RU2231077C2 - Device for measurement of frequency of electric signals - Google Patents

Abstract

FIELD: procedure of digital measurement of frequency of electric signals in low-frequency and infra-frequency bands.

SUBSTANCE: the device has an amplifier-driver, whose output is connected to the control input of the first pulse counter, whose complementing input is connected to the output of the reference pulse oscillator via a frequency divider, as well as the second pulse counter. In addition, the device uses the first and second parallel registers, time delay unit and a programmed frequency divider. The device converts an instantaneous period of measured signals to a period of radio-frequency pulses confined to a fixed time period lesser than the period of the measured signals.

EFFECT: enhanced speed of response and accuracy of frequency measurement.

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Description

FIELD OF THE INVENTION

The present invention relates to techniques for digitally measuring the frequency of electrical signals in the low-frequency and infra-low-frequency ranges.

State of the art

To measure the frequency of electrical signals, well-known electronic frequency meters are used, which are divided into analog and digital by the method of representing measurement information, and by direct and indirect devices by the method of generating the measurement result.

Known measuring Converter of the pulse repetition rate to voltage [1], which implements a direct analog method of measurement and consists of series-connected pulse shaper of stable duration and a linear averaging device. In this analogue, the pulse shaper is based on a quartz pulse generator and two triggers, which ensures high accuracy in measuring the frequency. The disadvantage of the analogue is that it takes a very long time to measure a low frequency, since a large number of input pulses are required to generate a constant voltage at the output of the linear averaging device.

An example of an analog indirect frequency counter is a pulse-to-voltage frequency converter [2], which contains an input trigger, ramp and exponential voltage generators, a comparator for comparing the indicated voltages, and an analog storage device. This analogue, with the help of a linearly varying voltage generator, converts the instantaneous period of the measured pulses to voltage, after which, in the next period, by double-starting the exponential voltage generator, it generates a voltage inversely proportional to the voltage of the linearly varying voltage generator obtained in the first period, i.e. voltage proportional to the measured frequency. This voltage is stored as a result of measurement with an analog memory device. This analogue is characterized by high speed, however, its accuracy and stability are insufficient, due to the presence of analog links.

Known digital direct-acting frequency counter [3], consisting of series-connected amplifier-driver, control circuit, pulse counter, decoder and digital reading device. The input of the control circuit is connected to the output of the reference pulse generator through a frequency divider. The measurement cycle t _C in this device is determined by the frequency of the reference pulse generator and the frequency divider module. During time t _C , the control circuit passes n pulses to the pulse counter, and n is proportional to the measured frequency f _X. With a stable frequency of the reference pulse generator, the measurement error is equal to the quantization error δ = 1 / n, therefore, accurate measurement of the frequency is possible with a large number n, i.e. with a long measurement time t _C. Thus, the disadvantage of this analogue is the excessively long measurement time.

A digital frequency measuring device [4] is also known, including a serially connected amplifier-driver, a key, a pulse counter and a functional converter, the control input of the key being connected to the output of the pulse generator. This device implements the indirect measurement principle and performs the primary measurement of the period of the signals of the measured frequency f _X and the subsequent calculation of the reciprocal of the result of the primary measurement. The measurement result is formed after measuring a single period of input pulses, which is its advantage, as it increases speed and expands functionality. The presence of a digital functional converter, such as a microprocessor, determines the complexity of this analogue. Such a technical solution is not always acceptable.

Of the known technical solutions, the digital frequency meter is closest in technical essence to the present invention [5]. The prototype device contains a series-connected amplifier-driver, the first key and the first pulse counter. The device has a second pulse counter, the input of which is connected via a second key and a cycle generator to the output of the amplifier-former. In this case, the remaining inputs of both keys are connected to the output of the reference pulse generator. The device also includes a code comparison circuit, the first and second inputs of which are connected to the outputs of the first and second pulse counter, and the output is connected to the input of the third pulse counter and the reset input of the second pulse counter.

The frequency measurement process in the prototype device consists of two stages. At the first stage, the first pulse counter forms a digital value n _T equal to the number of reference pulses that fit into the period T _{X of the} measured signals. At the second stage, the cycle generator opens at time t _{C the} second key, through which the second pulse counter is filled with the pulses of the reference generator, the contents of which are compared with the contents of the first pulse counter. The comparison circuit sends pulses to a third pulse counter, the contents of which at the time the interval t _C ends, is proportional to the measured frequency f _X

n _f = t _C f ₀ / n _T ,

where f ₀ is the frequency of the reference pulse generator.

