JPH0315961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a strain measurement circuit that measures the amount of strain from the output of a bridge circuit that includes a strain gauge connected to an AC power source.

Conventionally, in this type of circuit, the output signal of the bridge circuit was amplified, then demodulated using a detection circuit and a smoothing circuit, and converted into a digital quantity, but the zero point fluctuation after the detection circuit was added to the output, and There are disadvantages such as the circuit becoming complicated and being easily affected by noise, and in the case of multi-point measurement, due to the characteristics of the smoothing circuit, switching cannot be done at high speed, and when trying to measure at high speed, the amplifier and smoothing circuit etc. There was an inconvenience that made it necessary.

An object of the present invention is to provide a strain measurement circuit that does not have such inconveniences, and which supplies an output signal of a predetermined circuit including a strain gauge connected to an AC power source to an integrator via an AC amplifier. The integrator integrates the output signal in each half period of the AC power supply voltage, the integrated voltage is sampled and held in a sample hold circuit, and the arithmetic mean of each sample and hold value in mutually adjacent half periods of the AC voltage is calculated by the calculation circuit. It is characterized by the fact that it is carried out in

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a bridge circuit connected to a bridge power supply 2 and constituted by a resistor including a strain gauge that changes resistance when subjected to mechanical strain, 3 is an AC amplifier, and 4 is an AC amplifier. An integrator that integrates the 2/3 interval input signal in each half cycle of the bridge power supply voltage, 5 a sample hold circuit that samples and holds the voltage integrated by the integrator 4 every half cycle, and 6 an A-D converter. 7 is an arithmetic circuit that averages the difference between the sample and hold values in the positive half cycle and the negative cycle of the bridge power supply 2, and 8 is the integrator 4, sample and hold circuit 5, and arithmetic circuit 7, which will be described in detail later. This is a control circuit for performing such predetermined operations.

Next, to explain its operation, the output signal of the bridge circuit 1 is a signal modulated by the voltage of the bridge power supply 2 (Fig. 2A), which is amplified by the AC amplifier 3 and input to the integrator 4 (Fig. 2B). ). This integrator 4 integrates the 2/3 interval input signal in each half period of the bridge power supply voltage. When the input signal is constant, the input signal is integrated in the positive and negative directions each half period to a voltage V _I proportional to the input signal, as shown in FIG. 2C. Integral voltage V _I , −V _I
is sampled and held by the sample-and-hold circuit 5 (FIG. 2D), and then A-D converted by the A-D converter 6 to become a digital value, which is input to the arithmetic circuit 7. The arithmetic circuit 7 inverts the polarity of the digital value (V _I ) during the negative cycle of the bridge power supply voltage, and converts the digital value (V _I +
ΔV) and then divide by 2.

This ΔV is the drift voltage due to the zero point fluctuation after the integration circuit 4, and the above calculation process yields (V _I +ΔV)−(−V _I +ΔV)/2=V _I , resulting in an output signal from which the drift voltage has been removed. A proportional voltage is output.

When the output signal of the bridge circuit 1 contains the third harmonic H of the bridge power supply voltage as shown in FIG. Therefore, the third
As shown in Figure B, the third harmonic is removed by canceling the positive and negative waves.

In the above embodiment, the A/D conversion circuit 6 is used to convert the data into digital quantities, but the analog quantities may also be processed by the arithmetic circuit.

According to the present invention, the output signal of the bridge circuit is supplied to the integrator via the AC amplifier,
The integrator integrates the output signal in each half period of the AC power supply voltage, the integrated voltage is sampled and held in a sample hold circuit, and the arithmetic mean of each sample and hold value in mutually adjacent half periods of the AC voltage is calculated by the calculation circuit. Since this is carried out, drift voltage can be removed, and the influence of noise is also reduced. Furthermore, in the case of multi-point measurement, by inserting a switching device on the input side of the AC amplifier 3, it is sufficient to provide only one amplifier, etc., which has the effect of simplifying the configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
Figures A, B, C and D are waveform diagrams at various parts of the circuit shown in the first figure, and Figures A and B are operation explanatory diagrams. 1...Bridge circuit including strain gauge, 2...
... Bridge power supply, 3 ... AC amplifier, 4 ... Integrator, 5 ... Sample hold circuit, 6 ... A-D
Converter, 7... Arithmetic circuit, 8... Control circuit.

Claims (1)

[Claims] 1. The output signal of a bridge circuit including a strain gauge connected to an AC power supply is supplied to an integrator via an AC amplifier, the output signal is integrated in each half period of the AC power supply voltage by the integrator, and the integrated voltage is A distortion measurement circuit characterized in that a sample and hold circuit performs sample and hold, and an arithmetic circuit calculates the arithmetic average of each sample and hold value in half cycles of adjacent AC power supplies.