JPH06289066A - Ac input measuring apparatus - Google Patents

Abstract

PURPOSE:To realize an apparatus which can accurately measure an effective value or a mean value for a short measuring period even if a period of an input AC is varied without using a highly sophisticated apparatus such as a phase synchronous oscillator. CONSTITUTION:An apparatus for finding an effective value or a means value by a summation averaging method with the output of an analog/digital converter 2 for converting an AC input to be measured into a digital signal according to a sample clock comprises a D-type flip-flop 10 receiving at its clock terminal a signal corresponding to the period of the input to output a signal of a high level for a period of integer magnification of the period of the input to supply the sample clock to the converter 2 through a gate for a period of the high level of the output signal of the flip-flop 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring an effective value or an average value of an alternating current signal, and more particularly, to obtain an effective value or an average value of an alternating current input by a sum averaging method by a digital sampling method. The present invention relates to a measuring device.

[0002]

2. Description of the Related Art In the case where the effective value or the average value of an AC input is measured by a sum averaging method using a digital sampling method, when the measurement cycle is not an integral multiple of the cycle of the signal under measurement, as shown in FIG. An error E is produced. In addition, in FIG. 3, T represents a measurement period.

In order to eliminate the error caused by the difference between the measurement cycle and the cycle of the waveform of the AC input to be measured, the following method has been conventionally used. A phase-locked oscillator that causes the sampling frequency generated in the measuring instrument to follow the frequency of the measured input is used. The measurement is performed over many cycles of the measured input to reduce the error. The period of the input to be measured is measured and the measurement period is determined. However, this means must use a high-grade phase-locked oscillator that performs a tracking operation over a wide frequency range. In the other means, the measurement cycle becomes long, and in the means, there is no simultaneity between the cycle of the input to be measured and the measurement period.
Therefore, when the cycle of the measured input changes, the measurement period does not become an integral multiple of the cycle of the measured input. However, none of the conventional solutions have been satisfactory.

SUMMARY OF THE INVENTION An object of the present invention is not to use a high-quality phase-locked oscillator or the like, and even if the period of the input to be measured changes, the effective value or average value can be accurately measured in a short measurement period. It is to realize a measuring device capable of measuring a value.

[0004]

The present invention comprises an analog-to-digital converter for converting an AC input to be measured into a digital signal according to a sample clock.
In a device in which the effective value or the average value of the AC input is obtained from the output of the digital converter by the sum averaging method, a signal corresponding to the cycle of the AC input is applied to its clock terminal to obtain an integer of the cycle of the AC input. Equipped with a D-type flip-flop that outputs a high level signal for twice the period,
The output signal of the flip-flop is configured to supply the sample clock to the analog-to-digital converter via the gate during the high level period.

[0005]

According to the present invention as described above, the high level period of the output signal of the flip-flop is an integral multiple of the period of the input AC to be measured.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings by taking an example of an apparatus for measuring an effective value of an AC input to be measured. FIG. 1 is a circuit diagram of an embodiment of an effective value measuring device according to the present invention. In the figure, in indicates an AC input to be measured. Reference numeral 1 is an input circuit for converting the input in into a voltage having an appropriate value, and 2 is an analog / digital converter for sampling and holding the output of the input circuit 1 to convert it into a digital signal (hereinafter referred to as an A / D converter). Is. 3 is an A / D converter 2
Based on the instantaneous output value of
It is a digital signal processor that calculates the effective value of the input to be measured by performing the calculation of.

[Equation 1] In Expression 1, n represents the number of samples, and vn represents the instantaneous value of the measured AC input. Reference numeral 4 is a microprocessor (hereinafter referred to as CPU) which controls the entire circuit and causes the display unit 5 to display the effective value waveform obtained by the digital signal processor 3.

Reference numeral 6 is a sample clock oscillator, and 7 is an AND gate. The output of the sample clock oscillator 6 is applied to the gate 7 as one input, and the output of the gate 7 is applied to the A / D converter 2 as the sample clock. Reference numeral 8 is a waveform shaping circuit, the input end of which is connected to the output end of the input circuit 1. Reference numeral 9 is a temporary measurement time generator that outputs a high level signal for a certain period, and 10 is a waveform shaping circuit 8.
Is connected to the CK (clock) terminal, the output terminal of the temporary measurement time generator 12 is connected to the D terminal, and the output terminal Q
Is a D-type flip-flop connected to the other input terminal of the AND gate 7 (hereinafter referred to as D-FF). The operation of the device of the present invention having such a configuration will be described with reference to the waveform chart of FIG.

