RU2365925C1 - Way of determination of grounded capacity cx and resistance rx of passive two-terminal element connected in parallel - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention can be used for measurement of parametres of the objects represented by passive 2 element grounded RC two-terminal elements, having a capacity C_x and a resistance R_x connected in parallel. The way of determination of a grounded capacity C_x and a resistance R_x of a passive two-terminal element connected in parallel consists in determination of time of a transient phenomenon of the capacity C_x discharge on resistance R_x from electrical pressure U_B to electrical pressure U_H at cutting-off of a controllable two-terminal element from the power supply and forming of the square-topped impulses on an output of the device with duration equal to transient phenomenon time.

EFFECT: invention provides possibility of decrease in requirements to stability of parametres of the power supply and increase of accuracy of measurements.

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Description

The invention relates to electrical engineering and can be used to measure the parameters of objects represented by passive 2-element grounded RC two-poles having a capacitance C _x and resistance R _x connected in parallel.

Closest to the proposed one is the method, which consists in the formation of rectangular pulses of various frequencies obtained in the process of charge-discharge of the circuit when turning on and off the input signal of a rectangular shape from a controlled power source and changing the topology of the measuring circuit. The invention RU 2312366 C1 from 04/11/2006. Authors Zhugan L.I. et al. Bulletin No. 34.

The measuring device generates at the output a sequence of rectangular pulses whose frequency is determined by the time of charge and discharge. Three frequencies obtained by changing the topology of the measuring circuit are used to determine the parameters C _x and R _x .

The disadvantage of this method is the high requirements for the stability of the parameters of the power source.

The purpose of the invention is to reduce the requirements for stability of the parameters of the power source, improving the accuracy of measurements.

The proposed method for measuring grounded in parallel capacitance C _x and resistance R _{x of a} passive two-element bipolar (measurement object) consists in generating rectangular pulses at its output, the duration of which is determined by the discharge time of the circuit, for various topologies, followed by calculation of the values of capacitance C _x and resistance R _x according to the formulas given in the description of the invention.

In contrast to the prototype, only the discharge time of the capacitor C _x through the resistance R _{x is} used to determine the unknown parameters of the object, while the power supply is disconnected, i.e. its parameters do not affect the determination of the discharge time. Circuit switching is performed only once when measuring the discharge time, which reduces the number of circuit switching. In this case, two pulse durations are measured instead of three frequency measurements.

The measurement method can be demonstrated on the device shown in figure 1. The device comprises a power source 1, a switching unit 2, a measurement object 3, a reference capacitor 4 with a capacitance C _{0 of} known magnitude, a two-threshold comparator 5, a computing device 6, and switching elements 7, 8.

At the input of the object when the key 7 is closed, a signal is supplied from the power source, the C _x R _x circuit of the object is charged in accordance with figure 2 (mode 1). When the voltage on the capacitor reaches the upper level U _{in the} two-threshold comparator, the switching unit with the key 7 turns off the power source, and the process of discharging the circuit of the object begins. When the voltage at the object reaches the value of the lower level U _n, the switching unit again connects the power source to charge the circuit, and so on, providing a process of "charge-discharge" circuit within the reference upper and lower voltage levels of the comparator.

At the output of the comparator, a sequence of rectangular pulses U _{vx is formed} , the duration of which corresponds to the discharge time of the C _x R _x chain T _p1 and is determined by the formula:

where τ ₁ = R _x C _x is the time constant of the circuit;

U _in and U _n - the upper and lower voltage of the two-threshold comparator.

Then, using the key 8, a reference capacitor C _{0 is} connected in parallel with C _x (Fig. 2, mode 2), and the “charge-discharge” operations of the obtained circuit are again performed. Similarly to the previous procedure, the discharge time T _p2

where τ ₂ = R _x (C _x + C ₀ )

Dividing the expression (2) by (1), we obtain:

,

,

where we determine the unknown object capacity C _x :

The value of R _{x is} determined by the formula:

.Where

.

The technical implementation of the proposed method can be demonstrated in a simplified diagram shown in figure 3.

Chip DA 1 implements the functions of a two-threshold comparator.

There are 2 modes in the circuit.

Mode 1: input a = 0, the process is “charge-discharge" circuit of a two-terminal circuit C _x ,

R _x and measurement of discharge time T _p1

Mode 2: input a = 1, the “charge-discharge” process of the circuit C _x + C ₀ and the measurement of the discharge time T _{p2 are performed} .

Claims (1)

A method for determining grounded in parallel capacitance C _x and resistance R _{x of a} passive two-element bipolar device, comprising measuring the pulse duration corresponding to the discharge time of the capacitor, and calculating the capacitance C _x and resistance R _x , characterized in that rectangular pulses of different durations are formed at the output of the device, obtained during the discharge of the measuring circuit, consisting of a power source, a switching unit, a two-threshold comparator with two reference voltages of lower U _n and the upper U _{in the} levels of the reference capacitor and the computing device, when the power supply is turned off, by changing the topology of the measuring circuit: first connect your own two-terminal circuit and measure the discharge duration T _p1 , then connect the reference capacitor to the circuit and determine the discharge duration T _p2 , and values of capacitance C _x and resistance R _x are calculated by the formulas
C _x = C ₀ / (Tp ₂ / Tp ₁ -1),
R _x = Tp ₁ / (C _x A),
where A = ln (U _in / U _n ).

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