JP2012154701A - Carrier wave type dynamic strain measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically and constantly cancel unbalanced components by floating capacitance included in four sides of a measurement bridge to accurately measure actual resistance components in accordance with change of a resistance value according to a distortion gauge for forming the measurement bridge.SOLUTION: A carrier wave type dynamic strain measuring instrument includes: a measurement bridge 11; carrier wave amplifier circuits 21a, 21b; a resistance phase detection circuit 22; first and second capacitance cancellation drive circuits 24a, 24b which convert phase shift into a compensation amount; first and second phase shift circuits 25a, 25b which supply reference voltage which is used as a reference of the phase shift to the capacitance cancellation drive circuits 24a, 24b, respectively; and an oscillation circuit 26 which generates carrier waves. The carrier wave type dynamic strain measuring instrument further includes first and second capacitors Cb, Cd for feedback, and automatically cancels all unbalanced components due to floating capacitance (Cu1-Cu4) to be mixed in resistance of each of four sides of the measurement bridge 11 in parallel by actions of the capacitors Cb, Cd.

Description

  The present invention relates to a carrier-type dynamic strain measuring instrument, and more specifically, to each of one to four sides of four sides (resistance) of a strain gauge constituting a measurement bridge while preventing the influence of power supply noise. The present invention relates to a carrier-type dynamic strain measuring instrument that can automatically and automatically cancel all the capacitive imbalance components due to stray capacitance components generated in parallel.

Conventionally, a carrier type dynamic strain measuring instrument is frequently used for stress measurement using a strain gauge. The reason is that, in principle, it is strong against hum noise such as a power supply, and even if a contact is used for the connection wiring to the measurement bridge, it is not affected by the thermoelectromotive force, and highly accurate measurement can be performed.
In addition, when measuring stress using a strain gauge, the strain gauge is small and lightweight, and the greatest feature is that it hardly affects the measurement object.
In general, it is necessary to extend an input cable from a measurement point to a strain measuring device. However, when a carrier-type dynamic strain measuring device is used, a distributed capacitance (also referred to as stray capacitance) is generated by the input cable.
The distributed capacity appears as an initial unbalance value for the capacity together with an initial unbalance value of the resistance value of the measurement bridge. The change in resistance of the strain gauge is necessary for measurement, but the capacity is a factor that hinders accurate measurement (measurement accuracy impediment factor).
The capacity is constantly changed in the environment such as the length of the input cable, the ambient temperature, and the humidity.
Here, how the capacitance unbalanced component hinders obtaining an accurate measurement will be described with reference to FIGS. 18A and 18B.

FIG. 18A is an explanatory diagram schematically showing a circuit configuration from a strain measuring instrument to a measurement bridge having a Wheatstone bridge circuit configuration in a general carrier-type dynamic strain measuring instrument. FIG. FIG. 19 is an equivalent circuit diagram of FIG.
In FIG. 18A, a Wheatstone bridge circuit composed of the fixed resistances R1, R2, R3 of the measurement bridge 81 and the strain gauge R4 (resistance at the measurement point) is connected to the carrier dynamic strain measuring instrument 83 with an input cable 82. It shows the connected state. The measuring bridge 81 of the Wheatstone bridge circuit configuration uses a strain gauge R4 that is small and lightweight and hardly affects the deformation of the measurement object, but the input cable 82 has a distributed capacitance (both stray capacitance). Is called). This distributed capacity also appears as an unbalanced value for the capacity together with the initial unbalanced value in the output of the measurement bridge 81 composed of the fixed resistors R1, R2, R3 and the strain gauge R4. The resistance change of the strain gauge R4 is necessary for the measurement, but the capacitance and the change are factors that hinder accurate measurement (measurement accuracy impediment factor) as described above.

Hereinafter, this measurement accuracy impeding factor will be analyzed in more detail.
In the circuit configuration from the strain measuring instrument 83 to the measurement bridge 81 of the Wheatstone bridge circuit configuration shown in FIG. 18A, the input cable 82 is interposed so that each side of the measurement bridge 81 and the ground (GND) are connected. There are C minutes in between.
When the resistances on the four sides of the measurement bridge 81 are R1 to R4, and the C components on the four sides are C1 to C4, an equivalent circuit as shown in FIG. Furthermore, assuming that the four sides of the measurement bridge 81 have a resistance value R, an unbalanced portion of the capacitances of the four sides is a capacitance value Ca, and a C portion between the GND and the GND is a capacitance value Cg, an equivalent as shown in FIG. It becomes a circuit. However, in the equivalent circuit shown in FIG. 19, the carrier voltage E is applied between A and C, and the output voltage of the measurement bridge 81 is Eout.
In the following description, Cg can be ignored for the C portion (that is, Cg) with GND if the insulation from GND is sufficient.
If the angular frequency of the carrier voltage E is ω, the output voltage Eout of the equivalent circuit shown in FIG.

また、ひずみ量をεとし、ゲージ率をＫｓとすると、１枚ゲージである場合の等価ブリッジの出力電圧Ｅｏｕｔは、（２）式で示される。

Further, assuming that the strain amount is ε and the gauge factor is Ks, the output voltage Eout of the equivalent bridge in the case of a single gauge is expressed by equation (2).

（１）式および（２）式から（３）式が得られる。

Equation (3) is obtained from Equation (1) and Equation (2).

ゲージ率Ｋｓ＝２．００として、（３）式をひずみ量εに関して解くと、（４）式を得る。

When the gauge factor Ks = 2.00 and the equation (3) is solved with respect to the strain amount ε, the equation (4) is obtained.

さらに、（４）式を実数部と虚数部とに分けると、（５）式に変形される。

Furthermore, when the expression (4) is divided into a real part and an imaginary part, the expression (5) is transformed.

（５）式において、ａを（６）式、ｂを（７）式と置くと、（８）式を得る。

In formula (5), if a is set as formula (6) and b is set as formula (7), formula (8) is obtained.

但し、（８）式において、ｃｏｓθ、ｓｉｎθおよびｚは、それぞれ（９）式で示される。

However, in the equation (8), cos θ, sin θ, and z are represented by the equation (9), respectively.

（８）式は、位相のずれた正弦波の合成波形の式となることを示している。

Expression (8) indicates that the expression is a composite waveform of a sine wave having a phase shift.

Hereinafter, the relationship between the unbalanced portion of C (capacitance value Ca) of the equivalent bridge and the strain amount ε will be described.
FIG. 20 is a graph showing the relationship between the capacitance value Ca and the strain ε from the equations (5) and (8), respectively, when the resistance value of the strain gauge is 120Ω and 350Ω. It is.
From the graph shown in FIG. 20, when the unbalanced portion (capacitance value Ca) of C of the measurement bridge is 2000 [PF], when the resistance value of the strain gauge is 120Ω, a strain of about 4000 [μ] is measured. However, when the resistance value of the strain gauge is 350Ω, it is understood that a strain of about 11000 [μ] is output as the measured value.
Thus, it has been clarified that the capacity is greatly influenced not only by the length of the input cable, the ambient temperature, and the humidity but also by the resistance value of the strain gauge.
By the way, as a carrier-type strain measuring device capable of canceling even if a capacitance imbalance occurs in the measurement bridge, the applicant of the present application uses the strain amplifier described in Patent Document 1 (Japanese Patent Publication No. 2-16441). Proposed earlier.
The distortion amplifier of the sine wave carrier system of Patent Document 1 is obtained from a bridge power source with an output component corresponding to the capacitance change of the detector bridge on the output side of the detector bridge and an output amplitude of this circuit. And a circuit for controlling the voltage to be fed back to the detection unit bridge via a capacitor, and when a capacitance C is mixed in the detection unit bridge,

なる電圧を前記コンデンサに与える構成とし、検出部ブリッジに容量不平衡分が発生してもそれを完全に打消すことができるようにしたものである。
また、抵抗式ひずみゲージを含むブリッジ回路の初期不平衡の影響を補償しつつ、ブリッジ回路とひずみ測定器との間の接続線間の浮遊容量などによる位相のずれの影響を補償し、ひずみゲージのひずみに応じた抵抗値変化に伴う実際の抵抗成分を検波するようにした発明として特許文献２（特開２００５−１９５５０９号公報）に記載されたものがある。

The voltage is applied to the capacitor so that even if a capacitance imbalance occurs in the detection unit bridge, it can be completely canceled.
In addition, while compensating for the initial unbalance effect of the bridge circuit including the resistance strain gauge, it compensates for the effect of phase shift due to stray capacitance between the connection lines between the bridge circuit and the strain measuring instrument. Japanese Patent Application Laid-Open No. 2005-195509 discloses an invention in which an actual resistance component associated with a change in resistance value according to the strain is detected.

