SU1287038A1 - Device for measuring frequency - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used in the development of regulators of the frequency of power plants, rotational speeds of turbo-power units, as well as control systems and automation of electric drives. The purpose of the invention — improving measurement accuracy — is achieved by eliminating the amplitude error of the output characteristic, and improving reliability by simplifying the setting when the Q-factor of the resonant circuit is changed. The device contains limiting amplifiers 1 and 4, buffer cascades 2 and 5, frequency conversion to phase block 3, adder 6, subtractor 7, blocks 8 and 9 of rectifying analog subtractor 10, smoothing filter 11, output block 12. Error for the nonlinearity account in the narrow range is in the dead zone of the device less than 0.06%. 2 Il. (ABOUT

Description

FIG.

112

The invention relates to electrical measuring equipment and can be used in the development of frequency controllers of power plants, as well as speed controllers of rotation of turbine power units, control systems and automation of electric drives.

The aim of the invention is to improve the measurement accuracy by eliminating the amplitude error of the output characteristic and improving the reliability by simplifying the setting when the quality factor of the resonant circuit is changed.

Fig, 1 shows a functional diagram of the proposed device; Fig. 2 is a vector diagram explaining the operation of the proposed device.

The device contains the first amplifier-limiter 1, the first buffer stage 2, the frequency-to-phase unit 3, the second amplifier-limiter 4, the second buffer stage 5, the adder 6, the subtractor 7, the first and second rectifier blocks 8 and 9, the analog subtractor 10 , the smoothing filter 11 and the output unit 12. The device input is the input of the first amplifier-limiter 1, the output of which is connected to the input of the first buffer stage 2, the first output of which is connected to the first inputs of the adder 6 and the subtractor 7, and the second input through in series with a single frequency-to-phase conversion unit; a second limiting amplifier 4; and secondly, a buffer cascade 5 is connected to the second inputs of the adder 6 and the subtractor 7, whose outputs are connected to the inputs of the first and second rectifier blocks 8 and 9, respectively, whose outputs are connected respectively, with the first and second inputs of the analog subtractor 10, the output of which is connected to the input of a smoothing filter 11, the output of which is connected to the input of the output unit 12.

The device works as follows.

Voltage Ug of arbitrary shape and amplitude of the measured-frequency is fed to the input of amplifier limiter 1, which generates a Primolyg signal arriving at the buffer stage 2, which generates signals from a square signal for Adder 6

8 .2 and the subtractor 7 and the frequency conversion unit 3, performed on the series resonant circuit with a simultaneous phase shift of 90 by including the capacitance in the feedback of the amplifier. At the output of block 3, a "sinusoidal" waveform is generated, the amplitude of which is determined by the frequency response of block 3. To eliminate the uneven frequency response in the measured frequency range, this signal goes to the second limiting amplifier 4 and through a buffer stage 5 a stable square wave signal is fed to the adder b and subtractor 7. From the outputs of the adder 6 and the subtractor 7, signals are fed to the inputs of the full-wave blocks of the rectifier 8 and 9, after which they are fed to the analog subtractor 10, and then through the filter 11 to the output block 12, s is a current mirror, the output current is independent of the load.

If we consider the signal at the outputs of the adder 6 and the subtractor 7, then, starting from the vector diagram for the first harmonic (figure 2), we will have

v,

Vj. 4vT + V, + 2V ,,

where is) --Cf (w); Cf (w) arctg

 oc .;

Rx

| f, Cj., R | - parameters of the serial resonant circuit.

Since V, then

& Vp- | 2 + 2coscp V - j + coscf 2V „

45

50

Vj. V - 242coscf V-j24 -c.o7t7 2Vp.

These signals are fed to the inputs of the analog subtractor 10, the output of which is equal to

U, c,

V -V T 9U Cf ,, -, qJ. Qln-w

(about y: v cos2, (p) 21, (| - |) 2V, 42sin (| -f.M);

. Q (w) Mr,, where V is a stabilized value

U, „-2 U„ z1p 5,

voltage independent of frequency;

12

- in general

non-linear dependence on frequency. For frequency range + near

B (.) Resonant Q at

ъ: / h. (f (u) arctp (--- Q),

Ny

-G

i (0 Denote. Then

Wo

sin tp (Lo) sin arctg a; a

arctp a arcsin

f .a sin c (.w) sin arcsin

four(")

2Sin-j; For the case of iO} / Wo "1

. “(W)„ ucj. s ,,

So, in a given range

V

Bblx

242V / r.

° CP

To estimate the error due to

. W (w) nonlinearity, express through

ASO

d- without assumptions,

lm

a1

, l- -. -BUT"

Let us determine the error due to nonlinearity in measuring the magnitude of the frequency deviation from the nominal value.

eight %

BUT,

five %

rts this k-f

error

lii (Tn) 100%

, B & f

Ir - - - -

 uf.

oe „

The error due to nonlinearity in measuring the absolute value of the frequency can be defined as the error in hertz S, referred to the measured value of the frequency

th

one

287P38 8

S% k f ,, fi% kfv. five

00% (fl fH 100G

and correspondingly %. When the quality factor of the circuit, 1 will be, respectively, S, S% 0.1% - the maximum value of the error on the border of the range. Within the measurement range of frequency deviations from the nominal value, the error due to the non-linearity of S%; is 0.1%. In a real device, Q -1.5 and the error due to nonlinearity in a narrow range is in the dead zone of the device (less than 0.06%).

Claims (1)

Invention Formula ten 0 A frequency measuring device comprising a first limiting amplifier whose input is the input of the device, a frequency-to-phase conversion unit and a series-connected smoothing filter and 5 output block, ex: It is imperative that, in order to improve the measurement accuracy and reliability of the device, the first buffer stage was introduced, the second limiting amplifier and the second buffer stage, the adder, the subtractor, the first and second blocks were connected in series rectifier and analog subtractor, the output of which is connected to the input of the smoothing filter, and the first and second inputs are connected respectively to the outputs of the first and second rectifier blocks, the inputs of which are connected respectively to the outputs of the adder and output reader, the input inputs of which are connected to the first BbiM output of the first buffer stage, and the second inputs with the output of the second buffer stage, the input of the first buffer stage connected to the output of the first amplifier limiter, and the second output of the first buffer stage to the phase , the output of which is connected to the input of the second limiting amplifier. five 0 five