SU1580287A1 - Meter of big resistances of three-pole objects - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to determine high resistances of tripolar objects, for example, bulk and surface resistances of dielectrics using three electrodes. The purpose of the invention is to improve the accuracy of the conversion. The proposed meter contains an electrometric amplifier 1, which includes an inverting amplifier 3, an exemplary element 4, a switch 5, a constant voltage source 9 and clamps for connecting a three-pole object. The introduction of an additional amplifier and new connections reduces the influence of the output impedance of the three-pole object on the measurement process, thereby increasing the measurement accuracy. 1 il.

Description

The invention relates to electrical measuring equipment for determining high resistances of three-pole objects, in particular for determining the bulk and surface resistances of dielectrics using three electrodes.

The circuit of the invention is an increase in conversion accuracy by reducing the influence of the output impedance of a three-pole object.

The drawing shows a structural electrical converter circuit.

The high resistance meter consists of an electrometric amplifier 1, which includes an inverting amplifier 2, an amplifier 3 with non-inverting and inverting inputs, an exemplary element 4, a switch 5 and output terminals 6 and 7 connected to the measuring unit 8, and the non-inverting input of the amplifier 3 in the input of the electrometric amplifier 1, and the inverting input of the amplifier 3 is connected to its output and the input of the inverting amplifier 2, the output of the inverting amplifier 2 is connected to the output terminal 6, model element 4 and 5, an exemplary element 4 and a switch 5 are also connected to the input of an electrometric amplifier 1, the output terminal 7 is connected to the common bus of the converter, a constant voltage source 9 is connected to the three-pole object by one pole and the common bus to the other pole the converter, the second terminal 11 for connecting a three-pole object is connected to the input of the electrometric amplifier 1, and a third terminal 12 for connecting a three-pole object is connected to the inverting input of the amplifier 3. I

High resistance meter

works as follows.

A three-pole object 13 is connected to terminals 12, 10, 11 (see drawing) where R. is the measured resistance 13; K - output resistance 14 of a three-pole object; Ke - input impedance of 15 three-pole object; 1 and 1 currents flowing through the respective resistances.

Compose according to the drawing equations according to the Kirchhoff laws, taking into account the fact that at the initial moment of time

1580287 4

capacity of model element of the wife:

H

I +

Lo /

E - D11 - U

wasp

m

1gKg

Uu

ios + di + and i

about 1

J "C0R0

s

0

where Ig is the current flowing through the model element; capacity of the model element;

model element resistance;

voltage difference between the inverting and non-inverting input of amplifier 3; voltage at the output of the electrometric amplifier 1; voltage source 8 constant voltage.

C „K„ UU UOCE what

Lee

DOE

k7

thirty

or uu

and

K1K3

where Kg, K3 is the gain

amplifiers 2 and 3,

Kirchhoff's system of equations can be written as follows.i

ti - 1 ". + In

U

and to

I rfj

2КЭ

I-r

2dx2

U. + U + T ka + and

i

+ JCOC0R0

With K 1 and K 1 in the second and fourth equations, we can neglect speech in small quantities, then the equations are converted to the form:

H + 1 „;

55

F u

E to „

I, R,

at

Kgk5

)

and

Ro

about i

+

To find - U use the operator method. In view of this, the resulting system in the operator form is:

14 (P) MP) + 10 (p), j & g - I2 (p) R2; E is V & I, (p) R ,; U (p)

r / Ro

 IO (P) T + PC; R;

Solving the system of equations for U, we get

mRzEG,

and -

K3Ri Ro L Rt + K "R

k7k R

1 +

 ()

Taking into account the duality of the model element, it is possible to create a high resistance meter with a capacitive and resistive model element.

For a gauge with a capacitive element, it is possible to satisfy the condition when, then the term KiRi nom can be neglected and

The output meter can be written as follows:

U

Kie

™ W K3R2

1 + Rl

i keIg

l-exp (- ----- | - t)

We expand the exponential term of the equation in the Taylor series and, after contractions, the voltage at the output of the meter will take the form

1 + R U Et (1K3R,

COR,,

t)

From a comparison of accuracy with a prototype it can be seen that the meter has a K5 times less relative error.

For a meter with a resistive reference element, it is possible to satisfy the condition when Re "K2Rt, then after dividing the numerator and denominator of the established value of the voltage at the output of the electrometric

1580287

voltage amplifier will be with the equation:

v - ЕЈ ° - 5 L R,

1 +

 J

(J

five

0

five

0

five

0

five

0

five

those. selecting R0, one can achieve the same effect as in the capacitive version.

The positive effect is achieved by reducing the effect of the output impedance of the three-pole object by reducing the leakage current through it by applying a compensation voltage that is approximately equal to the voltage on the non-inverting input of amplifier 3, i.e. as if the apparent increase in the output impedance of the three-pole object occurs.

Claims (1)

Invention Formula A large-resistance meter for three-pole objects, containing an electrometric amplifier consisting of an inverting amplifier, parallel-connected exemplary element and a key, connected between the input and output of an electrometric amplifier; the output terminals of the converter connected to the measuring unit, one of which is connected to the output of an inverting amplifier, - with a common bus converter, a constant voltage source and three terminals for connecting three three-pole objects, the first of which It is connected to the first pole of a constant voltage source, the second to the input of an electrometric amplifier, and the second pole of a constant voltage source is connected to a common bus, characterized in that, in order to increase the conversion accuracy, an additional amplifier with an inverting and non-inverting inputs, while the non-inverting input of the additional amplifier is connected to the second terminal for connecting the object under study, the input of the inverting amplifier is connected to the inverting input ohm and the output of an additional amplifier and a third terminal for connecting the object under study.