SU605312A1 - Effective value digital voltmeter - Google Patents

Description

This invention relates to the field of digital electrical measuring technology.

A known effective value voltmeter based on integrating voltage converters with a quadratic conversion characteristic, comprising a voltage-code converter, a counter, a reference voltage generator, keys and a digital reading device 1. Its disadvantages are the low accuracy determined by the metrological characteristics of the integrating converters and poor performance due to the fact that the measurement process consists of several cycles.

Also known is an effective-value digital voltmeter comprising an input switch, a voltage-to-frequency converter, a control unit, keys, a reference frequency generator, a code-frequency converter, a reversible counter, a counter, a code-voltage converter, and a digital reading device. One of the signal inputs of the switch is connected to the input terminal of the device, and the other is connected to the output of the code-voltage converter; the output of the switch is connected to the input of a voltage to frequency converter, the output of which is connected to the signal inputs of one of the keys and one of the code-frequency converters; the control input of this key is connected with the control input of another key and connected to the output of the control unit, the other two outputs of which are connected to the control input of the switch and the counter reset input, respectively; the output of the first key is connected to the control input of the first code-frequency converter; the signal input of the second key is connected to the signal input of the first code-frequency converter and

reference frequency generator output; the output of this key is connected to the control input of the second code-frequency converter, and the outputs of both code-frequency converters are connected to opposite inputs of the reversible counter, the output of which, in turn, is connected to the counter input; the code inputs of the latter are connected to the control inputs of the code-voltage converter and the digital reading device 2. The accuracy of such a device is limited by the presence of an analog switch in the input signal circuit, the metrological characteristics of the code-voltage converter, as well as

cannot be provided sufficiently low due to the fact that the creation of high-frequency voltage transducers — a frequency with a quadratic characteristic, with sufficiently high metrological indicators, is a complex technical task. In addition, this device has low speed, since the measurement process consists of. "3 two cycles. The aim of the invention is to increase accuracy. .the device speed. The indicated target is: the effective value of a digital voltmeter containing the first and second keys, the first and second code-frequency converters, the reversible counter, the counter, the digital reading device and the reference frequency generator, the output of the first key associated with the control the input of the first code-frequency converter, the output of which is connected to the summing input of the reversible counter, the signal input of the second key is connected to the output of the reference frequency generator, and the input of the digital reading device is connected According to the invention, a voltage converter is inserted in the time interval, a third, fourth and fifth keys, code matching elements, a trigger, a second counter and a frequency divider, the output of the voltage converter in the time interval being connected to the control inputs of the first and the second key, and the quantization input - with the output of the first code-frequency converter; the signal input of the first code-frequency converter is connected to the output of the first key; The input of the frequency divider is connected to the output of the reference frequency generator, its first output is connected to the clock input of the voltage converter in a time interval and to the reset input of the first code-frequency converter, the second output is with the signal input of the first key and the control input of the second converter code- frequency, and the third output is connected to the reset input of the second code-frequency converter, to the reset input of the second counter, to the first separate trigger input, as well as to the reset input of the first counter; the signal input of the second code-frequency converter is connected to the output of the reference frequency generator; The control inputs of the% koh elements are connected to the parallel outputs of the reversible counter and the second counter, and their output is connected to the second separate input of the trigger, the output of the latter connected to the control inputs of the third, fourth and fifth keys, the signal inputs of which are connected respectively with the output of the second code-frequency converter, the first code frequency converter and the reference frequency generator; the outputs of the third, fourth and fifth keys are connected respectively to the subtraction inputs of the reversible counter, the second counter and the first counter. FIG. 1 shows the structural scheme of the proposed voltmeter; in fig. 2 are timing diagrams illustrating the process of obtaining information about the value of the input signal. The voltmeter contains a voltage-to-time converter 1, a first key 2, a second key 3, a first code-frequency converter 4, a second code-frequency converter 5, a third key 6, a fourth key 7, a reversible counter 8, a code matching element 9, a counter 10, a trigger 11, a fifth key 12, a digital reading device 13, a counter 14, a reference frequency generator 15, and a frequency divider 16. The measured voltage is fed to the input 17 of the converter 1, the output of which is connected to the control inputs of keys 2 and 3, and the quantization input to the output of the converter 4. The output of key 2 is connected to the control input, and the output of key 3 to the signal input converter 4. The opposite inputs of the counter 8 are connected to the output of the converter 4 and to the output of the key 6, the signal input of which is connected to the output of the converter 5. The output of the generator 15 is connected to the signal inputs of the keys 3 and 12, to the signal input of the converter 5 and to the input of the divider 16 , the first The output of which is connected to the clock input of the converter 1 and to the reset input of the converter 4, the second output is connected to the signal input of the key 2 and to the control input of the converter 5, and the third output is connected to the reset inputs of the converter 5, the counter 10 and one of the separate trigger inputs 11, as well as to the reset input of the counter 14. The output of the counter 14 is connected to the input of the device 13, and the input to the input of the key 12. The control inputs of the element 9 are connected to the parallel outputs of the counters 8 and 10, and its output is connected to the second separate trigger input AND, the output of which is connected to the control inputs of the keys 6, 7 and 12. The input of the counter 10 is connected to the output of the key 7, the signal input of which is connected to the output of the converter 4. The process of transforming the voltage into a time interval is described by the system of equations i / of / LT-X T 1 1 -1 t T, + T., T - const, where t is the integrator time constant; T is the conversion time of converter 1, i.e., the duration of the elementary conversion cycle of a digital voltmeter; TI and - informative time intervals; UQ is the reference voltage of converter 1; Ux is the input voltage. The implementation of this system gives the conversion function of the form T - - T. At time Ti, a signal appears at the output of converter 1 that permits the passage of pulses through keys 2 and 3. In converter 4, during this time, the number of pulses is equal to

