SU1742737A1 - Method of measuring amplitude value of alternating voltage - Google Patents

Abstract

Use: in measurement technology for measuring the amplitude of electrical signals at low signal-to-noise ratios. The device implementing the method comprises a phase shifter 1, a comparison unit 2, an integration unit 3, an integration unit 4, a threshold element 5, an analog-to-digital converter 6, a zero-organ 7, a timer 8, a division unit 9, a multiplication unit 10, a coefficient setting unit multiplying 11, display unit 12. Generate an additional signal that is shifted in phase relative to the test. At the moment of equality of these signals to, they begin to integrate both signals until the integral value of the signal under investigation reaches zero. At this time ti, the integral value of the additional signal is measured, and the amplitude value is determined by the formula (ti) (tg-F) / / 2 (ti-to) sinFcos j, where S2 (ti) is the result of integrating the additional signal interval (); F - phase shift. Moreover, the magnitude of the phase shift is chosen equal to .6929693 rad (97 °). 1 hp f-ly, 3 ill. SO with

Description

The invention relates to a measurement technique and can be used to measure the amplitude of electrical signals, in particular at low signal-to-noise ratios.

There is a known method for measuring the amplitude value of an alternating voltage based on introducing an additional phase shift, comparing the instantaneous values of the investigated and phase-shifted electrical signals, measuring when they are equal, the voltage value and determining the ratio. The disadvantages of this method are the difficulty of practical implementation and the low accuracy of measurements at low signal-to-noise ratios. The closest to the invention according to the technical essence is a method for measuring amplif beats, 1: alternating voltage value, tarred by introducing an additional phase shift into it, comparing the instantaneous values of the electrical signals and phase-shifted electrical signals, measuring when they are equal to the voltage value the determination of the ratio, and at the moment of equality of the test and phase-shifted electrical signals, the value of the test

XI GJ XJ

the signal, while the amplitude of the signal under study is judged by the ratio of the measured voltage to a constant value equal to the sine of half the phase shift.

A disadvantage of the known method is the low measurement accuracy when the signal under test influences the signal under test, in particular, at low signal-to-noise ratios. At low signal-to-noise ratios, in a known method, the stability and repeatability of measurement results are lost, the latter having a large scatter.

The purpose of the invention is to improve the measurement accuracy at low signal-to-noise ratios.

FIG. 1 shows a block diagram of a device that implements the proposed method; in fig. 2 is a timing diagram explaining the essence of the proposed method; in fig. 3 - schedule winnings in accuracy.

The device implementing the method comprises a phase shifter 1, a comparison unit 2, integration blocks 3 and 4, a threshold element 5, an analog-to-digital converter (ADC) 6, a zero-organ 7, a timer 8, a division block 9, a multiplication unit 10, a block 11 setting the multiplication factor, display unit 12,

The device input is connected to the input of the phase shifter 1, the input of the integration unit 3 and the first input of the comparison unit 2. The output of the phase shifter 1 is connected to the second input of the comparator unit 2 and the input of the integrated unit 4, the output of which is connected to the input of the A / D converter 6, the output of which is connected through the division unit 9 to the input of the multiplication unit 10, the output of which is connected to the input of the display unit 12. The output of the comparison unit 2 is connected to the first control inputs of the integration blocks 3 and 4 and the first control input of the timer 8. The output of the integration block 3 is connected via the threshold element 5 to the input of the zero authority 7, the output of which is connected to the second control inputs of the blocks 3 and 4 integrating the control input of the ADC 6 and the second control input of the timer 8, the output of which is connected to the control input of the division unit 9. The output of the block 11 is connected to the control input of the multiplication unit 10.

The invention is as follows.

The input signal yi (t) Asin on + g (t), where A is the amplitude, 2 n is the circular frequency, Ј (t) is the instantaneous value of the noise, is shifted by the phase shifter 1 in phase by the angle F. The shifted signal y2 (t) Asin (o tF) + Ј (t) is compared with the input in block 2 of the comparison. At time point to (see FIG. 2), their

Equality Comparison Unit 2 generates a resolution pulse. On this pulse, timer 8 is turned on, and blocks 3 and 4 begin integrating the signals yi (t) and y2 (t) in accordance with equations (1) and (2):

Si (ti) yi (t) dt (1)

to

S2 (tih7 y2 (t) dt. (2)

to

The integral value Si (t) is fed to the input of the threshold element 5.

When the integral value of Si (t) exceeds the threshold value, then element 5 will begin to transmit a signal Si (t) to the input of the zero-organ 7. The presence of threshold-element 5 excludes the triggering of the zero-organ 7 at the initial moment of time to (see

FIG. 2).

