shown in Patent Document 1 and uses many electric parts, so that the apparatus itself can be reduced in size, power consumption and cost. It is a hindrance.

JP 2010-266408 A

As described above, in the conventional carrier-type distortion measuring device as disclosed in Patent Document 1, in order to cancel the unbalanced component of the capacitance and measure only the resistance component, the circuit configuration is complicated and many electrical components are used. Therefore, the existence of such a capacitance canceling circuit is a factor that hinders downsizing, power saving, and cost reduction of the device itself.
The present invention has been made in view of the above-described circumstances, and can avoid the influence of the capacity without using a circuit having a complicated capacity, thereby simplifying the circuit structure and reducing the number of parts. It is an object of the present invention to provide a carrier-type distortion measuring device that can be made smaller, achieve power saving and cost reduction.

The present invention has been made to achieve the above-described object, and has the following characteristics.
A carrier-type distortion measuring apparatus according to the invention described in claim 1 is:
In a carrier-type strain measurement device that applies a carrier power supply voltage to a measurement bridge including a strain gauge and obtains a signal corresponding to the strain resistance of the strain gauge from the output of the measurement bridge.
A bridge power supply circuit for applying a rectangular wave carrier power supply voltage to the measurement bridge;
An amplifier circuit for amplifying the output of the measurement bridge ;
An inverting circuit that inverts the output of the amplifier circuit, a plurality of input terminals, a plurality of control terminals, and an output terminal, and an input signal to the plurality of input terminals according to a control signal input to the plurality of control terminals A multiplexer that selectively extracts and outputs from the output terminal, and a detection circuit comprising:
A control circuit that synchronously controls the bridge power supply circuit and the multiplexer by applying predetermined first control signals, second control signals, and third control signals to the plurality of control terminals of the bridge power supply circuit and the multiplexer. When,
A carrier filter circuit for removing a carrier wave component from an output signal including a signal component corresponding to a distortion resistance of the detection circuit,
The control circuit includes:
The first control signal is output to the bridge power supply circuit and is driven and controlled so as to output a rectangular wave carrier voltage having a predetermined period T1 from the bridge power supply circuit,
Drive control is performed so that the second control signal is output to the control terminal of the multiplexer, and the output of the amplifier circuit and the output of the inverting circuit are alternately output from the multiplexer at the same period T1 as the carrier wave period. And
The third control signal is output to the control terminal of the multiplexer, and a time during which ripple occurs near the rise and fall of the output waveform is preset as a capacity output time T2, and the capacity output time The third control signal is output to the control terminal of the multiplexer for a time T3 from immediately before the start of T2 to the time after the output time T2 for the capacity has elapsed, and the output from the output terminal of the multiplexer is zero. Drive control to become voltage,
By driving and controlling the bridge power supply circuit and the multiplexer with the control circuit, the influence of the capacitance is effectively removed, and the output corresponding to only the resistance is output from the detection circuit,
Further, the present invention is characterized in that a DC level signal corresponding to the resistance change of the strain gauge to be measured is detected by removing the carrier component through the carrier filter circuit . .

The carrier-type distortion measuring apparatus according to the invention described in claim 2 is the carrier-type distortion measuring apparatus according to claim 1,
The capacity output time T2 is:
It is set based on the time from the generation to the disappearance of the ripple generated near the rising and falling of the output waveform due to the influence of the distributed capacitance generated between each side of the measurement bridge or between the connection point and the ground potential. Yes.
The carrier-type distortion measuring apparatus according to the invention described in claim 3 is the carrier-type distortion measuring apparatus according to claim 1 or 2,
The capacity output time T2 is:
It is set in consideration of the resistance value of the strain gauge included in the measurement bridge, the length of the input cable from the measurement bridge to the measurement circuit, the carrier frequency , and the like.
The carrier-type distortion measuring apparatus according to the invention described in claim 4 is the carrier-type distortion measuring apparatus according to claim 3,
The measuring circuit, the amplifier circuit, the inverting circuit, the multiplexer, the control circuit is characterized by being composed of the bridge power supply circuit and the carrier filter circuit.