A n TrT-f ..

about

where Ux (t) is the instantaneous value of the input signal;

fi is the pulse frequency at the second output of the divider 16.

The output frequency of the converter 4 is equal to

 f f fl

f,. / o - and,

GDR / VQI-capacity of the counters of the converter 4;

5 is a constant division factor of divider 16 at the second output;

fn is the frequency of the generator 6 of the reference part.

Then during the time T of the elementary conversion cycle, the number of pulses appears at the output of converter 4, equal to

 FS WlM.

L „T, T,

ul, i-s

at the end of the elementary conversion cycle, the clock pulse frequency ft resets the control counter of converter 4 to zero, after which it is ready for a new conversion cycle. The duration of the elementary transformation T is significantly less than the period T: the signal under study, therefore, during one conversion cycle, voltage and (t can be assumed unchanged. As a result of summation over the conversion time Tn (to minimize the error from non-multiplicity Tg, integer number of periods Ux (t), Tn should be several tens of times longer than the period of the input alternating voltage), determined by the period of following the PULSES from the third output of the frequency divider 16, and further digital processing of the received sum oluchaets result, linearly coupled with the effective value of the input voltage. The accumulation of systematic error in the digital voltmeter is eliminated by quantization zaklyuchayuschegos output pulses in synchronization duration TI transducer 1 comprising counting (quantizing) impz lsami output transducer 4.

The above process is illustrated by time diagrams presented in FIG. 2, where 18 - pulses of the clock frequency fj at the first output of the frequency divider 16;

f - -L19

PULSES frequency G „

(n is a constant coefficient) at the third output of the divider 16, which specifies the conversion time; 20 - pulses at the output of the converter 4; 21 pulses at the output of the converter 5; 22 - codes values in the reversible counter 8 (dotted line) and in the counter 10 (solid line); 23 - pulses at the output of element 9; 24 - the signal at the output of the trigger P.

The pulse bursts from converter 4 are continuously fed to the summing input of the reversible counter 8. At the time point ft, when the frequency pulse fr flips trigger 11, thereby opening keys b and 7, the bursts start to arrive at the input of counter 10, and the reversing counter to read input 8 PULSES of linearly varying frequency are received from converter 5:

ffi / 0

f - iii. - liLf -

 f, f,

  r 1 ° -

M, oS

N02L oo

where f is the current time value;

five

dGy, is the capacity of the counters of the converter 5;

ultrasound

/ Ci L is the constant coefficient.