The prototype device measures the instantaneous value of the signal period, however, the process of converting this value to a frequency value takes a lot of time. This is his flaw.

SUMMARY OF THE INVENTION

The purpose of the present invention is to improve the speed and accuracy of frequency measurement.

This goal is achieved by digitally converting the instantaneous period of the measured signals into a period of high-frequency pulses, followed by counting the number of high-frequency pulses that fit into a fixed time interval shorter than the period of the measured signals.

For this, a device for measuring the frequency of electrical signals containing an amplifier-driver connected to the output of the control input of the first pulse counter, the counting input of which is connected to the output of the reference pulse generator through a frequency divider, as well as a second pulse counter, additionally introduced the first and second parallel registers , time delay unit and programmable frequency divider. The first and second parallel registers are connected by their information inputs to the information outputs of the first and second pulse counters, respectively, and their control inputs are connected to the control inputs of the corresponding pulse counters. The output of the time delay unit is connected to the control inputs of the second pulse counter and parallel register, the clock input of the time delay unit is connected to the output of the reference pulse generator, and its signal input is connected to the output of the driver-amplifier. The control digital inputs of the programmable frequency divider are connected to the information outputs of the first parallel register, its signal input is connected to the output of the reference pulse generator, and its output is connected to the counting input of the second pulse counter.

List of drawings

Figure 1 shows a functional diagram of a device for measuring the frequency of electrical signals according to the present invention. Figure 2 presents the timing diagrams of the signals in the device.

Information confirming the possibility of carrying out the invention

Presented in figure 1, a diagram of a device for measuring the frequency of electrical signals consists of an input amplifier-driver 1 connected by an output to the control inputs of the first pulse counter 2 and the first parallel register 3 and to the signal input of the time delay unit 4. The clock input of the time delay unit 4 is connected to the output of the reference pulse generator 5, to the signal input of the programmable frequency divider 6 and, through the frequency divider 7, to the counting input of the first 2 pulse counter. The information outputs of the first counter 2 pulses are connected to the information inputs of the first parallel register 3, the information outputs of which, in turn, are connected to the control digital inputs of a programmable frequency divider 6. The output of the time delay unit 4 is connected to the control inputs of the second pulse counter 8 and the second parallel register 9, connected by its information inputs to the information outputs of the second pulse counter 8, in which the counting input is connected to the output of the programmable frequency divider 6. The information outputs of the second parallel register 9 serve as digital outputs of the device for measuring the frequency of electrical signals on which the measurement result is generated.

Programmable frequency divider 6 can be made in the form of a universal subtracting pulse counter having a counting input (-1), which serves as a signal input of a programmable frequency divider b, control digital inputs (D), and a parallel boot input (L), which is connected to the output loan (P) of the same pulse counter. The loan output L is the output of a programmable frequency divider 6.

The block 4 time delay to improve the accuracy of the time delay can be made in the form of a digital conversion device fed by clock pulses from the output of the reference pulse generator 5 and triggered by pulses from the output of the amplifier-former 1.

The operation of the device of Fig. 1 is illustrated by the timing diagrams of Fig. 2, where the letters A ... D denote signals in the same communication lines in Fig. 1.

The input signals A of the measured frequency are converted by the driver amplifier 1 into short pulses B, which are fed to the control inputs of the first counter 2 pulses and parallel register 3, as well as to the signal input of the time delay unit 4. The first pulse 10 of the amplifier-driver 1, entering the control input C of the first parallel register 3, rewrites the contents of the first counter 2 pulses into it, and arriving at the control input R of the first counter 2 pulses, resets it to zero. The same pulse 10 starts the block 4 time delay, which forms a pulse with a low (zero) operating level of duration t _In .

During the period T _{X of the} measured signals, the first pulse counter 2 is filled with pulses B from the output of the frequency divider 7, the frequency of which is f ₀ / M, where M is the module of the frequency divider 7, and f ₀ is the pulse frequency of the 5 pulse reference generator. The total number of pulses that have passed during the time T _X and, therefore, the contents of the first counter 2 pulses, by the time the period ends, reaches the value N _T equal to

N _T = T _X f ₀ / M.

