SU1718135A1 - Method and device for measuring low-frequency change rate - Google Patents

Abstract

The invention relates to a measurement technique and can be used in devices for emergency response automatic power systems. The aim of the invention is to reduce the measurement time and simplify the device implemented in this method. The advantage of the device in comparison with the known ones is to provide a higher rate of measurement of the change in frequency due to the absence of loss of time for mathematical processing of the code difference, as well as ensuring higher reliability of the result while simplifying the instrumental composition of the device. 2 s and 2 z. P. f-ly, 2 ill.

Description

The invention relates to electrical measuring technology and can be used in devices of regime and emergency control systems of power systems.

The purpose of the invention is to reduce the measurement time and simplify.

The essence of the method for measuring the change in low frequency is as follows.

The duration of the period of the input signal is measured by filling it with pulses of a standard frequency and counting the number of these pulses, finding the difference in the duration of the periods between each two consecutive measurements of the period, while linearizing is performed during the period of filling the period of the input signal with pulses of the reference frequency by changing the number of these pulses by an amount previously determined by the formula

(f x | -1 fy). fcp TXI - Tx t- t

N

cor

where fx i - i, Tx i - 1 is the frequency (Hz) and the period (s) of the previous (I) measurement;

fxi. TX | is the frequency (Hz) and the period (s) of the current measurement;

, fx i - 1 - fxi

fcp - average

frequency, Hz;

AU — discreteness of measurement of the frequency measurement frequency, Hz / s;

di-tn3

to, y - exemplary period

i + ditn

frequency, s,

Tn is the period of the measured nominal frequency, s.

Indeed V frequency changes can be expressed

 Af-fxj-f-fxj U-- р-т

fx i -1 - fxj

T

 At

- (fx j - 1 - fxi) fcp

(one)

where At is the time interval between measurements, and Ter is -t. Ter

The rate of change of frequency can also be expressed through the period of the measured frequency.

I1

 f X | - 1 - f X |

vТс7

 (TX | --Tx | - i) T x | T x i - i TSR

In the described method, the frequency change rate is obtained as the difference in the measurement results of the durations of the periods of the measured frequency by filling them with the sample frequency pulses (the linear part of the formula (2), and the V F dependence (TX | - Tx | 1) takes the form

------ - with correction in the process of flow- -

full (the nonlinear part to formula (2), the V F (y) dependence is provided by the corrective impulses NKOP) and the counting of the number of these impulses.

Then the formula (2), expressed in the number of pulses, takes the form

Nv Th (Th-h h-mkor. (3)

to

The number of corrective pulses Mcor for each section is calculated in advance, taking into account the predetermined discreteness of measuring the rate of change of frequency А V to ensure that the required number of pulses is equal according to formula (1) and actually obtained (3)

(f x i - 1 - f xi) fcp t xi - t x t - i

- + NKOP,

w

to

(four)

from here

m (- 1 -fx |) fop Txi -Txl 1 NKOP -----

m /

to

(five)

FIG. 1 shows a block diagram of the device; in fig. 2 - time diagrams that show his work.

The device for measuring the rate of change of the low frequency contains serially connected generator 1 of exemplary frequency, element I2, digital linearizer 3 and subtraction unit 4, the output of which is the output of the device, as well as serially connected input driver 5 and control unit b, the second input of which is connected to the output of the generator 1 exemplary frequency, the third input - to the output of the digital l inoerizer 3.

The first output of the control unit 6 is connected to the second input of the subtraction unit 4, the third output to the second output of the And 2 element, and the fourth output to the installation input to

Initial state of the digital linearizer 3.

The control block b contains a control counter 7, the input of which is set to its initial state through an OR 8 element is connected to the first input of the control block b, the clock input of the control counter 7 through the And 9 element is connected to the second input of the control block 6, the first and second outputs of the counter 7 controls through a block 10 of amplification gels are connected, respectively, to the first and second outputs of the control block b. The third output of control counter 7 is the fourth output of control unit 6, and the fourth output is connected to

0 is the inverse of the input element AND 9 and is the third output of the control unit. The third input of the control unit 6 is connected to the input of the decoder 11, the output of which through the single-oscillator 12 is connected to the first input

5 elements OR 8.

Block 4 of the subtraction contains serially connected register 13 of the memory of the previous measurement result, adder 14, register .15 of the memory of the result of measuring the rate of change of frequency. The input of the memory register 13 is connected to the second input of the adder 14 and is the first input of the subtraction unit 4, the clock input of the memory register 13 is the third input of the subtraction unit 4, and the clock input of the memory register 15 is the second input of the subtraction unit 4.

The device for measuring the rate of change of the low frequency works as follows

0 way.

