SU61221A1 - Device for measuring the phase angle - Google Patents

Description

The subject of the invention is a device for measuring the phase angle using a thermocouple. In the proposed device for measuring the phase angle, the thermocouple heaters are connected in series to the reference voltage circuit, and the voltage under test is brought to the zero point of the heaters and to the midpoint of the voltage divider; galvanometer is included in the output circuit of thermocouples.

FIG. 1 is a schematic diagram of the device; in fig. 2 and 3 are voltage diagrams, the phase shifts between which are measured.

The device (Fig. I) contains two identical thermocouples ТП and ТП, the heaters of which are connected in series to the reference source circuit Ui (with zero phase), i.e. that source, with respect to which the phase shift of the second source is measured. 2 The voltage source f / 2 is connected between the midpoint of the voltage divider consisting of constant resistances and R-2 common point of the thermocouple heaters. As a result of this inclusion, the geometric sums of the currents 1 and 1–2 created by the traces (/ i and U-2) flow through the threads of the stopping of the torpopar.

Output thermocouples are connected in parallel. A magnetoelectric galvanometer G is turned on between the opposite poles of this system. Such an inclusion is advisable if there is a galvanometer with a low internal resistance (one order with the resistance of the thermocouples themselves); if the resistance of the galvanometer is greater, then the latter must be included in the input circuit of thermocouples in series.

With any method of switching on, the galvanometer will indicate zero in the case when the voltages given by both thermocouples are equal to each other. In case of inequality, egtey, an equalizing current / will pass through the frame of the galvanometer, which will cause some deviation of the galvanometer. The voltages removed

from the output of thermocouples, are equal only if the currents flowing through the heating wires of the thermocouple are the same.

Let the voltage t / i be twice as large as the voltage f / a and the phase angle α between them is 90 °. According to FIG. 2. It can be seen that in this case, the heating filaments of the thermocouple of the TP and the TP will be supplied with the voltage of the same size, therefore, the voltage (constant) on the galvanometer will be equal to zero. If the phase of the voltage t / 2 differs from 90 °, then under all other conditions the total voltages on the wires of the thermocouples will not be the same in magnitude.

According to FIG. 3, one can easily derive a formula for calculating the difference between the values of these voltages. The final form of the formula will be:

.

2 Cos --- Cos -r-

where D f / is the sought difference of the voltages applied to the thermocouple preheating threads, and a is the voltage deviation angle t / 2 from the quadrature with f / i. According to this formula, you can get an idea of the nature of the scale of the phase meter after graduation. The table below shows the results of the counting shown in the “Divisions of the scale” section, indicating that the intervals are generally uniform and easy readings are possible with a sufficient degree of accuracy over the entire measurement range.

.Cos oCos a

90-a-90 - "

The values of D V are calculated under the assumption that t / i is equal to Uz and the numerical value of each of them is equal to one. Under these conditions, the value of A U was obtained in terms of the complete deflection of the galvanometer. If you select a thermocouple so that at a 90 ° the galvanometer will receive a full deviation (for the whole scale) and if the scale has 100 divisions, then it is easy to calculate the number of divisions that the galvanometer will deviate at different values of the phase angle a.

The fact that thermocouples have a non-linear characteristic cannot be significant.

Thermocouples operate in a circuit not from a zero current (at which the characteristic is the most curvilinear), but with a current varying from only half the maximum value to the maximum, and in this interval the characteristic of the thermocouple can be considered almost linear.

Subject invention

A device for measuring the phase angle using thermocouples, wherein thermocouple heaters are connected in series to the reference voltage circuit, and the voltage under test is applied to the zero point of the heaters and to the midpoint of the voltage divider, the same galvanometer is included in the output thermocouple circuit.

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