SU1247765A1 - Method and apparatus for measuring root-mean-square values of voltages having arbitrary shape - Google Patents

Abstract

The invention can be used in instruments for measuring the effective value of a variable voltage. The purpose of the invention is to improve the accuracy, noise immunity and expansion of the frequency range. Alternately square the reference, which is a constant voltage, and the measured voltage. Squaring is performed for identical time intervals equal to the squaring time. In this case, a zero voltage level is formed, the first harmonic is extracted from the result of the quadration, and its initial phase is measured. A device implementing the method contains controllable keys 2 and 4, quad 3, phase measuring unit 6, reading unit 7, synchronizing unit 8 and clock generator 9. Implementing the invention reduces the error to 0.005%. In this phase, the first harmonic phase is less susceptible to interference than other signal parameters. In addition, the clock can be extended (L (PU8. 3

Description

current range of the measured voltage due to the appropriate choice of the frequency of the clock pulses relative to the frequency of the measured voltage

The invention is electrical measurements and can be used in instruments 6.x to measure the effective value of a variable voltage,

The purpose of the invention is to increase the accuracy and noise immunity and increase the frequency range by converting the rms value in the initial phase of the first voltage harmonic, formed from the reference and measured voltages.

FIG. Figure 1 shows a time diagram of the voltage generated from the reference and measured stresses; Fig. 2 shows the dependence of the initial phase of the first harmonic of the voltage shown in Fig. 2; 1, from the ratio of the frequency of the measured signal to the frequency of the first harmonic; Fig. 3 is a functional diagram of a device for measuring the RMS value of time-based voltage; in fig. A - time diagrams, in accordance with the device operation; in fig. 5- block synchronization.

:. .

The method of measuring the average values of voltages of arbitrary shape is that the reference and measured voltages form a periodic voltage, which during the third of its period is equal to the constant square of the reference voltage, during the second third of the period - the square of the measured voltage during the last third of the period is zero, after which the first harmonic is extracted from it and its initial phase is measured relative to the beginning of the last third of the period of the generated voltage,

An apparatus for carrying out the method comprises a constant voltage source 1, which through the first controlled switch 2 is connected to the input of the quadrant 3, to which

neither The method and device can be used in the case of the difference in the shape of the measured voltage from the sinusoidal, 2 pp. f-ly, 5 ill.

five

through the second control key 4 an input bus is connected. The output of the quadrant 3 through the filter 5 of the first harmonic is connected to the perpendicular input of the phase measuring unit 6, the output of which is connected to the digital readout unit 7. The control inputs of the controlled switches 2, 4 and the phase measuring unit 6 are connected respectively to the first, second and the third output of the synchronization unit 8, the input of which is connected to the output of the clock generator 9.

The essence of the method is as follows. ..

From the reference voltage of the square of the measured voltage form the voltage of the form (Fig. 1)

20

(ABOUT

25

the reference impulse and the square impulse of the measured voltage in the generated voltage;

A is the amplitude of the pulse of the reference voltage and the voltage generated;

B- is the amplitude of the measured voltage;

SI is the frequency of the measured voltage.

If T,

2

th

3

Tg

s

where t is the period of the formed p-ry;

cyclic frequency of the first harmonic,

And, you can determine the coefficients. Fourier for the first harmonic of the function (1)

U

2

B 1

Q.- | f (t) coScJt -, (t). (2)

T „.J.

. H

Initial phase of the first harmonic

equals

 B

.C arctq-1. By substituting the relations f (t) of the system (1),, transformations

/.M ..

.

em-e) - ()

fToJ UoJ

 -,)

(..I i V

h 3 i T 17

2 2 / Fsg:

HA

CHA-Y .uj

 city- / - Trsi

 l-mr-j-coSI

/,

(

Lxj

As a result of the substitution a., Equality (W), we get

12477654

after which the keys 2 and 4 are opened, and until the next clock pulse arrives from the generator 9, the voltage is open. at the input of the quad 3 is zero. 5 The output voltage of the quad (Fig. 4, g) is fed to the filter 5 of the first harmonic. The first harmonic (Fig. 4, h) is fed to the phase measuring unit 6, measuring the initial

10 is the phase of the first harmonic, which is fixed by the digital reading unit 7. The results of the experiments show that the proposed method of measuring rms values

15 AC voltage reduces the error to 0.005%. The first harmonic phase is less susceptible to interference than other signal parameters. In addition, it may be

20 . The frequency range of the measured voltage is rendered due to the appropriate choice of the frequency of the clock pulses relative to the frequency of the measured voltage.

.. 25 It can be shown mathematically that the proposed method and device can be used in different and b, in the form of the measured voltage from the sinusoidal.

(3)

(2) meaning is obtained after

icJ /

ATrS2i

lt, 1 AB (-.

-

, 2) 4 -arctg -j ------.

A.V. (.ts- |,.,).

If oJ, which is determined by the choice of the period of formed search (Fig. 1), it can be shown

g2

What do you want. the initial phase of the generated voltage is proportional to the rms value of the measured voltage. From FIG. 2 shows that it is necessary that

A device for implementing the method works as follows.

Generator 9 generates clock pulses (Fig. 4, a), arriving at block 8 of synchronization, consisting, for example, of three D-flip-flops (Fig. 5), Block 8 of synchronization for-FIpYet at the first and second outputs. . the pulses controlling the keys 2 and 4 as well as the phase-measuring unit (fig. 4 b, c, d). To the input of the quadrant, alternately, through the switch 2, the reference voltages from source 1 (Fig. 4, d) are supplied, through the switch 4-measurable voltage from the input bus (Fig. 4, e

icJ /

Claims (2)

1. A method of measuring the rms values of voltages of arbitrary shape, consisting in a-. regular squaring of the reference and measured voltages for the same time intervals, characterized in that, in order to increase accuracy, noise immunity and expand the frequency range, a constant voltage is used as the reference voltage during the time interval squares of the reference and measured voltage, form a zero level, the voltage, from the result of the square, isolate the first harmonic and measure its initial phase.  2. A device for measuring the rms values of voltages of arbitrary shape containing a quad, to the input of which the first and second controlled keys are connected, The input bus is connected to the input of the second key; to the control inputs of the keys, the outputs of the synchronization unit are connected, the input of which is connected to a clock generator output and also a digital readout block, characterized in that, in order to increase accuracy, noise immunity and expand the frequency range, a constant reference voltage source is additionally connected to the input the first controlled key, the first harmonic filter, connected between the quad output and the first input of the phase-measuring unit, the second input of which is connected to the additional output of the synchronization unit, and the output to the input of the digital reading unit. -Ti / 2 9u8. one ABOUT Ti / 2  3 ", 5 6. 7.5 9 10.5 f2 S2 / Uf Fiz. 2