RU2488130C2 - Scanning meter of cg-dipole parameters - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: scanning metre of CG-dipole parameters comprises an amplitude detector, conductivity and capacitance indicators, an integrator, a comparator, a high frequency generator, connected via a voltage-current converter with a metering circuit, to a signal input of which and to a common wire there is a metered dipole connected. Additionally the following components are introduced: a peak detector, a differentiator, a timer, a square ware generator, a solving device, a modulating capacitor. A conductivity indicator is connected to the output of the metering circuit via the peak detector, the first input of the comparator - via the amplitude detector and the differentiator, the second input of the comparator is connected to the common wire, the output - with the first input of the timer, the second input of which is connected with the first output of the square ware generator, the output - with the input of the solving device, the first output of the solving device is connected to the control input of the metering circuit, the second one - with the capacitance indicator, and the second output of the square ware generator is connected via an integrator to the control input of the modulating capacitor.

EFFECT: higher resolution capacity by a reactive component of admittance of CG-dipoles, reduced error of measurements.

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Description

The invention relates to measuring technique, is intended for measuring equivalent parameters of CG-two-terminal networks with increased dielectric losses and can be used in industrial control systems for electro-radio elements and technological control of dissipative substances and media.

Known automatic meter of the components of the conductivity of the CG two-terminal, containing a high-frequency oscillation generator, a measuring circuit including an inductor, a controlled capacitor, a modulating capacitor, a key, an adjustable attenuator, a controlled two-terminal, a synchronous detector, a measuring amplifier, a dynamic tracking unit, active conductivity monitoring units and capacitance, phase shifter [A.S. No. 924616 of the USSR, declared. 02.10.80, publ. 04/30/82].

The disadvantage of this device is the low noise immunity caused by transients in the measuring circuit during operation of the key.

The closest solution to the proposed device is a parameter meter of dissipative CG two-pole, containing a comparator, amplitude detectors, a conductivity indicator, a high-frequency generator connected through a voltage-current converter with a measuring circuit, to the information and common inputs of which the measured CG two-terminal is connected, and to the control input - integrator and capacity indicator [RF Patent No. 2314544, decl. 04/14/2006, publ. 01/10/2008].

The disadvantage of this device is the decrease in the resolution of the reactive component of the admittance of the CG two-terminal network, with an increase in the phase measurement error.

The objective of the invention is to increase the resolution of the reactive component of the admittance of a CG bipolar.

The task is achieved by the fact that in the scanning parameter meter of the CG two-terminal network, containing an amplitude detector, conductivity and capacitance indicators, an integrator, a comparator, a high-frequency generator, connected through a voltage-current converter to the measuring circuit, to the signal input of which and to the common wire measured two-terminal, additionally introduced a peak detector, a differentiator, a timer, a rectangular pulse generator, a decoding device, a modulating capacitor, and measure the output the conductor indicator is connected through a peak detector, the first input of the comparator through an amplitude detector and a differentiator, the second input of the comparator is connected to a common wire, the output is from the first input of the timer, the second input of which is connected to the first output of the square-wave generator, the output to the input of the decisive devices, the first output of the solver is connected to the control input of the measuring circuit, the second to the capacitance indicator, and the second output of the square-wave generator is connected via an integrator to control input of the modulating capacitor.

The figure 1 shows a diagram of a scanning parameter meter CG-two-pole; figure 2 - scanned resonant response.

The scanning parameter meter CG - two-pole contains a high-frequency generator 1 connected via a voltage-current converter 2 to the measuring circuit 3. The measured two-terminal 4 is connected to the signal input and the common wire of the measuring circuit 3. The first output of the measuring circuit 3 is connected through a peak detector 5 with an indicator conductivity 6, the second through the amplitude detector 7 and the differentiator 8 with the first input of the comparator 9, the second input of which is connected to a common wire. The output of the comparator 9 is connected to the first input of the timer 10, the output of which is connected to the input of the deciding device 11. The first output of the deciding device 11 is connected to the control input of the measuring circuit 3, the second to the capacity indicator 12. The first output of the square-wave generator 13 is connected to the second input of the timer 10, the second through the integrator 14 with the control input of the modulating capacitor 15.

