SU960654A1 - Digital low frequency meter - Google Patents

Description

The invention relates to electrical measuring equipment and can be used to measure the frequency of electric pulses with increased accuracy over a limited time interval.

A frequency counter is known that contains a counter, a unit for setting a one-second measuring time interval, an additional counter filled with a reference frequency and reset by each pulse of the monitored signal 1.

This frequency meter has high accuracy, but it is inconvenient to work, since to obtain the final result, additional calculations are required with the values of the number of pulses accumulated in the main and additional counters.

The closest in technical essence to the invention is a digital low and low frequency meter containing a reference oscillator, a divider, an auxiliary counter, outputs connected to the control inputs of a controlled frequency divider, the output of which is connected to the main counter input, and

also .rd additional elements 2 ...

The disadvantage of this meter is the low accuracy of the frequency measurement, which is explained by the accumulation during the entire measurement interval of the error of the divergence of the generation points of the k-fold frequency pulses as compared to their true moments. At the same time, it turns out that it is practically impossible to significantly reduce this error, since this would require the use of such high frequencies f (j and f-j that are not available to the element base currently used in measuring equipment.

The primary source of error in the known device — a digital measure of 20 le low-low and low frequencies — is the presence of a sampling error Y when measuring the duration. period t

25T, g

where n is the number of frequency pulses fg ,, accumulated in the auxiliary counter for the period Tj.

When applied to a controlled frequency divider h - kfv at its output

one(

a frequency -j is generated. differing from the frequency k-fx

one

X k-fx (l-l-ff).

In order for the accumulation of pulses of this frequency in the main counter for a measurement period of 1 s, a code equal to k-fx is obtained, it is necessary that

k- with 1, or maxf

we get

. with f k fx-1 s.

The last relation shows, for example, that in order for the indicated meter to be measured for 1 s at a frequency f 1 kHz with an accuracy of 0.01 Hz (kxlOO), it would be necessary to use the frequency f 10 GHz. This value of the frequency f substantially exceeds the capabilities of the modern: The element base on which the measuring equipment is built, which is the reason for the limited accuracy of the known device.

The aim of the invention is to improve the accuracy of frequency measurement while maintaining a small measurement time.

The goal is achieved by the fact that a digital low-frequency frequency meter containing a control unit, a reference frequency generator, two keys, a counter, a controlled divider and an auxiliary counter, whose input is connected to the output of the first key, and the outputs to control inputs of a controlled divider , whose information input is connected to the output of the second key, and the output is connected to the counting input of the counter, an additional key and an additional counter are entered, the input bus of the device is connected to the information input of the additional about the key and to the input of the control unit, the first output of which is connected to the control input of the first key, and the second output of the control unit - to the control inputs of the second key and additional key, the output of which is connected to the counting input of the additional counter, and the R input of the counter, The first and second outputs of the reference pulse generator are connected to the information inputs of the first and second keys, respectively.

The drawing shows the block diagram of the proposed frequency meter.

The frequency meter consists of unit 1 control, generator 2 reference

frequencies, additional, second and first keys 3, 4 and 5, additional counter 6, counter 7, auxiliary counter 8 and a controlled divider 9 .;

5 The monitored signal is fed to the control unit 1 and the information input of the additional key 3, the output of which is connected to the input of the additional counter 6 and the K-input of the counter 7. The counting input of the counter 7 is connected to the output of the controlled divider 9 with a variable division factor, the input of which is connected with the release of the second key 4,

and the control inputs with the outputs of the auxiliary counter 8. The input of the auxiliary counter 8 is connected to the output of the first key 5, the control input of which is connected to

the first output of control block 1,

the second output of which is connected to the control inputs of the additional and second keys 3 and 4. The information input of the second key 4 is connected to the second output of the reference frequency generator 2, the first output of which is connected to the information input of the first key 5.

Frequency meter works as follows.

The control signal with frequency x is fed to the input of control unit 1, which generates a pulse equal to T

and feeds it to the control input of the first key 5, thereby allowing the passage of the frequency Q from the generator 2 of the reference frequencies to the auxiliary counter 8. When T expires, the auxiliary counter 8 has a fixed number n associated with the frequencies fx and fp correlating

5 x

where f is the sampling error.

After that, the control unit generates an exemplary one-second pulse, synchronizing its beginning with the beginning of the next period T, and supplies it to the control inputs and keys .3 and 4. Additional key 3 allows the input of the monitored signal to the additional counter b, and the second key 4 passes to input controlled dekf- from the general 9 frequency f.

torus 2.

The division factor of the controlled 60 divider 9 is set equal to the number stored in the auxiliary counter 8. The pulses from the output of the controlled divider 9 with a frequency

s

65 f1 - 0 are fed to the counting input

counter 7, to the input of which a monitored signal is applied. Counter 7 has an overflow blocking circuit with a modulo k count (not shown). Upon completion of the exemplary one-second pulse in the additional counter 6, it turns out. a fixed number equal to the integer part of the result, and in the counter there are 7 fractional parts in the k-th parts of Hertz. Due to the fact that the measurement of the period T occurs with an error f, the value of the frequency ti is higher than the true frequency fk fx.

The values of the parameters n, f, f, required - in order for the contents of counter 7 not to contain an error greater than or equal to one unit of code, is determined from consideration of the case when the time interval between the passage of the last pulse of the monitored frequency f and the end of the measuring one-second interval, close to tx. Due to the presence of 7 additional overflow circuits in the counter 7, its contents cannot have a value greater than 4-1. The value of Y.-1 should not occur in the counter 7 of the duration of the specified period of time less than

k - 2

TX (K - 2) -

JCA

Framed f f about x f-

+ f max -f-,

about

get relations

n k - 2

fo (k - 2) to

fi k (k - 2) fx

The values obtained are substantially lower than those for the known device. The reason for this is the decrease in the accumulation time of the error of the divergence of the moments of generation of pulses of k -fold frequency in comparison with their true values. This time is reduced from the duration of the entire measurement period in a known device to the duration of one period of the monitored frequency. As a result, it becomes possible to significantly improve the accuracy of frequency measurements.

The technical and economic effect of the application of the proposed frequency meter will be expressed in increasing the accuracy

measurements in cases where it is necessary to measure the frequency in a short period of time. If we compare this frequency counter with the known one and assume that both

device built on the element base, having a boundary frequency of 25MGd, we get that with an accuracy of 0.1 Hz () the known device can operate at frequencies up to 500 Hz, and

the proposed frequency meter is up to 250 kHz, with an accuracy of 0.01 Hz (X-100); the known device is up to 50 Hz, the present frequency LR is up to 2.5 kHz, the accuracy is 0.001 Hz (K-1000) for a known device is unattainable, while the proposed frequency meter can work with such an accuracy up to a frequency of 25 Hz.

20

Claims (2)

1. Author's certificate of the USSR 524139, cl. G 01 R 23/10, 1975. 2. The author's certificate of the USSR 573768, cl. G 01 R 23/10, 1976. .h