In the invention according to Patent Document 2, an AC power supply voltage is applied to a bridge circuit including a resistance strain gauge, and an output voltage signal of the bridge circuit is input to an AC amplifier to be amplified. A signal component having a predetermined phase relationship with respect to the AC power supply voltage is detected from a signal as a resistance component corresponding to a change in the resistance value of the bridge circuit, and the detected resistance component is used in accordance with a strain value of the strain gauge. In a carrier-type strain measurement method for generating a strain measurement signal,
A capacitor having a phase difference of 90 ° with respect to the resistance component of the output voltage signal of the AC amplifier and the resistance component while inputting the output voltage signal of the bridge circuit in an unstrained state of the strain gauge to the AC amplifier. An initial unbalance adjustment step for determining an initial unbalance compensation signal to be additionally input to the AC amplifier so that the component becomes zero;
After determining the initial unbalance compensation signal, connecting a resistor having a fixed resistance value to the bridge circuit, and inputting the output voltage signal of the bridge circuit and the initial unbalance compensation signal to the AC amplifier, A phase shift determination step for determining a phase shift amount of the output voltage signal of the AC amplifier with respect to the AC power supply voltage,
After the phase shift is determined, when the distortion is measured by separating the resistor having the fixed resistance value from the bridge circuit, the AC voltage is output by the shift amount determined in the phase shift determination step in the output voltage signal of the AC amplifier. A carrier-type distortion measuring method is proposed in which a signal component having a phase difference with respect to a power supply voltage is detected as a resistance component corresponding to a change in the resistance value of the bridge circuit.

Further, the applicant of the present application has disclosed a sine wave carrier wave described in Patent Document 3 (Japanese Patent Laid-Open No. 2010-266408) as a carrier-type distortion measuring device capable of canceling out even if a capacitance imbalance occurs in the measurement bridge. A strain measuring device of the type has been proposed previously.
In this sine wave carrier type distortion measurement device, the circuit used is composed of RoHS-compliant components that take environmental issues into consideration, and automatically cancels unbalanced components such as stray capacitance while reducing power supply noise. This is a technique for accurately measuring an actual resistance component accompanying a change in resistance value according to a strain gauge included in a measurement bridge. Specifically, the carrier-type dynamic strain measurement apparatus includes a measurement bridge, an input transformer that inputs the output of the bridge, a cancellation circuit that corrects the output of the bridge with a feedback amount that is fed back, and a primary power source. A primary side circuit system including a circuit, a carrier amplifier circuit that generates the compensation amount from the output of the measurement bridge, a capacitive phase detector circuit, a capacitive cancellation drive circuit, a carrier oscillation circuit, and a secondary side The circuit is divided into a secondary circuit system including a power source. The primary-side circuit system and the secondary-side circuit system are coupled only via the magnetic coupling means and the optical signal transmission means that is an optical coupling means, and have no electrical connection portion. It is characterized by that.

In the measurement bridge, the initial unbalance value (unbalance value) of C appears together with the initial unbalance value of the resistance value. The change in resistance of the strain gauge is necessary for the measurement, but the C content is unnecessary for the measurement. This C component varies depending on the length and material of the cable, and varies depending on the environment such as ambient temperature and humidity. Conventionally, this has been a cause of a decrease in the stability of the measuring instrument.
If this change can be prevented from affecting measurement, highly accurate strain measurement can be performed. Thus, a so-called CST method (Capacitance Self Tracing) has been proposed as a measurement method that constantly detects this C component, cancels the amount, and automatically tracks to increase the stability. In this method, even if the C portion enters two adjacent sides of the measurement bridge, the zero point does not change, so the stability is improved.
Accordingly, an object of the present invention is to provide a CST-type dynamic strain measuring device in which the zero point does not change even if the C component enters each opposite side as well as adjacent sides. In other words, a measurement method is required that does not affect the zero point regardless of where the C component enters the four sides of the measurement bridge.
A carrier-type dynamic strain measuring instrument is often used for stress measurement using a strain gauge. The reason is that measurement can be performed at the measurement site without being affected by disturbance noise and power supply noise.
The strain gauge is small and light, and has almost no effect on the object to be measured, but it is necessary to connect the gauge to be used to the measuring instrument with an input cable. Various methods are conceivable for connecting the gauge and the measuring instrument. The cable length and wiring route vary depending on the number of gauges used and the measurement location.

Japanese Patent Publication No. 2-16441 JP 2005-195509 A JP 2010-266408 A

In the distortion amplifier in Patent Document 1, a primary side circuit portion such as a capacitance canceling circuit and a primary side power supply circuit that cancels a capacitance component generated in the measurement bridge and the measurement bridge, a carrier amplifier circuit, a capacitance phase Since circuit portions such as a detection circuit, a carrier wave oscillation circuit, and a secondary power supply are directly connected to each other, power supply noise affects the distortion measurement value, and the S / N ratio is not sufficient. Realization of measurement with high accuracy is desired.
In Patent Document 1 (Japanese Patent Publication No. 2-16441), the output of the imaginary term detection circuit is supplied to the amplitude control circuit via a low-pass filter to control the cancellation circuit. The amplitude control circuit is a circuit that drives the light emitting diode in accordance with the signal obtained from the low-pass filter, and the cancellation circuit has a resistance value that varies depending on the resistance and incident light from the light emitting diode, such as a Cds cell. Both ends of a series circuit with such a light receiving element are connected to a bridge power supply, and a signal taken out from a connection point of the series circuit is supplied to the capacitor Co through an amplifier.
However, the Cds included in the cancellation circuit is RoHS (Restriction of Hazardous Substances), ie, the “European Union Directive on the Restriction of Use of Specific Hazardous Substances in Electronic and Electrical Equipment” Contains cadmium which is designated as a regulated substance.

Cadmium is a dangerous substance that may cause functional damage to the kidney, and is restricted to 100 ppm or less (as of July 2007), so there is a problem in using Cds as a photoelectric conversion element.
Also in Patent Document 2 (Japanese Patent Laid-Open No. 2005-195509), a primary side circuit portion including a measurement bridge, a carrier wave oscillation circuit, a carrier wave amplifier circuit, a 90 ° phase detection circuit, a 90 ° phase balance circuit, and these Since a power source for supplying power to the circuit portion is electrically connected, as described above, there is a problem that power source noise is mixed into the strain measurement value and decreases the measurement accuracy.
However, in the sine wave carrier type strain measuring device described in Patent Document 3 (Japanese Patent Laid-Open No. 2010-266408), floating is generated in parallel on each of the four sides (resistances) of the strain gauge constituting the measurement bridge. It cannot be erased until there is an imbalance due to capacity.
The present invention has been made in view of the above-described circumstances, and the circuit used is composed of RoHS-compliant components that take environmental problems into consideration, while reducing power supply noise, and between the measurement bridge and the strain measurement circuit. A carrier-type dynamic strain measuring instrument that automatically cancels unbalanced components due to stray capacitance between connecting lines and accurately measures the actual resistance component associated with the change in resistance value according to the strain gauge included in the measurement bridge. It is intended to provide.

In order to achieve the above object, the carrier-type dynamic strain measuring instrument according to the invention described in claim 1
In carrier type dynamic strain measuring instrument,
A measurement bridge including a strain gauge;
A carrier amplifier circuit for amplifying a measurement signal superimposed on a carrier wave applied to the measurement bridge;
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;
Two capacity canceling drive circuits for automatically canceling the unbalanced component due to the capacity component generated in the measurement bridge in response to the output of the capacity phase detecting circuit;
A resistance phase detector circuit that extracts an unbalanced portion of the resistance of the measurement bridge and removes a carrier wave component;
A phase shift circuit for supplying a reference voltage serving as a reference for the phase shift to the capacitance phase detection circuit;
A carrier oscillation circuit for generating a carrier wave to be applied to the measurement bridge;
Two systems of feedback capacitors respectively connected between the two output terminals of the measurement bridge and the two systems of capacitance canceling drive circuits;
The unbalanced component due to the stray capacitance component mixed in parallel with the resistance of one or all four sides of the four sides of the measurement bridge is reversed in phase from the two capacitance canceling drive circuits to the two feedback capacitors. It is characterized in that it is configured to cancel automatically by applying a voltage of.