The device operates as follows.

The conversion function current I - voltage U of the measuring circuit 3 has the form

$$\frac{U\left(j\omega \right)}{I}=\frac{\mathrm{one}}{Y\left(j\omega \right)},(\mathrm{one})$$

where the complex conductivity is

$$Y\left(j\omega \right)=G+g_L+j\omega C_E-j{b}_L,(2)$$

Where

$$g_L=\frac{r}{r^2+{\omega }^2{L}^2}(3)$$

- equivalent active conductivity of the inductive branch,

$$b_L=\frac{\omega L}{r^2+{\omega }^2{L}^2}(\mathrm{four})$$

is the equivalent inductive conductivity, r is the active resistance of the inductor, G is the measured conductivity,

$${\mathrm{FROM}}_E=C_0+C_B+C(5)$$

- equivalent capacity, determined by the sum of the initial capacity C ₀ , the capacity of the varicap C _B and the measured capacity C.

Complex module (2)

$$Y\left(\omega \right)=\sqrt{{(G+g_L)}^2+{(\omega C_E-b_L)}^2},(6)$$

phase

When ωC _E = b _L , a resonance occurs in the measuring circuit, at which the phase

$$\varphi (\omega )=0(8)$$

and the module of the complex

$$Y(\omega )=G+g_L.(9)$$

As a result, the output voltage according to (1) reaches a maximum in which it does not depend on the reactive conductivity of the measuring circuit:

$$U=\frac{I}{G+g_L}.(\mathrm{one}0)$$

For a fixed amplitude of the supply current and active conductivity of the inductive branch g _L, this voltage is determined only by the measured conductivity G, i.e. invariant to the capacitance of a CG bipolar.

To search for resonance, a modulating capacitor 15 is connected to the measuring circuit. An exponentially varying sawtooth voltage is applied to the control input of this capacitor, which is generated by integration in the block 14 of pulses taken from the second output of the rectangular pulse generator 13.

At the stage of exponential decay of the control pulse, the time dependence of the capacitance C _b2 (t) of the modulating capacitor is close to linear, therefore, a periodic change in this capacitance leads to the formation of an alternating voltage at the output of the measuring circuit 3, the envelope of which reflects the resonance characteristic in the form of a periodic function of time (Fig. 2 ) The amplitude detector 7 recovers the envelope; as a result, an alternating voltage is generated in the form of a scanned resonant characteristic periodically repeating with the modulation frequency (Fig. 2).

In figure 2, the scanned characteristic K1 (t) was obtained at a frequency of f = 10 MHz at r = 1 Ω, R = 1 kΩ, L = 1.7 μH, C = 80 pF, G = 0 and G _x = 1 mS. The curve K2 (t) was also obtained with a capacitance C = 80 pF, but with a conductivity G _x = 2 mS. It is seen that a change in the conductivity G _x shunting the circuit is reflected by a change in the amplitude of the scanned characteristic, but does not lead to a temporary shift in resonance, which ensures the invariance of G _x = inv (C _x ). The maximum position of the functions K (t) is determined only by the value of C _x , which ensures the determination of C _x = inv (G _x ). The most distinct change in the capacitance of the circuit is manifested in the time shift of the slopes of the resonance characteristics.

To improve the accuracy of control of the position of the branches of the scanned characteristic, one should switch from the time function of the resonance characteristic to its derivative, for which the voltage from the output of the amplitude detector 7 is differentiated in block 8. Figure 2 shows one period of the differentiated scanned characteristic D (t) at the output of the differentiator 8 . At the moment of passage of the resonance, the function D (t) vanishes. Therefore, it is enough to fix by the comparator 9 the moments of the transition of the characteristics D (t) through zero (for which the second input of the comparator is connected to a common wire) in order to decide on the occurrence of the measuring circuit 3 at resonance. To this end, rectangular pulses from the output of the comparator 9 are input to the first input of the timer 10, the second input of which receives pulses from the rectangular pulse generator 13. The output voltage of the timer is supplied to the input of the resolver 11. The solver 11 when the measured two-terminal 4 is off (no-load mode ) sets the voltage U ₀ at the control input of the measuring circuit 3, at which the capacitance C _v1XX + C ₀ = C ₁ introduces the measuring circuit 3 into resonance at a time