The carrier-type distortion measuring apparatus according to the invention described in claim 5 is the carrier-type distortion measuring apparatus according to claim 1 ,
Before Symbol detection circuit is characterized in that it is configured to include said and said inverting circuit multiplexer.

According to the present invention, it is possible to avoid the influence of the capacity without using the capacity canceling circuit having a complicated configuration, and it is possible to simplify the circuit configuration and reduce the number of parts. It is possible to provide a carrier-type distortion measuring apparatus that can achieve power reduction and cost reduction.
That is, according to the carrier-type distortion measuring apparatus of claim 1 of the present invention,
In a carrier-type strain measurement device that applies a carrier power supply voltage to a measurement bridge including a strain gauge and obtains a signal corresponding to the strain resistance of the strain gauge from the output of the measurement bridge.
A bridge power supply circuit for applying a rectangular wave carrier power supply voltage to the measurement bridge;
An amplifier circuit for amplifying the output of the measurement bridge ;
An inverting circuit that inverts the output of the amplifier circuit, a plurality of input terminals, a plurality of control terminals, and an output terminal, and an input signal to the plurality of input terminals according to a control signal input to the plurality of control terminals A multiplexer that selectively extracts and outputs from the output terminal, and a detection circuit comprising:
A control circuit that synchronously controls the bridge power supply circuit and the multiplexer by applying predetermined first control signals, second control signals, and third control signals to the plurality of control terminals of the bridge power supply circuit and the multiplexer. When,
A carrier filter circuit for removing a carrier wave component from an output signal including a signal component corresponding to a distortion resistance of the detection circuit,
The control circuit includes:
The first control signal is output to the bridge power supply circuit and is driven and controlled so as to output a rectangular wave carrier voltage having a predetermined period T1 from the bridge power supply circuit,
Drive control is performed so that the second control signal is output to the control terminal of the multiplexer, and the output of the amplifier circuit and the output of the inverting circuit are alternately output from the multiplexer at the same period T1 as the carrier wave period. And
The third control signal is output to the control terminal of the multiplexer, and a time during which ripple occurs near the rise and fall of the output waveform is preset as a capacity output time T2, and the capacity output time The third control signal is output to the control terminal of the multiplexer for a time T3 from immediately before the start of T2 to the time after the output time T2 for the capacity has elapsed, and the output from the output terminal of the multiplexer is zero. Drive control to become voltage,
By driving and controlling the bridge power supply circuit and the multiplexer with the control circuit, the influence of the capacitance is effectively removed, and the output corresponding to only the resistance is output from the detection circuit,
Furthermore, by configuring the output of the detection circuit to detect a DC level signal corresponding to the resistance change of the strain gauge to be measured by removing the carrier component through the carrier filter circuit ,
Without using a complicated capacity canceling circuit, the output generated in the remaining DC portion obtained by decimating and removing the output time T2 from the carrier wave period T1 can be obtained effectively and continuously . It is possible to achieve simplification and reduction of the number of parts, and to realize downsizing, power saving and cost reduction of the apparatus.