In order to achieve the above object, the carrier-type dynamic strain measuring instrument according to the invention described in claim 2
Capacities of the unbalanced component included in the adjacent side of one output end of the measurement bridge are Cu1 and Cu2, respectively, and capacitances of the unbalanced component included in the adjacent side of the other output end of the measurement bridge are respectively Cu3. And Cu4,
The feedback first capacitor and the second capacitor are Cb and Cd, the carrier voltage applied to the input terminal of the measurement bridge is E,
When the resistance components forming the measurement bridge are balanced, the cancellation voltage Vbc obtained by the following [Equation 1] and the cancellation voltage Vdc obtained by the following [Equation 2]:

を、前記測定ブリッジの一方の出力端および他方の出力端に、それぞれ印加するように構成したことを特徴としている。

Is configured to be applied to one output end and the other output end of the measurement bridge, respectively.

In order to achieve the above object, the carrier dynamic strain measuring instrument according to the invention described in claim 3 is configured such that the feedback capacitor selects and sets one of a plurality of predetermined capacitance values. This is a capacitor that can be used.
According to a fourth aspect of the present invention, there is provided a carrier-type dynamic strain measuring instrument that includes a secondary power source that supplies power to each circuit on the secondary side and power from the secondary power source in order to achieve the above object. A primary-side power supply circuit that receives power through a transformer and supplies power to each circuit on the primary side, and applies the output of the carrier wave oscillation circuit to a measurement bridge through a coupling transformer; It is characterized by that.
According to a fifth aspect of the present invention, in order to achieve the above object, a carrier-type dynamic strain measuring device includes at least one light emitting diode between the primary side circuit and the secondary side circuit. And an optical signal transmission means composed of a light-receiving diode arranged so as to be opposed thereto, wherein the measurement bridge, the capacitance canceling circuit, the light-receiving diode, and the primary power supply circuit are the carrier wave amplifier circuit The input phase transformer, the optical signal transmission means, the coupling transformer, and the power transformer for the capacitive phase detection circuit, the capacitive cancellation drive circuit, the light emitting diode, the carrier wave oscillation circuit, and the secondary power source. It is connected by the electromagnetic means which consists of this, and the said optical signal transmission means, It is connected in the electrically insulated state, It is characterized by the above-mentioned.

According to the carrier dynamic strain measuring instrument of claim 1 of the present invention,
In carrier type dynamic strain measuring instrument,
A measurement bridge including a strain gauge;
A carrier amplifier circuit for amplifying a measurement signal superimposed on a carrier wave applied to the measurement bridge;
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;
Two systems of first and second capacity canceling drive circuits that receive the output of the capacity phase detecting circuit and automatically cancel the unbalanced component due to the capacity component generated in the measurement bridge;
A resistance phase detector circuit that extracts an unbalanced portion of the resistance of the measurement bridge and removes a carrier wave component;
A phase shift circuit for supplying a reference voltage serving as a reference for the phase shift to the capacitance phase detection circuit;
A carrier oscillation circuit for generating a carrier wave to be applied to the measurement bridge;
Two systems of feedback first and second capacitors respectively connected between the two output terminals of the measurement bridge and the two systems of the first and second capacitance canceling drive circuits; With
The first and second capacitance cancellations of the two systems are used to cancel out the unbalance component due to the stray capacitance component mixed in parallel with the resistance of one or all four sides of the measurement bridge. Since the drive circuit is configured to automatically cancel the unbalanced component due to the capacitance by applying to each output terminal of the measurement bridge via the first and second feedback capacitors, the measurement bridge is configured. All of the unbalance components due to the stray capacitance component generated in parallel with each of the four sides (resistance) of the strain gauge can be automatically canceled out.

According to the carrier dynamic strain measuring instrument of claim 2 of the present invention, the capacities of the unbalanced components included in the adjacent side of one output end of the measurement bridge are Cu1 and Cu2, respectively, and the other of the measurement bridges The capacities of the unbalanced components included in the adjacent side of the output end are Cu3 and Cu4, respectively.
The feedback first capacitor and the second capacitor are Cb and Cd, the carrier voltage applied to the input terminal of the measurement bridge is E,
When the resistance components forming the measurement bridge are balanced, the cancellation voltage Vbc obtained by the following [Equation 1] and the cancellation voltage Vdc obtained by the following [Equation 2]:

を、前記測定ブリッジの一方の出力端および他方の出力端に、それぞれ印加するように構成したので、測定ブリッジを構成するひずみゲージ（抵抗）の１辺乃至４辺のすべてに含まれる浮遊量成分による不均衡成分を、常に自動的に、全て打消すことができる。

Is applied to one output end and the other output end of the measurement bridge, respectively, so that the floating amount component included in all of one to four sides of the strain gauge (resistance) constituting the measurement bridge All the unbalanced components due to can be automatically canceled out.

According to the carrier-type dynamic strain measuring instrument of claim 3 of the present invention, the feedback capacitor is a capacitor capable of selecting and setting any one of a plurality of predetermined capacitance values. It is possible to select and set a capacitance value capable of canceling out a wide range of the imbalanced component due to the stray capacitance component measured in advance.
According to the carrier dynamic strain measuring instrument of claim 4 of the present invention,
A secondary power supply for supplying power to each circuit on the secondary side, and a primary power supply circuit for receiving power from the secondary power supply via a power transformer and supplying power to each circuit on the primary side. In addition, since the output of the carrier wave oscillation circuit is applied to the measurement bridge via the coupling transformer, the primary side and the secondary side can be connected in an electrically insulated state.
According to the carrier dynamic strain measuring instrument of claim 5 of the present invention,
Since it further comprises at least one light emitting diode between the primary side circuit and the secondary side circuit, and an optical signal transmission means comprising a light receiving diode disposed so as to face the light emitting diode, The measurement bridge, the capacitance canceling circuit, the light receiving diode, and the primary power supply circuit are the carrier wave amplification circuit, the capacitance phase detecting circuit, the capacitance canceling drive circuit, the light emitting diode, and the carrier oscillation circuit. And connected to the secondary power source by 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, and are electrically insulated. Has the effect of being connected.
Furthermore, while the measurement bridge is insulated from the output side (secondary side), it is possible to reduce power supply noise and measure strain at high potentials. It can always be completely countered.

It is a block diagram which shows the circuit structure of the principal part of the carrier wave type | mold dynamic strain measuring device which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows the detailed structure of only one system as a basic composition of the carrier-wave type dynamic strain measuring device which concerns on the 1st Embodiment of this invention shown in FIG. It is a circuit diagram which shows an example of the circuit structure for feeding back the output voltage (compensation amount) from the cancellation circuit in the carrier wave type dynamic strain measuring device which concerns on embodiment of this invention. FIG. 4A is a circuit diagram showing a circuit for connecting a measurement bridge, a measuring instrument, and an input cable. FIG. 4A shows a connection between the measuring bridge, the measuring instrument, and the input cable, and FIG. The equivalent circuit in the case where a C component (floating capacitance Cu1) is generated in parallel with R1 is shown. It is a graph which shows the result of having compared the output amplitude value at the time of changing the capacity | capacitance of C part (floating capacity Cu1) (horizontal axis) with the measured value and the calculated value. FIGS. 6A and 6B show an equivalent circuit in the case where a waveform for canceling the C component is applied to point B as Vbc. It is a block block diagram of the circuit used for verification of the formula which shows the cancellation waveform (voltage) Vbc when R component is balanced. It is a graph which shows the comparison data with the case where the distortion amount (= output voltage Eout) output by C component in the circuit shown in FIG. 7, and the CST system are not applied. An equivalent circuit of the measurement bridge in the case where the stray capacitance Cu3 and the stray capacitance Cu4 are mixed as C components in the CD side and the AD side which are opposite sides of the AB side and the BC side of the measurement bridge is shown. It is a graph which shows the comparison data of the calculated value and experimental value of Eout (strain amount) at the time of changing Cu3 and Cu4 shown to FIG. 9 and (25) Formula. It is a circuit diagram of the equivalent circuit for demonstrating the cancellation method when C component mixes into four sides of a measurement bridge. It is a circuit diagram of the 1st circuit which decomposed | disassembled the equivalent circuit shown in FIG. It is a circuit diagram of the other 2nd circuit which decomposed | disassembled the equivalent circuit shown in FIG. FIG. 13 is a circuit diagram of still another third circuit obtained by disassembling the equivalent circuit shown in FIG. 11. FIG. 12 is a circuit diagram of another fourth circuit obtained by disassembling the equivalent circuit shown in FIG. 11. (A), (b) is a characteristic diagram showing a graph of a zero point change measured by adding from 0 to about 2000 pF as C minutes to each side of the measurement bridge when a resistance of 120Ω is used as the measurement bridge. is there. (A), (b) shows the characteristic diagram of the zero point change measured by adding from 0 to about 2000 pF as C minutes to each side of the measurement bridge when a 350Ω resistor is used as the measurement bridge. (A) is explanatory drawing which represented the circuit structure from a distortion measuring device to the measurement bridge of a Wheatstone bridge circuit structure in the general carrier-type dynamic strain measuring device, (b) is (a). FIG. The Wheatstone bridge circuit configuration is an equivalent circuit including a capacity component. It is the graph which showed the relationship between each capacitance value (DELTA) C when the carrier wave frequency of 5 KHz is used in the case where the resistance value of a strain gauge is 120 ohms, and 350 ohms, and distortion | strain amount (epsilon).

