JPS5827442B2 - Hizumi Soku Teiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain measuring instrument, and more particularly to a dynamic strain measuring instrument using a carrier wave amplifier.

Generally, a Wheatstone bridge is used in the detection section of a strain measuring instrument.

Methods for supplying voltage to this detection bridge include a DC voltage method and an AC voltage method, and the AC voltage method includes a carrier wave, ie, a sine wave method, and a square wave method.

Currently, the sine wave method is widely used, but in this method it is necessary to alternately adjust the unbalance of the resistor button and capacitor in order to compensate for the initial unbalance of the detection bridge.

Further, in the square wave method and the DC voltage method, there is no need to adjust the capacitance unbalance.

However, the sine wave method has the best gain, stability, and signal-to-noise ratio necessary for a strain measuring instrument, except for the fact that it takes time to adjust the initial unbalance of the detection bridge.

Therefore, if the capacitance unbalance can be adjusted automatically without any trouble, the sine wave method can be used in a much wider range of applications.

In general, in strain measuring instruments that use a sinusoidal AC voltage with a high carrier frequency as the bridge power supply, an unbalanced portion of the resistance button and capacitance occurs in the input bridge into which the strain gauge is inserted. It is necessary to balance both.

In conventional strain measuring instruments, this balance adjustment was performed manually.

However, since it is necessary to alternately adjust the balance of the unbalanced resistance and capacitance, it takes a lot of time to prepare for measurement, and it is therefore difficult to automate dynamic strain measurement.

SUMMARY OF THE INVENTION An object of the present invention is to provide a strain measuring instrument of the type described above, which is appropriately connected and arranged so that such capacitance unbalance can be electrically compensated not only at the beginning of the measurement but also continuously during the measurement.

According to the present invention, there is a detection bridge whose input voltage is an output voltage from a sine wave generator, and a carrier wave which has an input terminal coupled to an output terminal of the detection bridge and amplifies the output signal of the detection bridge and outputs the amplified signal. In a strain measuring instrument comprising an amplifier circuit and an output circuit that receives the amplified output voltage from the carrier amplifier circuit via an output transformer and outputs a strain output signal from the amplified output voltage, each side is connected to a capacitor. A capacitive bridge is constructed of a capacitive element, and the capacitive element on one side is a voltage-responsive capacitive element whose capacitance value changes depending on the voltage, and the output terminal is connected to the input terminal of the capacitive bridge, and the input terminal 90 connected to the sine wave generator to supply the input terminal of the capacitive bridge with a bridge excitation voltage phase-shifted by 90° with respect to the output voltage of the sine wave generator.
a 0-shift sum circuit, further comprising a direct current coupled between the output transformer and the voltage responsive capacitive element to generate a direct current from the amplified output voltage supplied to the output circuit in accordance with the capacitance unbalance generated in the detection bridge. a capacitance unbalance detection circuit that detects a feedback voltage and supplies the DC feedback voltage to the voltage-responsive capacitance element; The output terminal of the capacitive bridge is connected to the output terminal of the sensing bridge and the sensing bridge so that a feedback output voltage is generated at the output terminal of the capacitive bridge, and the feedback output voltage compensates for the capacitance unbalance of the sensing bridge. It is characterized in that it is coupled between input terminals of a carrier wave amplification circuit.

The invention will be explained with reference to the drawings.

In the strain measuring instrument of the present invention shown in FIG. 1, an input transformer is provided before the carrier amplification circuit.

That is, the input side of the carrier amplifier 1 is connected to the secondary winding W2 of the input transformer 2, and one end (inside end) of the primary windings W1a and Wlb of the input transformer 2 is connected to the resistive unbalance compensation bridge 3. The other ends (outside ends) of the primary windings W1a and Wlb are connected to the output terminal of the Wheatstone bridge 4 constituting the detection section.

This bridge 4 is configured, for example, with fixed resistors on two sides and variable resistors, ie, strain gauges 4a and 4b, on the other two sides to form a gauge circuit.

The input terminal of the detection bridge 4 is connected via a coupling transformer 5 to a first output terminal of a sinusoidal oscillator 6.

The input terminal of the bridge 3 is also connected to a first output terminal of a sine wave oscillator 6 via a coupling transformer 5.

Furthermore, the output terminal of the carrier wave amplifier 1 is connected to the primary winding W1 of the output transformer 7, and one of the secondary windings W2a is connected to the distortion measuring instrument through the resistance valve phase detection circuit 8 and the low band pass filter 9. Connect to the output terminal 10 of.

The detector circuit 8 and filter 9 constitute an output circuit.

