JPS5912562Y2 - Calibration circuit for strain measurement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain measurement calibration circuit that is comprised of two calibration resistors, one bridge power supply, and two switches for switching between them.

Conventional methods for calibrating strain measuring instruments include the parallel resistance method, reference voltage insertion method, and double bridge method.

Figure 1 is a circuit diagram showing an example of a calibration method using the conventional parallel resistance method, in which 1 is a Wheatstone strain gauge. ridge, 2 is a bridge power supply, 3 is an amplifier, r is a calibration resistor, and S1 is a calibration switch.

Figure 2 is a circuit diagram showing an example of a calibration method using the conventional reference voltage insertion method, where r2, r3, r4, r5, and r6 are calibration resistors, S2 and S3 are measurement and calibration switches,
When S2 and S3 are selected to the a side, the measurement state is entered, and when they are set to the b side, the calibration state is entered.

Figure 3 is a circuit diagram showing an example of a calibration method using the conventional double bridge method, where 4 is a calibration bridge power supply, r7, r8, r
9, rto, rll are calibration resistors, and S4 is a calibration switch.

The parallel resistance method has the disadvantage that the calibration value changes depending on the gauge resistance and that calibration during measurement is difficult.

The reference voltage insertion method has the disadvantage that the operation method is more complicated than other methods, and the calibration value changes depending on the gauge resistance.

The double bridge method is the most widely used, and its calibration value is constant regardless of the resistance value of the strain gauge, and calibration can be performed even during measurement, but it requires a bridge power source for calibration. However, if there is a zero point fluctuation in the calibration Wheatstone bridge, it has the disadvantage of inducing measurement errors.

A common drawback of these conventional techniques is that the power source for the Wheatstone bridge, which is constructed from strain gauges, is either a constant voltage source or a constant current source (when the distance to the strain gauge is long, a constant current method is used).

), it had the disadvantage that it could not be used without some kind of circuit modification.

In order to eliminate the drawbacks of these conventional strain measurement calibration circuits, the present invention allows the bridge power supply for strain gauges to be used in either a constant voltage source or a constant current source, and is accurate with a simple circuit configuration. The present invention aims to provide a calibration circuit for strain measurement that allows accurate calibration.

FIG. 4 is a circuit diagram of an embodiment of the present invention, in which Ss, S
s is a bridge power supply changeover switch, and R1 and R2 are calibration resistors.

Figure 5 is an equivalent circuit diagram when S5 and S6 are switched to the a side in Figure 4, that is, when strain is measured, and Figure 6 is an equivalent circuit diagram when S5 and S6 are switched to the b side in Figure 4, that is, during calibration. FIG.

During strain measurement shown in FIG. 5, the bridge power source excites the Wheatstone bridge 1, while during calibration shown in FIG. 6, the bridge power source forms a closed loop circuit with the calibration resistor RLR2.

Because of this structure, if the bridge power supply is a constant voltage source and its output voltage is E in FIG. 6, a calibration voltage is generated to be input to the amplifier 3.

Similarly, if the bridge power supply is a constant current source, and its output current is I, a calibration voltage R2I is generated.

The calibration resistor R2 is set so that the calibration voltage generated in the case of these constant voltage sources and the calibration voltage R2I generated in the case of the constant current source are equal to each other. , R2 can be used in common, regardless of whether the bridge power source is a constant voltage source or a constant current source.

That is, in Fig. 6, the calibration voltage generated during calibration is determined as e, and if we first consider the case where the bridge power supply is a constant current source, its output current is preset to a value ■ that is advantageous for strain measurement. Therefore, the value of the calibration resistor R2 is determined as follows.

On the other hand, if we consider the case where the bridge power supply is a constant voltage source, the calibration voltage e has the relationship as described above, and when we calculate R1 from equation (2), we get (3)
Substituting equation (1) into the equation to find R1, we get:

Based on this relationship, the bridge power supply voltage E, the calibration voltage e, the calibration resistor R. , R2, the same calibration circuit can be used regardless of whether the strain gauge excitation bridge power source is a constant voltage source or a constant current source.

Since the strain measurement calibration circuit of the present invention has the structure described above, it has the following effects.

(1) In FIG. 6, if the input impedance of the amplifier 3 is set to be sufficiently larger than the sum of the calibration resistor R2 and the output resistance of the Wheatstone bridge 1, accurate calibration that is not affected by the resistance value of the strain gauge becomes possible.

(2) As is clear from FIG. 6, when the calibration according to the present invention is performed, the Wheatstone bridge 1 is not excited, so the calibration value is not affected by the resistance of the gauge at all.

(3) Since the calibration circuit is not a Wheatstone bridge, there is no fluctuation in the zero point of the calibration circuit.

(4) Whether the bridge power source is a constant voltage source or a constant current source, the calibration circuit can be shared without any special changes.

(5) Even if the strain gauge is used as a multi-point input using a switch box or the like, and each gauge has a different resistance value, one calibration circuit can be used in common.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are circuit diagrams showing examples of calibration methods using the conventional parallel resistance method, reference voltage insertion method, and double bridge method, respectively, and Figure 4 shows an example of the calibration method of the present invention. 5 is an equivalent circuit diagram at the time of measurement of FIG. 4, and FIG. 6 is an equivalent circuit diagram at the time of calibration of FIG. 4. 1...Wheatstone bridge composed of strain gauges, 2...Bridge power supply, 3...
・Amplifier, 4...Bridge power supply for calibration, r1~
rll... Calibration resistor of conventional calibration circuit example, R
1, R2... Calibration resistor of the calibration circuit of the present invention,
S1-S6...Switch.

Claims (1)

[Scope of utility model registration request] An L-type attenuation circuit consisting of two resistors is inserted in series as a calibration circuit between one output terminal of a Wheatstone bridge composed of a strain gauge and one input terminal of an amplifier that amplifies the output of the Wheatstone bridge. Furthermore, during strain measurement, the strain gauge excitation bridge power supply is applied to a pair of input terminals of the Wheatstone bridge composed of the strain gauge, and strain is measured.On the other hand, during calibration, the strain gauge excitation bridge power supply is applied to a pair of input terminals of the Wheatstone bridge. By switching and applying to both ends of the pair of calibration resistors,
A calibration circuit for strain measurement, which is independent of the resistance value of a strain gauge, and is characterized in that a bridge power source for strain gauge excitation can be commonly used as either a constant voltage source or a constant current source.