SU700842A1 - Frequency measuring device - Google Patents

Description

SUBSTANCE: device is used for frequency measurement based on zero-intersection analysis, containing sequentially connected zero pulse generation unit and pulse counter U The disadvantage of this device is low accuracy, frequency measurements . It is also known a device for measuring the frequency of voltage transitions through a zero level, containing a serially connected counter of numbers, corresponding to zero-crossing points, a multiplier and a cumulator, a zero-non-intercept number counter, the output of which is connected to the second input of the multiplier, and the input is connected to the first input of a counter of numbers corresponding to zero-crossing times, as well as a generator of reference time stamps connected by an output to the second input of a number counter corresponding to zero-crossing moments 21, Nedos The device is its sensitivity to an unknown random initial phase of the signal, which leads to significant systematic errors in the case of initial phase inequality zero. The purpose of the invention is to improve the measurement accuracy. The goal is achieved by; that the device for measuring the frequency, containing the first counter connected in series, the multiplier and the adder, the second counter whose input is connected to the first input of the first counter, and the reference oscillator whose output is connected to the second input of the first counter, has entered a subtraction unit, memory block and a divider, the first input of which is connected to the input of the adder, and the second with the first output of the memory unit, the second output of which, as well as the output of the second counter, is connected to the inputs of the subtraction unit, the output of which is connected to the second the progress of the multiplier. The drawing shows a block diagram of a device for measuring frequency. The device contains a reference generator 1, a first counter 2, a multiplier 3, an adder 4, a second counter 5, a subtraction unit 6, a memory block 7 and a divider 8,

The device works as follows.

Let the signal under study be

UH Tle SCt expjZltftl-vntf), (1)

where S (t) is the complex signal envelope ;,

f is the signal frequency; n (t) is the calling noise component. ,

With a sufficiently large signal-to-noise ratio, according to power, the moments of zero-intersections of the signal can be represented as

 H o, i.2, ... N; (2)

where TO is the signal period; . n is the zero-crossing number; - the random fluctuation of the i-th null intersection due to the noise component of the signal.

Using the least squares method, the signal frequency estimate can be found from the condition

(o - xv "to.: (3)

by this

, Nbv,

  I

(four)

about nl nn .l

N Sint, -TlnS - t

 mo mo h - o

The disadvantage of the algorithm (4) is the need to form two

statistician. 5itt-t., M hO

Expression (4) can be significantly simplified without degrading the quality indicators of the algorithm, if we assign the estimate I to the middle of the observation interval, ° i. summing in the expression (4) to produce in the symmetric limits -i, while the frequency estimation algorithm takes the form

N-t

2tcp

(five)

N-I / Z l

Z1 n-t

M

-Y- ||

From the comparison of expressions (4) and (5), it is important that the latter requires a smaller amount of calculations, which provides a simpler technical implementation of the device.

The proposed device for frequency measurement provides the implementation of the operations defined by expression (5). The flow of zero-intersections of the signal under study is fed to the combined inputs of the counter of 2 numbers, corresponding to the zero-crossing points, and counter 5 of the number of zero-intersections. At the output of the counter 5, the number n is formed, equal to the number of transitions of the signal under study through the zero level during the interval from the observation. At the same time, in the counter 2 the numbers -t y, are formed, which correspond to the time interval from the beginning of the observation interval to the n-th intersection by the signal of the zero level. These numbers correspond to the number of counting pulses of the reference generator that allowed the counter input for the specified time intervals.

Since the elimination of the influence of the accidental initial phase is provided by transferring the estimate of the frequency f to the middle of the observation interval,: Number 7 is entered in memory block 7, equal to half the number of zero-intersections that must be analyzed, i.e. the length of the sample is fixed by the number of zeros. A number of memory block 7 and the number n of counter 5 are fed to the inputs of subtraction block b, the output of which forms the difference of numbers. The indicated difference of the numbers Vi from the output i of the subtraction unit 6 from the output of the counter 2 is fed to the input of the multiplier 3, which implements the oner 0

the product is fed to the input of the adder 4, the output of which forms a number equal to and enters the input of the divider 8. In addition to 5 of this, the memory cell 7 is entered the number 2, S h. This constant is used by the B ika4ecTBe divisible in divider unit 8, the output of which gives the desired frequency estimate f

Claims (2)

Invention Formula A device for measuring the frequency, containing in series the first counter, a multiplier, and an adder, the second, a counter, the input of which is connected to the first input of the first counter and the input bus and A reference generator, the output of which is connected to the second input of the first counter, characterized in that, in order to improve the measurement accuracy, a block is inserted into it. a subtractor, a memory unit and a divider, the first input of which is connected to the output of the adder, and the second to the first output of the power unit, the second output of which, as well as the second counter, is connected to the inputs of the subtraction unit, the output of which is connected to the second input of the multiplier. Sources of information, pr. tie into account during the examination 1. Kolchinsky B.E ... Mandurovsky I.A. Konstantinovsky M.i. Autonomous Doppler devices and aircraft navigation systems. M., Sov, Radio, 1975, p. 233. 2. Andronoy I.S. Snitko B.N. On the measurement of the frequency of voltage transitions through the zero level. Radio engineering, t. 29, 6, 1974.