At time ti, when the condition Si (ti) 0 is satisfied, the zero-authority 7 outputs a signal to the second control input of timer 8, to the second control inputs

blocks 3 and 4 of the integration and the control input of the ADC 6. According to this signal, timer 8 stops counting time, blocks 3 and 4 stop integrating, and ADC 6 converts the value of signal S2 (ti) to a digital equivalent, which is input to the block 9. The control input of the division unit 9 receives the value of the time interval ti-to from the output of the timer 8. The digital equivalent of the signal

$ 2 (ti) in block 9 is divided by the value of ti-to. As a result, at the input of the division block 9, the value of the ratio

y2

S2 (ti)

t1 -to

(3)

The value of y2 in block 10 is multiplied by a constant coefficient

TO

lf

2sinF-cosЈ

(four)

55

the value of which is entered in advance in block 11. The value

(five)

equal to the amplitude of the signal under study, is displayed on the display device 12.

The increase in the accuracy of measurements at low signal-to-noise ratios is achieved by significantly reducing the influence of the Ј (t) noise and the influence of the phase shift instability on the amplitude measurement result A. At the same time, the features of the formation of the signals Sifti) and S2 (ti) are in the following. After integrating the signal under study and phase-shifted signals over the time interval ti-to, the signals at the output of blocks 3 and 4 are equal

Si (ti) / yi (t) dt

to

A 1 p (cos (p0 -cos ipi) + Rfc

(6)

 }

S2 (tl) / Y2 (t) dt to

- A j cos (p0 -F) -cos (pi -F) + Rv (7)

Here po, (p are the phases of the signal under investigation, corresponding to the moments of time to and ti (see Fig. 2)

p0 (l + g) (8)

p - 1l - p0.

In practice, the interference correlation interval is usually substantially less than the period of the signal under study, therefore

R ,, / Ј (t). With t0

After transforming the equations (7), taking into account relations (8),

(ti)

n -F

(ti -t2) -2sinFcos-2

(9)

The value of the optimal phase shift, at which the instability of the phase shift has little effect on the dispersion of the measurement result of the amplitude A, is determined from the condition - 0, where

, 6929693 glad, while

, 10-S2 (ti) / (ti-to). (Yu)

If the phase shift is F / 2, then

, 11-S2 (ti) / (ti-t0).

(eleven)

The achieved gain in the accuracy of the amplitude measurement for the proposed method in comparison with the known for the case of F nil is

-r

13.9 +

91 af h cfr

(12)

where o ,, is the relative dispersion of the amplitude measurement results for the known and proposed methods;

0i2, 0ЈF - relative dispersion of noise and phase shift, respectively, h - signal-to-noise ratio.

The invention is illustrated by the following example.

For example, with a -a F 0.05, the gain in the accuracy of amplitude measurements is 7 times (see Fig. 3).

When choosing the optimal phase shift F0pt, the gain achieved dramatically increases,

In the implementation of the proposed method, a phase shift can be made both in the lag and in advance of the output signal of the phase shifter 1, relate the signal under study. If a phase advance is used, then the output of the phase shifter should be connected to the input of the integration unit 3, and the input of the phase shifter 1 - connected to the input of the integration unit 4.

In this case, the integration of the signals yi (t) and y2 (t) is stopped when the condition S2 (ti) 0 is fulfilled, and the amplitude value of the signal under study is determined by the formula of indirect measurement

BUT

Si (ti) - (jr-F)

2 (ti t0) sinF-cos-2

F

(13)

where Si (ti) is the result of integrating the signal under study yi (ti) over the time interval ti-to.

The proposed method, in comparison with the known, provides a higher accuracy of amplitude measurement due to a decrease in the coefficients of the influence of the corresponding primary errors (phase shift dispersion and noise dispersion) on the error of indirect amplitude measurement.

Thus, the proposed method provides an increase in the accuracy of amplitude measurements at low signal-to-noise ratios. The gain in measurement accuracy increases with decreasing signal-to-noise ratio,

Claims (2)

Claim 1. A method of measuring the amplitude value of an alternating voltage based on generating an additional voltage by introducing a phase shift into the signal under study, comparing the instantaneous values of the studied and additional electric signals and determining the amplitude value according to a calculation formula, characterized in that accuracy of measurement at low signal-to-noise ratios, at the moment to equality of the studied and additional signals integrate both signal until the integral value of the signal under investigation reaches zero, at this time ti the integral value of the additional signal is measured, the amplitude value of the signal under investigation is determined by the formula L S2 (ti) rfrr-F) 2 (ti -t0) sinF-cosЈ where S2 (ti) is the result of integrating the additional signal over the time interval (ti-to); F - phase shift. 2. A method according to claim 1, characterized in that the magnitude of the phase shift is taken to be 6929693 rad (97 °). P / 1 R 3 J FIG. 3