RU2589351C1 - Method of measuring frequency ratio - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to measurement equipment and can be used for measuring periodic signals frequency ratio. Method consists in fact that first measuring time interval is formed from number of periods of first signal frequency to obtain first code, suring which whole number of periods of third signal is determined to obtain third frequency code, simultaneously, from number of second signal frequency periods measurement time interval is formed to obtain second code, during which whole number of frequency periods of third signal is determined to obtain fourth code, wherein ratio of frequencies of first and second signals is obtained by multiplying first code by fourth code, second code by third code and by division of first product of codes on second product of codes.

EFFECT: technical result consists in reduction of sampling maximum relative error when measuring frequency ratios.

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Description

The present invention relates to the field of measurement technology and can be used to measure the frequency ratio of periodic signals.

A known method of measuring the frequency ratio of two signals having a sinusoidal shape [Atamalyan E.G. Instruments and methods for measuring electrical quantities. - M.: Higher School, 1989 .-- 383 p. with ill.]. The method consists in the fact that the signals are converted into Lissajous figures, which are displayed on the oscilloscope screen by connecting the first signal to the horizontal deflecting plates of the CRT and the second signal to the vertical deflecting plates of the CRT. The image on the screen of the oscilloscope is stabilized if the ratio of the frequencies of the first and second signals can be expressed in whole numbers.

The disadvantage of this method is the narrow scope of its application, because Lissajous figures appear only if the ratio of the frequencies of the first and second signals can be expressed in whole numbers. In addition, difficulties arise in determining the values of integers on the oscilloscope screen when the integers are large, for example, with values greater than 100.

A known method of measuring the frequency ratio of two signals, which is the prototype of the invention [Ornatsky, P.P. Automatic measurements and instruments (analog and digital). - K .: Vishka school., 1986. - 504 p.]. The method consists in counting an integer number of frequency periods of the first signal, obtaining the first code that fit within the total number of frequency periods of the second signal, obtaining the second code, and the ratio is determined by dividing the first code by the second code.

, где m - целое число периодов второй частоты, из которых сформирован измерительный интервал времени. Например, если F₁ (первая частота) близка к 1000 Гц, a F₂ (вторая частота) близка к 100 Гц, то за время измерения 1 с максимальная относительная методическая погрешность дискретизации будет равна 0,1%. Для уменьшения ее значения в 100 раз потребуется увеличить время измерения до 100 с.However, this method is characterized by a large maximum relative methodological sampling error, especially at low frequencies. The absolute value of the sampling error when calculating the periods of one frequency during the measuring time interval, which is formed from an integer number of periods of the second signal, lies in the range (-T ₁ ... + T ₁ ), where T ₁ is the period of the first frequency. Thus, the maximum relative sampling error of the prototype method will be equal to $$\frac{\mathrm{one}}{m\cdot {\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="00000009.png"\; state="\{\{state\}\}">T</figure-callout>}}_2}$$

, where m is the integer number of periods of the second frequency from which the measuring time interval is formed. For example, if F ₁ (first frequency) is close to 1000 Hz, and F ₂ (second frequency) is close to 100 Hz, then during a measurement time of 1 s the maximum relative methodological sampling error will be 0.1%. To reduce its value by 100 times, it will be necessary to increase the measurement time to 100 s.

The objective (technical result) of the present invention is to reduce the maximum relative methodological sampling error when measuring the ratio of frequencies.

The problem is solved as follows. A first measuring time interval is formed from an integer number of frequency periods of the first signal, obtaining a first code, during which an integer number of frequency periods of the third signal is calculated, obtaining a third code, and at the same time, a measuring time interval is formed from an integer number of frequency periods of the second signal, obtaining a second code , during which an integer number of frequency periods of the third signal is calculated, obtaining the fourth code, while the frequency ratio of the first and second signals is obtained by multiplying the first code and on the fourth code, the second code on the third code and dividing the first product of codes by the second product of codes.

The figure 1 shows a functional diagram of a device that implements the proposed method.

The device contains:

Shapers of impulses (Ф) 1, 2;

Keys (K) 3, 4, 5, 6;

Impulse counters (MF) 7, 8, 9, 10;

The control device (UU) 11;

Pulse Generator (GI) 12;

Reading device (OS) 13.

The outputs of the pulse shapers 1 and 2 are connected to the information inputs of the keys 3 and 4, respectively, as well as to the pulse inputs Uimp.in1 and Uimp.in2 of the control device 11, respectively. The outputs of the keys 3 and 4 are connected to the counting inputs of the pulse counters 7 and 8, respectively. The output of the pulse generator 12 is connected to the information inputs of the keys 5 and 6, and their outputs are connected to the pulse counters 9 and 10, respectively. The information outputs of the counters 7, 8, 9, 10 are connected to the information inputs Uin.in1, Uinin.in2, Uinin.in3, Uinin.in4 control device 11, respectively. The pulse outputs of the control device 11 Uimp.out1, Uimp.out2, Uimp.out5, Uimp.out6 are connected to the reset inputs to zero pulse counters 7, 8, 9, 10, respectively. Key management inputs 3, 4, 5, and 6 are connected to the pulse outputs Uimp.out3, Uimp.out4, Uimp.out7, Uimp.out8 of control device 11, respectively. The information output of the microcontroller Uinf.out1 control device 11 is connected to the input of the reading device 13.