The carrier-type dynamic strain measuring instrument according to the present invention is provided with a CST (Capacitance Self Tracing) system circuit of two systems (including a part of which is partially composed of one system), and the C portion is located anywhere on the four sides of the measurement bridge. Can eliminate the fluctuation of the zero point.
Hereinafter, embodiments of a carrier-type dynamic strain measuring device of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a circuit diagram showing a circuit configuration of a main part of the carrier-type dynamic strain measuring instrument according to the first embodiment of the present invention.
In the circuit of the carrier-type dynamic strain measuring instrument of this embodiment shown in the figure, two independent CST circuits are provided, and feedback capacitances Cb and Cd are connected to points B and D of the measurement bridge, respectively. In this circuit, the C part of the side is canceled out.
More specifically, the circuit of the carrier dynamic strain measuring instrument according to the first embodiment includes a Wheatstone bridge circuit (hereinafter, abbreviated as “measurement bridge”) 11 configured with a strain gauge shown in FIG. The carrier voltage amplifying circuits 21a and 21b that amplify the output voltage (voltage between B and D) of the measurement bridge 11 as a carrier wave output, and the resistance unbalanced part of the carrier wave output (the real term in the above equation (5)) And a resistance phase detection circuit 22 for removing the carrier wave component, a capacitance cancellation drive circuit 24a, 24b for converting the phase shift due to the unbalanced component of the capacitance into a compensation amount, Phase shift circuits 25a and 25b for canceling the reference voltage (voltage waveform whose phase is shifted by 90 degrees from the carrier wave) to the drive circuits 24a and 24b as a reference for the phase shift due to the balanced component, and the measurement bridge Carrier input to 11 (e.g., 5KHz～28kHz) includes an oscillation circuit 26 as a carrier wave oscillation circuit for outputting a.

In addition to this, although not shown in FIG. 1, as shown in FIG. 2, the power amplifier 27 that supplies the power transformer 20 (primary coil) as the excitation power of the carrier power, and each terminal of the measurement bridge 11 A capacitance phase detection circuit 23 for converting a phase shift due to an unbalanced component of the stray capacitance generated between the ground and the ground into a compensation amount, an optical signal transmission means 13, and the like can be provided.
In the first embodiment described above, among the circuits constituting the CST circuit, among the carrier wave amplifier circuits 21a and 21b and among the capacity canceling drive circuits 24a and 24b, a capacity phase detection circuit 23 described later. Although the phase shift circuits 25a and 25b are shown as being configured to use two systems, these circuits can be configured to use one system without necessarily using two systems.
Further, as a characteristic configuration of the present invention, a feedback first capacitor Cb is connected between one output terminal B of the measurement bridge 11 and one system of the first capacity cancellation drive circuit 24a. A second capacitor Cd for feedback is connected between the other output terminal D of the measurement bridge 11 and the other one line of the second capacitance canceling drive circuit 24.
As the first and second capacitors Cb and Cd for feedback, capacitors that can be selected and set from any of a plurality of predetermined capacitance values to be described later can be used. The functions of the first and second capacitors will be described later with reference to the drawings shown in FIG.
FIG. 2 is a circuit diagram according to the second embodiment showing a more specific and detailed configuration of the carrier-type dynamic strain measuring instrument according to the first embodiment of the present invention shown in FIG.
However, FIG. 2 shows a detailed circuit configuration of the carrier-type dynamic strain measuring instrument according to the first embodiment of the present invention shown in FIG. 1, but in terms of form, a secondary having two systems of the same circuit. The circuit on the side (FIG. 1) is shown for only one system.

In FIG. 2, the carrier-type dynamic strain measuring device of the second embodiment includes a Wheatstone bridge circuit (hereinafter abbreviated as “measurement bridge”) 11 configured with a strain gauge, and an output of the measurement bridge 11 will be described later. And a compensation circuit for generating the compensation amount from the output of the measurement bridge 11 and a primary circuit system (hereinafter abbreviated as “primary side”). And a secondary circuit system (hereinafter abbreviated as “secondary side”). The primary side and the secondary side are coupled only via magnetic coupling means, for example, input transformer 12, coupling transformer 19, power transformer 20, and optical coupling means, for example, optical signal transmission means 13, Not electrically connected directly.
First, as a primary side, a measurement bridge 11 composed of a Wheatstone bridge circuit, an input transformer 12 (primary coil) that receives the output of the measurement bridge 11 and transmits it to the secondary side by magnetic coupling, and optical signal transmission means 13 receives the same carrier wave as that input to the measurement bridge 11 and the reference voltage to the cancellation circuit 14. V waveform supply circuit 15 is included.

Further, on the primary side, a calibration value generating circuit 16 that superimposes specific one or a plurality of calibration values on a carrier wave and supplies the input transformer 12 and a resistance component included in the output of the measurement bridge 11 in a non-distortion state. A resistance adjustment circuit 17 that superimposes a voltage for adjusting an error due to the initial equilibrium component on the carrier wave and injects it into the input transformer 12, a primary side power supply circuit 18 that supplies power used by the primary side circuit, and 2 A coupling transformer 19 (secondary coil) that transmits a carrier wave output from the oscillation circuit 26 as a secondary side carrier wave (in this case, a sine wave) oscillation circuit to the measurement bridge 11 and an output from the power amplifier circuit 27 on the secondary side A power transformer 20 (secondary coil) that receives the power of the carrier wave transmitted to the primary power supply circuit 18.
Next, as the secondary side, a carrier wave amplifier circuit 21 that amplifies the carrier wave output output from the input transformer 12 (secondary coil), and of the carrier wave output, the unbalanced portion of the resistance (the real term of the above equation (5)) And a resistance component phase detection circuit that removes the carrier wave component, the carrier filter circuit 22, and a capacitive imbalance (ie, an imaginary term component of the above equation (5)) from the carrier wave output, Further, a capacitive phase detection circuit and carrier filter circuit 23 for removing the carrier wave component, a capacitive cancellation drive circuit 24 for converting a phase shift due to the unbalanced component for the capacitance into a compensation amount, and an unbalanced component for the capacitance. And a phase shift circuit 25 for supplying a reference voltage (voltage waveform whose phase is 90 degrees out of phase with the carrier wave) to the capacitance phase detection circuit 23.

Further, as a secondary side, an oscillation circuit 26 as a carrier wave oscillation circuit that outputs a carrier wave (for example, 5 kHz) input to the measurement bridge 11, and an output of the oscillation circuit 26 as a carrier wave bridge voltage to the measurement bridge 11 on the primary side. A primary coil of the coupling transformer 19 to be supplied, a power amplifier 27 to be supplied to the power transformer 20 (primary coil) as excitation power of the carrier power, and 2 to supply power used by all circuits included in the secondary side And a secondary power source 28.
Hereafter, each circuit component which the carrier-type dynamic strain measuring device of 1st and 2nd embodiment has is demonstrated, referring FIG.
First, on the primary side, the measurement bridge 11 is configured as a Wheatstone bridge circuit with a strain gauge, and the strain gauge is attached to an object to be measured by means such as adhesion, fusion, vapor deposition, and sputtering. , Detect the strain.
The input transformer 12 (primary coil) receives the output (voltage value) from the measurement bridge proportional to the strain of the object to be measured on the primary side (primary coil) and transmits it to the secondary coil by magnetic coupling.
B. The V waveform supply circuit 15 receives the same carrier wave as that input to the measurement bridge 11 and supplies the carrier wave cancel circuit 14 as a carrier wave reference.