It is a block diagram which shows a circuit structure as a state which connected the measurement bridge | bridging to the said carrier-type distortion measuring apparatus about the structure of the measuring circuit of the carrier-type distortion measuring apparatus which concerns on one embodiment of this invention. It is a block diagram which shows the detailed circuit structure of the detection circuit in the measurement circuit of the carrier wave type | mold distortion measuring apparatus of FIG. FIG. 2 is a connection entity diagram showing a connection configuration in which a measurement bridge that constitutes a Wheatstone bridge is connected to the carrier-type strain measurement apparatus of FIG. 1 using a strain gauge and a resistance attached to a site to be measured for strain. It is an equivalent circuit diagram which shows the detailed connection structure which connects a measurement bridge to a carrier wave type distortion measuring device. FIG. 5 is a waveform diagram showing in detail an example of a waveform of a measurement bridge output in the equivalent circuit of FIG. 4. FIG. 3 is a waveform diagram of each part showing the waveform of each part in the detection circuit of FIG. 2. FIG. 5 is a diagram showing an equivalent circuit in which the measurement bridge portion in the equivalent circuit of FIG. 4 is further simplified and a bridge output waveform with respect to application of a bridge power supply. In order to explain the processing principle of the detection circuit in the measurement circuit of the carrier-type strain measurement device of FIG. 1, the magnitude of the time constant τ with respect to the change in the distributed capacity when the resistance value of the strain gauge is 120Ω, 350Ω and 1000Ω, respectively. FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a carrier-type distortion measuring apparatus according to the present invention will be described below in detail with reference to the drawings.
1 to 4 show the configuration of the main part of a carrier-type distortion measuring apparatus according to one embodiment of the present invention. FIG. 1 is a block diagram showing the configuration of a measurement circuit of a carrier-type strain measurement apparatus according to an embodiment of the present invention as a state in which a measurement bridge is connected to the carrier-type distortion measurement apparatus, and FIG. FIG. 3 is a block diagram showing a detailed configuration of the detection circuit in the measurement circuit of the strain measuring apparatus, and FIG. 3 is a diagram showing a measurement bridge in which a Wheatstone bridge is configured using a strain gauge and a resistance attached to a portion where strain is to be measured. FIG. 4 is a connection entity diagram schematically showing a connection configuration connected to one carrier-type strain measurement device, and FIG. 4 is an equivalent circuit diagram showing a detailed connection configuration for connecting a measurement bridge to the carrier-type strain measurement device.
FIG. 1 is a block diagram showing a configuration of a measurement circuit of a carrier-type distortion measuring apparatus according to one embodiment of the present invention. In general distortion measurement, FIG. 1 shows a carrier-type distortion measuring apparatus according to this embodiment. A measurement bridge composed of a Wheatstone bridge is shown as connected.

FIG. 1 shows a measurement bridge 11 connected to a carrier wave distortion measuring apparatus according to one embodiment and a measurement circuit 12 constituting the carrier wave distortion measuring apparatus body.
The measurement bridge 11 shown in FIG. 1 has four connection points, a connection point A, a connection point B, a connection point C, and a connection point D, between the connection point A and the connection point B of the measurement bridge 11. Connect the strain gauge R1, connect the resistor R2 between the connection point B and the connection point C, connect the resistor R3 between the connection point C and the connection point D, and connect the connection point D and the connection point A. A resistor R4 is connected between the two to constitute a Wheatstone bridge circuit. Strain gauges R1 is strain-generating-portions of the object, i.e. at a site try to strain deformation occurs measuring, for example, contact bonding, fusion bonding by means of welding or the like, are affixed, of the strain-generating-portions strain The resistance value changes according to the size.
The measurement circuit 12 shown in FIG. 1 includes an amplifier circuit 13, a detection circuit 14, a carrier filter circuit 15, a bridge power supply circuit 16, and a control circuit 17. The bridge power supply circuit 16 applies a rectangular wave carrier power supply voltage to the measurement bridge 11. The amplifier circuit 13 detects and amplifies the output from the measurement bridge 11. The detection circuit 14 performs signal processing on the output of the amplifier circuit 13 and extracts a signal including a signal component corresponding to a change in the resistance value of the strain gauge R1 of the measurement bridge 11. The carrier filter circuit 15 removes a carrier wave component based on the bridge power supply voltage from the output of the detection circuit 14. The control circuit 17 controls the bridge power supply circuit 16 and the detection circuit 14 to operate synchronously at a predetermined timing.

1, the output of the bridge power supply circuit 16 in the measurement circuit 12 is connected to the connection point A and connection point C of the measurement bridge 11 via cables 11a and 11c, respectively. A rectangular wave carrier bridge voltage is applied between these connection points A and C. The output from the measurement bridge 11 is detected and amplified by the amplifier circuit 13 via the cables 11b and 11d connected to the connection point B and the connection point D, respectively. The output of the amplifier circuit 13 is signal-processed by the detection circuit 14 as will be described in detail later, and a signal including a signal component corresponding to a change in the resistance value of the strain gauge R1 of the measurement bridge 11 is extracted. An unnecessary carrier component is removed from the output of the detection circuit 14 by the carrier filter 15, and a required signal component is output from the carrier filter 15.
The control circuit 17 supplies the two control signals 17a and 17b as the second control signal and the third control signal to the detection circuit 14 to control the detection circuit 14, and also controls as the first control signal. The signal 17c is supplied to the bridge power supply circuit 16, and the carrier wave period of the bridge power supply circuit 16 is controlled.
Next, a detailed configuration and processing operation of the detection circuit 14 will be described with reference to FIG.

