SU1404997A1 - Method of testing voltmeters of mean square value of alternating current - Google Patents

Abstract

The invention relates to electrical measuring technology. A method for calibrating voltmeters (B) of the rms AC value is as follows. Measure the time interval of the averaging W of the calibrated B, calculate the values of the sequence of frequencies necessary for the calibration of B, f; (i + 1/4) W, where i - integers lying in the interval W-f min max W, where f, f / wekc lower and upper limits of the frequency range of calibration, respectively. A three-level two-pole square-wave calibration signal with a period T is formed; 1 / f; described by the expression + C p, / 4, where t T; o, T; / 4tt T; / 2, -U, T; / 2 t 3T; / 4, 0, ZT; / 4ё t.i T ;, period of the calibration signal; and - signal amplitude. The generated calibration signal is synchronized with the beginning of the interval averaging B so that the beginning of the first pulse coincides with the beginning of the measurement interval. A calibration signal with a frequency f is supplied, Bj is changed by changing the amplitude of the calibration signal at frequency f ,, by comparing the amplitude value with the readings of the scale indicator B. The calibration signals with frequencies f are applied to B, the amplitude is changed, produced; The method has a higher accuracy of calibration B. 2 Il. about fS

Description

The invention relates to electrical measuring technology and can be used in the construction of calibration systems of voltmeters of the rms computational type in the infrasonic frequency range.

The purpose of the invention is to improve the accuracy of calibration of voltmeters of the mean square value of the computational type by reducing the methodological error due to the non-multiplicity of the calibration signal period and the time interval of the averaged calibrated voltmeter.

Figure 1 shows the block diagram of a device for carrying out the method; FIG. 2 shows diagrams of a test signal (a) and a test signal squared (8).

The method is based on the fact that in the low frequency region the determining error of verification is the marginal effect error caused by the non-multiplicity of the verification signal during the averaging time interval of the calibrated voltmeter, and all other components are in absolute value Less than permissible if in the rest of the frequency range the instrument satisfies technical conditions

Thus, to calibrate computational-type voltmeters in the low-frequency range, it is sufficient to carry out the calibration, giving a calibration signal, the measurement of which results in a low-frequency error of the edge effect. For this, the test signal is selected so that the low-frequency error created by it is maximum.

The method is carried out as follows.

The averaging time interval W of the calibrated voltmeter is measured. The values of the sequence of frequencies required for calibration of the instrument are calculated using the following formula:

iilM (,. ij i

Where. i - integers lying in the interval

   Max

W,

f is the lower and upper limits of the frequency range in which the voltmeter is facing.

A three-level two-field rectangular calibration signal with a period is formed, described by the expression

U (t)

+ U

m

about / 4,

o, t; / 4 6t T; / 2,

-i, T; / 2 t.c ЗТ; / 4,

  Oh, ST; / 4, where Uj is the signal amplitude.

The generated verification signal is synchronized with the beginning of the averaging interval of the voltmeter so that the beginning of the first pulse (positive or negative) coincides with the beginning of the measurement interval.

A test signal is given to the input of the calibrated voltmeter with a frequency f, determined by the formula (1).

The instrument is calibrated by changing the amplitude of the calibration signal at frequency f, by comparing the amplitude values with the readings of the voltmeter scale indicator.

The instrument is posed by applying test signals with frequencies to the instrument input, changing their amplitude.

An apparatus for carrying out the method comprises a calibrated device 1, a frequency meter 2, a generator of 3 square-wave signals, a counter 4, a calibrating signal shaper 5, a source 6 of calibrated constant voltage, a frequency meter 7, the output of the measurement time interval of the gauge 1 being connected to the input of the frequency meter 2 and the first input of the counter 4. The output of the generator 3 is connected

the second input of the counter 4, the output of which is connected to the input of the frequency meter 7 by the first input of the imaging unit 5, the first and second outputs of which are connected to the first and second inputs of the testable device 1. The first and second outputs of the source 6 are connected to the second and third inputs of the imaging unit 5.

Shaper 5 verification signal consists of electronic keys 8

and 9, switching the calibrated constant voltage with the help of the control unit 10, which contains the inverter 11, the triggers 12 and 13, the AND-NE logic gates 14-17, the AND 18 logic element.

