JP3002078B2 - Distortion amount measurement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strain measuring circuit using a strain gauge bridge circuit (hereinafter, referred to as a bridge circuit).

[0002]

2. Description of the Related Art Conventionally, in this kind of distortion amount measuring circuit, a DC power supply is used as a bias power supply of a bridge circuit, and an output signal thereof is amplified by a high-performance DC amplifier (a chopper amplifier or the like). There is a type in which an output signal is AC-amplified using a wave AC power supply and then demodulated using a detection circuit and a smoothing circuit.

[0003]

However, the former is very expensive in terms of cost, and the latter also has disadvantages such as zero point fluctuation after the detection circuit and the circuit becoming complicated and susceptible to noise. Was.

An object of the present invention is to provide a distortion measuring circuit free of such inconvenience.

[0005]

In order to solve this problem, a distortion amount measuring circuit according to the present invention uses an output signal of a strain gauge bridge circuit connected to an AC power supply to two independent signals via an AC amplifier. The sample-and-hold circuit alternately samples and holds the output signal of the AC amplifier every half cycle so as to match the polarity of the AC power supply voltage, and has a function of integrating the difference between the two outputs. It is configured to be obtained by a differential amplifier.

[0006]

According to the above configuration, the AC-amplified output signal is efficiently demodulated to a DC output having the same amplitude value by two independent sample-hold circuits and a differential amplifier having an integrating function. It is possible to realize a distortion amount measuring circuit which is low-cost and relatively simple, has no zero point fluctuation, and has good noise resistance performance.

[0007]

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

FIG. 1 is a block diagram of the present invention.
1 is a bridge circuit which is connected to a square wave AC bridge power supply 2 and generates a resistance value by receiving a mechanical distortion, 3 is an AC (differential) amplifier, 4 and 5 are square wave output signals having different phases and the same polarity. , A sample-and-hold circuit that independently samples and holds, 6 is a differential amplifier having an integration function, and 7 is a sampling timing circuit that generates a sampling pulse in synchronization with the voltage phase of the square-wave AC bridge power supply 2.

The operation of the distortion amount measuring circuit configured as described above will be described with reference to FIGS.

FIG. 2A shows a voltage waveform (frequency f1) of the square-wave AC bridge power supply 2, in which a square-wave bias voltage of the same level (+ V) having a phase difference of 180 ° is applied to the bridge circuit 1. I have. As an example of mechanical distortion, a sinusoidal distortion amount (frequency f0) as shown in FIG.
Is received by the bridge circuit 1 and its output is amplified by the AC (differential) amplifier 3, f1 becomes a square wave AC output signal demodulated by f0 as shown in FIG. Is input to

The sample and hold circuits 4 and 5 are provided with a sampling pulse generated by a sampling timing circuit 7 synchronized with the square-wave AC bridge power supply voltage.
By (D), the peak value of the in-phase square wave voltage is held, and the waveform output signal of the + side envelope and the − side envelope as shown in FIG. 2 (E) is obtained.

The differential amplifier 6 having an integrating function is composed of
The difference between the two output values, that is, the values of (1)-(2) in FIG.

FIG. 3 is a specific circuit example of the sample-and-hold circuits 4, 5 and the differential amplifier 6. FETs Q1 and Q2 and a capacitor C are connected to the inputs of two differential AMPs (gain = 2).
1 and C2, a sample and hold circuit is provided.
4 forms an extremely simple circuit configuration forming an integrating circuit.

Further, the bridge power supply frequency (f1) in the present embodiment is set to about 10 kHz, has a sufficiently large resolution with respect to the frequency of the distortion force (f0 = 0 to 300 Hz), and has a high resolution. The function suppresses sampling noise and disturbance noise to extremely low levels.

FIGS. 4A and 4B schematically show a square-wave AC bridge power supply according to the present invention. At the frequency f1, the switch S is set to + V (Sa side) and GND.
(Sb side), and the signal is supplied to the bridge circuit. In the state where the bridge circuit has no distortion force (when there is no signal), the resistance values of the respective strain gauges R constituting the bridge are equal, and the c and d output points are zero potential (hereinafter referred to as GND).
Is always kept at + V / 2.

The bridge circuit is subjected to a distortion force, and the opposite 2
When the number of strain gauges becomes R + Δr, the output c,
d becomes Δev and −Δev at points Sa and Sb, respectively, centered on the + V / 2 value.
Output 0 is {Δev − (− Δev)} · A = 2Δev
A: That is, a bridge output twice as large as that of the conventional DC bias method is obtained. Needless to say, a circuit corresponding to the switch S is, for example, an output inversion type C-MOS. IC
It can be easily realized by using.

Although the above embodiment has a circuit configuration using a single power source, the basic operation is the same even when two positive and negative power sources are used, and only the reference voltage is different.

Further, although a square wave AC voltage is used as a bias power supply for the bridge circuit, any other AC waveform of the present invention can be used if the sampling timing is arranged at a fixed point of the AC peak value. The goal is achieved.

[0019]

As described above, according to the present invention, the AC voltage is crossed and symmetrical with respect to the bridge circuit so that the output point of the bridge circuit is always at a constant level with respect to the GND (zero potential) level. In addition to the characteristic that there is no output offset and the bridge output sensitivity is doubled because of the AC amplification and the simple demodulation circuit,
It is possible to realize a low drift, low noise distortion amount measurement circuit at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a distortion amount measuring circuit according to the present invention.

FIG. 2 is a waveform chart at each point.

FIG. 3 is a specific circuit diagram of a main part of FIG. 1;

FIG. 4 is a schematic diagram of a square-wave AC bridge power supply, which is a main part of the same.

[Description of Signs] 1 Strain gauge bridge circuit 2 Square wave AC bridge power supply 3 AC amplifier 4,5 Sample hold circuit 6 Differential amplifier 7 Sampling timing circuit

Claims (3)

(57) [Claims] An output signal of a strain gauge bridge circuit connected to an AC power supply is supplied to two sample-and-hold circuits independent from each other via an AC amplifier, and the output signal of the AC amplifier is supplied to the AC power supply by the sample-and-hold circuit. A distortion measuring circuit which alternately samples and holds every half cycle so as to match the polarity of the voltage, and obtains the difference by a differential amplifier which integrates a difference between these two outputs. 2. The distortion according to claim 1, wherein the AC power supply voltage is applied to the bridge in a crosswise and symmetric manner so that the output point of the strain gauge bridge circuit does not fluctuate with respect to the zero potential level. Quantity measurement circuit. 3. The distortion amount measuring circuit according to claim 1, wherein the AC power supply applied to the strain gauge bridge circuit is a square wave AC voltage.