At the end of the measured period, the input driver 5 produces a short pulse (Fig. 26), starting a new period measurement cycle. This pulse sets the count 7 of the control to the initial state (to zero), and at its fourth output a signal is set that permits the passage of the pulses of the reference frequency from the output of the generator 1 (Fig. 2a) through the element

0 And 9 to the clock input of the control counter 7 and at the same time prohibiting their passage through the element AND 2 to the input of the digital linearizer 3 (Fig. 2c). Digital linearizer 3 stops, result code

5, the period measurement from its output goes to the second input of the adder 14, and the first input of the adder 14 at this time contains the measurement result code of the previous period recorded in memory 13, while the output of the adder 14 forms the difference code of the measurements of the two adjacent periods corresponding to the rate of change of frequency, which is stored in the register 15 of memory on the signal from the first output of the counter 7 of control (Fig. 2d). The signal from its second output (Fig. 2d) stores the code from the output of the digital linearizer 3 to the memory register 13, and then, the signal from the third output of Control Counter 7 (Fig. 2e) is reset to the digital linearization The torus 3, in the initial state of which, takes into account the number of pulses transmitted to the counter 7 of the control from the generator 1 of the reference frequency to generate control signals. The signal from the fourth output of the control counter 7 (Fig. 2c) prohibits the passage of pulses from the generator 1 of the reference frequency to the input of the counter 7 of the control, which stops in this state, and allows the passage of these pulses through the And 2 element to the input of the digital linearizer 3, which counts the pulses of the corrected sequence until the end of the period of the measured frequency, which is the beginning of the measurement of the next period.

With the disappearance of the measured frequency, the digital linearizer 3 reaches the state determined by the decoder 11, at the signal from which the one-shot 12 produces a short pulse setting the control counter 7 to the initial state. Before the signal of the measured frequency appears, the device operates according to the signal from the decoder 11, therefore the code at the output of the digital linearizer 3 will each time reach the same value. Since the control signals from the output of the control counter 7 are formed in the usual sequence, in register 15 of the memory from the output of the adder 14, the zeros will be rewritten, i.e. in the absence of a measured frequency, the device issues a code for the rate of change of the measured frequency equal to zero, in contrast to the known device, where the code for the rate of change of the frequency of the previous signal that is present before its disappearance is issued.

As an example, we can consider a device for measuring the rate of change of the frequency of an industrial network of 50 Hz, with a range of variation from 45 to 55 Hz, with a speed measurement resolution of 0.1 Hz / s. As a result of the calculation, the frequency range from 44.938 to 55.075 Hz is divided into 200 sections with a duration of 0.2048 ms.

For the measured nominal frequency (Tn-0.02 s), we determine the period of the reference frequency.

to

8 TO 7 s.

reference frequency f0 MHz.

B

The number of corrective pulses per area is calculated by the formula (5).

The advantages of the proposed device in comparison with the known one are in providing a higher rate of measurement of the change in frequency due to the absence of loss of time for mathematical processing of the code difference, as well as in 5 higher reliability of the result while simplifying.

Claims (4)

1. A method of measuring the rate of change of the low frequency, which consists in measuring the period of the input signal by filling it with pulses of an exemplary frequency and counting their number, finding the period difference between two each successive measurements of the period 5 and linearization, different from that, in order to reduce the measurement time and simplify, the linearization is carried out during the filling of the period of the input signal with pulses of exemplary frequency by changing the number of these pulses by an amount previously limit according to a mathematical expression .. (f x} - 1 - f xi) fcp t xi - t x i - 1 5 NKOp -DUЈ- where fx i - i, Tx i -1 - frequency (Hz) and period (s) of the previous (1-1) measurement; fxi, Tx | -frequency (Hz) and period (s) of the current measurement; iff TX i - 1 xi tcp -; - o - average value frequency, Hz; Di-discrete speed measurement 5 frequency change, Hz / s; to -5- - period sample 1 + AU Tn howl frequency, s; Tn is the period of the measured nominal frequency, s. 2. A device for measuring the rate of change of the low frequency, comprising an exemplary frequency generator, a subtraction unit, the output of which is the output 5 of the device, serially connected an input driver and a control unit, the output of which is connected to the second input of the subtraction unit, decrease time In addition, simplified, a serially connected AND element and a digital linearizer are introduced in it, the output of which is combined with the first input of the subtraction unit and the third input of the control unit, and the output of the reference frequency generator is combined with the first input of the And element and the second input of the control unit whose second output is connected to the third input of the subtraction unit, the third output to the second input of the element I, and the fourth output to the input of the installation to the initial state of the digital linearizer. 3. The device according to claim 2, characterized in that the subtraction unit comprises a first memory register connected in series, an adder and a second memory register, the output of which is the output of the subtraction unit, the first input of the subtraction unit being connected to the input of the first the memory register and the second input of the adder, the second input - with the clock input of the second register memory, and the third input - with a clock input of the first memory register. 4. The device according to claim 2, which is designed so that, in order to increase the reliability, the control unit contains serially connected decoder, one-shot, OR element, control counter and amplifier unit, while the clock the control counter input is connected to the output of the AND element, the first input of the control unit is connected to the second input of the OR element, the second input is connected to the first input of the AND element, the third input is to the input of the decoder, the first and second outputs of the block control units are connected via the amplifier unit, respectively, with the first and second outputs of the control meter, the third output of the control unit is combined with the inverse input of the And element and the fourth output control meter; and the fourth output is connected to the third control meter output. :"".,.one FogL "Lllll .... Lillp ... lg s II ... l g P j.; P l ... FIG. 2 .... l ... r P l ..