The calibration value generation circuit 16 generates a calibration voltage corresponding to one or more specific calibration values and applies the calibration voltage to the input transformer 12 without actually applying a load to the strain gauge.
The resistance adjustment circuit 17 generates a voltage corresponding to a voltage value that can adjust (cancel) the initial unbalance component of the resistance included in the output of the measurement bridge 11 when no load is applied to the strain gauge. And superimposed on the carrier wave and transmitted to the input transformer 12.
The primary power supply circuit 18 is connected to a power transformer 20 (secondary coil) that is excited by a power amplifier circuit 27 that is driven by power supplied from the secondary power supply 28. The primary power supply circuit 18 is for supplying power used by all circuit elements on the primary side.
The coupling transformer 19 (secondary coil) is a carrier power source (so-called bridge power source) that inputs a carrier wave (for example, an oscillation frequency of 5 kHz) generated by the secondary-side oscillation circuit 26 to the measurement bridge 11 when measuring distortion. Received by magnetic coupling and transmitted to the measurement bridge 11.
On the secondary side, the carrier amplifier circuit 21 is an amplifier circuit that amplifies the carrier wave output including the measurement distortion output from the input transformer 12 (secondary coil). The signal is sent to the detection circuit, the carrier filter circuit 22, and the capacitive phase detection circuit, the carrier filter circuit 23.

The resistance phase detector circuit and the carrier filter circuit 22 extract initial unbalance components corresponding to the resistances of the four sides constituting the Wheatstone bridge of the measurement bridge 11 from the carrier wave output including the measurement distortion, and further remove the carrier wave component. Output a signal corresponding to the distortion. However, the circuit portion for canceling and compensating for the initial unbalance component of the resistance detected by the resistance phase detector circuit and the carrier filter circuit 22 is outside the scope of the present invention. Description is omitted.
The capacitive phase detection circuit and the carrier filter circuit 23 receive the carrier wave output including the measurement distortion from the carrier wave amplifier circuit 21 and also receive the output shifted by 90 ° from the output of the oscillation circuit 26 from the phase shift circuit 25. Thus, the capacitive unbalanced component is extracted, the carrier wave is removed, and the capacitance is canceled and sent to the drive circuit 24.
The phase shift circuit 25 shifts the phase by 90 ° with respect to the output of the oscillation circuit 26 and sends it to the phase detection circuit and the carrier filter circuit 23 by the capacitance. Further, the oscillation circuit 26 generates a carrier wave output to be applied to the measurement bridge 11 on the primary side via the coupling transformer 19. The output of the oscillation circuit 26 is also sent to the transfer circuit 25, the secondary resistance phase detection circuit, the carrier filter circuit 22, and the power amplifier circuit 27.
The power amplifier 27 amplifies the output of the carrier wave (sine wave waveform) generated by the oscillation circuit 26 and supplies the excitation voltage obtained by this amplification to the power transformer 20 (primary coil).

A primary power supply circuit 18 is connected to the secondary coil of the power transformer 20. From the primary side power supply circuit 18, a smoothed DC voltage is generated and supplied to circuit elements included in the primary side.
The secondary power supply 28 supplies power used by all circuit elements on the secondary side.
FIG. 3 is a circuit diagram showing an example of a circuit configuration for feeding back the output voltage (compensation amount) from the cancellation circuit in the carrier wave type dynamic strain measuring instrument according to the second embodiment of the present invention.
In the circuit diagram shown in FIG. 3, for example, the output of the first capacitance canceling drive circuit 24a is supplied to one input terminal of the input transformer 12 via the feedback first capacitor Cb. It is supplied to one output terminal B of the measurement bridge 11. The output of the second capacitance canceling drive circuit 24b is supplied to the other input terminal of the input transformer 12 through the second capacitor Cd for feedback, and the other output terminal D of the measurement bridge 11 is used. To be supplied.
One output terminal B of the measurement bridge is supplied with Vbc of formula (38) or formula (42) to be described later, and the other output terminal D is Vdc of formula (37) or formula (41) to be described later. Supply.

That is, in the case of the second embodiment, the first cancellation circuit 14a that receives and amplifies the output of the capacitance cancellation drive circuit 24a is connected to one of the input transformers 12 via the first capacitor Cb. A canceling voltage is superimposed on the carrier wave and supplied to one end of the secondary coil.
Further, the output from the second cancellation circuit 14b that receives and amplifies the output of the second capacitance cancellation drive circuit 24 is canceled at the other end of the primary side coil of the input transformer 12. Supply voltage superimposed.
With this configuration, the amplitude of the cancellation voltage is only ½ that of the configuration shown in FIG. 2, so that a portion with good linearity can be used, and the cancellation waveform is distorted. Therefore, it is possible to provide a carrier-type dynamic strain measuring device that can always cancel out the capacity imbalance with higher accuracy.
Furthermore, the carrier-type dynamic strain measuring device according to the embodiment of the present invention is similar to the carrier-type dynamic strain measuring device described in Patent Document 3 (Japanese Patent Laid-Open No. 2010-216408) described above from the secondary side. It is also possible to realize the feedback coupling to the side through the optical signal transmission means 13 such as the light emitting diode 13a and the light receiving diode 13b.

Hereinafter, the functions of the first and second capacitors Cb and Cd, which are characteristic components of the carrier-type dynamic strain measuring device according to the first and second embodiments of the present invention, will be described.
First, an equivalent circuit of the measurement bridge will be described, and an outline of how much the zero point change is caused by the C component due to the stray capacitance will be shown.
4 is a circuit diagram showing a circuit for connecting a measurement bridge, a measuring instrument, and an input cable. FIG. 4A shows a connection between the measuring bridge, the measuring instrument, and the input cable, and FIG. These show an equivalent circuit in the case where a C component (floating capacitance Cu1) is generated in parallel with the gauge resistor R1.
In the measurement bridge shown in the figure, the C component (floating capacitance Cu1) is unbalanced by C component, R1 to R4 are R, and a carrier wave is applied between AC. When the carrier frequency is represented by ω and the amplitude voltage is E, the output voltage Eout of the bridge is expressed by equation (11).

ここで、ひずみをε、ゲージ率をＫｓとすると、１枚ゲージの場合のブリッジの出力電圧は、（１２）式で示される。

Here, assuming that the strain is ε and the gauge factor is Ks, the output voltage of the bridge in the case of a single gauge is expressed by equation (12).

よって、（１１）式及び（１２）より、（１３）式が得られる（但し、Ｋｓ＝２．００としている）。

Therefore, the equation (13) is obtained from the equations (11) and (12) (however, Ks = 2.00).

この式を実数部と虚数部に分けると、（１４）式となる。

When this expression is divided into a real part and an imaginary part, expression (14) is obtained.

