SU1402951A1 - Device for measuring the mean square value of a.c.voltage - Google Patents

Abstract

The invention relates to electrical measuring equipment and makes it possible to increase the accuracy of voltage measurement. The device contains detectors 1 and 2 of mean square and mean values, source 3 of controlled voltage, controlled voltage divider 4, voltmeter E; voltage divider 7, comparator 8 and low-pass filter 9. The introduction of the functional converter 10 makes it possible to obtain an error not worse than that specified for a given set of forms of the voltage being measured. 1 il.

Description

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The invention relates to electrical measuring, engineering, and can be used when measuring the RMS values of the voltage of a single form.

The purpose of the invention is to improve the accuracy of voltage measurements,

The drawing shows a block diagram of a device for measuring the rms value of an alternating voltage.

The device contains a rms detector 1 and a rms detector 2, the inputs of which are connected to a source 3 of a monitored voltage, a rms value at the detector of a rms value through a controlled voltage divider 4 connected to a shorted 5 volt meter. the capacitor 6, the output of the detector 2 of the average value through the voltage divider 7 is connected to the first input of the comparator 8, to the second input of which the output of the controlled voltage divider A is connected. The output of the comparator 8 is through a series-connected low-pass filter 9 and a functional converter 10 connected to the control input of the controlled voltage divider 4.

The device works as follows.

With the (fixed) ratio of the shoulders of the voltage divider 4 DC, the voltage U applied to the DC voltmeter 5 corresponds to the RMS value of the monitored voltage Ug only for a certain number of functions of the distribution of the input signal. In the case of a significant change in the shape of the measured voltage, the value of Up no longer corresponds to the sought-after S-value of U. The measurement error is excluded by changing the ratio of the shoulders of the voltage divider 4 in accordance with the shape of the measured voltage. The form is determined by comparing the average direct value and estimating the RMS value of the monitored voltage using a comparator 8. The average direct value is obtained at the output of the voltage divider 7, the estimate of the rms value at the output of the controlled divider 4

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tension The ratio of these values is called the shape factor.

Previously, using a divider 7, the voltages on the inputs of the comparator 8 are set to equal voltages for a given shape of the input voltage (for example, a sinusoidal). At the same time, at the output of the comparator 8, the average value of the voltage is zero. The voltage divider 4 mode is adjusted so that the output voltage of the device corresponds to the root-mean-square value Ug. When the input waveform deviates from the one set at the output of the comparator 8, pulses appear, the mean value and polarity of which determine the control voltage at the output of the low-pass filter 9. The functional converter 10 converts the output voltage of the low-pass filter 9, corresponding to the shape factor of the measured signal, into a control voltage supplied to the control input of the controlled voltage divider 4. Since the control voltage corresponds to the shape factor, the voltage divider changes the division factor so that the measurement error is minimized.

The amplitude response of the functional converter is defined as follows.

A functional converter 10 is excluded from the device circuit, an additional DC voltmeter is connected to the output of the low-pass filter 9, an adjustable DC voltage source controlled by a voltmeter is connected to the control input of the controlled voltage divider 4.

Alternatively, sources with different voltage forms are connected alternately as the source 3 of the measured voltage. For each voltage form, the control voltage at the control input of divider 4 is changed to a measurement error equal to zero, the value of this voltage is fixed, and then the voltage at the output of the low-pass filter 9 is fixed. The dependence of the voltage values thus obtained on the control input of the divider 4 on the voltage values at the output of the low-pass filter 9 is a sought amplitude characteristic of the functional converter 10. A functional converter with such an amplitude characteristic makes it possible to obtain an error not worse than the specified measurement voltage.

Claims (1)

Invention Formula A device for measuring the quadratic value of an alternating voltage containing a mean square value detector, the input of which is connected to the input of the device, and the output is controlled by means of a controlled voltage divider connected to the input of a DC voltmeter 50 capacitor, the detector of the mean-rectified value, the input of which is connected to the input of the device, the voltage divider, the output of which is connected to the first input of the comparator, the output of the comparator is connected to the input of the low-pass filter, characterized in It has a functional converter, the input of which is connected to the output of the low-pass filter, and the output is | with the control input of the controlled voltage divider, the output of the controlled voltage divider is connected to the second input of the detector, and the detector output, the average value is connected to the input of the voltage divider.