$$t_{Re{s}_0}=t_0+{\tau }_0,(\mathrm{one}\mathrm{one})$$

where t ₀ is the moment of transition of the control pulse from the front to the slice, taken as the reference point, τ ₀ is the time shift of the moment of resonance occurrence, which corresponds to the idling of the measuring circuit 3. On the capacity indicator 12, the decisive device generates a reference 0.

When a measured two-terminal 4 is connected, its capacitance C _x increases the capacity of the measuring circuit 3 to C ₁ + C _x , which is accompanied by a decrease in the time shift fixed by timer 10 to τ ₁ <τ ₀ . To restore the original value C _{1 of the} equivalent capacity of the loaded measuring circuit 3, the solver 11 increases the voltage at its control input until the equality τ ₁ = τ ₀ is restored. In this case, the capacitance of the capacitor C _B1 decreases to a value of C _B1n , at which the additional capacity C _{x is} compensated. Difference

$${\mathrm{FROM}}_{\mathrm{at}\mathrm{one}}-{\mathrm{FROM}}_{\mathrm{at}\mathrm{one}n}=C_x,(\mathrm{one}2)$$

therefore, the compensating voltage generated by the decider 11 can be used to indicate the measured capacitance C _x . For this, the decisive device 11 must enter a voltage proportional to C _x onto the indicator 12 calibrated in units of capacity _.

Information about the conductivity G _{x is} contained in the amplitude of the signal taken from the circuit; therefore _{, a} peak detector 5 is included in the channel for measuring the conductivity G _x . At the block output, in accordance with (10), the constant voltage in idle mode is

$$U_{G_0}=\frac{I}{G_0+g_L},(\mathrm{one}3)$$

where G ₀ is the initial equivalent active conductivity of the unloaded measuring circuit 3. When the measured two-terminal 4 is connected after resonance is restored, the voltage at the output of the peak detector 5

$$U_{G_n}=\frac{I}{G_x+G_0+g_L}\text{.}(\mathrm{one}\mathrm{four})$$

Attitude

$$\frac{U_{G_0}}{U_{G_n}}=\mathrm{one}+\frac{G_x}{G_0+g_L}\text{.}(\mathrm{one}6)$$

From (16) follows the measurement conversion function of the conductivity indicator 6:

$$G_x=(G_0+g_L)\left(\frac{U_{G_0}}{U_{G_n}}-\mathrm{one}\right),(\mathrm{one}7)$$

where g = G ₀ + g _L is the parameter determined during calibration of the meter.

Thus, the proposed device allows the invariant measurement of C _x and G _x in the scanning mode of the transfer characteristic of the measuring circuit, which, unlike the known technical solutions, increases the measurement accuracy by 10 ... 15% and provides digital signal processing at all links of the measuring chains.

Claims (1)

A scanning CG diode parameter meter containing an amplitude detector, conductivity and capacitance indicators, an integrator, a comparator, a high-frequency generator connected via a voltage-current converter to a measuring circuit, to the signal input of which and to a common wire a measured diode is connected, characterized in that additionally introduced a peak detector, a differentiator, a timer, a rectangular pulse generator, a decoding device, a modulating capacitor, an indicator connected to the output of the measuring circuit conduction ator through a peak detector, the first input of the comparator through an amplitude detector and a differentiator, the second input of the comparator is connected to a common wire, the output is to the first input of the timer, the second input of which is connected to the first output of the square-wave generator, the output is to the input of the resolver, the first the output of the solver is connected to the control input of the measuring circuit, the second to the capacitance indicator, and the second output of the square-wave generator is connected through the integrator to the control input to the module capacitor.

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