SU48797A1 - Device for measuring electrical resistance - Google Patents

Description

Devices for measuring ac resistances are already known, based on the use of a ferrodynamic device without an opposing moment, the moving part of which is automatically set in such a position when the electromotive force induced in it by a variable magnetic flux of the frame becomes equal to the voltage drop on the measured resistance applied to frame. If both the measured resistance and the magnetizing winding of the device are powered from a common voltage source, and some constant resistance is connected in series with the measured resistance, the deviation of the device will depend only on the measured resistance, not dependent on the voltage and frequency of the supply current and also from resistance of connecting wires.

However, such devices have the disadvantage that they allow measuring only the absolute value of the resistance, while, in general, in some cases, for example, when measuring temperature electrically, it is desirable to know only the changes in resistance.

The present invention aims to eliminate this disadvantage. For this purpose, the circuit of the frame of the ferrodynamic measuring device is connected in series with the measured resistance

known constant resistance, with both supply voltages being directed so that the difference in voltage across the measured and known resistances is applied to the instrument frame.

The device consists of a transformer T with two secondary windings (Fig. 1), one of which is connected via a constant resistance to the measured resistance /, and the second also through a constant resistance - nz known resistance / h. Resistors / and R connected

In series, they are connected to the frame of the device G through the compensation winding 5. The primary winding of the transformer and the device winding connected in parallel with the device winding are supplied from an AC network. Winding A serves to coordinate the phases of the applied voltage and the electromotive force of the frame.

The operation of the device is as follows. Initially, when the voltage drops across the measured and known resistances and, and are equal to each other, the voltage is not applied to frame C. The voltage induced in it is compensated by the electromotive force of the winding 5 and the frame takes the position shown in FIG. 1. As / changes, the voltage applied to the frame and and, - and increases, a current is induced in the frame, which turns it into a new position, so that it: s. d. compensated for the increment of the applied voltage.

If we use a device with a cylindrical iron core and concentric pole tips, then, as experience shows, the electromotive force induced in the frame increases in proportion to the angle of rotation within 150 ° (Fig. 2). In this case, the deviation of the instrument will be proportional to the change in resistance /.

If desired, you can get an uneven scale. To do this, you need to appropriately change the shape of the core or pole tips. If you remove the compensation winding S, then in the initial position the frame of the device will be installed on the axis taK, that the zero mark will be in the middle of the scale. In this case, one half of the scale will correspond to a decrease in resistance /, and the second to an increase.

The described device can be applied in all those cases where the measured value causes a change in resistance. In this case, the measurement can be transmitted to a distance. Convenient: but, for example, use it to measure temperature. Selecting device parameters is easy to obtain a scale. Desired temperature range measures from 900 to 1000 °:

The device also allows the summation of the readings of several sensors. FIG. 3 shows the corresponding circuit, where through r g, Gz o6o3Ha4eifii rheostat converters. Without further explanations, it is clear that the device allows receiving both separate readings and partial amounts in any combination.

The subject matter of the invention.

A device for measuring electrical resistances with the use of a phrodynamic device without a valid moment, is ejected to the frame KOfroy in the equilibrium position. d. s., is equal to the opposite to the applied voltage, from the fact that the secondary coils of the supply transformer contain measured and known coefficients connected in series by the CMM so that the resultant

, The voltage at the ends of the windings, npi to the frame of the device, was the difference between the voltage drops on the extracted and known resistances.

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