図５は、Ｃ分（浮遊容量Ｃｕ１）（横軸）の容量を変化させた場合の出力振幅値を、実測値と計算値とで比較した結果を示すグラフ図である。
同図に結果を示す測定において、ひずみゲージの抵抗値として１２０Ωを使用し、ブリッジ電圧を２Ｖとし、搬送波周波数として５ｋＨｚ，１２Ｍｚ，２８ｋＨｚを、それぞれ印加した（ブリッジ電圧が２Ｖのとき、１με＝１μＶに相当する）。
同図に示す測定結果からは、計算値と実測値とはほぼ合致していることが分かる。
また、２８ｋＨｚの搬送波でＣ分アンバランスが２０００ｐＦの時、出力は、２００００με以上、５ｋＨｚの場合でも４０００με以上となっている。
同図に示すように、測定ブリッジの初期不平衡値は、Ｃ分のアンバランス容量と搬送波周波数とに大きく影響を受けていることが分かる。
測定に使われるひずみゲージは、抵抗変化分が低抗値の１％以下の微小変化を検出し、利用する。このため、測定ブリッジからの出力電圧は数百μεから数千με（数ｍＶ）と小さい。よって、浮遊容量Ｃｕ１で発生する出力が数ｍＶ以上となると、Ｒ分の出力を超えてしまって、入力に非常に大きな影響を与えることになる。
さらに判定器の増幅回路は、数千倍の増幅度を持たせるため、Ｃ分で増幅回路が飽和しないように、増幅回路に入る前にバランスさせる必要がある。抵抗であるＲ分は、ひずみゲージであるので、被測定体に取付けてから、別途調整するものとする。

FIG. 5 is a graph showing the result of comparing the output amplitude value between the measured value and the calculated value when the capacitance of C (floating capacitance Cu1) (horizontal axis) is changed.
In the measurement results shown in the figure, 120Ω is used as the resistance value of the strain gauge, the bridge voltage is 2 V, and the carrier frequencies are 5 kHz, 12 Mz, and 28 kHz, respectively (when the bridge voltage is 2 V, 1 με = 1 μV) Equivalent to
From the measurement results shown in the figure, it can be seen that the calculated values and the actually measured values almost coincide.
Further, when the C-balance imbalance is 2000 pF with a carrier wave of 28 kHz, the output is 20000 με or more, and even when 5 kHz, the output is 4000 με or more.
As shown in the figure, it can be seen that the initial unbalance value of the measurement bridge is greatly influenced by the unbalance capacity of C and the carrier frequency.
The strain gauge used for the measurement detects and uses a minute change in which the resistance change is 1% or less of the resistance value. For this reason, the output voltage from the measurement bridge is as small as several hundred με to several thousand με (several mV). Therefore, when the output generated in the stray capacitance Cu1 is several mV or more, it exceeds the output for R, which greatly affects the input.
Furthermore, since the amplification circuit of the decision unit has an amplification factor of several thousand times, it is necessary to balance before entering the amplification circuit so that the amplification circuit is not saturated in C minutes. Since the resistance R is a strain gauge, it is separately adjusted after being attached to the object to be measured.

Hereinafter, a method for canceling an unnecessary waveform in a general CST type strain measuring device will be described.
The unnecessary voltage due to the C component of the measurement bridge appears as an imaginary part. Therefore, if the imaginary part is detected and returned to the input side and added as a waveform whose phase is shifted by 180 °, it can be canceled. As described above, this method is called a CST method.
The calculation formula of the unnecessary waveform canceling method in a general CST type carrier dynamic strain measuring instrument will be shown below.
FIG. 6 shows an equivalent circuit when a waveform for canceling the C component is applied to point B as Vbc.
This figure shows an equivalent circuit in the case where there are C portions on adjacent sides of the measurement bridge as a sensor, and a waveform that cancels this C portion is applied to point B as Vbc. (At this time, it is assumed that the C content distributed on the four sides is small and balanced.)
First, in FIG. 6A, when the stray capacitance Cu1 is added between AB, the output voltage Eout is expressed by equation (15).

（１５）式から実数部と虚数部とを求め、虚数部を零にするＶｂｃを求めると、Ｖｂｃは（１６）式として求まる。

When the real part and the imaginary part are obtained from the equation (15), and Vbc is obtained by setting the imaginary part to zero, Vbc is obtained as the equation (16).

（１６）式を（１５）式に代入すると、（１７）式が得られる。

Substituting equation (16) into equation (15) yields equation (17).

（１７）式は、Ｖｂｃを（１６）式で示されるようにコントロールすると、出力電圧Ｅｏｕｔは、測定ブリッジに印加する搬送波周波数に関係しないで、Ｒ分である抵抗値だけの式になることを示している。
次に、図６（ｂ）に示す等価回路についても上記と同様に出力電圧Ｅｏｕｔを算出する。
まず、図６（ｂ）において、ＢＣ間に浮遊容量Ｃｕ２が加わった場合、出力電圧Ｅｏｕｔは（１８）式で示される。

In the equation (17), when Vbc is controlled as shown in the equation (16), the output voltage Eout is not related to the carrier frequency applied to the measurement bridge, but only the resistance value corresponding to R. Show.
Next, the output voltage Eout is calculated for the equivalent circuit shown in FIG.
First, in FIG. 6B, when the stray capacitance Cu2 is added between BC, the output voltage Eout is expressed by the equation (18).

（１８）式から実数部と虚数部とを求め、虚数部を零にするＶｂｃを求めると、Ｖｂｃは（１９）式として求まる。

When the real part and the imaginary part are obtained from the equation (18), and Vbc for making the imaginary part zero is obtained, Vbc is obtained as the equation (19).

（１９）式を（１８）式に代入すると、（２０）式が得られる。

Substituting equation (19) into equation (18) yields equation (20).

（２０）式は、Ｖｂｃを（１９）式で示されるようにコントロールすると、出力電圧Ｅｏｕｔは測定ブリッジに印加する搬送波周波数に関係しないで、Ｒ分である抵抗値だけの式になることを示している。
ここで（１６）式と（１９）式に注目し、Ｒ１＝Ｒ２とすると、（１６）式は、（２１）式になる。

Equation (20) shows that when Vbc is controlled as shown in Equation (19), the output voltage Eout is not related to the carrier frequency applied to the measurement bridge, but only the resistance value corresponding to R. ing.
Here, paying attention to the equations (16) and (19) and assuming R1 = R2, the equation (16) becomes the equation (21).

また、（１９）式は（２２）式となる。

Also, equation (19) becomes equation (22).

（２１）式と（２２）式とから解るように、Ｒ分がバランスしている場合は、ブリッジ電圧（Ｅ／２）と不平衝Ｃ分（浮遊容量Ｃｕ１または浮遊容量Ｃｕ２）とを乗算して成る逆位相の電圧を加えれば良いことが解る。
以下、これを実際の回路で検証した結果を示す。
図７は、Ｒ分がバランスしている場合のＶｂｃを示す算式の検証に使用した回路のブロック構成図である。
同図に示す回路において、測定ブリッジＡＢ間のＣ分を変化させ、ＣＳＴ動作をさせた場合と、ＣＳＴ動作をしない場合とを比較した。
図８は、図７に示す回路におけるＣ分によって出力するひずみ量（＝出力電圧Ｅｏｕｔ）の比較データを示すグラフ図である。
同図に示すデータは、ＣＳＴ動作をさせた場合と、ＣＳＴ動作をしない場合とで、搬送波周波数を５ｋＨｚ、１２ｋＨｚ、２８ｋＨｚとし、ブリッジ抵抗を１２０Ωとして、それぞれ取得したものである。同図から解るように、ＣＳＴ方式では零点がほとんど変化しない。Ｃ分によって出力するひずみ量はグラフ上では零に近く、改善度は非常に大きい。この動作で、搬送波型動ひずみ測定器の測定ブリッジの初期不平衡の調整は、Ｒ分のみで済むことが理解される。

As can be seen from the equations (21) and (22), when the R component is balanced, the bridge voltage (E / 2) and the unbalance C component (the stray capacitance Cu1 or the stray capacitance Cu2) are multiplied. It can be seen that it is sufficient to apply a reverse phase voltage.
The results of verifying this with an actual circuit are shown below.
FIG. 7 is a block configuration diagram of a circuit used for verifying the formula showing Vbc when the R component is balanced.
In the circuit shown in the figure, the case where the C portion between the measurement bridges AB is changed and the CST operation is performed is compared with the case where the CST operation is not performed.
FIG. 8 is a graph showing comparison data of the amount of distortion (= output voltage Eout) output by C in the circuit shown in FIG.
The data shown in the figure is obtained when the CST operation is performed and when the CST operation is not performed and the carrier wave frequencies are 5 kHz, 12 kHz, and 28 kHz, and the bridge resistance is 120Ω. As can be seen from the figure, the zero point hardly changes in the CST method. The strain output by the C component is close to zero on the graph, and the improvement is very large. With this operation, it is understood that the adjustment of the initial imbalance of the measurement bridge of the carrier-type dynamic strain measuring instrument is only R.

