SU1539667A1 - Method of measuring electric resistance of resistors by means of d.c. bridge - Google Patents

Abstract

The invention relates to particularly accurate electrical measurements on direct current and is intended for use in instrument making, as well as in state and departmental calibration services. The purpose of the invention is to improve measurement accuracy and labor productivity in determining the stability of resistances by eliminating the influence of ambient temperature and the self-heating of precision resistors by the current passing through them — achieved by calculating the bridge arm values required for measuring any resistance, reduce not less than ten times. The resulting reduced shoulder values are exposed on the bridge. Then, the shoulder impedances are restored to the calculated values using external units constructed mainly of unambiguous electrical resistance measures or their combinations designed for operation in an oil medium. After that, these external units are immersed in an oil thermostat. At the same time, the same accuracy is achieved, as if all the shoulders of the bridge were in an oil thermostat. 2 Il.

Description

The invention relates to particularly accurate electrical measurements on direct current and is intended for use in the instrument-making industry, as well as a hedgehog in state and departmental calibration services.

The purpose of the invention is to improve the measurement accuracy in determining the stability of resistances by eliminating the influence of ambient temperature and the self-heating of precision resistors through the thickness of them.

FIG. 1 and 2 are schematic diagrams of the method implementation.

FIG. Figure 1 shows a simplified diagram of a single-double bridge included in a double bridge scheme. The scheme contains one of the main arms 1, which is the reference one, another main arm 2 adjacent to it, the additional arm 3, which is also the reference one, the reading decades of which are mechanically paired with the reference decades of the main shoulder 1, another additional arm 4 adjacent to the reference additional , four clamping measuring cond with

05 C5

The motive 5, the potential leads 6, is connected to the reading main and additional arms, the block 7 is a four-clamping tare measure, the potential conclusions 8 of which are connected to another main and additional arms, the block 9 of the null indicator, connected by clips 10 and 11 to the tops of the main and additional arms, power supply unit J 12 with a polarity switch, a load magazine and a device for monitoring the current value, a clamp 13 connected to one of the potential terminals of the measured resistance, a jumper 14 connecting the Dean of the potential conclusions tare measure unit with one of the other shoulder.

FIG. 2 shows a complete schematic diagram of a single-double washing machine 2, necessary for practical operation.

The method is applied to one of the specific examples of its implementation - measuring the resistance of 540 ohms in a double bridge circuit. The circuit 2 comprises an external unit 15 connected externally by one of the leads in series to the reference main arm 1 by means of a clamp 16 located on the outer panel of the bridge, an external block 17 connected to the other main arm 2 in series with it by means of a clamp 18 located on the outer bridge panels, an external unit 19 connected externally to the reference additional arm 3 by means of a clamp 20 located on the external panel of the bridge, an external unit 21 connected by one of the leads to the other additional arm 4 of a series via clip 22, which is also located on the outer panel of the bridge, clip 23 connected to another output of the external unit connected by one of the leads to the main reading arm, exemplary measure 24, depicted as a four-clamping resistor, additional arm 2b, connected by jumpers and Clamps 26 with a clip of an external unit connected to the main reading arm, additional arms 27 and 28 connected alternately by means of clamps and jumpers 29 to external current clamps 30 and 31 of the measured resistance or braztsovoy measures total peak additional shoulder is connected to one of the terminals of the power unit, the other terminal of which is connected to an external current terminal

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20 30

35

25

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32 tare measure units, an external jumper 33 connecting internal current clamps 34 and 3b or 36 tare measure units and a measurable resistance or exemplary measure, node 37 connecting the circuit of one of the extension arms to the external unit circuit connected to the main reading arm , nodes 38 and 39, connecting the potential and current terminals of the measured resistance and the reference measure, respectively, a low-precision resistor 40, for example, about 100 ohms, connected between the anchor point connected to the external block of the main reading arm and nodes oic point soedinen- hydrochloric potential and the measured current output or resistance exemplary steps jumper 41, shorting the resistor bridge k2 installation.

FIG. 2 shading marked measures immersed in a thermostat.

The method is characterized by the following operations.

The entire range of measured resistances, for example, 10 to 10 Ohms, is divided into subbands, for example, 10-100, 100-500, 500-700 Ohms, etc. depending on the specific measurement task. Further, the boundaries between subranges may be refined. Next, approximate resistances of the bridge shoulders are selected that correspond to the calculated values of the resistances to be measured within a certain subband, taking into account the greatest loads on the measured resistance fj, for example, within 500-700 ohms, with a load of up to 1 watt. At the same time, schemes with significant shoulder asymmetry are avoided, since the diagrams must have sufficient sensitivity also when measuring model measure 24, which is under a smaller load than the measured resistance 5 ". In addition, the nominal resistance of the counting arm 1 (Fig. 1) is convenient for removing the relative reference that is preferred. Before absolute reading, it should have simple values of the form 1000, 2000, 5000, etc.

