SU918873A1 - Digital frequency meter - Google Patents

Description

(54) DIGITAL FREQUENCY

The invention relates to converters of the frequency form of information representation in digital and can be used in various measuring and converting devices, automatic control systems with frequency-pulse sensors and information transmission systems.

A digital device for frequency measurement is known / Based on counting an integer number of periods and taking into account the fractional part of a period in the reference measurement time interval, the beginning of which coincides with the beginning of the period of the measured mouth part til.

The disadvantage of this device is a must. synchronization of the reference intervals with the period of the measured frequency, and the frequency, which leads to an incomplete measurement. the use of input information for successive measurements, and, consequently, to a decrease in the measurement accuracy and an inaccurate estimate of the speed of measurement of the frequency from two adjacent measurement intervals.

The closest in technical essence to the present invention is a digital frequency meter comprising a reversible counter, a reference frequency divider, a set of coincidence elements, an assembly element, a memory register and a timing circuit for recording information from a reversible counter into a register with measured frequency 2.1 pulses.

This device has a high speed, the possibility of obtaining a multiplied value of the measured frequency.

The disadvantage of it is low accuracy due to the unstable time interval between the moments of transfer of information in the output register. Moreover, the multiplied value of the measured frequency is reproduced with a large dynamic error, and at a low measured frequency, the transfer of information to the output register, due to the synchronization of the transfer by signals of the measured frequency, results in the appearance of oscillatory transients. These disadvantages limit the application of the device. The purpose of the invention is to improve the measurement accuracy, expanding the range of measured frequencies and functionality due to the possibility of obtaining a multiplied value of the measured frequency and frequency proportional to its derivative. The goal is achieved by the fact that in the CCFR frequency counter containing a reversible counter, a reference frequency divider, the outputs of which the group inputs are connected to the first match, the inputs of which elements are connected to the inputs of the assembly element, and a key, the count input of the frequency divider is connected to the reference frequency bus, entered phase discriminator, two keys and a frequency divider, with the control inputs of the first and second keys connected to the first output of the phase discriminator, the second input of which is connected to the control input the third key, the information input of which is connected to the frequency reference bus, and the output with the summing input of the reversible counter and one of the inputs of the assembly element whose output is connected to the information inputs of the first and second keys, the output of the last of which is connected via an additional frequency divider the first input of the phase discriminator, the second input of which is connected to the bus of the measured frequency, the output of the first switch is connected to the subtractive input of the reversible counter, the outputs of the bits of which are connected to the second m inputs of the group of matching elements. The drawing shows a block diagram of a digital frequency meter. The digital frequency meter contains a reversible counter 1, a divider 2 of the reference frequency, a group of 3 coincidence elements, an assembly element 4, a phase discriminator 5, an additional frequency divider 6, keys 7, 8, and 9. You devices are reversible counter 1 outputs, the code of which changes is proportional to the measured frequency, the output of the switch 7, which forms the multiplied value of the measured frequency, and the outputs of the switches 8 and 9, which form a frequency proportional to the derivative of the measured frequency. A frequency meter is a tracking system with a frequency form of information representation. The comparison of the measured frequency with the feedback frequency is carried out in phase using phase discriminator 5. The phase difference is converted to frequency using keys 8 and 9. This frequency is integrated by reversing counter 1, the code of which is converted to proportional frequency by divider 2, by matching elements of the group 3 and the assembly element k. Divider 6 serves to match the frequency scales, proportional to the reversible counter code, with the input frequency. . The presence of two integrators in a closed loop tracking system (a reversible counter and an integral relationship between the frequency and phase of the feedback signal) can cause self-oscillations. Therefore, to ensure the stability of the measurement circuit and to obtain high-quality transients, the frequency from the input of the reversible counter 1, the average value of which is proportional to the derivative of the output code of the reversible counter, is summed (taking into account the sign of the derivative) with the frequency of the feedback signal by the element and key 7. Reverse counter code 1 is applied to the control inputs of a group of 3 match elements. The pulse inputs of each coincidence element of group 3 from divider 2 are supplied with a frequency proportional to the weight of the discharge of the reversible counter connected to the control input of this coincidence element. Assembly element A sums the frequencies proportional to the weights of the bits of the reversible counter, in which the units are written, i.e. At the output of this circuit, a frequency is formed, proportional to the code in the reversible counter f. f N oy N +1 where N is the code in the reversible counter; mcw is the maximum