Next, let us consider a case where the stray capacitance Cu3 and the stray capacitance Cu4 are mixed as C components into the CD side and the AD side which are opposite sides of the AB side and the BC side of the measurement bridge. (At this time, it is assumed that the C component capacity distributed on the four sides of the bridge is small and balanced.)
FIG. 9 shows an equivalent circuit of the measurement bridge in the case where the stray capacitance Cu3 and the stray capacitance Cu4 are contained as C components in the CD side and the AD side which are opposite sides of the AB side and the BC side of the measurement bridge.
In this case, first, the output voltage Eout is obtained for the equivalent circuit shown in FIG. 9A, and the voltage Vbc that makes its imaginary part zero is calculated.
The output voltage Eout is expressed by equation (23), and the voltage Vbc is expressed by equation (24). Substituting equation (24) into equation (23) yields equation (25).

（２５）式から解るように、出力電圧Ｅｏｕｔは、印加する搬送波の周波数と抵抗値にも依存し、Ｃ分の変化では零にならない。
次に、図９（ｂ）に示す等価回路についても同様な計算をして出力電圧Ｅｏｕｔを求める。
求められた式で、Ｒ＝１２０Ω（Ｒ１＝Ｒ２＝Ｒ３＝Ｒ４）とし、辺ＡＤと辺ＣＤにＣ分である浮遊容量Ｃｕ４と浮遊容量Ｃｕ３とが加わり、その変化量を０〜２２００ｐＦまで変えた場合の出力電圧Ｅｏｕｔを算出した。
搬送波周波数には、５ｋＨｚ、１２ｋＨｚ、２８ｋＨｚの３種類を用いた。その結果は図１０に示す。
図１０は、図９に示す等価回路についての、ひずみ量（＝出力電圧Ｅｏｕｔ）の比較データを示すグラフ図である。
同図に示すグラフを見ても解るように、１２０Ωのブリッジ抵抗で搬送波周波数が２８ｋＨｚのとき、１３００μεも変化する（この時、容量値Ｃｂは、２２００ｐＦである）。

As can be seen from the equation (25), the output voltage Eout also depends on the frequency and resistance value of the applied carrier wave, and does not become zero with a change of C minutes.
Next, the same calculation is performed for the equivalent circuit shown in FIG. 9B to obtain the output voltage Eout.
In the obtained formula, R = 120Ω (R1 = R2 = R3 = R4), and the stray capacitance Cu4 and stray capacitance Cu3 which are C minutes are added to the side AD and the side CD, and the change amount is changed to 0 to 2200 pF. In this case, the output voltage Eout was calculated.
Three types of carrier frequencies of 5 kHz, 12 kHz, and 28 kHz were used. The result is shown in FIG.
FIG. 10 is a graph showing comparison data of the distortion amount (= output voltage Eout) for the equivalent circuit shown in FIG.
As can be seen from the graph shown in the figure, when the carrier frequency is 28 kHz with a bridge resistance of 120Ω, 1300 με also changes (at this time, the capacitance value Cb is 2200 pF).

If the C component of the AB and BC sides is unbalanced, the initial unbalance value becomes zero. However, the AD and CD sides do not have zero initial unbalance value, and must be improved.
As an improvement method, a voltage generation portion Vdc that cancels the C component can be used at the point D of the measurement bridge as in the case of the point B.
The unnecessary waveform canceling method when there are C components on the four sides of the measurement bridge applied to the CST system dynamic strain measuring instrument of the present invention will be described below.
First, an equivalent circuit of the model is set in order to show this method by a calculation formula.
The AB side and the BC side are handled by the circuit of the voltage Vbc and the capacitance Cb with the B point of the measurement bridge as the center, and the AD side and the CD side are newly provided with the D point as the center, and the voltage Vdc and the capacitance Cd. If this circuit is used, the zero point change can be suppressed regardless of which side of the measurement bridge C is added (the equivalent circuit is shown in FIG. 11).
FIG. 11 is a circuit diagram of an equivalent circuit for explaining a canceling method when there are stray capacitances C (Cu1 to Cu4) on four sides of the measurement bridge.
In the equivalent circuit shown in the figure, in order to calculate the output voltage Eout, from the principle of superposition, it can be decomposed into first to fourth circuits as shown below (decomposition results are shown in FIGS. 12 to 15). To show).

FIG. 12 is a circuit diagram of a first circuit obtained by disassembling the equivalent circuit shown in FIG.
FIG. 13 is a circuit diagram of a second circuit obtained by disassembling the equivalent circuit shown in FIG.
FIG. 14 is a circuit diagram of a third circuit obtained by disassembling the equivalent circuit shown in FIG.
FIG. 15 is a circuit diagram of a fourth circuit obtained by disassembling the equivalent circuit shown in FIG.
That is, the output voltage Eout is Eout = (VD1 + VD2 + VD3 + VD4) − (VB1 + VB2 + VB3 + VB4).
Here, VD1 and VB1 in FIG. 12, VD2 and VB2 in FIG. 13, VD3 and VB3 in FIG. 14, and VD4 and VB4 in FIG. 15 are calculated.
First, VD1 is obtained by equation (26).

（２６）式を整理すると、（２７）式が得られる。

By rearranging equation (26), equation (27) is obtained.

同様にＶＢ１は、（２８）式で求められる。

Similarly, VB1 is obtained by the equation (28).

ＶＤ２は、（２９）式で求められる。

VD2 is determined by equation (29).

ＶＢ２は、（３０）式で求められる。

VB2 is determined by equation (30).

ＶＤ３は（３１）式で求められる。

VD3 is obtained by equation (31).

VD3 = 0 (31)
VB3 is determined by equation (32).

ＶＤ４は、（３３）式で求められる。

VD4 is determined by equation (33).

また、ＶＢ４は、（３４）式で求められる。

Moreover, VB4 is calculated | required by (34) Formula.

VB4 = 0 (34)
Here, VD and VB are obtained.
Since VD = VD1 + VD2 + VD3 + VD4, Equation (27), Equation (29), Equation (31) and Equation (33) are added to obtain Equation (35).

次に、ＶＢを算出する。
ＶＢ＝ＶＢ１＋ＶＢ２＋ＶＢ３＋ＶＢ４であるから、（２８）式、（３０）式、（３２）式および（３４）式を加算し、（３６）式を得る。

Next, VB is calculated.
Since VB = VB1 + VB2 + VB3 + VB4, Equation (28), Equation (30), Equation (32) and Equation (34) are added to obtain Equation (36).

（３５）式と（３６）式とを、それぞれ実数部と虚数部に分けて、虚数部を零にする電圧Ｖｄｃと電圧Ｖｂｃを算出すると、電圧Ｖｄｃは（３７）式となり、電圧Ｖｂｃは（３８）式となる。

By dividing the expression (35) and the expression (36) into the real part and the imaginary part, respectively, and calculating the voltage Vdc and the voltage Vbc that make the imaginary part zero, the voltage Vdc becomes the expression (37), and the voltage Vbc becomes ( 38).

‥……（３８）
以上により、図１１に示した等価回路の出力電圧Ｅｏｕｔは、（３９）式として求まる。

(38)
From the above, the output voltage Eout of the equivalent circuit shown in FIG. 11 is obtained as equation (39).

（３９）式に、前述の虚数部を零にする（３７）式と（３８）式とを、それぞれ電圧Ｖｄｃと電圧Ｖｂｃの項に代入すると、（４０）式が得られる。

By substituting (37) and (38) into the terms of voltage Vdc and voltage Vbc, respectively, the above-described equation (37) and (38) for setting the imaginary part to zero in equation (39), equation (40) is obtained.

（４０）式は、抵抗Ｒだけの式であることが理解される。
以上の結果から、測定ブリッジのＤ点とＢ点に、それぞれ独立したＣ分の打消し回路を設けて、電圧Ｖｄｃと電圧Ｖｂｃとを（３７）式と（３８）式のようにコントロールすれば、測定ブリッジの４辺にＣ分が加わっても零点変動は生じなくなることになる。
抵抗Ｒ分は別途バランスさせるので、測定ブリッジ４辺の抵抗Ｒ分は全て等しいとして、Ｒ＝Ｒ１＝Ｒ２＝Ｒ３＝Ｒ４と置くと、（３７）式と（３８）式は（４１）式と（４２）式となる。

It is understood that the equation (40) is an equation of only the resistance R.
From the above results, it is possible to provide an independent cancellation circuit for C at points D and B of the measurement bridge, and to control the voltages Vdc and Vbc as shown in equations (37) and (38). Even if C is added to the four sides of the measurement bridge, the zero point fluctuation does not occur.
Since the resistance R components are separately balanced, assuming that the resistance R components on the four sides of the measurement bridge are all equal, and R = R1 = R2 = R3 = R4, Equations (37) and (38) are expressed as Equation (41). (42).