The operations according to the method are shown on the example of the 500-700 ohm sub-band, which is fairly typical. When selecting estimated values of the shoulders

40

45

50

55

based on the scheme shown in figure 1, included as a single or double

a bridge that does not matter when pre-selecting the shoulders. Approximately 2000 ohm impedance is chosen as shoulder 1, about 50 ohm impedance as a block 7 measure, and resistance approximately 2-100 ohm as shoulder 2. The greatest load on block 7 of the tare measure occurs at the beginning of the subrange — at 500 ohms. Therefore, it is constructed from two P331 measures of 100 Ohms connected in parallel. Then the load on each of them will not exceed 0.05 W, which is permissible. Arm 1 has a load of approximately 0.25-0.3 watts. Therefore, to redistribute the loads, this shoulder is constructed from the combination shown in FIG. 2 (external unit 15), ko1

2000 ohms, for example, a magazine of type Р3026-1 кл. 0,002. The resistance of the external unit 17 is equal to 181.82 ohms. Therefore, only 3.36 ohms are exposed on the shoulder 2. The resistors of the additional arms 3 and C (Fig. 1 and 2) are equalized to the resistances of the main arms using external blocks 19 and 21 connected

successively with the additional arms 3 and k by means of the clamps 20 and 22 located on the outer panel of the bridge 42 in the event that the additional arms 3 and k lack resistance. External blocks 19 and 21

they are generally resistive shops, e.g. 0.02. In this example, the additional arm 3 is set to 1000 ohms,

the torus has a nominal resistance of 20 external block 19 - also 1000 OHM, on

1900 ohms to the sum of the reference. shoulder 1 to make 2000 ohms. In this case, in the whole subrange of 500 - 700 ohms, the load on the measures of the external unit 15 does not exceed 0.05 watts. Then the nag-25 is rushed to the thermostat. If the resistance on the shoulder 2 (Fig. L2) does not exceed 0.03 watts. After that, choose the scheme of the bridge. It is determined by the resistances of the terminals of the measured resistances. They can be neglected;

if the conclusions are so significant that the simple use of a double bridge is not enough to eliminate their influence, then the so-called separate balancing of the arms should be applied so that not only their magnitude is determined, for the realization of which

but also the resistance of the selected arms, as well as the nature of the problem to be solved, then the single bridge scheme is selected. As a concrete example, a 500-700 ohm subrange is shown for measuring ohms with a 1.0 W load, a double bridge circuit. Therefore, shoulders 1 and 2 (Fig. 1). Become the main arms of the double bridge. However, instead of the estimated 2000 ohms on arm 1 (fig. 2), 100 ohms are set, and my value is restored using an external unit 15 connected to the main reading arm from the outside using clamp 16 located on the outer panel of the bridge. The implementation of the method is shown on the basis of the use of a bridge of the type IIA, which is part of the UMIS unit equipped with an oil thermostat with automatic maintenance of the set temperature. The calculated resistance of the main arm 2 (Fig. 1) is 185, 18 ohms. Its resistance is reduced to several ohms, and brought up to the calculated banner with the help of an external unit 17. consisting of two P331 measures of 100 ohms connected in series and bypassed

additional shoulder 4 - 185.18 ohms, and on the outdoor unit 21-0 ohms.

Then the external blocks 15 and 17, block 7 of the tare measure, the model measure 2k are immersed in a thermostat. If you resist

if the conclusions are so significant that the simple use of a double bridge is not enough to eliminate their influence, then the so-called separate balancing of my shoulders should be applied

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45

five

have the necessary schematic and design solutions to eliminate these effects with extremely high accuracy. Introduce three additional arms 25,27,28. Additional shoulders 25 and 27 are connected using clamps and jumpers 26.23 and 29.30 to nodes 37 and 38 when connecting measured resistance 5 to a bridge, and additional shoulders 25 and 28 - using clamps and jumpers 26.23 and 29, 31 to nodes 37 and 39 when an exemplary measure of 2k is connected to the bridge. The calculated value of the ratio of the additional arm 25 to the resistance of the additional arm 27 or 28 is equal to the ratio of the adjacent main arm and the model measure 2k.

After the described techniques for preparing the measuring circuit, a measured resistance 5 is connected to the bridge and a full load of 1.0 W is given to it. Balance the bridge with paired reference primary and secondary arms 1 and 3 and record the count. A jumper 41 is then disconnected from one of the terminals and a resistor with an impedance of about 100 ohms is introduced into the circuit between nodes 37 and 38.

It is achieved by selecting the resistance of the additional arm 27 so that the count with resistance 0 turned on would differ from the previous count,

one

when resistor 0 is shorted, for example, by no more than 0.001%. Then the resistor 40 is short-circuited with the jumper M. Next, the jumper 33 is broken and, using the additional arms 3 and 4 of the low-impedance tuning stores, in the circuits, again balance the circuit. After that, jumper circuit 33 is restored, the bridge is balanced, and a final count is obtained when the measured resistance 5 is inserted into the bridge.

