SU1318920A1 - Bridge for measuring capacitance and tangent of loss angle of capacitors - Google Patents

Description

The invention relates to the field of measurement technology and can be used in instruments for accurately measuring the capacitance of capacitors.

The aim of the invention is to improve the measurement accuracy of capacitance and loss tangent of capacitors using an autotransformer bridge circuit by performing its autonomous calibration.

The drawing shows a diagram of the device.

The device contains a generator with quartz frequency stabilization, connected to the diagonal of the bridge power supply, autotransformer shoulders 2 ratios, indicator 3, included measuring diagonal of the bridge, set of capacitors 4.1-4.4 (in the reference arm, determining the measuring subrange, keys 5.1-5. corresponding measuring subrange, terminals 6 for connecting the measurement of the capacitive object (C), an additional set of capacitors 7.1-7.3 with capacitors kz exemplary resistors 8 and 9 (R 1, R 2), operational amplifier 10, in reverse which communicates through the respective keys are coupled 11.1-11.10 exemplary resistors 8 and 9 and the capacitors of the additional set of capacitors, wherein the keys 1.1-11.10 provide connection circuit elements during the battery gauge.

The necessary error correction of the bridge during its calibration can be carried out either by adjusting the capacitance (Cd, Cp) of condensates 4.1-4.4, or adjusting the autotransformer ratio 2 arms, or (in the case of using microprocessor technology) by making appropriate corrections to the measurement result. :

Calibration can be done both manually and automatically.

Calibration is carried out as follows.

Disable the measured object and close the keys 11.5 and 11.6. In this case, instead of the measured object, a capacitor 7.3 () is turned on.

The measuring sub-range is switched on with the help of capacitors 4.1-4.4, corresponding to the measurement

CL capacity

Capacity С „, it is advisable to choose the appropriate middle range, for example Ср (-Cgj). Next, the bridge is balanced. This results in a PI count corresponding to

P1

 KZ

(one)

02

The keys 11.5 and 11.6 are then opened, the keys are closed 11.7-11.10, and the bridge is balanced on the same measuring subband.

Neglecting a static error (which can be reduced to a small value by using an operational amplifier 10 with a sufficiently large gain factor, or using an iterative error correction), we get a count

one

 u; iRlR2

(2)

where U) is the frequency of the measuring voltage.

On the basis of expressions (1) and (2), we obtain the relation that allows us to determine the capacitance of the capacitor C

C -1. , | 7 i.

° i w I P1P2 R1R2

The error in determining C is determined by the error of the frequency of the measuring voltage and resistors 8 (R1) and 9 (R2), the values of which are due to the use of quartz

Stabilization of the generator frequency and highly stable samples of resistors can be determined at the manufacturing stage of the device with an error of more than one thousand to one percent.

This capacitance value can be used to adjust it, or to adjust the leverage ratio (if any), or to correct the result.

measurements in the case of a microprocessor.

Further calibration of the bridge is performed as follows.

From the expression (), the actual value of capacitance C i is determined. Then the keys 11.7–11.10 open, the keys 11.5–11.6 close again, and the next measuring band Co (Coa) is switched on.

The bridge is balanced and the RH count is obtained.

Based on the RP reference, the actual value of the capacitance is calculated.

Sz

WITH,

 rz

and the bridge is adjusted or a correction is remembered for this measurement subband,

The keys 11.5 and 11.6 are then opened and the keys 11.3 and 11.4 are turned on. A capacitance is included in the measuring arm of the bridge. The balancing of the bridge is made and is determined taking into account the previously determined actual value of the capacitance. C value of capacitance C

C, P4C „.

Sub-band C is then turned on, and after equilibrating the bridge, the value of Co4 is determined.

C. S „

TO

-rz

The bridge is calibrated in the same way to the lower measuring subranges.

Thanks to the autonomous calibration system, the device in the lOpF - .IMF capacitance range provides a measurement error of no more than 0.02%.

Thus, the technical and economic advantage of the proposed technical solution in comparison with the known one consists in increasing the measurement accuracy by no less than 5 times.

Formula-from gain

Claims (3)

1. A bridge for measuring capacitance and loss tangent of capacitors, containing adjustable autotransformer ratio arms, a set of capacitors in the reference arm, the number of which is equal to the number of measurement subranges, with the first terminals of all lerez capacitors corresponding first keys connected to the first top of the power diagonal VNIIPI Order 2505/38 Circulation 730 Subscription Proizv.-poly. pr-tie, Uzhgorod, st. Design, D the bridge, and the second terminals of all capacitors are connected to the first vertex of the measuring diagonal of the bridge, the second vertex of which is connected to the common terminal, through the corresponding second keys, terminals for connecting the measurement object in the other arm of the comparison, the generator connected to the diagonal of the bridge power supply, the indicator, connected to the measuring diagonal of the bridge, distinguished by the fact that, in order to improve measurement accuracy, an operational amplifier, two model resistors, an additional set of capacitors, the third, fourth, fifth, sixth, seventh and eighth keys are inserted into it, with the outputs of each capacitor from the additional set of capacitors through the corresponding third and fourth keys are connected to the second vertex of the diagonal of the power bridge and the first vertex of the measuring diagonal of the bridge, respectively, the first the output of the first reference resistor is connected via the fifth switch to the second vertex of the bridge diagonal; the second output to the inverting input of the operational amplifier, the non-inverting input of which is connected to the common bus; the second output of the first resistor is connected to the first output of one of the additional set capacitors capacitors, the second output of which is connected via the seventh switch to the output of the operational amplifier and to the first output of the second reference resistor, the second output of which through the eighth key is connected to the first vertex of the measuring diagonal of the bridge. 2. Bridge according to claim 1, characterized in that the capacitance of the capacitors of the additional set of capacitors corresponds to the upper limit of the measurement of n-1 junior measuring subranges, where n is the number of measuring subranges. 3. The bridge according to claim 1 is different from the fact that the generator is made with quartz frequency stabilization.