SU1205045A1 - Digital wattmeter - Google Patents

Description

The invention relates to measurement technology and can be used to build digital AC power meters.

The purpose of the invention is to increase the measurement accuracy.

Fig, 1 shows the structural scheme of the proposed wattmeter; Fig. 2 shows timing charts of the control unit; in fig. 3 - output signal, converter n1tr g: e- not to frequency.

The digital power meter contains the first 1, second 2 and third 3 switches, multiplication unit 4, differential integrator 5, key 6, sampling and storage unit 7, voltage-to-frequency converter 8, element 9, pulse counter 10, and a control unit 11 consisting of a period generator 12, a counting trigger 13 and a logic element, AND 14.

The input sources x (t) and Xj (t) through the first fixed contacts of the first and second switches 1 and 2 are connected to the inputs of the multiplication unit 4, the output of which through the third switch 3 is connected to the inputs of the differential integrator 5. The output of the integrator 5 through the key 6 and Sampling and storage unit 7 is connected to the input of the FNC 8, the output of which through the element 9 is connected to the input of the pulse counter 10. The output of the FNC 8 is connected to the second fixed contacts of the first and second switches 1 and 2. The control inputs of the switches 1, 2 and 3 and element 9 are connected to. the first output of the control unit 11, the second and third outputs of which are connected to the input of the pulse counter to zero and the control input of the key 6, respectively, and the input of the block 11 is connected to the first input source X (/ (t).

The input of the control unit 11 is the input of the period generator 12, the output of which is connected to the counting input of the trigger 13 and to one input of the element 14, to the other input of which the inverse output of the trigger 13 is connected. Forward and inverse outputs

about

the trigger 13 and the output of the And element 14 are the outputs of the control unit 11.

The digital power meter works as follows.

five

0

five

0

In the initial state (conditionally), the trigger 13 of the control unit 11 is reset to zero, the switches 1, 2 and 3 are in position a, the key 6 is closed, the output voltage of the differential integrator 5 is recorded in the sampling and storage unit 7, the logical element E9 closed, the counter 10 pulses reset.

The frequency-digital wattmeter operates cyclically (iteratively), with each cycle always consisting of the following two cycles.

In the first cycle, the control signal from the output of the period generator 12 (Fig. 26) sets the flip-flop 13 to state 1 (Fig. 2c), whereby the switches 1, 2, 3 go to the position in, the key 6 opens, the logical element E9 opens , allowing the passage of pulses of the PNC 8 to the input of the counter 10 pulses.

The output signal of the FNC 8 poses on both inputs of block 4 multiplication; the square of the output of the FNC 8 is integrated; the flow of time T, equal to the period of the input signal x (t) (Fig. 2a). As a result, after the completion of the first clock cycle, the output voltage of the differential integrator 5 is equal to

Xc.) Sf4Xo) c | tty8j,

where Xj, is the initial voltage of the integrator 5;

f (xg) is the output signal of the FNC 8; dL B - respectively, the total multiplicative and the total additive errors of the series-connected multiplication unit 4 and the integrator 5.

Simultaneously with the operation of the integrator 5, the pulse counter 10 counts the number of pulses N of the output frequency of the low-frequency digital converter B, which arrived at the integrator 5 during the first clock cycle.

The second cycle starts with the arrival of the second control pulse from the output of the period generator 12, when the trigger 13 is set to the state O, the switches 1, 2, 3 are switched to the position a, the element I9 is closed (Fig. 2e), the key 6 is closed (Fig . 2d.

31205045

Produced integration

the input voltage) .X2 (t) of the multiplication unit during the same time interval T. As a result, after the completion of the second cycle, the output voltage of the differential integrator 5 is equal to t

Xo- (l + fl) 5f tXjc / t4p + T o

(J), ii- x (i) () jf (Xo) dt

then

((. (t) x COclt.

Since the key 6 is closed during the entire clock cycle, the voltage from the output of the integrator 5 is copied to the sampling and storage unit 7.

So at the end of the second

tact at the output of block 7, we have t

Ai V () jfWc / t + o

t

) 5x, Ct) x (t) dt. about

The resulting voltage Hz will determine the new refined value of the frequencies f (x,).

The pulse counter 10 at the end of the second clock cycle is reset by the pulse from the output of the AND 14 element (Fig. 2e). This cycle of operation of the device ends.

Further operation of the device is similar to that described. as a result, after n cycles of operation of the device, at the output of the sampling and storage unit 7, we obtain the voltage

 Xv,) KHXv .. o

- (itoCjSX-, Ct) X2. (t) Jt (1)

about

in steady state, the output voltage of block 7 does not change from cycle to cycle. This means that the negative increments at the output of the integrator 5, obtained in the first tact

 l f Kjcft, - o

. (x - steady-state value) are exactly equal to positive increments.

() jx, (i) x, (tjat,

received in the second measure. In this way,

 ocjKaiK.cOc / bd-ocjff xJcIt.

 -

(one

The integral value in the right-hand side of (2) is the volt-second area (Fig. 3)

S (x ,,) vn. (3)

As follows from expressions (2) and (3), code N

M. -u.Z, x, a) X, (t.) CJtСМ

impI lo about

20

determines the energy of the input measured signal for the period, and the output

frequency (f. -) LEL 8 - power- -i

25 ness

| HD) L, (1M1 - (5)

about

thirty

From the description of the operation of the device,

as well as from expressions (2), (4) and (5), it follows that additive and multiplicative errors are

the included multiplication unit 4, the differential integrator 5, the sampling and storage unit 7, and the IFC 8 are excluded from the final result and have no effect

measurement accuracy.

Unlike the prototype, the measurement accuracy of which depends on the errors of the nodes and blocks used, in the proposed device, the overall accuracy is much higher and is limited almost only by the stability of the volt-second output area

foot. pulse php 8.

If the cycle time is desired to be set equal to pT, then in control block 11, instead of trigger 13, a frequency divider with

the division ratio of p. This will further improve the measurement accuracy.

u

m ri t

Claims (2)

1. A DIGITAL WATMETER containing a voltage to frequency converter, the output of which is connected via an AND element to the counting input of a pulse counter, a first switch, the first fixed contact of which is connected to the first input bus and to the input of the control unit, the first and second outputs of which are connected respectively to another the input of the And element and the reset input of the pulse counter, characterized in that, in order to increase the measurement accuracy, a multiplication block, a second and third switch, a differential integrator are introduced into it, a key and a sampling and storage unit, the movable contacts of the first and second switches being connected to the corresponding inputs of the multiplying unit, the output of which is connected to the movable contact of the third switch, the fixed contacts of which are connected to the inputs of the differential integrator, the output of which is connected through the key and the sampling and storage unit with the input of the voltage to frequency converter, the output of which is connected to the second fixed contacts of the first and second switches, the control inputs of which are connected with the control input of the third switch and the first output of the control unit. the third output of which is connected to the control input of the key, and the first fixed contact of the second switch is connected to the second input bus. 2. The power meter according to claim 1, wherein the control unit comprises a period former, a counting trigger and a second element And, the output of which is the second output of the control unit, the first input is connected to the inverse output of the counting trigger, direct and inverse outputs which are respectively the first and third outputs of the control unit, and the counting input is connected to the second input of the second element And and the output of the period former, the input of which is the input of the control unit.