SU1597780A1 - Converter of difference of impedances of two-terminal networks to voltage - Google Patents

Abstract

The invention relates to a measurement technique and can be used in measuring various physical quantities by means of differential parametric sensors. The purpose of the invention is to increase speed and improve the linearity of the conversion function. The two-terminal impedance to voltage difference converter contains a source of excitation signal 1, a diode 2, 3, an integrator 4, a switch 5, a capacitor 6, a repeater 7, a reference resistor 10, a control unit 11, a voltage to current converter 12, a section 13 of a coaxial cable The common bus is 14, and 8, 9 are measurable two-pole networks. 2 Il.

Description

The invention relates to a measurement technique and can be used to measure various physical quantities by means of differential parametric sensors.

The purpose of the invention is to increase speed and improve the linearity of the conversion function.

FIG. Figure 1 shows a structural electrical circuit for converting the difference between the impedances of the two-terminal and the two-terminal; pas figs. 2 shows the voltage plots at the output of the excitation signal, the integrator and the control unit. The two-terminal impedance-to-voltage-to-voltage converter contains the source 1 of the excitation signal, the first 2 and second 3 diodes, the integrator 4, the switch 5, the capacitor 6, the repeater 7, the first 8 and the second 9 measured two-poles, the reference resistor Yu, the control unit 11 , voltage-to-current converter 12, coaxial cable section 13, and common busbar 14.

The excitation signal from source 1 enters through a segment 13 of the coaxial cable, the outer conductor of which is connected to a common length of 14 to a common point of the first 2 and second 3 diodes, as well as to the first input of the integrator 4. The input and output of the first 2 and second 3 diodes are respectively connected the inputs of the first 8 and second 9 measured bipolar networks, the outputs of which are connected to a common bus. The output of the integrator 4 is connected via a switch 5 to a capacitor 6, and is also connected in series with a repeater 7, a voltage-to-current converter 12, a reference resistor 10 and a total thickness of 14. The output of the converter 12 is connected to the first controlled input of the source 1 and the second input of the integrator 4 The control unit 11 is connected to a first output with a switch 5, and a second output to a second control input of source 1.

The converter of the difference of the full resistance of the two-pole to voltage works as follows.

The excitation signal source 1 generates an alternating current of symmetrical shape with an amplitude of 1 ° (the current may also be rectangular). The negative polarity pulses are passed through the first diode 2, the first two-terminal 8, having an impedance Zi, and a reference resistor 10 (Ro). And the positive polarity pulses pass through the second diode 3, the two-pole 9, having the impedance Z-, and the reference resistor 10. The polarity of the excitation signal varies in pulses of duration T / 2, which follow with a period T, controlling the effect on source 1 is the signal from the second output of control unit 11. The voltages generated on the two-terminal 8 and 9 and the reference resistor 10, under the action of the excitation signal from the source 1 and the current from the converter 12, are integrated by the integrator 4.

If the source 1 of the excitation signal generates a sinusoidal current signal Ui with an amplitude value equal to b, then at time 1 "the voltage at the integrator output is equal to n. During the first half-period of the signal it is excited and the inputs of the integrator have three voltages: loZi, loRo and (Kt is the constant transmission coefficient of the converter 12). Under their action, the voltage U4 at the integrator output decreases with speed

5 I oZ 1 I oRo + u “inj K :: o.

Rde t is a constant of integrator time 4. During the second half period T / 2 after the change of the sign of the excitation signal, the voltage at the integrator output increases with speed

IoZ2-loRo-U "n KnKrRo.24 - I;

25 At the end of the transformation period T at time i, + voltage at the output of the integrator, taking into account the fact that with zero initial conditions on the integrator 4 RC -1- j U8x (t) Uo const, the voltage up to which zhizha integrator 4 for

30 time T, equal to

(T)

(3)

and the fact that the time over which the voltage on the integrator reaches the value of the voltage - 35, applied to its input, when the condition is equal, and also taking into account expressions (1) and (2) is determined by the following expression

.zh (40 in

 X (loZ | -InRo + Uex pn K ntRo) dt- | - (InZ2-IoRo-U.) Dt. (four

t-o

45 In the steady state, the voltage conversion at the output of the integrator 4, UebU (nf 1, ..., which takes place at times 1 ", U + i, ..., will be equal, i.e., Taking this into account, and also believed that at this time 50 the impedance Zi has a transformation relative to its nominal value () -AZ, and the impedance 7, -f-AZ, from the expression (4) we get

55

(UenK-jAZIo UiwxKnHTRn

- +

+

AZlo UBbi "K Ro

(five)

from where

,, AZlo

)

KC

This voltage on the signal Ui, ii from the first output of the control unit 11 is stored on the capacitor 6. Since the capacitor 6 is charged through a small resistance of the switch 5 from the voltage source, which in this case is the integrator 4 with respect to the capacitor 6, for its charge, a pulse of sufficiently short duration, i.e. fulfilling the conditions 1 „« T. The specific numerical value of the duration t is determined in the practical implementation, taking into account the choice of the element base.

The resulting expression (6) is a conversion function. In general terms, it can be presented in the following form:

, (7)

where K const. K-wrRo

The view functions are linear, therefore the transformation function (7) is also linear.

Claims (1)

Invention Formula The converter of the difference of the impedances of the two-terminal to voltage, U; i containing the first diode connected in series, the inner conductor of the coaxial cable segment, the integrator outer conductor coaxial cable 5 is connected to a common bus; a second diode connected by a positive polarity to the output of the first diode; and a capacitor and a source of excitation signal, the input of the first diode and the output of the second are terminals for connecting the inputs  and the common ground is a terminal for connecting the outputs of the first and second measurable two-terminal through the outer conductor of the coaxial cable, characterized in that, in order to increase the speed and improve the linearity of the conversion function, sequentially connected control unit, switch, repeater, voltage converter are introduced to the current, the reference resistor and the common bus, the output of the voltage to current converter is connected to the second input of the integrator and the first output of the source of the excitation signal, the second od which is connected to the first input of the integrator, the second output controlling unit is connected to the control 25 is the input of the source of the excitation signal, the integrator output is connected to the second output of the switch, the capacitor input is connected to the first output of the switch, and its output is connected to the common bus, the repeater output and the common bus being 30 terminals for removing the informative voltage. h Y / 2 H II   I  -. ,, XT Xt xIP + SbiK. CnJKfjHT XT X x