JPH055504Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to a resistance meter that uses alternating current as a measurement signal source.

[Conventional technology]

There are two types of measurement signal sources for resistance meters: those using alternating current and those using direct current. As an example of the former, a resistance meter having a configuration as shown in FIG. 4 is generally known.

That is, it is equipped with, for example, a 1kHz oscillator 1 as a measurement signal source, and its output is connected to a photocoupler 2.
The signal is applied to the waveform shaper 3 via the waveform shaper 3, and is shaped into an approximate sin waveform. The sinusoidal AC signal shaped by the waveform shaper 3 is made into a constant voltage by the automatic gain controller 4, and then the voltage /
The current converter 5 converts the signal into a constant current signal for measurement, and the signal is applied to the resistor 6 to be measured.

This constant current signal causes an AC voltage proportional to the resistance value of the resistor 6 to be measured to be generated. This AC voltage is applied to the isolation transformer 7, for example.
The signal is applied to the amplifier 8 via the signal line, and is input to the detector 9 as a detected wave signal.

For example, a branched output from the oscillator 1 is given to the detector 9 as a control signal for synchronous detection. The detector 9 uses the given branch signal to
In one half cycle, for example, the (+) side of the test signal input from the amplifier 8 is detected, and in the other half cycle, the (-) side of the test signal is detected. . The two detection outputs thus obtained are added in time series within the detector 9 to form a full-wave rectified waveform.

The detected output is, for example, removed by a filter 10 to remove its pulsating current component and becomes a substantially flat DC signal voltage, which is digitally converted via an integral type A/D converter 11 having a clock oscillator 13, and then converted to a digital signal by a measuring section 12. is input. Measuring section 12
, the resistance value of the resistor to be measured 6 is calculated from this input data and displayed on a display (not shown) or the like.

[Problem that the invention attempts to solve]

In this type of resistance meter, if the pulsating flow component is to be sufficiently removed from the detected output, the configuration of the filter 10 becomes complicated and the price becomes high. Therefore, in general, the integration time of the A/D converter 11 is set to be a common multiple of, for example, the repetition period of the clock pulse of the clock oscillator 13 and the repetition period of the output of the oscillator 1. be. If you set it like this,
At the time when the A/D converter 11 finishes counting a predetermined number of clock pulses and reverses from integration to inverse integration, the output phase of the oscillator 1 is 0 or
2π, 4π, etc., and the pulsating current component included in the output of the filter 10 no longer affects the final integrated voltage of the A/D converter 11.

However, if the internal temperature of the device rises, for example due to the start of operation, the two oscillators 1 and 13
It is difficult to keep the frequency constant,
In general, it varies according to the respective temperature characteristics.
For this reason, the above setting conditions may be violated, and when the integration period ends after counting a predetermined number of clock pulses, the output phase of the oscillator 1 does not become zero, and pulsating flow components may be integrated. Since the magnitude of the pulsating flow component due to this phase shift changes with frequency fluctuations, it not only causes errors in the digitally converted data depending on its degree, but also causes the data itself to fluctuate each time it is converted, making high-precision measurement difficult. There was a drawback of doing so.

This idea was created in view of the above points, and its purpose was to create a highly accurate system that would prevent the integrated voltage of the A/D converter from being affected even if the oscillator frequency fluctuates due to temperature rise, etc. Our goal is to provide resistance meters.

[Means for solving problems]

Referring to FIG. 1, which shows an embodiment of this invention, in order to solve the above problems, in this resistance meter, the AC signal for measurement and the clock signal for digital conversion are obtained from the same signal source. It is being done. That is, a clock oscillator 20 is provided for digital conversion, and its output is given as a clock signal to an A/D converter 29, and the frequency of the clock signal is divided into a predetermined frequency by a frequency divider 21, and the divided output is In this case, the signal is applied to the resistor 6 to be measured as an AC signal for measurement, and to the detector 27 as a control signal for synchronous detection.

[Effect]

In the above embodiment, since the synchronous detection control signal is obtained by frequency-dividing the output of the clock oscillator 20, when the frequency of the clock signal changes due to temperature rise, etc., the frequency division ratio of the frequency divider 21 changes. The synchronous detection control signal changes accordingly, and the ratio of both frequencies is constant. As a result, the final integrated voltage of the A/D converter 29 is no longer affected by the pulsating current component.

〔Example〕

This invention will be explained in detail below with reference to the embodiment shown in FIG. 1 above.

