JPS5829443B2 - Hizumi Soku Teiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain measuring instrument that measures mechanical strain using a resistance strain gauge.

In particular, the present invention relates to a strain measuring instrument that has low noise, has a simple mechanism, and is easy to measure.

Conventionally, strain measurement using a resistance strain gauge is carried out by measuring the change in resistance of the gauge using a bridge or double bridge, and using a strain measuring instrument to measure the balanced voltage of the bridge by magnifying it.

In this case, typically two separate floating power supplies must be used, one for the bridge and one for the amplification or calibration.

Therefore, noise occurs across the common potential between the floating power supplies, which has the drawback of deteriorating strain measurement accuracy.

Further, since an additional circuit is configured at the input of the amplifier, the input impedance of the amplifier is reduced, and the effective sensitivity is also reduced.

Furthermore, many measuring instruments have complicated configurations, making operations complicated and requiring a long time for measurement, which is inconvenient when measuring a large number of strain gauges.

SUMMARY OF THE INVENTION An object of the present invention is to provide a strain measuring instrument that has low noise, high accuracy, and is simple in structure and operation.

The present invention comprises a DC balanced bridge including a strain gauge on one side of a constituent arm, a differential amplifier having positive and negative inputs as the balanced outputs of the balanced bridge, and a DC power source whose midpoint is connected to a common potential point. A first switching circuit that applies the output voltage of the DC power supply to the balanced bridge, a variable resistor that obtains a positive or negative resistance-divided voltage output from the DC power supply, and a second switching circuit that switches the output of the variable resistor. The switching circuit includes a switch for inputting the positive and negative DC voltages of the DC power source, one or more resistors, and a switch that can be switched by operation. a third switching circuit configured to open and close the output of the calibration circuit; and a third switching circuit configured to open and close the output of the calibration circuit; an amplifier circuit that adds or subtracts the output and sends it to the output terminal, and when the first switching circuit is closed before mechanical strain is applied to the strain gauge, the unbalanced output that appears at the output terminal is , by closing the second switching circuit and adjusting the variable resistor, and closing the first switching circuit and the second switching circuit when mechanical strain is applied to the strain gauge. The measurement output that appears at the output terminal when the first switching circuit and the second switching circuit are open is the output of the calibration circuit that appears at the output terminal when the third switching circuit is closed. It is characterized in that it is configured to be measured based on .

This will be explained in detail in Examples.

FIG. 1 is a block diagram of an embodiment of the present invention.

In the figure, A1 is a differential amplifier, A2 is a summing amplifier, EB is a battery, RBI to RB4 are resistor arms forming the bridge, and R
v is a variable resistor, R1 to R4' are resistors, 81 to S3 are open/close switches, and S4 is a changeover switch.

To explain the configuration of Fig. 1, the resistance arm RB of the bridge
Among I to RB4, RB+ is a strain gauge.

A power supply EB is led to the power supply terminal of the bridge constituted by these resistors via a switch S1, and a balanced voltage is led to a differential amplifier A1.

The output of differential amplifier A1 is led via resistor R1 to the input of summing amplifier A2.

Summing amplifier A2 has a feedback resistor R3 that determines its gain, and its output is coupled to output terminal OUT.

Further, the power supply EB has its midpoint connected to a common potential, the fixed terminal of the variable resistor Rv is connected to the positive and negative terminals of this power supply, and its sliding terminal is connected to the summing amplifier A2 via a resistor R2 and a switch S2. Connect to one summing point.

Switches S4a and Sob are interlocking switches, terminals 1 and 2 of the switch Sob are connected to the negative output of the power supply, and terminals 4 and 2 of the switch Sob are connected to the negative output of the power supply.
5 are respectively connected to the positive outputs of the above power supply, and terminal 3 is left open.

The movable piece of switch S4b has two resistors R4 and R4.
', and the other end of resistor R4 is connected to switch S4a.
The other end of resistor R4' is connected to terminals 1 and 5 of switch S4a.

The movable piece of this switch S4a is connected to one summing point of the summing amplifier A2 via an on/off switch S3.

Here, switches S4a, S4b and resistors R4, R4'
The circuit configured by connecting as shown in the figure is called the "calibration circuit".
That's what it means.

The operation of the device configured in this way will be explained.

First, only switch S1 is closed to apply voltage to the bridge.

However, if the bridge is balanced, there will be no balanced output;
There is no voltage at the output terminal OUT.

When strain is applied to the strain gauge and the balance is disrupted, a balanced output is produced, and a voltage corresponding to the strain is generated at the output terminal.

. Generally, an initial unbalanced voltage occurs due to variations in elements, etc., so if an unbalanced voltage is generated when the switch S1 is closed, switch S2 is closed, and the variable resistor Rv is adjusted before strain measurement.
A voltage opposite to the balanced voltage is applied to the input of the summing amplifier A2, and adjustment is made so that the output of the summing amplifier A2 becomes zero.

That is, the initial unbalanced voltage of the measurement bridge is directly amplified by the differential amplifier A1 and canceled by the summing amplifier A2 in the next stage.

When strain is measured in this state, the voltage appearing at the output terminal is a voltage corresponding to the amount of strain.

This voltage is now recorded before closing switch S3 and opening switch S1 and switch S2 for strain measurement.

Next, one of the switches S4 is selected and the output of the calibration circuit is applied to the summing amplifier A2, and the output of the summing amplifier A2 is adjusted to be equal to the output voltage recorded during the strain measurement.

The magnitude of the strain voltage can be determined from the position of the switch S4 of this calibration circuit, that is, the polarity of its output and the value of the resistor used.