FIG. 2 shows a detailed configuration of the detection circuit 14, and the detection circuit 14 includes an inverting circuit 18 and a multiplexer 19. The multiplexer 19 has input terminals 19a, 19b, 19c, 19d, an output terminal 19e, and control terminals 19f, 19g. The output signal 13 a of the amplifier circuit 13 is input to the input terminal 19 a of the multiplexer 19 and the inverting circuit 18. The inverting circuit 18 inverts the output of the amplifier circuit 13 (“× (−1)”, that is, −1), and inputs the inverted signal to the input terminal 19 b of the multiplexer 19. The input terminals 19 c and 19 d of the multiplexer 19 are both connected to a reference potential point (usually a ground potential point called a so-called ground level) 20.
Here, the operation of the multiplexer 19 will be described.
The multiplexer 19 turns on one of the input terminals 19a, 19b, 19c, and 19d based on whether the voltage level of the control terminals 19f and 19g is high (HIGH) level or low (LOW) level. ), The input signal of the turned-on terminal is output to the output terminal 19e. The voltage levels of the control terminals 19f and 19g are controlled by control signals 17a and 17b supplied from the control circuit 17. The following table shows the relationship between the voltage levels of the control terminals 19f and 19g of the multiplexer 19 and the input terminals that are turned on by the combination thereof and led to the output terminal 19e.

According to Table 1, for example, as the second control signal, when the control terminal 19f is at the low level and the control terminal 19g is at the low level, the input terminal 19a is turned on and the input terminal 19a that receives the output of the amplifier circuit 13 is received. Is directly output to the output terminal 19e.
According to Table 1, for example, as the second control signal, when the control terminal 19f is at a high level and the control terminal 19g is at a low level, the input terminal 19b is turned on and an output from the inverting circuit 18 is received. The voltage of the input terminal 19b is output as it is to the output terminal 19e.
FIG. 3 shows a connection configuration from the measurement circuit 12 to the measurement bridge 11 as a substantial diagram, and FIG. 4 shows an electrical equivalent circuit of the configuration of FIG. The measurement bridge 11 is configured as a Wheatstone bridge using the strain gauge R1 and the resistors R2 to R4 attached to the portion where the strain is to be measured as described above.
FIG. 3 shows a state in which a measurement bridge 11 comprising a Wheatstone bridge with fixed resistors R2, R3, R4 and a strain gauge R1 is connected to a measurement circuit 12 via an input cable 21 consisting of four connection lines. Show. In such a state, distributed capacitance is generated in the measurement bridge 11. This distributed capacity appears in the output signal of the measurement bridge 11 as an initial unbalance value and also as an unbalance value for the capacity. In this case, the change in the resistance value of the strain gauge R1 is necessary for the measurement, but as described above, the capacitance and the change are a factor that hinders accurate measurement, that is, a measurement accuracy impediment factor.

This measurement accuracy impeding factor will be examined in more detail.
In the circuit configuration between the measurement circuit 12 and the measurement bridge 11 shown in FIG. 3, the input cable 21 is interposed, so that each connection point on two adjacent sides of the measurement bridge 11 and the ground (ground to GND) potential are There is a distributed capacity between the two.
That is, the resistances of the four sides of the measurement bridge 11 are R1 to R4, the distributed capacitances between the sides are Cb1 to Cb4, the cable resistances of the connection lines of the input cable 21 are r1 to r4, the connection points, that is, the connection lines. If the distributed capacitance between the ground potential is Cg1 to Cg4, an equivalent circuit as shown in FIG. 4 is obtained. In FIG. 4, the carrier wave bridge voltage is indicated as E, and the bridge output voltage is indicated as e.
In the strain measurement, what is required is the resistance change of the strain gauge R1. FIG. 5 shows an example of an output waveform when a strain measurement is actually performed, a resistance change ΔR1 occurs in the strain gauge R1, and the bridge output voltage e is amplified by the amplifier circuit 13. In FIG. 5, the output waveform is shown with the carrier wave period with respect to the time axis t as T1.
The waveform shown in FIG. 5A is obtained when the distributed capacitances Cb1 to Cb4 between the sides and the distributed capacitances Cg1 to Cg4 between the connection points and the ground potential are zero and the resistance change ΔR1 occurs. This is an ideal output waveform.