Further, the other secondary winding %b of the output transformer 7 is connected to the low band pass filter 12 via the capacitive phase detection circuit 11, and its output terminal is connected to the input terminal of the voltage responsive conductive element drive circuit 13. .

helmet, these detection circuit 11, filter 12 and drive circuit 1
3 constitutes a capacitance unbalance detection circuit.

Further, the other primary winding W1c of the input transformer 2 is connected to the output terminal of the capacitance unbalance compensation bridge 14, and the input terminal of this capacitance bridge 14 is connected to one output terminal of the 900 transfer sum circuit 15. do.

90' The input terminal of the phase shift circuit 15 is connected to the second input terminal of the sine wave oscillator 6.
The other output terminal of the 90° phase shift circuit 15 is connected to the other input terminal of the capacitive phase detection circuit 11.

Further, the third output terminal of the sine wave oscillation circuit 6 is connected to the other input terminal of the resistance valve phase detection circuit 8.

Further, in this example, each of the four sides of the capacitive bridge 14 is used as a capacitive side, and in particular, one side of the capacitive bridge 14 is constituted by a voltage responsive capacitive element 14a, such as a variable capacitance diode, whose capacitance value changes depending on the voltage.

This voltage responsive capacitive element 14a is connected to the voltage responsive element drive circuit 1.
Connect to output terminal 3.

This capacitance bridge 14 is connected to a 90° phase shift circuit 15 via a 90°
00 shifted and summed sinusoidal voltage is supplied.

When a capacitance unbalance occurs in the bridge 4 of the detection section during operation, the output side has a phase shift of 90° (phase leading or A slow phase) voltage waveform appears.

Therefore, this 90° phase-shifted voltage waveform a is amplified by the carrier wave amplifier 1 via the input transformer 2, and the output voltage is supplied to the capacitive phase detection circuit 11 via the output transformer 7, where the capacitive component is The phase of the signal is detected, and the output is converted into a DC voltage by a low band pass filter 12 and supplied to a voltage responsive capacitive element drive circuit 13 of a known structure consisting of an ordinary linear amplifier. It is fed back to the capacitive element 14a.

When the detection bridge 4 is in a capacitance balanced state, this feedback voltage has the reference voltage value, in which case no output voltage of the capacitance bridge 14 occurs.

However, if a capacitance unbalance condition occurs and, for example, the output voltage of the detection bridge 4 lags the input voltage supplied to it by 90°, the feedback voltage will increase from the reference voltage value mentioned above, and the feedback voltage will increase by 90° When this happens, the capacitance of the voltage-responsive capacitive element 14a changes in a direction opposite to the direction of change in the feedback voltage and by an amount corresponding to the amount of change.

In this case, the input voltage supplied to the capacitive bridge 14 is advanced by 90° relative to the input voltage supplied from the sine wave generator 6 to the detection bridge 4 by the 900 phase shift circuit 15.

As is clear from the explanation from FIGS. 7 to 9, which will be described later, when the feedback voltage increases from the reference voltage value, the output voltage of the capacitor bridge 14 is in phase with the input voltage of the capacitor bridge, If the feedback voltage decreases from the reference voltage value, this output voltage will be in opposite phase to its input voltage.

Therefore, the output voltage output from the capacitance bridge 14 is always in a phase-shifted relationship of 1800 with respect to the output voltage from the detection bridge 4 due to capacitance imbalance.

Therefore, the voltage waveform from the bridge 4 due to capacitive imbalance is completely compensated by the output voltage waveform from the capacitive bridge 14.

Further, the resistance unbalance that occurs in the bridge 4 of the detection section is compensated by the resistance unbalance compensating bridge 3.

Therefore, an output voltage to be measured having a correct value can be generated at the output terminal 10.

This measured output voltage is processed as usual depending on the purpose.

FIG. 2 shows a modification of the strain measuring instrument shown in FIG.

In the figure, the same parts as the circuit elements in FIG. 1 are given the same reference numerals and will be explained.

The configuration of the strain measuring instrument in this example is almost the same as that of the strain measuring instrument shown in FIG. 1, except that the capacitive bridge 14 is connected to the secondary winding W2 instead of being connected to the primary winding of the input transformer 2. .

Therefore, a description of the operation of the strain measuring instrument of this example will be omitted.

First mentioned above. In the examples shown in Figures 1 and 2, an input transformer is provided on the input side of the carrier amplifier, but since such an input transformer amplifies a very small voltage, it is necessary to provide strict shielding.

Examples in which such an input transformer is omitted are shown in FIGS. 4, 5 and 6.

In the figure, the same parts as the circuit elements in FIG. 1 are denoted by the same reference numerals.