In this way, the two voltages compared at the output terminal OUT are both supplied from the same power supply EB, and there is no need to calibrate the power supply voltage.

By changing the order of operations and calibrating with the output of the calibration circuit before measuring strain, it is possible to directly read the strain.

※※ Furthermore, the relationship between the output voltages will be explained in detail using equations.

If the gauge factor of the resistance strain gauge is k, then the gauge RB
When strain is applied to t, the resistance value of gauge RBt is (1
+ to ε) times.

Now, assuming that the measuring bridge is initially balanced before applying strain, the output e1 of the measuring bridge is expressed by the following equation.

'.

Therefore, the potential e8 of the slider point E of the variable resistor Rv = O
, that is, exactly at the midpoint, the output ec
The gain of the summing amplifier A2 is as follows.

Here, G is the gain of the differential amplifier A1.

If there is an initial unbalanced voltage Je, on the bridge, the output e before the strain measurement.

Adjust Rv so that it becomes zero.

At this time, the potential e at point E. becomes.

Since the initial unbalanced voltage is canceled here, a new measurement can be performed, and the measurement result is the output of equation (3).

Next, when calibrating this obtained result, switch S1
Since the switch S2 is then opened, the output of the measuring bridge becomes zero and the balance circuit is disconnected.

In response to the voltage from the resistive divider circuit, output e.

If it is assumed that when the switch S4 is in the changeover switch 1 position, the value coincides with the value measured just before.

When this value is converted into differential amplifier A1, Input value e.

to becomes.

As is clear from equation (2), this value is equal to the output voltage of the bridge when a strain of is applied to the strain gauge.

Equation (5) does not include the term of bridge voltage EB, and R
1, G, and R4 can all be regarded as stable constants.

That is, when the switches S1 and S2 are open, the switch S3 is closed, and the switch S4 is in the changeover switch 1 position, the output of the summing amplifier A2 is expressed by equation (5), regardless of the value of the bridge voltage EB. A calibration voltage corresponding to the strain represented is generated.

Next, a more specific explanation will be given using numbers.

For example, when the gauge factor is 2, the gain of the differential amplifier A1 is 100, the resistor R1, and the resistor R4°R in the calibration circuit.
4' value to 10Ω, 1.00 kΩ, 500 respectively
Let it be Ω.

At this time, if switches S1 and S2 are opened, switch S3 is closed, and switch S4 is sequentially switched from switch 1 position to switch 5 position, 1000xlO' strain, 200xlO' strain, O strain, 200xlO' strain, the calibration voltage e corresponding to -1000xlO' strain.

is obtained from the output terminal OUT.

As described above, the features of the present invention can be summarized as follows.

(1) Since there is only one power supply system, there is no need to perform voltage calibration during measurement and calibration, and the operation is simple and the time required for measurement is shortened.

(2) Since there is only one power supply system and there is no floating potential between them, there is no influence of noise generated between common potentials.

Therefore, accuracy is increased.

(3) Since no additional circuit is required for the input circuit of the amplifier, it is possible to prevent the amplifier's manual impedance from decreasing;
Sensitivity error is eliminated.

(4) The circuit is simple, has few parts, and is reliable and economical.

(5) Since the calibration circuit can calibrate the device at any time, fluctuations in the device over time due to fluctuations in power supply voltage and other factors do not affect the measured values, and highly accurate measurements can be performed.

Note that the calibration circuit described in the above description does not limit the scope of the present invention, and the present invention can be practiced by generating an appropriate calibration voltage using other circuits.

In addition, for displaying the amount of strain, in addition to a direct reading scale on the calibration circuit, an interpolation scale is attached to the voltage indicator at the output terminal.
Furthermore, other applications such as making it easier to read strain may also be considered.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an apparatus according to an embodiment of the present invention. B...Measurement bridge, RB1 to RB4...
...Resistor (RBt is resistance gauge) that constitutes the arm of the measurement bridge, A1 ...Differential amplifier, A2...
...Summing amplifier, R1-R4...Resistor, RV...Variable resistor, EB...Power supply,
S1~S4...Switch.

Claims (1)

[Claims] 1. A DC balanced bridge including a strain gauge on one side of the component arm, a differential amplifier A1 having the balanced outputs of this balanced bridge as positive and negative inputs, respectively, and the midpoint of which is connected to a common potential point. a first switching circuit S1 that supplies the output voltage of the DC power supply to the balanced bridge; a variable resistor Rv that obtains a positive or negative resistance-divided voltage output from the DC power supply; A second switching circuit S2 that opens and closes the output; and one or more resistors R4 and R4' that receive positive and negative DC voltages from the DC power source and switches S4a and S4b that are switched by operation, and select the DC voltage. a calibration circuit configured such that the selected polarity is guided to the output via a selected resistor; a third switching circuit S3 that opens and closes the output of this calibration circuit; an amplifier A2 that adds or subtracts the output of the second switching circuit S2 and the output of the third switching circuit S3, and sends the result to the output terminal OUT;
The unbalanced output that appears at the output terminal OUT when the first switching circuit S1 is closed before mechanical strain is applied to the strain gauge is the same as the unbalanced output that appears at the output terminal OUT when the second switching circuit S2 is closed. is canceled by adjusting the variable resistor RV, and appears at the output terminal OUT with the first switching circuit S1 and the second switching circuit s2 closed when mechanical strain is applied to the strain gauge. The measurement output is measured based on the output of the calibration circuit that appears at the output terminal OUT when the third switching circuit S3 is closed with the first switching circuit s1 and the second switching circuit S2 open. A strain measuring instrument characterized in that it is configured to