value of N; - reference frequency. In order to obtain an intelligent frequency value, the frequency reference value must satisfy condition 7 In the initial state of phase discriminator 5, keys 8 and 9 are closed, key 7 connected to the output of phase discriminator 5 through the inverse input is open. When the input frequency pulse arrives before the feedback frequency pulse, the phase discriminator 5 enters the second state, in which key 8 opens, pulses with frequency x are fed to summing input of reversible counter 1 and summed by element 4 with a frequency proportional to the reversing code. counter 1, until then. until the pulse at the output of the divider 6 is developed and the phase discriminator 5 is returned to its original state. With an earlier arrival of the pulse from the output of the divider 6, the phase discriminator 5 enters the third state, in which the key 9 opens and the key 7 closes. At the same time, the frequency pulses, etc., of the reversible counter code begin to flow to the reverse subtracting input counter 1 and are disconnected from the input of the divider 6, which is equivalent to subtracting from the feedback frequency the frequency fed to the subtracting input. Upon arrival of the input frequency pulse, the phase discriminator 5 returns to the initial state. In the established mode of operation at a constant input frequency, the number in counter 1 is proportional to the input frequency, the frequency at the output of switch 7 is equal to the input frequency multiplied by the division factor of divider 6. The input pulses and pulses at the output of divider 6 coincide not only in frequency, but also out of phase with an accuracy of the period of the multiplied frequency at the input of the divider 6. Exact coincidence of the phases of the input feedback pulses is impossible; therefore, the phase discriminator works on each period, skipping to the summing (subtracting) input rever 1 ivnogo one pulse counter. The same pulse is summed with the multiplied frequency in the feedback circuit (subtracted from it). Thus, the ripple numbers in counter 1 per unit low-order characteristic of digital systems, measurements, are also observed in the proposed device. When increasing (decreasing) the input frequency at the output of the phase discriminator 5, connected to the key 8 (9), pulses appear with a certain duty ratio. Key 8 (9) transmits to the summing (subtracting) input of counter 1 of a burst, increasing (decreasing) the contents of counter 1 until the phases of the input signal and feedback signal match. At a constant rate of change of the input frequency, the duty cycle at the output of the phase discriminator Q is set to such a value that the rate of change of the code in counter 1 is equal to the input frequency proportional to the speed and: change the input frequency. The maximum dynamic frequency tracking error, which varies with a constant speed, is 1.5 times larger in the known cyclic frequency meter than in the proposed-following frequency meter. There is also no dynamic error of the multiplied value of the measured frequency at the output of the key of the proposed device in this mode. With the disappearance of the input frequency in a known device, the transfer of information to the output register disappears, which leads to the preservation of the last measured frequency value for an unlimited time. The proposed frequency meter does not have this drawback, since the code change in the reversible counter begins before the end of the input frequency period. The use of a phase discriminator as a comparison element in a frequency meter, which is a digital tracking system with a frequency form of information representation, allows for a high accuracy comparison of the measured frequency and the feedback frequency. Due to the correction of the multiplied value of the measured frequency and the change of the number in the reversible counter at the end of each period, the input frequency is significantly reduced; Uts dynamic errors in the multiplied value of the measured frequency, 1.5 times reduced dynamic errors in the measured frequency value, expands frequency stability range in the low frequency range. The invention The digital frequency meter containing a reversible counter, a divider of the reference frequency, the outputs of which are connected

Claims (2)

Claim A digital frequency meter containing a reversible counter, a reference frequency divider, the outputs of which are connected to the first inputs of the group of matching elements, the outputs of which are connected to the inputs of the assembly element, and a key, the counting input of the reference frequency divider being connected to the reference frequency bus, characterized in that, in order to increase the accuracy of measurements, expand the range of measured frequencies and functionality, a phase discriminator, two keys and a frequency divider are introduced into it, and the control inputs of the first and second keys connected to the first output of the phase discriminator, the second output of which is connected to the control input of the third key, the information input of which is connected to the reference frequency bus, and the output is connected to the summing input of the reversible counter and one of the inputs of the assembly element, the output of which is keyed to the information inputs of the first and the second key, the output of the last of which, through an additional 5th frequency divider, is connected to the first input of the phase discriminator, the second input of which is connected to the measured frequency bus, the output of the first yucha ¹⁰ is connected to the subtract input of down counter conductive, discharges the outputs of which are connected to the inputs of the second group elements coincide. * 5 Sources of information taken into account during the examination 1. USSR copyright certificate No. 567145, cl. G 01 R 23 / S, 1974. 2. Copyright certificate of the USSR 20 No. 402818, cl. G 01 R 23/00, 1972.