As a result of this, the code value in counter 10 increases, and the current code value in

0 reversible counter 8 decreases. At time fz, the codes in the reversible counter 8 and in the counter 10 become equal, and at the output of the element 9 of the codes coincidence there appears an impulse which, triggering

5 flip-flop 11, closes keys 6 and 7. After that, the code in counter 10 stops changing and remains constant until the end of the conversion cycle Tn, and the code in reversing counter 8 is increased due to the summation of bursts of pulses that continue to flow to its summation input. At time t. It comes with a frequency / t iulus, which resets counters 10 and 14 and converter 5 to zero and triggers a trigger

5 11. Next, the next conversion cycle begins.

The process of changing the code in the reversible counter 8 during the time Tn of one transformation cycle is described by the system of equations

rm t

..fN ,,

T „+ T,„ T „SOP81

45

P,

f, fdi N ,, + Y

 f KUl (О df КТ „- г Ul (f} dt

50

 ktA.

55 from

7 „(, f LAF.

Claims (2)

At the time Tp, the key for the passage of the pulses fo key 12 is opened, and in the counter 14 a number proportional to the effective value of the input voltage Ux (t) is recorded, which is fixed and processed by the device 13. At the end of time Г "1 the counter 14 is reset by the pulse / t After which it is ready for the next measurement cycle. Thus, the speed of the offer is proposed by akimiiiii, JDi: f. voltmeter due to the time G „v mwi-j uw.iJ. J of one conversion cycle instead of two cycles in a known device. To eliminate the transient process that occurs in this kind of system when the input signal changes abruptly and consists in adjusting the informative time T, the counter 14 is used, which provides the code change counter scan of the code in the reversible counter 8. ObCUllVC ptD p -riiJHk lYl h iiiix - -. The error rate of discreteness in the device is determined by the value of the output frequency of the gene, - o. ,, -, - r, a rator 15 of the reference frequency, which may be several orders of magnitude larger than the maximum achievable output frequency of the voltage to frequency converter. DETAILED DESCRIPTION A digital voltmeter of effective values comprising first and second keys. The first T-code converters are frequency, reversible counter, first counter, digital reading device and reference frequency generator, the output of the first key is connected to the control input of the first code-frequency converter, the output of which is connected to the summing input of the reversible counter: ka , the signal input of the second key is connected to the output of the reference frequency generator, the input of the digital reading device is connected to the output of the first counter, characterized in that, in order to increase accuracy and speed, enter The voltage converter in the interval of time, the third, the fourth, and the interpolation are IShSrSAL Dp.,, ii., i, t- ,,,. .. -. ... KEYS, code match elements, trigger, second counter and frequency divider, with the output of the voltage / time converter being connected to the control inputs of the first and second keys, and the quantizing input with the output of the first code-frequency converter, signal input lane - “- --- g.„ „“ nllTJOTJ converter code-frequency is connected to the output of the second key, the input of the divider hour, t, tt. The -ovnn GT.RPMTR.GIA TSNPtoty is connected to the output of the reference frequency generator, and its first output is connected to the clock input of the voltage converter and to the reset input of the first code-frequency converter, the second output is connected to the signal input of the first key and the control the input of the second code-frequency converter, the third output 1 of the keys to the reset input of the second code-frequency converter, to the reset input of the second, tt tgtg L tt TG TS-PLLG LG PaELR GGT-.RMPML counter input and to the first separate trigger, as well as to the entrance reset the first counter, the signal input of the second code-frequency converter is connected to the output of the reference frequency generator, the control inputs of the code match elements are connected to the parallel outputs of the reversible counter and the second counter, and their output is connected to the second separate trigger input, and the output of the latter is connected to the control Yusch, it inputs the third fourth and fifth keys, the signal inputs of which are connected respectively to the outputs of the second code-frequency converter, the first code-frequency converter of the reference oscillator, wherein the outputs of the third, fourth and fifth keys are respectively connected to the inputs of subtracting the down counter, the second counter and the first counter. Sources of information taken into account during exertiz 1. USSR Copyright Certificate No. 367389, - f ,. „.. Q7, cl. l U1K, 1U1-. m- 2. USSR author's certificate No. 4U4 / i1, cl. G 01R 13/02, 1973. 1 rrn (, Tn2 (GngY) Tn () (Tri.n tiJ)