SU1164617A1 - Voltmeter - Google Patents

Description

The invention relates to techniques for electrical measurements, in particular to voltmeters, and can be used to measure voltages.

The purpose of the invention is expansion. dynamic range.

Figure 1 shows the block diagram of a voltmeter; in FIG. 2, the first control unit, an embodiment of '; in fig. 3 and 4 - timing charts of the voltmeter.

The voltmeter contains the first analog. gob key 1, the first output of which is connected to the input bus, and the other through the first resistor 2 is connected to the input of the operational amplifier 3 connected to the output of the operational amplifier 3 through the first capacitor

4, the second analog switch 5, the first output of which is connected to the output. the first reference voltage source 6, and the other through the second resistor 7 to the input of the operational amplifier 3, the first comparator 8, the first input of which is connected to the output of the operational amplifier 3, the second with a common bus, a coincidence unit 9, the input of which is connected to the output of the first comparator 8 and the output is with an indicator counter 10, and the first control unit 11, the first output of which is connected to the control input of the first key 1, the second output to the control input of the second key

5, the third output - with the control input of the coincidence unit 9, as well as the second capacitor 12 connected in series and the third analog switch 13 connected in parallel to the first capacitor 4, the second comparator 14, whose first input

I is connected to the output of the operational amplifier 3, the second source 15 of the reference voltage, connected to the second input of the second comparator. 14, the second control unit 16, the first input of which is connected to the output of the second comparator 14, the second - to the output of the first comparator 8 and the input of the first control unit 11, and the output to the control input of the third key 13.

The first control unit 11 comprises, for example, a master oscillator 17, the output of which is connected to a frequency divider 18, the output of which is connected to the first input of the first element I 19, the second input of which

connected to the output of the master oscillator 17, the inverter 20, the output of which is connected to the first input of the second. element And 21, the second input of which is connected to the output of the frequency divider 18. The output of the frequency divider 18 is the first output, the output of the second element And 21 is the second output, the output of the first element And 19 is the third output, and the input of the inverter 20 is the input of the control unit 11.

The second control unit 16 may be implemented as a short-circuit trigger.

The voltmeter works as follows.

In the initial state, all analogue switches are open, capacitors 4 and 12 are discharged. Thus, zero initial conditions are provided for the integrator at the time of the start of measurements.

The cycle of the voltmeter includes two cycles.

In the first cycle, the measured randomly varying pulsating voltage (for example, the modulus or square of the voltage of a random signal) or the deterministic pulsating voltage is integrated, and in the second cycle, the opposite reference voltage is integrated. For this purpose, to the control input of the first analog key 1 from the first control unit 11. a signal is sent (fig.Za), which opens the key in the first bar • and closes in the second. The control input of the second analog key 5 in the first cycle is supplied from the first block 11 of the control locking signal (Fig.36). The third analog key 13 at the beginning of the first cycle is closed by a signal (FIG. 3) from the second control unit 16 '.

In the first cycle T1, under the influence of the input voltage and _ah , a current flows through the resistor 2, due to which the capacitor accumulates a charge концу proportional to the integral value of the input voltage over the integration period T1 by the end of the first cycle.

τ,

1164617

where and is the integral value

input voltage for? time from 0 to T1;

- resistance of resistor 2. Capacitor voltage 4 5

(fig.Zv) at the same time is proportional to the integral value of the converted voltage and _6x for the period of integration and inversely proportions-. the integral time constant of the integrator · 10 torus

'out

% _

WITH.

6X

(2)

15

where C is the capacitance of the capacitor 4; E ₁ -C ₁ - the time constant of charge ^ zyr. four '

The charge time constant 'Г' _{3е) р η is} chosen so that the voltage on the capacitor is in the Kth part of the integration interval T1 of the input voltage at the maximum integral value of the input voltage and _in . _{Mo (ks} . Reached the maximum voltage at the output of the integrator and the output max., I.e.

20

25

(3)

The maximum voltage at the output of the integrator is determined by the magnitude of the reference voltage of the source 15, which is fed to the second input of the comparator 14. When the inputs are equal, the comparator 14 is activated and its output signal (Fig. 3g) is fed to the first input of the second control unit 16, which outputs a signal (fig.Zd), which included ₄₀ chaet third analog switch 13.

For reliable operation comparator

14 must have a hysteresis.

The capacitance in the feedback circuit of the operational amplifier 3 increases

l g g - ^ “p

Phy / SfF "β, - β ^

•(four)

50

where C ₂ is the capacitance of the capacitor 12.

As a result, there is a re-.

charge distribution between two capacitors 55 and 5 capacitors. Voltage at the integrator output after charge distribution between the capacitors

happening (6)

and _{vj (V} £, if one ignores the voltage on which the capacitors charge during the transient process by the input voltage, it becomes

out-mix " ^{and out-} max ^and out-G" 4 = -k- ''

Further integration runs with a time constant.