As additional shoulders 27 and 28, cl. 0.02 - | 0.05, as shoulder 25 - also ma-2 gazin or an unambiguous measure of resistance. When selecting the nominal resistances of the additional arms, it is taken into account that the overload of the shoulder 2J should be avoided when the load of the measured resistance is 2 with a 5 to 1.0 W. Therefore, its nominal resistance is usually chosen to be less than the measured resistance, taking into account the load on its section. For the same reason, 3 additional arm 27 can be constructed from a mixed mix of unambiguous measures or from a combination of such measures with a resistance box.

Further, the resistance 5 and the additional arm 27 are disconnected and instead they are switched on by the additional arm 28 and the exemplary measure 2k, but by applying to it a significantly smaller load than 1.0 W, for example, 0.05-0.1 W, not exceeding the allowable hell To connect its coils in incremental steps. Resistances equal to units of Ohms, tenths and hundredths of Ohms are exposed on the main arm 2 of the bridge 2 itself.

A significant factor in improving the measurement accuracy inherent in this method is the reduction in temperature errors, which simultaneously leads to an increase in labor productivity in measuring the resistances of series of resistors. Indeed, at least 90% of the nominal resistances of the main arms are immersed in a thermostat, in which the temperature regime is maintained with stability by an order of magnitude higher than in the surrounding air space, which is also subject to thermostatic control. Improved stability of measurement results, leading to a low value. The same operations are repeated as when a measured resistance 5 is connected to the bridge. The calculated value is taken as the difference by the final readings when the model measure 2k and the resistance 5 are measured or the difference of these differences during certain time intervals.

If the resistances of the leads can be neglected, then measurements should be made in the single bridge circuit. To jump to it, jumper 14 is disconnected from pin 8, one of the outputs of the null indicator unit 9 is disconnected from clamp 11 and switched to clamp 13, extension arm 25 is disconnected from clamp 23, jumper 26 is removed from it, and left connected to the bridge one of the extras 50

55

0

five

0 5 30

or

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Arrows 27 or 28, which turns into an additional resistance in the circuit of power supply unit 12. In the single bridge circuit, the tare unit 7 is the third one, with a fully outer arm connected to the bridge outside.

In order to reduce the effect of leakage currents at the end of the range, for example, when measuring 100,000 Ohm, when building external units, they are preferred among such options, consistent with the thermostat capacity, in which their component measures have lower resistances. For example, if the nominal resistance of the external unit 15 is 50,000 ohms, then it is preferable to construct it from five successively connected measures of 10,000 ohms each, than from two parallel connected measures of 100,000 ohms each.

When measuring any other resistances within this subrange, the circuits of the external unit 15 and the Tare measure unit 7 are left unchanged, and the total resistance of the main arm 2 and the external unit 17 varies from 200 to Ohms. In the external block 17, it should be concentrated not less than yO / j of the total matching of it and the main arm 2. This is achieved by building the external block 17 from the series-connected measure P 331 to 100 Ohms and the single-decade shop 10x10 Ohms immersed in the thermostat. This store should have a metal oil-proof housing and clamps or plug switches

To improve the measurement accuracy, it allows refusing the previously practiced multiple measurements of the resistances of each resistor by replacing r with a subsequent averaging of the measurement result, thus trying to improve the measurement accuracy. The observed repetition of measurement results at a level of accuracy that was unattainable for several hours allows us to restrict a single measurement, which significantly reduces the time of each measurement cycle. Measurement of the resistance of an exemplary measure in a series of monitoring can be performed on the installation just a few times a day. It should be noted that a change in the measurement result even by 0.00001% during their execution allows one to judge about a temperature shift in the thermogram due to a change in the thermostatting mode.

The presence of additional shoulders in a number of cases eliminates the need to perform trimming operations each time to eliminate the effect of pin resistance and is limited only by the traditional adjustment of the additional, double bridge arms 3 and k, which is

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with an additional factor to increase productivity.

Claims (2)

1. A method of measuring the electrical resistances of resistors with a DC bridge, which consists in calculating the resistances of the elements of the shoulders of the bridge, balancing the bridge, determining the measurement result from the readings of the reference decades of the adjustable shoulder of the bridge, characterized in that, in order to improve the measurement accuracy, the values of the resistances of the elements of the shoulders of the bridge are ten times smaller compared with the calculated values, then the resistances of the shoulders of the bridge are adjusted to the calculated values using one measures of electrical resistance, which are placed in a thermostat. 2. A method according to claim 1, in order to improve the measurement accuracy by eliminating the resistance of the terminals of the measured resistors, the DC bridge circuit is converted into an eight shoulder bridge. ten 11 h bf Uw D eight 1 -tri3 ± i