SU1709261A1 - Method of voltmeter calibration testing of root-mean-square value - Google Patents

Abstract

The invention relates to electrical measuring technology and can be used when calibrating a rms meter voltmeter in the mode of measuring a low-frequency voltage of an arbitrary shape with a zero constant component. The purpose of the invention is to improve the accuracy of calibration in the specified voltage measurement mode with a given root-mean-square value (RMS) and amplitude coefficient (KA). limited preset value. A sample voltage without a constant component with a given RMS and limited KA is applied to the input of the voltmeter, and it is measured. The error modulus of the measurement result is determined and stored. The entire sequence of operations is repeated many times, each time before applying the three-level model voltage, different values of its levels are set, and its RMS is maintained equal to the specified one. From the stored error modules, the maximum is selected and set as the limit of permissible error in the specified mode. 2 il. ^

Description

The invention relates to the technique of electrical measurements and is intended for use in the calibration of voltmeters of the rms value in the mode of measuring a low-frequency voltage of arbitrary shape with a zero constant component. ,

The purpose of the invention is to improve the accuracy of verification in the voltage measurement mode of arbitrary shape with a zero constant component with a given root-mean-square value and an amplitude factor limited by a given value of Kamax.

FIG. Figure 1 shows a block diagram of a device for carrying out the proposed method for calibrating a rms voltmeter: FIG. 2 is an example of an exemplary three-level voltage.

The device contains (Fig. 1) serially connected computers 1, interface 2, a precision digital-to-analog converter (DAC) 3 and a calibrated voltmeter 4. A connection between the calibrated voltmeter 4 and the computer 1 exists if the digital voltmeter of the root-mean-square value has a code value There is no output, or it is not present if the digital voltmeter being calibrated does not have a code output or if the analog voltmeter is turned.

The proposed method is carried out as follows.

E.VM 1 calculates the parameters of an exemplary three-level voltage with a zero constant component (Fig. 2), the root-mean-square value of which is equal to Uc, and the amplitude does not exceed Dm. The initial data for the calculation are the values of the levels Ui, Uj and Uk lying within ± Um.

Since the rms value of the reference voltage is Uc, i.e.

 + (1-Pl-P2) Uc.

and the mean is zero:

UiPi + UjP + Uk (1-Pi-P2H. Then, taking into account the system of these two equations, the values of Pi and P2 (Fig. 2) are calculated by the computer1 by the expressions:

Ug + U Uk

(U | -U) (Ui-Uk)

Ug-bUjUk (Uk-Uj) (Ui-U)

Physically realizable is a three-level voltage, in which O PI S 1; A: P2 $ 1;

Therefore, if the specified conditions are not met, then such a set of levels Ui, U) Uk is not used.

Next, using the software timer, computer 1 via interface 2 supplies control codes to the DAC 3 in such a way that the code corresponding to the voltage Ui enters the input of the DAC 3 during the PiT time interval, the code corresponding to the voltage U - during the time interval P2T, and the code corresponding to the voltage Uk - during the time interval (1-P1-P2) T. The period T of the reference voltage is chosen to correspond to the lower limit of the operating frequency range of the voltmeter being turned 4.

The three-level voltage under consideration has a spectrum consisting of an infinite number of harmonics, whose amplitude tends to zero with increasing harmonic number.

When using an exemplary three-level low-frequency voltage, the frequency errors of a calibrated voltmeter can be neglected, resulting in high harmonics, because of their smallness.

 The calibrated voltmeter 4 measures the reference voltage, and the measurement result is input into the computer 1 (either automatically via the code output of the calibrated voltmeter 4, or if the code output does not have a code output manually). The computer 1 calculates and remembers the error of the measurement result.

Next, the computer 1 selects new values

0 levels Ui, U, Uk, lying within ± Um. and the process is repeated,

Ui values. Uj, Uk cover the entire range of possible instantaneous values of the input voltage of arbitrary shape

5 from -Um to + Um, and their change is realized. It appears with some selected step. In this range, there are also two-level voltages, i.e. in this case, the values of Ui and Uj or Uj and Uk coincide.

0 After repeating the process, the number of times required by the computer 1 selects the maximum value of the error modulus among the stored values and indicates the limit of permissible measurement error.

5 of a low-frequency voltage of arbitrary shape with a zero constant component, the root-mean-square value of which is equal to Uc, and the amplitude coefficient does not exceed Qmax.

0 The use of the invention makes it possible to strictly determine the limit of permissible error of measurement of a low-frequency voltage of arbitrary shape with a zero constant component.

Claims (1)

The invention of the method of calibration of voltmeters rms, which consists in applying to the input of a calibrated voltmeter 0 exemplary voltage with a given rms value and a limited amplitude coefficient, measuring it, determining and storing the error modulus of the measurement result, that is, in order to improve the accuracy of the calibration in the voltage measurement mode -forms with a zero constant component with a given root-mean-square value and an amplitude factor limited to a given value, use three-level voltage as the reference voltage, the entire specified sequence The sequence of operations is repeated many times. 5, each time they set a three-level voltage with a different set of levels, change the levels within the limits bounded by a given value of the amplitude coefficient with a given step, and use all possible combinations of these levels. moreover, each time the three-level voltage levels change, the ratio of the durations of the levels is changed so that the rms value of the three-level voltage is maintained at the specified value, the maximum value is chosen from the stored error modules and set as the limit of the permissible measurement error. FIG. I FIG. g