In the example shown in FIG. 4, a capacitance unbalance compensation bridge 14 is connected in series to the bridge 4 of the detection section, and
The other output terminal of 4 is connected to the input side of carrier wave amplifier 1.

The resistance unbalance compensating bridge 3' is in the form of a voltage divider and is connected between the input terminals of the detection bridge 4, and the voltage divider sun tap is connected to one output terminal of the detection bridge 4.

The operation of the distortion amplifier of this example is also substantially the same as that described with reference to FIG. 1, except that no input transformer is inserted, so a detailed explanation thereof will be omitted.

In the example shown in FIG. 5, a resistance imbalance compensation bridge 3 and a capacitance imbalance compensation bridge 14 are connected in parallel between the bridge 4 of the detection section and the carrier wave amplifier 1.

In the example shown in FIG. 6, a resistance unbalance compensating bridge 3 and a capacitive unbalance compensating bridge 14 are arranged in series between the bridge 4 of the detection section and the carrier wave amplifier 1.

In the examples shown in FIGS. 5 and 6, the operation is the same as that described above, so a description thereof will be omitted.

Next, the purpose button and effect of using the capacitive bridge will be explained.

The output voltage due to capacitance unbalance of the detection bridge 4 may be shifted by 2700 or phase shifted by 900 with respect to the voltage supplied to the detection bridge depending on the state of the unbalance.

(There are various stray capacitances on each side of the detection bridge,
The unbalanced portion can be expressed in any number of ways by concentrating it on one side, and the case is equivalent to the case where a capacitor is connected in parallel to the side containing the strain gauge 4a of the detection bridge 4 in Fig. 1. (in the case of the side including the strain gauge 4b, the phase shift is 90°).

Therefore, in order to cancel the output voltage due to capacitance imbalance of the detection bridge, it is necessary to phase shift the voltage supplied to the detection bridge by 90° or 270° (detection bridge 4
For the output voltage due to capacitance unbalance, 180
0 phase shift) is required.

Furthermore, the amplitude of the canceling voltage must be able to be adjusted arbitrarily in accordance with the magnitude of the capacitance unbalance of the detection bridge.

A circuit that satisfies these two conditions can be easily constructed using a υ capacitance bridge circuit that includes an element that can be controlled by voltage or current on at least one side.

In the present application, a canceling voltage is obtained by a capacitive bridge 14 having on one side an element 14a (for example, a voltage responsive capacitive element such as a variable capacitance diode) whose capacitance value can be controlled by voltage.

When using a capacitive bridge, even if the measurement state is such that a DC voltage is applied from either or both of the voltage-responsive capacitive element drive circuit 13 and the 900 phase shift circuit 15, the DC component can be cut off and only the AC component can be detected. There is an advantage that the unbalanced capacity of the bridge 4 can be compensated for.

Next, the capacitive bridge 14 will be explained in detail.

As an example, assume that the bridge excitation voltage, which is the input voltage of the capacitor bridge 140, is the sum of the input voltages of the detection bridge 40 by 90 degrees, and the voltage-capacitance characteristic of an element whose capacitance value can be controlled by voltage is taken as an example. It shall change as shown in the figure.

The horizontal axis represents the DC feedback voltage from the drive circuit 13, which changes by ±JD from the center voltage, which is the reference voltage.

The vertical axis shows the capacitance change C♀AC corresponding to this change in the feedback voltage of element 14a.

FIG. 8 is a diagram illustrating a capacitive bridge constructed of capacitive elements having the element 14a on one side and the other three sides having a capacitance value of C2F.

The output e from the capacitive bridge corresponding to the voltage to be supplied to the carrier wave amplifier 1 is in opposite phase or in phase with the bridge excitation voltage E from the -9900 phase shift circuit 15, as shown in FIG. 9, and the feedback voltage of the element 14a. A voltage with an amplitude corresponding to the voltage can be obtained.

That is, the load RL is now placed between the output terminals of the capacitive bridge 14.
(not shown) is connected, and if the feedback voltage changes by 1.4D from the center voltage, the capacitance of the element 14a changes by +JC, and therefore, in the capacitance bridge 14, the current is an alternating current indicated by E. source, that is, the 90° phase shift circuit 15, the connection point between the resistor R and the element 14a, the element 14a, and the load R.
L, and flows through the capacitor C on the upper right side of the bridge to the 900 phase shift circuit 15, so that the output voltage e has the opposite phase to the excitation voltage E.

Conversely, the feedback voltage changes by +JD, and the capacitance of the element decreases by -J.
When only C changes, the current flows from the 90° phase shift circuit 15 to the resistor R.
It flows to the 90° phase shift circuit 15 through the connection point between and element 14a, the capacitance on the upper left side of the bridge, the load RL, and the capacitance C on the lower right side of the bridge, so that the output voltage e becomes in phase with the excitation voltage E. .