The next pulse 11 of the amplifier-former 1 rewrites the contents N _{T of the} first counter 2 pulses in the first parallel register 3, where it is stored for the entire next period of the measured signals. The same pulse 11 resets the first counter 2 pulses and starts the block 4 time delay, which begins to form a pulse 12 with a low working level of duration t _In , which is selected less than the smallest period of the measured signals. The number N _T stored by the first parallel register 3, determines the module programmable frequency divider 6, which operates as follows. When in the process of subtracting pulses from the output of the reference 5 pulse generator at the output P of the subtracting pulse counter, which forms the basis of the programmable frequency divider 6, a loan signal corresponding to zeroing this counter appears, this signal, entering the parallel load input L, writes the number N to the counter _T. Subsequently, the loan signals P, which are the output signals of the programmable frequency divider 6, appear with a frequency f _D , which depends on the module N _{T of the} programmable frequency divider 6 and frequency f _{0 of the} reference pulse generator 5

f _D = f ₀ / N _T.

The frequency f _{D is} much higher than the frequency of the measured signals.

The pulse 12 of the block 4 time delay determines the counting time of the second counter 8 pulses, the contents of which in time t _In the light of the above expressions reaches the value

N _f = f _D t _B = f ₀ t _B / N _T = Mt _B / T _X = Mt _B f _X.

At the end of the pulse 12 on its positive edge, this number N _{F is} recorded in the second parallel register 9 as a digital frequency measurement result. Thus, the measurement result is proportional to the measured frequency

N _F = Kf _X.

The conversion coefficient K = MT _B and the frequency f ₀ are selected taking into account the range of measured frequencies and the given measurement accuracy.

Given the boundaries f _{X min} and f _{X max of the} range of measured frequencies and the maximum relative measurement error δ, the device parameters in the preferred embodiment are selected from the following relationships:

- bit width n of counters 2 and 8 pulses, parallel registers 3 and 9, programmable frequency divider 6

where lb is the binary logarithm,] ... [is the operation of rounding to a larger integer;

- conversion coefficient K

K = 1 / (f _{X min} δ),

- frequency f ₀ reference generator 5 pulses

f ₀ = Kf $\genfrac{}{}{0ex}{}{\text{2}}{\text{X max}}$ / δ;

- module M divider 7 frequency

M = (f ₀ δ) / f _{X max} ;

- duration t _In block 4 time delay

t _B = 1 / f _{X max} .

With a simple structure, the device in accordance with the present invention has high accuracy in measuring the frequency of electrical signals at maximum speed, since a digital measurement result is formed after a single period of electrical signals. The device can be used, in particular, for quick measurement of heart rate.

Sources of information

1. Measuring converter of pulse repetition rate to voltage. - Auth. testimonial. USSR No. 548097.

2. The pulse repetition rate to voltage converter. - Auth. testimonial. USSR No. 482884.

3. Tokheim R. Fundamentals of Digital Electronics. - M .: Mir, 1988, p. 333, Fig. 11.29.

4. Meizda F. Electronic measuring instruments and measurement methods. - M .: Mir, 1990, p. 226, fig. 10.6.

5. Shlyandin V.M. Digital measuring devices: Textbook for high schools. - M.: Higher School, 1981, p.171, Fig.3.32 (prototype).

Claims (1)

A device for measuring the frequency of electrical signals, comprising a driver amplifier connected to the control input of the first pulse counter by an output, the counting input of which is connected to the output of the reference pulse generator via a frequency divider, as well as a second pulse counter, characterized in that the first and second parallel registers connected by their information inputs to the information outputs of the first and second pulse counters, respectively, and their control in moves - with the control inputs of the respective pulse counters, a time delay unit, where the output is connected to the control inputs of the second pulse counter and parallel register, the clock input - to the output of the reference pulse generator, and the signal input - to the output of the amplifier-driver, and a programmable frequency divider while the control digital inputs of the programmable frequency divider are connected to the information outputs of the first parallel register, its signal input is connected to the output of the reference generator and pulses, and its output connected to the counting input of the second pulse counter information outputs of the second parallel register outputs are digital devices.

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