SU497527A1 - Bridge for remote measurement of complex resistances - Google Patents

Description

one

The invention relates to electrical measuring technology and can be used in remote measurements of complex resistances and fixed frequencies at the length of the connecting lines, comparable to the wavelength of an electromagnetic field.

For remote measurements of complex impedances, balanced bridges are used with a separate reading of the components of resistance, and among them those for which the equilibrium is formed by model variable resistance. Unknown resistance is connected to the bridge by shielded lines with grounded shields. The bridge measures the input resistance between the internal conductors of the lines, which is almost equal to the unknown resistance when using lines that are much shorter than the length of the electromagnetic wave. The input resistances between the internal conductors and the shields of the lines do not affect the operation of such a bridge, because they are either insensitive to them due to their design features, or have the means to neutralize them. The parameters of the connecting lines are not included in the equilibrium condition of the bridge, which has the form

Z, Zo7V,

where Zj: is the unknown, measurable resistance;

Zo - exemplary resistance; / V - real or imaginary number.

However, when using long connecting lines, the resistance measured by a known bridge is not equal to the unknown resistance and differs from it in the general case both in absolute value and in phase. In this case, the parameters of the lines are included in the equilibrium condition of the bridge, breaking the separate counting and deteriorating the measurement accuracy.

The purpose of the invention is to eliminate the influence of connecting lines on the accuracy of measurement and to eliminate the violation of the separate reading of the resistance components.

This goal is achieved by performing shoulder hanging in the form of star-connected resistances, with the model variable resistance being connected between one of the bridge's vertices and the star's top, and the other two, connected between the star's top and the other bridge's top and between the star's top and the ground bus, complex resistances, the value of which depends on the parameters of the lines and the ratio of the values of the model and measured resistances.

FIG. Figure 1 shows a circuit of measured resistance 1 and two shielded lines 2 and 3. At points 4, 5 and b, the circuit of measured resistance is connected to the bridge, and at point 6 the line screens are connected to the ground bus. The input resistance of the Z4-5 circuit between points 4 and 5 as follows is related to the Zy resistance. measured resistance and А-parameters of quadrupoles, equivalent to the line m 2 (Ai, and 3 (W, h): Z4-5 2u4.0z + 5.0z + B, A, -: Z., K + M,, 0 „, D, + B, A ,. The equilibrium condition of a known bridge in the case of long lines has the form 7 - ZpN - M - 1 As can be seen, the parameters of the lines in the form of complex quantities / C and M enter into an equilibrium condition, deteriorating the measurement accuracy and breakdown of the split countdown. Fig. 2 shows a bridge circuit in accordance with the invention. The circuit consists of measurable resistance 1, connecting lines 2 and 3 with grounded shields, shoulder of hanging in a star from model resistance 7 and complex resistances 8 and 9, shoulders ratio 10 and 11, Wagner branches from resistances 12 and 13, switch 14. Figures 4, 5, 15 designate three of the bridge's vertices.The bridge from the generator 16 feeds, the imbalance signal is supplied to the equilibrium indicator 17. The ratio of the values of the resistances Zjo and Zii of the arms, the ratio 10 and 11, as in the known bridge, is Zio / Zii A, the values of the resistances 8 and 9 (Zs and Zg) are chosen as follows:) Equilibrium condition this bridge has the form: Z.5 152jo, where Zj-is - equivalent shoulder resistance cheers noveshivani between points 5 and 15, Z, .. Zo / V. In order to achieve equilibrium, double equilibration is applied using switch 14 and the Wagner branch. This makes it possible to neutralize the resistance between the TOC 4 and the ground and the point 15 and the ground, created respectively by the chips of the object to be measured and the balancing arm. Subject of the invention Bridge for remote measurement of complex resistances to which the measured resistance is connected by means of shielded lines with grounded shields, characterized in that, in order to eliminate the influence of connecting lines on the accuracy of measurement and to eliminate the violation of the separate counting of the resistance components, the balance arm the bridge is made in the form of star-connected resistances, and an exemplary variable resistance is connected between one of the bridge's vertices and the star's top, and the other two, connected between the top of the star and the other top of the bridge and between the top of the star and the earth bus, are complex resistances, the magnitude of which depends on the parameters of the lines and the ratio of the values of the model and measured resistances.

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five

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five

FIG. I

FIG. 2