Chir ^C 4

Moreover, if at the input of a voltmeter a voltage acts for a time T1 with a value equal to _{eX mo (ks} , then at the output of the integrator the voltage reaches again the value · υ _{β4> ιχ} max ·

The second integration clock T2 begins with closing the key 1 and opening the key 5 from the signal control unit 11 (FIG. 3a and b) and integrating using a constant reference voltage resistor 7_op from source 6, opposite in sign input. Key 13 continues to remain indoor, which is determined by the signal from the second control unit 16 (FIG. 3).

Since the beginning of the integration of the reference voltage ϋ _{οη, the} charge on the capacitor, and hence the voltage at the integrator output, decreases linearly with time:

out ’

about

Eh

(7)

(at)

where ^ time = K ₂ - - constant

discharge time ·,

₂ - the resistance of the resistor 7.

In block 9 of coincidence, during the second clock cycle T2, counting pulses are fed from control unit 11 (FIG. Ze), however, when triggered, comparator 8 stops their flow through block 9 in coincidence into counter-indicator 10.

The operation of the comparator 8 occurs at time b, with

five . one

equal to zero voltage at the output of the integrator, i.e. when compensating for charge with a reference voltage, from where:

ίχ

ABOUT)

² "

(.ten)

ET "ί

At the time of operation of the comparator 8 is disconnected from the input of the integrator reference voltage analog key 5.

As a result, at the beginning of the new integration cycle, a zero initial condition is provided on the integrating capacitors 4 and 12, as well as a reset to the initial state of the second control unit 16, the signal from the output of which opens the analog key 13. Thus, the initial state of the voltmeter is again set.

The integration time of the reference voltage ϊ _{2 is} proportional to the integral value of the voltage over the integration interval T, (10), the same is true for the number of pulses n accumulated in the counter-indicator 10,

'2.

^ ET ^ 2. ^T MF

(1-1)

where T _ss is the period of counting pulses. The ratio of time constants ·

direct and reverse integration (resistance and K ₂ ), the period of the counting pulses' T _C and the value of the reference voltage and ^ _t are chosen in such a way that the number of them is 164617 6

pulses, and consequently, the code in the counter-indicator 10 is equal to the numerical value of the parameter of the input quantity (voltage or power).

₅ With the beginning of a new work cycle

The voltmeter turns on key 1. Measurement processes are repeated.

If the average value of the voltage at the input ¹⁰ for the period of integration Bani T1 ^ and less. _BxMax , then the second

the capacitor 12 is not connected throughout the T1 interval. Having received the charge determined by the input voltage 15 θΜ υ _βχ , the capacitor 4 has a voltage K times the end of the cycle than it would have been if the capacitor 12 was connected in the feedback circuit of the amplifier 3.

20

' ^T 1 P

^{1 r} and _a «сП = · ^ - [υ _Β χ άΐ, (and)

^Ζ ΒΧ

25

thirty

The time of reverse integration ί ₂ does not change here, since it does not depend on the size of the capacitance (10).

Consequently, the slope of the output voltage u and _Bb integrating the second cycle (Figure 4) in the 'X times greater than the voltage

35 ϋβΐ, ι * ^with capacitance C _{0Bi (} which causes K times less error Δί "in comparison with error Δί 'due to the error of operation and drift of comparator thresholds ΔΐΙ ,, ορ,

40 and also due to the noise of the integrator and the comparator. As a result, the dynamic range of эeon increases by approximately K times.

I

1164617

entrance

Fiá.1

1164617

Fig.Z

Claims (1)

VOLTMETER containing the first analog switch, the first pin of which is connected to the input bus, and the other is connected via the first resistor with the input of the operational amplifier connected to the tricks of the operational amplifier through the first capacitor, the second analog switch, the first output of which is connected to the output of the first reference voltage source and the other through the second resistor. · - to the input of the operational amplifier, the first comparator, the first input of which is connected to the output of the operational amplifier, and the second - with a common bus unit matches, the input of which is connected to the output of the first comparator, the output with an indicator counter, and the first control unit, the first output of which is connected to the control input of the first key, the second output to the control input of the second key, the third output to the control input of the coincidence unit, so that, in order to expand the dynamic range, the second capacitor and the third analog switch connected in parallel with the first capacitor, the second comparator, the first the stroke of which is connected to the output of the operational amplifier, the second reference voltage source connected to the second input of the second comparator, the second control unit, the first input of which is connected to the output of the second comparator, the second with the output of the first comparator and the input of the first control unit, and the output to the control input third key. 1164617 > 1164617