However, in reality, since distributed capacitance always exists between each side or between each connection point and the ground potential, the output waveform does not become the waveform as shown in FIG. ) Often occurs. In FIG. 5, the ripple period with respect to the time axis t is shown as T2. The cause will be described next.
In order to calculate the size of one side (half cycle) of the ripple, the bridge circuit of FIG. 4 is simplified. The resistance of the four sides of the bridge is the same resistance value (resistance balance is balanced), the resistance value of each side is R1 = R2 = R3 = R4≈R, and the distributed capacitance between each side is It is assumed that Cb1 ≠ Cb2, Cb3 = Cb4 = 0, and the distributed capacitance between each connection point and the ground potential is Cg1 = Cg2 = Cg3 = Cg4 = 0. The distributed capacities Cb3, Cb4, Cg1, Cg2, Cg3, and Cg4, which are assumed to be zero here, actually exist and must be taken into account, but in order to understand the magnitude of only one side of the ripple, Regarding the distributed capacity, Cb3 = Cb4 = 0 and Cg1 = Cg2 = Cg3 = Cg4 = 0 may be set.
FIG. 7A is a simplified diagram of FIG. 4 based on such consideration, and FIG. 7B is a diagram when the bridge power supply voltage E is applied between the connection point A and the connection point C. The bridge output voltage e between the connection point B and the connection point D is shown.
The transfer function of the equivalent circuit in FIG. 7A is expressed by the following equation (1).

  When a one-step bridge power supply E is applied between the connection point A and the connection point C in FIG. 7A and Laplace conversion is performed, the output voltage e is expressed by the following equation (2).

  It becomes. The size of the ripple is given by the following formula (3):

Cb1-Cb2 << Cb1 + Cb2 (3)
Therefore, it is almost determined by the time constant τ = R (Cb1 + Cb2) / 2.

FIG. 8 shows the magnitude of the time constant τ with respect to the change in distributed capacity when the resistance value of the strain gauge is 120Ω, 350Ω, and 1000Ω, respectively.
For example, when the input cable 21 shown in FIG. 3 is extended by 100 m, assuming that Cb1 + Cb2 = 4000 pF and gauge resistance R = 120Ω as the distributed capacitance, the time constant is 240 nS.
FIG. 5B shows an example of an output waveform when a resistance change ΔR occurs in the strain gauge R1 and there is a distributed capacitance between each side or between each connection point and the ground potential. In the waveform of FIG. 5B, ripples are generated near the rise and fall of the output waveform due to the influence of the capacitance. In FIG. 5 (b), the time during which ripple occurs at this time is T2, and is referred to herein as a capacity output time. This capacity output time T2 corresponds to the time constant shown in FIG. The lower the carrier frequency, the lower the ratio of the output time T2 corresponding to the capacity to the carrier cycle T1 from the time axis t.
What is required in the strain measurement is the measurement of the resistance change, and it is sufficient that the output generated in the remaining direct current (DC) portion obtained by thinning out the output time T2 for the capacity from the carrier wave period T1 is obtained.

FIG. 6 is an example of an output waveform when the detection circuit 14 shown in FIG. 2 is used.
FIG. 6A shows the output waveform of the amplifier circuit 13, and this signal is input to the input terminal 19 a of the multiplexer 19. FIG. 6B shows the output waveform of the inverting circuit 18, and this signal is input to the input terminal 19 b of the multiplexer 19. FIG. 6C shows the signal waveform of the control signal 17 a output from the control circuit 17, and this signal is input to the control terminal 19 f of the multiplexer 19. FIG. 6D shows the signal waveform of the control signal 17 b output from the control circuit 17, and this signal is input to the control terminal 19 g of the multiplexer 19.
Here, the control operation of the control circuit 17 will be specifically described with reference to FIGS. 2 and 6 and Table 1. FIG.
First, the control circuit 17 controls the bridge power supply circuit 16 by the control signal 17c (see also FIG. 1). In this case, control is performed so that the carrier wave period of the carrier wave bridge power supply voltage is T1. Therefore, the output of the amplifier circuit 13 and the output of the inverting circuit 18 based on the bridge output of the measurement bridge 11 caused by the carrier wave bridge power supply voltage are shown in waveforms in FIGS. 6 (a) and 6 (b), respectively. In addition, the cycle is the same as the carrier cycle T1.

