SU885913A1 - Method of measuring frequency - Google Patents

Description

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The invention relates to a measuring technique and can be used in instrument making, as well as in automated production control systems and technological processes.

The known method of frequency measurement is based on quantization of the sample time interval by pulses of the measured frequency and counting the number of the last Cl).

The known method does not provide high accuracy of measurement when changing the frequency during the measurement interval.

The closest in technical essence is a method of measuring the pulse frequency, including quantizing an exemplary time interval with measured frequency pulses and counting the number of the latter, forming a continuous scale of reference time marks, the period of which is equal to the exemplary time interval, fixing the number of pulses of the measured frequency on previous current 9 (5 times

the time interval and the measurement of the time interval from the moment of the appearance of the last time mark to the current time point, and the determination of the current result based on the formula

: „., .., (K, -K;.,),

where m the number of pulses of the measured frequency on the two preceding current intervals of time; TP - the duration of the model

time interval; e is the time interval from the moment of the occurrence of the last time stamp to the current time point.

This method is effective in measuring the frequency varying according to the law of a monotonically increasing or decreasing function 2 ....

However, when measuring the frequency varying according to the pulsating law, especially if the pulsation period is close in its value to the value of the sample time interval, the magnitude 1 of the dynamic error due to the measurement method reaches considerable limits, which is an underexposure of the known frequency measurement method.

The purpose of the invention is to reduce the dynamic measurement error.

The goal is achieved by the fact that the method of measuring the frequency, which includes quantization of the sample time interval by the measured frequency pulses AND counting the number of the latter, the formation of a continuous scale of reference time stamps, the follow-up period of which is equal to the model time interval fixed to the number of pulses of the measured frequency on the previous current sample the time interval and the measurement of the time interval from the moment of the appearance of the last mark-time to the current time point, the counting of the number of impulses is introduced of the measured frequency from the moment of the occurrence of the last time stamp to the current time point and the determination of the result by the formula

i ..Kl) .M, -1

TO

where TO is the duration of the model time interval;

- time interval from the moment of occurrence of the last time mark to the current time point;

-% number of pulses measured by chao

N; ttots on the previous current reference time interval NCP - the number of pulses measured

frequencies on the time interval until the last time mark appears before the current time point.

FIG. 1 to 3 are graphs of frequency variations; on .fig. 4 - device, structural scheme.

 FIG. Figure 1 shows a graph of the measured frequency f (t), built on the basis of the possibility of facilitating the construction of a graph of variation; the pre-integral value (.fc) of the frequency being measured and the graph of the change in the frequency measurement result according to the present method of frequency measurement. For comparison, in FIG. Figure 3 shows with a dotted line a graph of the change in the average integral value (t) of the measured frequency.

FIG. 3 that the measurement error is present only under the conditions

4To -fc 5T

about i

6 TO 4: 7 TO)

those. on the fifth and seventh model time intervals, with the largest error occurring at

t 6,5 TO

and is equal to

f 0.25l

T

The device contains counters 1 and 2 pulses, the arithmetic unit 3, the output register 4, the generator 5 of the reference frequency and the generator 6 of the model time interval.

The frequency measurement process is as follows.

Counter 1 counts the number of N (.TU) pulses of the measured frequency from the time 1 T of the occurrence of the last time mark to the current time t, and the result of the counting in the form of a code continuously outputs to the arithmetic unit 3. During the same time, counter 2 continuously converts in the code, the number of pulses of the exemplary frequency of the generator 5 and thus keeps track of the time f from the time i Tr after the last time mark to the current time point. With the arrival of the reference mark from the generator 6, the arithmetic unit 3 erases the previous record and remembers the counter code 1, which corresponds to the number N of pulses of the measured frequency at the previous sample time interval TQ. At the same time, the generator reference mark 6 causes a reset and a new run of counters 1 and 2. Using the current codes of counters 1 and 2, as well as the counter code 1 recorded at the end of the previous model time interval, the arithmetic unit 3 continuously determines the current result

Bnn)

and continuously outputs it to output register 4.

With the advent of the new reference label, the processes are repeated.

The proposed frequency measurement method allows to reduce the measurement error, which makes it possible to improve the quality of the operational control and regulation of technological processes.

Claims (2)

1. Ermolov RS. Digital frequency meters. L., Energie, 1973, p. five. 2. USSR author's certificate number 572714, cl. G, O1 R 23/00. fr o STP 2GP Thats 1 Go S-tn em „ 7 TO S FIG. 2 h h Zto about goto T ST. Fig.Z H /; / 1 f / V / h u / h / h ig