The fact that the feedback voltage changes by jjD means that the output voltage of the detection bridge 4 is 90 degrees ahead of the input voltage, so the fact that the output voltage of the capacitive bridge 14 is in reverse phase with the excitation voltage means that the detection bridge 4 The output voltage of the detection bridge 4 is also in reverse phase with respect to the output voltage, and the fact that the feedback voltage changes by +, (D means that the output voltage of the detection bridge 4 is delayed by 90 degrees with respect to the input voltage. The fact that the output voltage is in phase with the excitation voltage means that it is in reverse phase with respect to the output voltage of the detection bridge 4, so that the capacitance unbalance can be canceled out.

The button feedback voltage corresponds to the state of capacitance unbalance of the detection bridge 4, and is the center voltage D when there is no capacitance unbalance, and the DC feedback voltage D+ when it is parallel to the side including the strain gauge 4a.
, (D, if it is parallel to the side including the strain gauge 4b, the voltage is JD, and due to the fluctuation of the feedback voltage according to the capacitance imbalance, the corresponding outputs e(+JC) and e(-JC
) is obtained.

In the above explanation, the case where the bridge excitation voltage is 90° phase-advanced has been explained, but it is also possible to select a 90° phase-lag.

In that case, the direction of increase/decrease in the feedback voltage may be opposite to that in the former case.

As is clear from the above, according to the present invention, by configuring one side of the capacitive bridge with a voltage responsive capacitive element and feeding back the capacitance unbalance to this, it is possible to constantly compensate for the capacitance unbalance even during measurement. There are advantages that can be achieved.

The present invention is not limited to the above-mentioned example, but can be modified in many ways.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the connection arrangement of an example of the strain measuring instrument of the present invention, Fig. 2 is a block diagram showing the connection arrangement of a modification of Fig. 1, and Fig. 3 is for explaining the operation of the strain measuring instrument of the present invention. Waveform diagrams, Figures 4, 5 and 6 are block diagrams showing connection arrangements of other examples of the strain measuring instrument of the present invention, and Figures 7, 8 and 9 are diagrams for explaining the capacitive bridge used in the present invention. be. 1...Carrier amplifier, 2...Input transformer, 3.3'
... Resistance unbalance compensation bridge, 4... Detection bridge, 4a, 4b... Strain gauge, 5... Coupling transformer, 6... Sine wave oscillator, 7... Output transformer, 8・・・
・Resistance component phase detection circuit, 9...Low band pass filter
10... Output terminal (distortion measuring instrument), 11... Capacitance phase detection circuit, 12... Low band pass filter, 13
... Voltage responsive capacitive element drive circuit, 14... Capacitance unbalance compensation bridge, 14a... Voltage responsive capacitive element, 1
5...900 phase shift circuit.

Claims (1)

[Claims] 1 a detection bridge whose input voltage is the output voltage from a sine wave generator; a carrier amplification circuit which has an input terminal coupled to the output terminal of the detection bridge and amplifies and outputs the output signal of the detection bridge; A strain measuring instrument is provided with an output circuit that receives the amplified output voltage from the carrier wave amplification circuit via an output transformer, extracts and outputs a distortion output signal from the amplified output voltage, and each side of the strain measuring instrument is provided with a capacitive element. and a capacitive bridge in which the capacitive element on one side is a voltage-responsive capacitive element whose capacitance value changes depending on the voltage,
Furthermore, when an output terminal is connected to an input terminal of the capacitive bridge, an input terminal is connected to the sine wave generator, and the output voltage of the sine wave generator is 90%
The 0 phase shift circuit includes a 9 cP phase shift circuit that provides a 1-nudge excitation voltage, and is coupled between the output transformer and the voltage responsive capacitive element to detect the amplified output voltage from the amplified output voltage that is supplied to the output circuit. comprising a capacitance unbalance detection circuit that detects a DC feedback voltage corresponding to a capacitance unbalance generated in the bridge and supplies the DC feedback voltage to the voltage responsive capacitance element;
The capacitive bridge is configured to generate a feedback output voltage in phase or in phase with respect to the bridge excitation voltage at the output terminal of the capacitive bridge depending on the DC feedback voltage, and the feedback output voltage causes the capacitive bias of the detection bridge to be generated. A distortion measuring instrument characterized in that the output terminal of the capacitive bridge is coupled between the output terminal of the detection bridge and the input terminal of the carrier wave amplification circuit so as to compensate for the balance component.