The control signal 17a output from the control circuit 17 shown in FIG. 6C is controlled so as to alternately repeat a low (LOW) level and a high (HIGH) level in the same cycle as the carrier cycle T1. In order to remove the influence of the capacity, it is necessary to thin out the output waveform corresponding to the capacity generated in the capacity output time T2 shown in FIG.
According to Table 1, when the control signal 17 b, that is, the voltage level of the control terminal 19 g of the multiplexer 19 is high (HIGH) level, the output of the output terminal 19 e of the multiplexer 19 is the multiplexer 19 connected to the reference potential point 20. The voltage at the input terminal 19c or 19d is zero voltage because it is the reference potential.
The control signal 17b as the third control signal output from the control circuit 17 shown in FIG. 6 (d) has a high voltage level earlier than the start time of the capacity output time T2, and is output by the capacity. It needs to be controlled to become a low (LOW) level later than the end time of the time T2. A period T3 shown in FIG. 6D corresponds to a period in which the voltage level of the waveform of the control signal 17b is high (HIGH), and the output waveform of the output terminal 19e at this time is shown in FIG. It becomes the waveform.

As can be seen from Table 1, the control terminal of the multiplexer 19 from the control circuit 17 as the second control signal whose waveforms are shown in FIGS. 6 (c) and 6 (d) and the control signals 17a and 17b as the third control signal. Depending on the voltage levels of the control signals 17a and 17b applied to 19f and 19g, the output of the amplifier circuit 13 and the output of the inverting circuit 18 applied to the input terminals 19a and 19b of the multiplexer 19, respectively, and the zero voltage as the reference potential One of them is selected, led to the output terminal 19e of the multiplexer 19, and outputted.
The hatched portion shown in FIG. 6 represents the output selected in this way. The hatched portion in FIG. 6 (e) is an output obtained by extracting only the portion corresponding to the resistance change necessary for the strain measurement, and the carrier filter component in this output is removed by the carrier filter circuit 15. As a result, a waveform as shown in FIG. 6F is obtained.
As described above, by controlling the bridge power supply circuit 16 and the multiplexer 19 by the control circuit 17, an output corresponding to only the resistance is obtained, and further, the carrier wave component is removed and measured through the carrier filter circuit 15. It is detected as a DC level signal corresponding to the resistance change of the strain gauge.

The carrier-type distortion measuring apparatus according to this embodiment uses a voltage applied as a power source to the measurement bridge as a carrier wave, and in principle has a configuration that is resistant to noise. Further, the carrier wave power supply voltage is a rectangular wave, By controlling the control signal of the multiplexer and the multiplexer, the output corresponding to the capacitance unnecessary for the strain measurement is thinned out and removed, and only the output corresponding to the resistance change necessary for the measurement can be detected effectively. In this case, it is possible to effectively remove the influence of the capacity by simply devising signal processing in a detection circuit that is almost the same as that used in the past, and the capacity canceling circuit that has been used in the past is unnecessary. Therefore, the circuit can be simplified, and at the same time, the number of parts can be reduced, the measuring device itself can be reduced in size, the power can be saved, and the cost can be reduced.
The carrier-type distortion measuring apparatus according to this embodiment uses a voltage applied as a power source to the measurement bridge as a carrier wave, and in principle has a configuration that is resistant to noise. Further, the carrier wave power supply voltage is a rectangular wave, By controlling the control signal of the multiplexer and the multiplexer, the output corresponding to the capacitance unnecessary for the strain measurement is thinned out and removed, and only the output corresponding to the resistance change necessary for the measurement can be detected effectively.