また、（４１）式と（４２）式とから解るように、抵抗Ｒ分が平衡していれば、ブリッジのＤ点とＢ点の隣辺のＣ分の差分のＥ／２の打消し波形を加えればよいことが理解される。即ち、抵抗Ｒ分に関係せず、また、搬送波周波数にも関係しないで、Ｃ分は打消すことが可能となる。

Further, as understood from the equations (41) and (42), if the resistance R is balanced, the cancellation waveform of E / 2 of the difference of C by the adjacent side of the point D and the point B of the bridge. It is understood that it may be added. That is, it is possible to cancel the C component regardless of the resistance R component and the carrier frequency.

(Example)
In the implementation circuit of the carrier-type dynamic strain measuring instrument according to the first embodiment of the present invention shown in FIG. 1, an SSG (Standard Strain Generator) is a device that generates a strain change amount based on a resistance change of a strain gauge. And the reference input of the measuring instrument. This corresponds to a measurement bridge. Based on this SSG input, the amount of strain was measured.
FIGS. 16 and 17 show data of zero change measured by adding 0 to about 2000 pF as C minutes to each side of the measurement bridge.
FIGS. 16A and 16B are graphs showing data of zero point changes between A and B and B and C in the implementation circuit.
The figure shows the measurement results when the resistance value of each side of the measurement bridge is 120Ω and the carrier frequency is changed to 5 kHz, 12 kHz and 28 kHz (however, in this experiment, the output is zero at 0 and 2200 pF). Adjusted to be).
FIG. 17 is a graph showing other data of zero point change between AB and CD in the implementation circuit.
This figure shows the measurement results when the resistance value of each side of the measurement bridge is 350Ω and the frequency of the carrier wave is similarly changed to 5 kHz, 12 kHz, and 28 kHz.

As can be seen from the measurement results shown in FIGS. 16A and 16B and FIGS. 17A and 17B, when the carrier frequency is 5 kHz, even if the resistance value of each side of the measurement bridge is 120Ω, Even if 350Ω or even if there are C components on the four sides of the measurement bridge, the change in the output voltage Eout in the implementation circuit is almost zero.
In the case of 12 kHz, the change in the output voltage Eout in the implementation circuit is a dozen με.
Furthermore, in the case of 28 kHz, the resistance value of each side of the measurement bridge is 40 με or less at 120Ω, but is about 100 με in the case of 35 OΩ.
The reason for this residual is that it handles minute voltages, so that the higher the carrier frequency and the higher the resistance value, the more electromagnetic noise will affect the input from circuit components and circuit patterns via stray capacitances. It is. It is thought that better results will be obtained if the arrangement of parts to reduce stray capacitance and the shielding are improved.
As understood from FIG. 10, in the conventional normal device, the change in the output voltage Eout changes by 1200 με or more when the resistance of each side of the bridge is 120Ω and the carrier frequency of the carrier wave is 28 kHz. On the other hand, since the carrier-type dynamic strain measuring instrument according to the present embodiment is 40 με or less as shown in FIG. 16, a remarkable improvement effect is obtained.

Since the strain measurement used in stress measurement is several hundred to several thousand με, the initial imbalance value of the measurement bridge can be sufficiently suppressed by using the carrier-type dynamic strain measuring instrument according to this embodiment. it can. Therefore, it can be said that the two-system CST operation, which is a feature of the carrier-type dynamic strain measuring device according to the present embodiment, functions sufficiently.
In addition, as with conventional CST type carrier-type dynamic strain measuring instruments, it is possible to measure dynamic phenomena that change very quickly by using a carrier wave. In addition, it is possible to cancel with high accuracy. Further, a primary side circuit portion including a measurement bridge, a cancellation circuit, and a secondary side power supply circuit, and a circuit including a carrier wave amplifier circuit, a capacitive phase detection circuit, a capacitive cancellation drive circuit, an oscillation circuit, and a secondary power source It is also possible to adopt a configuration in which the portion is not directly connected. For example, similarly to the carrier-type dynamic strain measuring instrument described in Patent Document 3 (Japanese Patent Laid-Open No. 2010-266408), feedback coupling from the secondary side to the primary side is performed as in the light emitting diode 13a and the light receiving diode 13b. It is also possible to achieve a configuration realized through a simple optical signal transmission means, so that noise, in particular, noise from the secondary side circuit is not mixed, and dynamic strain can be measured with high accuracy. Become.

11 Measurement Bridge 12 Input Transformer 14, 14a, 14b Cancellation Circuit 15B. V waveform supply circuit 16 Calibration value generation circuit 17 Resistance adjustment circuit 18 Primary power supply circuit 19 Coupling transformer 20 Power transformer 21, 21a, 21b Carrier wave amplifier circuit 22 Resistance phase detection circuit, carrier filter circuit 23 Capacitance phase detection circuit , Carrier filter circuit 24, 24a, 24b capacity canceling drive circuit 25, 25a, 25b phase shift circuit 26 oscillation circuit 27 power amplifier circuit 28 secondary power supply Cb, Cd, feedback capacitor (for cancellation)
R1-R4 resistance Cu1-Cu4 stray capacitance

Claims (5)

In carrier type dynamic strain measuring instrument,
A measurement bridge including a strain gauge;
A carrier amplifier circuit for amplifying a measurement signal superimposed on a carrier wave applied to the measurement bridge;
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;
Two systems of first and second capacity canceling drive circuits that receive the output of the capacity phase detecting circuit and automatically cancel the unbalanced component due to the capacity component generated in the measurement bridge;
A resistance phase detector circuit that extracts an unbalanced portion of the resistance of the measurement bridge and removes a carrier wave component;
A phase shift circuit for supplying a reference voltage serving as a reference for the phase shift to the capacitance phase detection circuit;
A carrier oscillation circuit for generating a carrier wave to be applied to the measurement bridge;
Two systems of feedback first and second capacitors respectively connected between the two output terminals of the measurement bridge and the two systems of the first and second capacitance canceling drive circuits; With
The first and second capacitance cancellations of the two systems are used to cancel out the unbalance component due to the stray capacitance component mixed in parallel with the resistance of one or all four sides of the measurement bridge. A carrier wave configured to automatically cancel the unbalanced component due to the capacitance by being applied to each output terminal of the measurement bridge via the first and second feedback capacitors from the drive circuit. Type dynamic strain measuring instrument. Capacities of the unbalanced component included in the adjacent side of one output end of the measurement bridge are Cu1 and Cu2, respectively, and capacitances of the unbalanced component included in the adjacent side of the other output end of the measurement bridge are respectively Cu3. And Cu4,
The feedback first capacitor and second capacitor are Cb and Cd,
The carrier voltage applied to the input end of the measurement bridge is E,
When the resistance components forming the measurement bridge are balanced, the cancellation voltage Vbc obtained by the following [Equation 1] and the cancellation voltage Vdc obtained by the following [Equation 2]:

The carrier-type dynamic strain measuring device according to claim 1, wherein each is applied to one output end and the other output end of the measurement bridge.   2. The carrier-type motion according to claim 1, wherein the first and second capacitors for feedback are capacitors that can be set by selecting any one of a plurality of predetermined capacitance values. Strain measuring instrument.   A secondary power supply for supplying power to each circuit on the secondary side, and a primary power supply circuit for receiving power from the secondary power supply via a power transformer and supplying power to each circuit on the primary side. The carrier-type dynamic strain measuring instrument according to any one of claims 1 to 3, further comprising a configuration in which an output of the carrier wave oscillation circuit is applied to a measurement bridge via a coupling transformer.   The measurement bridge further includes at least one light emitting diode and a light signal transmitting means including a light receiving diode disposed so as to face the light emitting diode between the primary side circuit and the secondary side circuit. The capacitance canceling drive circuit, the light receiving diode, and the primary-side power supply circuit include the carrier wave amplification circuit, the capacitance phase detecting circuit, the capacitance canceling drive circuit, the light emitting diode, the carrier wave oscillation circuit, and Connected to the secondary side power source by 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, and electrically connected. The carrier-type dynamic strain measuring instrument according to claim 4, wherein

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