FIG. 2A shows the waveform of the input AC in which is measured. This AC input in is input via the input circuit 1 to A /
It is added to the D converter 2. The A / D converter 2 is the input circuit 1
Is converted into a digital signal, and the converted digital signal is added to the digital signal processor 3 to perform the digital calculation shown in the equation (1), and the effective value is obtained by the sum averaging method. The waveform shaping circuit 8 is the input circuit 1
The waveform of the input AC in obtained via the signal is shaped, and a square wave signal corresponding to the cycle of the input AC in is output as shown in FIG. The output of this waveform shaping circuit 8 is D-FF.
10 CK terminals.

On the other hand, the tentative measurement time generator 9 generates a high level signal for a certain period at the timing shown in FIG. 2C, and this high level signal is D of the D-FF 10.
Added to the terminal. The D-FF 10 has its Q output waveform, as shown in FIG. 2D, the next waveform shaping circuit applied to the CK terminal after the output of the temporary measurement time generator 9 applied to the D terminal becomes high. 8 goes high at the rising edge of the output, the output of the temporary measurement time generator 9 goes low, and then goes low at the next rising edge of the waveform shaping circuit 8. The output of the D-FF 10 is applied to the AND gate 7 as a gate control signal.

The sample clock oscillator 6 oscillates a clock as shown in FIG. 2E, and this clock is applied to the AND gate 7. This clock is DF
While the Q output of F10 is at the high level, it passes through the gate 7 as shown in (v) of FIG. The clock that has passed through the gate 7 is added to the A / D converter 2 as a sampling signal. The A / D converter 2 samples the output of the input circuit 1 with this clock and converts the input AC in into a digital signal.

Here, in the present invention, the D-FF 10
The output signal of the waveform shaping circuit 8 applied to the CK terminal of corresponds to the cycle of the input alternating current in to be measured, and the AND gate 7 is opened for an integer multiple of this cycle to convert the sample clock into an A / D converter. Since the input alternating current in is digitally converted by being given to 2, the measurement cycle is an integral multiple of the cycle of the input alternating current waveform to be measured, and the error E as shown in FIG. 3 does not occur. The effective value measured in this way is CP
It is displayed on the display 5 under the control of U4.

In the above-mentioned embodiment, the device for measuring the effective value has been described, but in the circuit of FIG. 1, the digital signal processor 3 performs the calculation of the following formula 2 when the number of samples is n, and the input is performed. If an apparatus for obtaining an average value of AC in is used, the apparatus of FIG.
An average value measuring device for measuring the average value of

[Equation 2]

[0013]

According to the present invention, the sample clock is configured to be input to the analog-to-digital converter for a period that is an integral multiple of the period of the input AC waveform to be measured.
The measurement cycle is an integral multiple of the cycle of the input waveform to be measured, and it is possible to obtain an apparatus in which no error occurs due to the measurement cycle. Moreover, since an expensive phase-locked oscillator is not required, the measurement time is short, and the period measurement of the input waveform and the measurement period of the measured input are synchronized, the measurement period is always input even if the period of the input waveform changes. The relationship is an integer multiple of the waveform period.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a measuring apparatus of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the measuring device in FIG.

FIG. 3 is a waveform diagram for explaining the operation of a conventional measuring device.

[Explanation of symbols]

 2 analog-digital converter 6 sample clock oscillator 8 waveform shaping circuit 10 D-type flip-flop

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Shioda 2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa Electric Co., Ltd.

Claims (2)

[Claims] 1. An effective value of an AC input to be measured, comprising an analog-digital converter for converting an AC input to be measured into a digital signal according to a sample clock, and an output of the analog-digital converter being summed and averaged. In a device for determining the above, a signal corresponding to the cycle of the AC input waveform to be measured is applied to its clock terminal to output a high level signal for a period of an integral multiple of the cycle of the AC input waveform. A flip-flop is provided, and the output signal of the flip-flop is gated to the analog
An AC input measuring device, characterized in that it is arranged to supply a sample clock to a digital converter. 2. An analog-to-digital converter for converting an AC input to be measured into a digital signal according to a sample clock, and an average value of the AC input to be measured by a sum averaging method from an output of the analog-digital converter. In a device for determining the above, a signal corresponding to the cycle of the AC input waveform to be measured is applied to its clock terminal to output a high level signal for a period of an integral multiple of the cycle of the AC input waveform. A flip-flop is provided, and the output signal of the flip-flop is gated to the analog
An AC input measuring device, characterized in that it is arranged to supply a sample clock to a digital converter.