SU1665314A1 - Digital integrating voltmeter - Google Patents

Abstract

The invention relates to a digital measurement technology, in particular to voltmeters, which provide for the suppression of network interference and the intrinsic noise of circuit elements intended for measuring small signal levels. In order to improve the accuracy of measuring low-level signals, additional scaling units 7 and 9, a DC amplifier 8 integrating the voltage converter 5 into the time interval, and a computing unit 6 are introduced into it. The control unit 4 generates a control signal, under the influence of which Modulator 1 produces a signal equivalent to an input signal with an interference signal present in it. The modulator 1 signal enters converter 2 and through block 9 into converter 5, the output signals of which are processed in computing block 6 by the algorithm described in the description, as a result of which digital readout block 3 displays the corrected measurement result. 2 Il.

Description

1

The invention relates to digital electrical measuring equipment, in particular, to digital voltmeters, which ensure ine net network interference and the intrinsic noise of the elements of the integrating converter circuit included in their composition, and can be used for accurate measurements of small signals.

The purpose of the invention is to improve the accuracy of measuring low level signals.

Figure 1 shows the functional diagram of the digital integrating voltmeter; in Fig. 2, time diagrams, (in Fig. 2a, the input signal with interference, in Fig. 2b, the signal at the control input of the modulator, in Fig. 2b, the output signal of the modulator).

The voltmeter contains a modulator, 1, an integrating voltage converter 2 in the time interval, a digital terminal unit 3, a control unit 4, the first output of which is connected to the control input of the modulator 1. The second output of control unit 4 is connected to the control inputs of the integrating transformer voltages 2 and 5 in the time interval, and the third output of the control unit 4 is connected to the control inputs of the digital reading unit 3 and the calculated unit 6, the scaling unit 7, the DC amplifier 8, the second scaling unit 9, The scaling unit 7 is connected to the first signal input of the modulator 1, and the output to the second signal input of the modulator 1, the output of which is connected to the input of the integrating voltage converter 2 in the time interval through the DC amplifier 8 and the output of through the integrating voltage converter 5 in the time interval is connected to the second input of the computing unit 6, the first input of which is connected to the output of the integrating voltage converter 2 in the time interval, the output computing voltage The second block 6 is connected to the input of the digital readout block 3, and the first signal input of the modulator 1 with the input of a 10 voltmeter.

The voltmeter works as follows.

The measurement process is as follows. During time T (see Fig. 26, the signal at the control input of the modulator 1) the input signal consisting of the wanted signal Vx and the interference Un (t), U1x (t) Vx + Un (t), is connected by the modulator 1 to the input of the amplifier 8 DC, the transmission coefficient of which is equal to K const At the input of the amplifier 8, in addition, a signal acts

Own noise Um (t), whose spectrum corresponds to the spectrum of flicker noise (tfsh from 0 to 1-5 kHz).

The signal from the output of the amplifier 8 is fed to the input of the voltage converter 2 at a time interval and to the input of the scaling unit 9, the transmission coefficient Kg of which is frequency-dependent and is determined by the following expression

. . fl. When f TF W

const 1, with

eleven

where F sp-ppp Tpjp .uj is the modulation frequency of the modulator.

Since the input i signal Ux Vx + Un (t) is modulated by the frequency F, and the noise signal of the dc amplifier 8 is not, then at the output of the scaling unit 9 we get a signal equal to

Kg (f) U1 KK2Vx + KK2Un (t) + KUu, (t). As a result, signals will be present at the inputs of voltage converters 2 and 5 in the time interval during time T, respectively

W U KVx + KUn (t) + KUuj (t):

U2 K2 (f) Ui KK2Uh + KK21) pM + ish (1), where U1 is the signal at the output of the amplifier 8.

Due to the fact that the input signal turns out to be an amplified DC amplifier 8 times K, the influence of the intrinsic noise of the voltage converters 2 and 5 in the time interval on the result of the conversion can be neglected. Therefore, at the end of time T at the outputs of converters 2 and 5, time intervals equal to

  shchT1 T T Ui

T12 I Sh- where V0 is the reference voltage.

In computing unit 6, codes N i and N 2 will be formed proportional to time intervals T1c and T 12.

Ni1 N Ui1:

where N is const.

Next, in computing unit 6, the difference is calculated

Ni1 - N12 NUi1-NU12 NKVX (t) + NKUiu (t} -NKK2Vx - (xJKK2Un (t), - NKUui (t) NK (VX + Un (t)) (1-K2)

Dividing the received code by the number (1-Kg) which is stored in the memory of the computational block 6, we get the code

N1 NK (Vx + Un (t)) NKU1K (t) which is then stored in the computing unit 6

During the time T, the signal that arrives at the second input of the modulator 1 from the output of the scaling unit 7 is inverted and fed to the input of the DC amplifier 8. Taking into account that the transmission coefficient K of the scaling unit 7 is frequency-dependent and equal to npnf fn const 1, fade where Fn "Pf.sh is the frequency of network interference, then obviously the signal arriving at the input of amplifier 8 will be equal to U11x (t) -Vx-KiUn (t).

The inputs of the integrating converters 2 and 5 of the voltage in the time interval will receive, respectively, the signals Ui (Vx + KiUn (t) + Uiii (t));

N112 - -KK2 (Vx + KiUn (t)) + KUu, (t).

At the end of time T, time intervals will be formed at the outputs of converters 2 and 5

t ,, -. иГ. t 21 7 7 W

t1122

t t N1 7 H If1 and in the computing unit 6 corresponding to these intervals codes

N i-NU; 1i:

N112 NU112. Then the difference will be obtained

N111-N112 NK (Vx + KiUn (t) -Um (t) - NKK2 (Vx + KiUnWJ + NKUiuW - NK (Vx + KiUn (t)) (1-K2), after dividing by the number (1-Cd) will get

N11 - NK (Vx + KiUn (t)) NKU11x (t).

Since the modulation frequency F is significantly higher than the interference frequency fn, we can assume that the interference signal does not change during the modulation period 2T. In view of this, subtract the code of the previously received code N1 and dividing the result by a number (1-K), which is permanently stored in the memory of the computing unit 6, find a code proportional to the interference

Nn NKUn (t).

Subtract the found code from the N code, we get the code proportional to the measured signal Vx

NX - N - Nn NK (Vx + Un (t)) - NKUn (t) - NKVX,

which is then transmitted to a digital counting unit 3 for indicating

Claims (1)

Invention Formula Digital integrating voltmeter containing modulator, first integrating voltage converter in the time interval, digital reading black, a control unit, the first output of which is connected to the control input of the modulator, the second output of the control unit is connected to the control input of the first integrating voltage converter in the time interval, and the third output of the control unit is connected to the control input of the digital reading unit, characterized in that In order to improve the accuracy of measuring low-level signals, a computing unit was additionally introduced into it, the first scaling unit whose input is connected to the first signal input of the modulator, which is vho- house also voltmeter and the output of the first the scaling unit is connected to the second signal input of the modulator additionally inputted, the DC amplifier whose input is connected to the output of the modulator, and the output of the DC amplifier current is connected to the inputs of the first integrating voltage converter in the time interval and the second scaling unit, the output of which is connected to the input of the second integrating voltage converter in the time interval, and its control input is connected to the second input of the control unit, the first input of the computing unit is connected to the output of the first integrating voltage converter in the time interval, the second input of the computing unit is connected to the output of the second integrating voltage converter in the time interval , the control input of the computing unit is connected to the third output of the control unit, and the output of the computing unit is connected to the input of the digital reading unit. y / ... rll Phys, 2