The pulse shapers 1, 2 can be performed on the basis of a comparator, for example, MAX9692 (manufactured by MAXIM). As keys 3, 4, 5 and 6, MAX14778 microcircuits (manufactured by MAXIM) can be used. The pulse counters 7, 8, 9, and 10 can be performed, for example, according to the traditional scheme on triggers MAX9381 (manufactured by MAXIM) or contained in the microcontroller of the control device 11. As a microcontroller of the control device 11, a circuit, for example, AT32AR7000 (manufactured by Atmel) can be selected ) The pulse generator 12 can be made on the basis of a crystal oscillator, for example, GK137-TS (manufactured by MORION). As the reading device 13, a personal computer with a USB input can be used.

The method is as follows. At the input of the pulse former 1 (see Fig. 1) a signal with a frequency of F ₁ is supplied, and at the input of the pulse former 2 a signal with a frequency of F ₂ . In the initial state, the control device 11 through Uimp.out1, Uimp.out2, Uimp.out5, Uimp.out6 sets the pulse counters 7, 8, 9 and 10 to zero and through Uimp.out3, Uimp.out4, Uimp.out7, Uimp .out8 breaks keys 3, 4, 5, and 6.

The figure 2 presents a timing diagram of a device that implements the proposed method.

Starting from a certain point in time (indicated by a line with the inscription "start" in figure 2), which is set by the control unit 11, the control unit 11 resets the readings of the pulse counters 7, 8, 9, 10 through the pulse outputs Uimp.out1, Uimp.out2, Uimp .out5, Uimp.out6, respectively, and expects a pulse to arrive at the pulse input of Uimp.in1 and Uimp.in2 from the output of pulse shaper 1 and pulse shaper 2, respectively.

Let the pulse coming first from the output of the pulse shaper 1 to the pulse input Ump.in1 of control device 11, initiate a control device 11, which closes keys 3 and 5, respectively, through the pulse outputs Ump.out3 and Upp.out7. The counter 7 starts the count of pulses following with a frequency F ₁ , which is set by the input signal supplied to the input of the pulse shaper 1. Pulse counter 9 counts the pulses with a frequency F _g coming from the pulse generator 12.

When the expected pulse arrives from the output of the pulse shaper 2 to the pulse input Uimp.in2 of the control device 11, the control device 11 closes the keys 4 and 6, respectively, through the pulse outputs Uimp.out4 and Uimp.out8. In this case, the pulse counter 8 starts the count of pulses following with a frequency F ₂ , which is set by the input signal supplied to the input of the pulse shaper 2. The pulse counter 10 starts counting pulses with a frequency F _g coming from the output of the pulse generator 12.

This mode of operation of the device is maintained for a certain time interval, which is set by the control device 11. After the end of this time interval and the arrival of the next pulse from the output of the pulse shaper 1 to the pulse input Uimp.in1 of the control device 11, which through the pulse outputs Uimp.out3 and Uimp .out 7 breaks keys 3 and 5, respectively. And after the arrival of the next pulse from the output of the pulse shaper 2 to the pulse input Uimp.in2 of the control device 11, which breaks the keys 4 and 6 through the pulse outputs Uimp.out4 and Uimp.out8, respectively.

Next, in the control device 11, the ratio of the frequencies F ₁ and F _{2 is} calculated by the formulas

where N ₇ , N ₈ , N ₉ , N ₁₀ are the codes of the pulse counters 7, 8, 9, 10, respectively, at the end of the measurement determined by the control device 11. Then we can write

From the essence of the proposed method for measuring the frequency ratio, it follows that the maximum relative methodological sampling error is formed by counting the number of pulses following with a frequency F _g for an integer number of periods following with a frequency F ₁ (counting time equal to N ₇ · T ₁ ), and for an integer number of periods following with a frequency of F ₂ (counting time equal to N ₈ · T ₂ ), on pulse counters 9 and 10, respectively. Given this fact, we can write

Then the maximum relative methodological sampling error will be equal to

And in the prototype it is equal to

In the proposed device, F _g is selected based on the possibility of speed of logic elements and pulse counters. Currently, F _g can be selected from 100 MHz to 1 GHz or more. Thus, choosing the measurement time, which is set by the control device 11, approximately equal to 1 s, you can get the maximum relative methodological sampling error, not exceeding 2 · (10 ^-8 -10 ^-9 ). Moreover, this error is practically independent of the values of F ₁ and F ₂ in the frequency range from units of hertz to hundreds of MHz. While in the prototype the maximum relative methodological error of sampling depends on the values of F ₁ and F ₂ , for example, F ₂ = 10 ³ Hz, and N _m · T _{1 is} close to 1 s, then the maximum relative methodological error of sampling is 10 ^-3 . Moreover, it follows from formula (3) that the result of the frequency ratio in the proposed method does not depend on the frequency F _g and its stability, since the frequencies F ₁ and F ₂ are measured simultaneously.

Thus, in the proposed method, the maximum relative methodological sampling error can be significantly reduced in comparison with the prototype.

Claims (1)

The method of measuring the frequency ratio, which consists in forming the first measuring time interval from an integer number of frequency periods of the first signal, obtaining a first code, characterized in that during the first measuring interval, an integer number of frequency periods of the third signal is counted, obtaining the third code, simultaneously with this forms a measuring time interval from an integer number of frequency periods of the second signal, obtaining a second code, during which an integer number of frequency periods of the third signal is calculated, obtaining I’m the fourth code, and the ratio of the frequencies of the first and second signals is obtained by multiplying the first code by the fourth code, the second code by the third code and dividing the first product of codes by the second product of codes.

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