Moreover, the first fixed contact key 8 and the third fixed contact key 9 is connected to the second input of the imaging unit 5, the third fixed

the key contact o and the first fixed contact of the key 9 are connected to the third input of the driver 5, the second fixed contacts of the keys 8 and 9 are connected to one another, the fixed contacts of the keys 8 and 9 are connected to the first and second outputs of the driver 5. The first input of the driver 5 is connected to

the input of the inverter 11 and the C input of the trigger d to the input of the device under test 1.

12. The C-input of the trigger 13 is connected to the output of the inverter 11. The direct output of the trigger 12 is connected to the first inputs of the AND-HEY elements 14 and 15, and the inverse of the constant frequency 2f changes the amplitude of the test signal (using a constant voltage source 6 ) and produced by

49974

A constant voltage of a given amplitude from a source 6 of a constant voltage is applied to the second and third inputs of the former of the verification signal 5. p marry

The shaper 5 generates a three-level two-pole calibration signal with a frequency f that feeds 5

to the input of the test instrument 1.

Leaving the frequency 2f unchanged, the amplitude of the test signal is varied (using a constant voltage source 6) and produced

20

output output — with the first inputs to the element of the instrument — with test signals of signals NOT 16 and 17 and the D input of the trigger 12. The direct output of the trigger 13 is connected to the second inputs of the elements AND 15, 17 and the inverse output to the second inputs of elements AND 14 and 16 and D are inputs of trigger 13. The outputs of elements AND 14, 17 are connected to the first and third control inputs of keys 8 and 9. The inputs of elements 18 are connected to the outputs of elements AND 15, and 16, and the output is connected to the second control input of the keys 8 and 9.

The device works as follows.

With the help of frequency meter 2, the interval W of averaged instrument 1 is determined. Calculate the values of the pulse frequency and different amplitudes. The instrument is calibrated at frequencies f - if ,.

Claims (1)

The Invention Method A method for calibrating voltmeters with the mean square value of an alternating current, which consists in forming a calibration signal of different frequencies, serves it to the input of the voltmeter. 25. And compare the voltmeter readings with a 1.111 amplitude of the verification signal, the results of which judge the accuracy of the calibrated voltmeter, characterized in that, in order to improve the calibration accuracy of the computational voltmeters, the average time interval is measured before forming the verification signal the voltmeter W, combine the beginning of the calibration signal with the beginning of the time interval of the averaging of the voltmeter, and the frequency of the frequency of the oscillating signal is set according to the formula thirty f, - f, by The sequence of frequencies is the formula (1). The counter 4 synchronizes the generated by the generator 3 of a pulse of a rectangular shape with the beginning of the interval of time of averaging the instrument to be checked 1. The synchronization is carried out due to the fact that the generator 3 generates rectangular pulses with a frequency 2 times greater than the frequency f, determined from expression (1), where n is the counter size. Thus, at the output of the counter, a sequence of pulses is formed, phased with the beginning of the interval W with a delay Frequency and frequency .  f The counter can be selected in such a way so that the simulated error caused by the delay is negligible. The frequency of the pulses 2f at the output of the counter is monitored by a frequency meter. The generated pulse train with a frequency of 2 f is fed to the first input of the imaging unit 5 of the calibration signal. instrument test signals with frequency and different amplitude values. The instrument is calibrated at frequencies f - if ,. The Invention Method A method for calibrating voltmeters of the mean square value of an alternating current, which consists in forming a calibration signal of various frequencies, supplies it to the input of a voltmeter. and comparing the voltmeter readings with a measuring signal amplitude, which results judging the accuracy of the calibrated voltmeter, characterized in that, to increase the calibration accuracy of the computational type voltmeters, the time interval for the averaging of the voltmeter W is combined the beginning of the test signal with the beginning of the averaging time interval of the voltmeter, and the frequency of the frequency of the signal is set according to the formula  ± +1/4 W where i are integers from the interval f; W f, with i W. f Max -Min five Max the lower and upper limits of the frequency range of verification, and the form of the test signal is set according to the system of equations t; 0 u (t) v + and about -and t T, 3Tj   g - 2 t, Tgr, Oh, -f t "cT ;, where is the amplitude of the test signal; T; - the period of the test signal. S L)