In this case, it is possible to effectively remove the influence of the capacity by simply devising signal processing in a detection circuit that is almost the same as that used in the past. Therefore, the circuit can be simplified, and at the same time, the number of parts can be reduced, the measuring device itself can be reduced in size, the power can be saved, and the cost can be reduced.
The present invention is not limited to the embodiment described above and shown in the drawings, and various modifications can be made without departing from the scope of the invention.
For example, Oite to the above-described embodiment, the measuring bridge 11, a strain gauge R1,
Although a Wheatstone bridge is configured using resistors R2 to R4, all four strain gages are used to construct a bridge, or two strain gages and two fixed resistors are used to construct a bridge. Also good.

DESCRIPTION OF SYMBOLS 11 Measurement bridge 11a-11d Cable 12 Measurement circuit 13 Amplification circuit 14 Detection circuit 15 Carrier filter circuit 16 Bridge power supply circuit 17 Control circuit 17a, 17b, 17c Control signal 18 Inversion circuit 19 Multiplexer 19a-19d Input terminal 19e Output terminal 19f, 19g Control terminal 20 Reference potential point R1 Strain gauge R2 to R4 (Fixed) resistance

Claims (5)

In a carrier-type strain measurement device that applies a carrier power supply voltage to a measurement bridge including a strain gauge and obtains a signal corresponding to the strain resistance of the strain gauge from the output of the measurement bridge.
A bridge power supply circuit for applying a rectangular wave carrier power supply voltage to the measurement bridge;
An amplifier circuit for amplifying the output of the measurement bridge ;
An inverting circuit that inverts the output of the amplifier circuit, a plurality of input terminals, a plurality of control terminals, and an output terminal, and an input signal to the plurality of input terminals according to a control signal input to the plurality of control terminals A multiplexer that selectively extracts and outputs from the output terminal, and a detection circuit comprising:
A control circuit that synchronously controls the bridge power supply circuit and the multiplexer by applying predetermined first control signals, second control signals, and third control signals to the plurality of control terminals of the bridge power supply circuit and the multiplexer. When,
A carrier filter circuit for removing a carrier wave component from an output signal including a signal component corresponding to a distortion resistance of the detection circuit,
The control circuit includes:
The first control signal is output to the bridge power supply circuit and is driven and controlled so as to output a rectangular wave carrier voltage having a predetermined period T1 from the bridge power supply circuit,
Drive control is performed so that the second control signal is output to the control terminal of the multiplexer, and the output of the amplifier circuit and the output of the inverting circuit are alternately output from the multiplexer at the same period T1 as the carrier wave period. And
The third control signal is output to the control terminal of the multiplexer, and a time during which ripple occurs near the rise and fall of the output waveform is preset as a capacity output time T2, and the capacity output time The third control signal is output to the control terminal of the multiplexer for a time T3 from immediately before the start of T2 to the time after the output time T2 for the capacity has elapsed, and the output from the output terminal of the multiplexer is zero. Drive control to become voltage,
By driving and controlling the bridge power supply circuit and the multiplexer with the control circuit, the influence of the capacitance is effectively removed, and the output corresponding to only the resistance is output from the detection circuit,
Further, the output of the detection circuit is configured to detect a DC level signal corresponding to the resistance change of the strain gauge to be measured by removing the carrier component through the carrier filter circuit. Carrier type strain measuring device. The capacity output time T2 is:
It is set based on the time from the generation to the disappearance of the ripple generated near the rising and falling of the output waveform due to the influence of the distributed capacitance generated between each side of the measurement bridge or between the connection point and the ground potential. The carrier-type distortion measuring apparatus according to claim 1. The capacity output time T2 is:
3. The setting according to claim 1 or 2 , wherein a resistance value of the strain gauge included in the measurement bridge, a length of an input cable from the measurement bridge to a measurement circuit, the carrier frequency, and the like are set. The carrier-type distortion measuring apparatus described in 1. The carrier-type distortion measuring apparatus according to claim 3, wherein the measurement circuit includes the amplifier circuit, the inverting circuit, the multiplexer, the control circuit, the bridge power supply circuit, and the carrier filter circuit. . Before Symbol detection circuit, carrier wave type strain measuring device according to claim 1 you characterized in that it is configured to include a said said inverting circuit multiplexer.

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