SU892334A1 - Low frequency digital meter - Google Patents

Description

(5) DIGITAL LOW FREQUENCY METER

one

The invention relates to electrical measuring equipment and can be used to set up a frequency-controlled electric drive, power supply systems, as well as to measure and control the frequency in power systems.

A known frequency meter of instantaneous values, comprising a reference frequency generator, three impulse sweepers, a period meter, an AND circuit, an OR circuit, and a delay element Cl3.

The disadvantage of this frequency meter is that it does not provide the required speed.

Of the known devices, the closest in technical essence to the invention is a device containing two pulse counters, a generator of pulses of a reference frequency, an output connected to the input of a frequency divider, two outputs of which are connected respectively to the first inputs of keys, the second input of the first one

which is connected to the first output of the pulse generator, and the output of the first key is connected to the input of the first pulse counter, the outputs of which are connected to the control inputs of a frequency divider with a variable division factor, the counting input of the latter is connected to the output of the second key pulse inputs

10 shaper exemplary time intervals are connected respectively to the second output of the pulse shaper and the third output of the frequency divider, and the shaper output of the 15 time intervals is connected to the second input of the second key 12.

A disadvantage of the known device is low speed.

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The purpose of the invention is to increase the speed of the low-frequency meter while maintaining high measurement accuracy. The goal is achieved by the fact that a digital low frequency meter containing a serially connected pulse shaper, a first key, a first main pulse counter, a frequency divider, and a reference frequency generator, the output of which is connected to the second input of the first key and to the first The second key input, the output of which is connected to the second input of the frequency divider, has a trigger and an additional pulse counter, the input of which is connected to the output of the frequency divider, and the first trigger input is connected It is connected to the second output of the pulse generator, the second input of the trigger is connected to the output of the additional pulse counter, and the output of the trigger is connected to the second input of the second key. The drawing shows a block diagram of a digital low frequency meter. The digital low-frequency meter contains a shaper of 1 pulses, a generator of 2 pulses of the reference frequency, keys 3 and, a counter of 5 pulses, a trigger 6, a divider of 7 frequencies, counters of 8 and 9 pulses. The meter low frequencies works as follows. The measured signal with a pulse-following frequency is fed to the input of a 1. impulse generator, in which a rectangular pulse is fsexed with a duration equal to the period followed by the measured frequency. Tu. This pulse arrives at the first input of the key 3, the second input of which receives a sequence of pulses from the output of the generator 2 pulses of the reference frequency fjj. The pulses appearing at the output of the key 3 arrive at the input of the counter 5. At the end of the pulse T, the counter 5 is fixed. The back edge of the pulse Tu trigger 6 is placed in such a position that the passage of the pulses of the reference frequency Q through ct) h k to the inputs of the divider 7 is allowed. frequencies with a variable division factor and counter 9 Herewith, the division ratio of the frequency 7 body is determined by the number N recorded in the counter 5- The pulses from the output of the frequency divider 7 with a variable division factor arrive at the input of the binary counter 8 with a conversion factor equal to K. In this case, the average frequency of the pulses at the input of counter 8 turns out to be proportional to the number recorded in counter 5, namely where n is the number of bits of the frequency divider 7 with a variable division factor. The time t required to fill the counter 8 is determined by an overflow pulse from the output of the counter 8, the trigger 6 returns to its original position, thereby prohibiting the passage of the reference frequency pulses from the output of the generator 2 through the key k to the inputs of the frequency divider 7 with a variable division ratio of the counter 9 “During time i, counter 9 gains the number of pulses. NQ t or taking into account the expressions (1) 2.K.fx l Thus, with an appropriate choice of the number of bits n of the splitter 7 frequency with a variable division factor K of the conversion of counter 8 and the frequency of the generator 2, the inductors of the counter 9 display the directly measured frequency y . The introduction of a third pulse counter and a trigger instead of a former for exemplary time intervals and a frequency divider allows to significantly increase the meter performance with a sufficiently high accuracy and simple circuit of the device. In this meter, the oscillator frequency is 2 5-10 Hz, the number of bits of division 7 of a frequency with a variable division factor of counter 5 is 17, the K coefficient of recalculation of counter 8 is, the number of bits of counter 9 is five. At the same time, the range of measured frequencies is 38.2 ... 76.2 Hz.;. The error in measuring the frequency y, in this meter is formed (without

5892 ZZ

taking into account the error of the generator 2 pulses of the reference frequency) of the two components - the error of measuring the period and the error of conversion. The maximum value of the relative conversion error will be ghcTx Total frequency error is determined from the expression For f 38.2 Hz the frequency measurement error (3.38 TO or 3.38-10 For fn Hz the frequency measurement error is set to (Y 2, t or 2, conversion will be determined from expressions (1) ... (3 and will be A fn 38.2 Hz; t 7.6 ms; "76.2 Hz; t 15.2 ms. Thus, the measurement time of the frequency in the specified frequency range is not exceeding 33 V ms. At the same time, the frequency measurement error in the temperature range 4-5 ... did not exceed. Thus, the proposed digital A low-frequency meter provides high speed with low noise and a simple circuit.

If it is necessary to measure lower frequencies, it is necessary to increase the number of bits of counter 5 and frequency divider 7 with a variable division factor.

Claims (2)

A digital low-frequency meter comprising a serially connected pulse generator, a first key, a first main pulse counter, a frequency divider, and a reference frequency pulse generator, the output of which is connected to the second input of the first key and to the first input of the second key whose output is connected to the second input of the frequency divider and the input of the second main pulse counter, characterized in that, in order to improve speed, a trigger and an additional pulse counter are introduced into it s, the latter connected to the output of the frequency divider input, the first input of the flip-flop is connected to the second output of the pulse shaper, a second input connected to the output trigger additional pulse counter and vyhoM trigger is connected to the second input of the second switch. Sources of information taken into account during the examination 1. USSR author's certificate “537306, class C. 01 R 23t, 1976; 2. USSR author's certificate No. 573768, class C 01 R 23/10, 1976 (prototype). I / / G7 / / “0