SU1471145A1 - Method of measuring frequency of sine signal - Google Patents

Abstract

The invention relates to electrical measurements and is intended to determine the frequency of a sinusoidal signal in a time shorter than the duration of one period. The purpose of the invention is to expand the functionality and improve the accuracy of determining the frequency. The method of determining the frequency of a sinusoidal signal involves the formation of an additional signal shifted by an angle ϕ / 2 towards the advance, simultaneous measurement of the instantaneous values of the input and additional signals at reference intervals and determination of the frequency by two values of each signal corresponding to two successive moments measurement time. The description provides a formula for determining the frequency of the signal. The device implementing the method contains a voltage level converter 1, a phase shifting unit 2, an analog storage unit 3 and a digital decision unit 4. The functionality and accuracy are achieved by shifting the input signal by an angle ϕ / 2 and measuring its instantaneous values This denominator and numerator of the formula for determining the frequency of the signal do not take zero values. 2 Il.

Description

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fpuz.l

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The invention relates to electrical measurements and is intended to limit the frequency of a sinusoidal signal in a time shorter than g and a single period.

The purpose of the invention is to expand the functional capabilities and increase the accuracy of frequency determination.

Figure 1 shows the Q structure of the device for implementing the method; 2 shows graphs explaining the essence of the method.

The method of determining the frequency of a sinusoidal signal is based on the formation of an additional signal out of the input signal, which is shifted in phase by an angle of / 2 towards the front, and simultaneously measuring the instantaneous values of the input and additional signals followed by a reference time interval. The frequency of the signal is determined according to a mathematical expression.

I25

1i, 1 and, 1 + UnUiT.

f 2F.t

 u, + ii

21

thirty

()

where & t is the value of the reference time interval;

Uh

U, - instantaneous input values

signal following a reference time interval;

Uli,

  instantaneous value of the additional signal, following through the reference time interval.

The essence of the method for determining the frequency of a sinusoidal signal is the following.

35

If at the time of measurement t, (FIG. 2) the current value of the phase of the sinusoidal signal 1, then its connection with the instantaneous values of the input U i corresponding to this time instant and shifted in phase by the angle ahead of the U signals is expressed by the equation mi

Guy, Un, -sinW. (2)

lUi, Um-cos ;, where У „is the amplitude of the sinusoidal

signal

; A similar connection for the point in time (t, + flt) is represented by the equations

WITH

1471145

U, j (Lf + w at) Uti Ufti CosC × + t t),

(3)

five

0

five

45 50

where s is the angular frequency.

Expressions (2) and (3) form a system of four equations in which the unknowns are U, ij. The solution of this system is carried out by the substitution method in the following sequence.

The first equation of expression (3) is resolved with respect to sin t and the value obtained is substituted into the second equation.

After transformations, an equation is obtained.

li f2 sin cf Ull cos4

cos co lt ,,

 In

(four)

Permit equations (2) with respect to Uf, sin gj, cos V and the values obtained are substituted into expression (4),

After simple transformations, taking into account that ui 2 (f, get the expression (1) to determine the frequency of the sinusoidal signal.

 The directly used parameters for calculating the frequency by the formula (1) are the instantaneous values of the input and if / I angle shifted towards the advance of the signals.

The proposed method for determining the frequency of a sinusoidal signal in comparison with the known one has broader functionality and increased accuracy, independent of the Measurement Moment (phase) of the instantaneous sinusoidal signal, since both the denominator and the numerator of expressions (D) do not like zero values.

A device for determining the frequency of a sinusoidal signal comprises a voltage level converter connected in series 1, the input of which is supplied with a sinusoidal voltage U, a phase-shifting unit 2, an analog storage unit 3, the second input of which is connected to the output of the converter 1, and a digital decision unit 4 connected via information and control inputs-outputs with corresponding inputs-outputs of the analog storage unit 3.

. The device works as follows.

in a way.

A sinusoidal voltage U is supplied to the input of a voltage level converter 1, which also performs the function of galvanic separation of the device and the input signal. The output voltage of the converter 1 is fed to the input of the phase-shifting unit 2, the output of which is a voltage of the same amplitude, but shifted in phase by 1/2 in the direction of advance with respect to the input voltage. The output voltage of converter 1 U is fed to one of the inputs of the analog storage unit 3, and the second voltage of the output voltage of the phase shifting unit 2 U is applied to its second input. At the command coming from the digital solver unit 4, the analog storage unit 3 simultaneously fixes and remembers the instantaneous values of the voltages U, and G. After that, they are alternately read, convert and enter into the memory of the digital decision unit 4. Simultaneously with the fixation of the instantaneous values of the voltages U, and 1 using a digital timer The decision block 4 counts a predetermined reference time interval, after which the process of fixing, reading, transforming and storing subsequent instantaneous values of the voltages U and U is repeated.

Frequency determination is performed by digital solver unit 4 in accordance with expression (1) by two values of each of the voltages, which are pairwise corresponding to two successive measurement points.

The device can be used to build high-speed measuring organs of the frequency of emergency devices and other devices.

types of automation systems

and implemented using well-known digital decision elements, made on the basis of microprocessor

technology.

Claims (1)

Invention Formula The method for determining the frequency of the sinusoidal signal, based on the measurement of three instantaneous values of the input signal, of which the first and second are taken through a reference time interval, differing in that, in order to expand functionality and improve accuracy, the input signal is formed the additional signal is shifted in phase by the angle li 12 to the side of the alternation, and the third and additional fourth instantaneous values of the additional signal are measured at times coinciding with the first and volts Measuring the instantaneous values of the input signal, and the frequency f is determined according to the mathematical. expression  1 UiiU p + UliUii 35, where ut is the value of the reference time interval; and -1,  n - instantaneous input values 40 2 signal; 11.71, and, - - instantaneous values of the additional signal, fa g