In this embodiment, clock oscillator 20 is provided as a common signal source as described above. The frequency of this clock oscillator 20 is
The clock signal is determined in consideration of the conversion speed required by the D converter 29, and the clock signal is, for example, an A/D converter.
It is added to converter 29 and frequency divider 21. In the frequency divider 21, this clock signal is frequency-divided by a predetermined frequency division ratio, and this frequency-divided output is applied, for example, as an AC signal for measurement to a waveform shaper 23 via a photocoupler 22, and also as a synchronous detection control signal. It can also be added to the detector 27 as a signal.

The AC signal input to the waveform shaper 23 is shaped into an approximate sine waveform with few harmonic components, and is converted into a voltage signal with a constant amplitude by the automatic gain controller 24 in the next stage, for example, and then sent to the voltage/current converter 25. Added. In the voltage/current converter 25, a current signal with a constant amplitude is formed from the voltage signal with a constant amplitude, and is supplied to the resistor 6 to be measured as a constant current signal for measurement. This results in
A voltage proportional to the resistance value is generated in the resistor 6 to be measured. This voltage is inputted to an amplifier 26 via, for example, an isolation transformer 7, and its output is applied to a detector 27 as a wave signal to be detected.

The detector 27 includes, for example, a non-inverting amplifier 31, an inverting amplifier 32, an analog switch 33, and a summing amplifier 34, as shown in FIG.
The divided output e _k from the frequency divider 21 is applied to the analog switch 33 as a synchronous detection control signal. This detector 2
7, the non-inverting amplifier 31 is connected to the amplifier 26
For example, if the detected wave signal e ₁ is added to the signal e 1 , then the relationship between the outputs e ₂ to e ₆ of each stage and the final output e ₀ sent from the detector 27 to the filter 28 and the synchronous detection control signal e _k is as follows: is as shown in FIG.

The output from the detector 27 has its pulsating current components removed by a filter 28, becomes a substantially flat DC voltage, and is input to the A/D converter 29.

Since the AC signal for measurement sent out from the frequency divider 21 is obtained by dividing the frequency of the clock oscillator 20 as described above, the integration time of the A/D converter 29 is equal to the AC signal for measurement, that is, the synchronous detection. If it is set to an integral multiple of the repetition period of the control signal e _k , even if the clock signal fluctuates, the phase of the synchronous detection control signal e _k , that is, the phase of the output _e0 of the detector 27, will be the same at the end of the integration time. 0 or 2π, 4π…
..., and the pulsating flow component included in the converted signal is A/
It does not affect the integrated voltage of the D converter 29.
Note that when the clock signal fluctuates, the integral time changes proportionally, so the magnitude of the integral voltage changes proportionally, but the inverse integral time also changes in the same proportional relationship, so the change in the integral voltage is canceled out during the inverse integral period. , the converted data sent from the A/D converter 29 remains constant.

The measuring unit 30 calculates the resistance value of the resistor to be measured 6 from the above conversion data, and displays it on a display (not shown) or the like as in the conventional device.

〔effect〕

As explained above in detail, the resistance meter according to this invention has a clock oscillator that provides a clock signal to the A/D converter, and the AC constant current signal for measurement flowing through the resistor to be measured and the detector. The synchronous detection control signal to be added is formed by frequency-dividing the clock signal at a predetermined frequency division ratio.

Therefore, even if the clock signal fluctuates due to a rise in the temperature of the equipment, etc., the integrated voltage of the A/D converter will not be affected by the pulsating current component contained in the output of the detector, and will always be accurate. This allows you to obtain stable digital conversion data and perform highly accurate resistance measurements.

[Brief explanation of the drawing]

Figures 1 to 3 relate to embodiments of the resistance meter according to this invention, with Figure 1 being a block diagram showing an example of its configuration, and Figure 2 showing the configuration of the detector shown in Figure 1 above. A circuit diagram showing an example, FIG. 3 is a waveform diagram for explaining input and output signals of the detector, and FIG. 4 is a block diagram showing the configuration of a conventional device. In the figure, 6 is the resistor to be measured, 20 is the clock oscillator, 21 is the frequency divider, 27 is the wave detector, and 29 is the A/D.
The converter 30 is a measuring section.

Claims (1)

[Scope of Claim for Utility Model Registration] An AC signal source that causes a constant AC current for measurement to flow through a resistor to be measured, and a control signal from the AC signal source that generates an AC voltage in the resistor to be measured by the AC constant current. A resistor that has a detector that performs synchronous detection and an integral type A/D converter that converts the detected output of the detector into digital, and that determines the resistance value of the resistor to be measured from the conversion data of the A/D converter. The meter is equipped with a frequency divider that divides the clock frequency of the A/D converter to a predetermined value, and the frequency divider is used as an AC signal source that supplies an AC constant current for measurement to the resistor to be measured. A resistance meter featuring: