SU111359A1 - A method for measuring power in AC circuits and a device for carrying out this method - Google Patents

Description

When measuring power in high-frequency AC circuits, wattmeters with two heat generators are used, the heaters of which are fed, respectively, the sum and difference of the current on the voltage of the controlled circuit, and the instrument measuring the difference between them and the thermocouple circuit (heating resistances). er d.

In such wattmeters there must be a strictly quadratic relationship between e. d. thermal converter and heating current. However, to obtain such a relationship is very difficult, since the heat output of the heater increases with increasing temperature, and the amount of heat released in it does not depend on temperature and is always strictly proportional to the square of the flowing current.

The quadratic relationship between e. The thermal converter and the heating current are also disturbed by the non-linear relationship e. d. on the temperature of the heater.

For non-evacuated thermal converters, the required quadratic dependence can be obtained at an excessive temperature of the heat exchangers not exceeding 10-12 °. In this case, e. d.-s the output of the thermocouple is very small, which makes use of bulky and complex thermopiles in the wattmeter, limiting its frequency range. Evacuated thermocouples also do not have a sufficiently strict quadratic characteristic, so that they do not allow to create a thermoelectric wattmeter operating in a wide frequency band and possessing at the same time high precision.

The proposed method of measuring power with such wattmeters eliminates this drawback and improves the measurement accuracy. For this purpose, it is proposed to measure by the compensation method by supplying one of the heaters (heated to a lower temperature) with an additional direct current to the full mutual compensation e. d. both thermocouples or resistances and determine power by the magnitude of the compensation current.

No. 111359

In order to perform measurements using this method, a device is proposed which provides automatic compresion of the difference e. d. both thermocouples. This is achieved by connecting thermocouples to the input of an electronic amplifier, the output current of which is used to add power to one of the heaters. When used in the wattmeter of the heating resistances, automatic compensation of the difference between them, ed. S. This can be done by including these resistances in the AC bridge circuit and using the current of its output diagonal to power one of the heaters.

The heaters used in the device described can be made up of separate wires isolated from one another, one of which is included in the day being measured, and the other is used to supply a compensating current.

FIG. 1, 2 and 3 are schematic diagrams of the proposed device in three versions.

The main elements of the wattmeter are two thermocouple thermocouples / and .2, to the heaters of which the sum and difference of the current / and voltage U of the controlled circuit are applied. The current / is supplied to the device by the current transformer 3, and the voltage by the voltage transformer 4. When used as thermocouples thermocouples / and 2 (Fig. 1), they are connected to the input of an electronic amplifier 5, the output current (which is used to add power to the heater of the thermobar 2 heated to a lower temperature than the terlyunar).

When uh. d. Both thermocouples will be mutually compensated, the amount of current I, measured by the magnetoelectric device 6, will determine the measured power.

For the separation of the measured ac current / n circuits in the slewing current circuit / in the device circuit, separation capacitors 7 and throttle 8 are provided.

When used as thermal converters of heating resistors / and 2 (Fig. 2), they are included in the AC bridge circuit in conjunction with Sonata 5, and an electronic amplifier 5 is connected to the output diagonal of the bridge. The output current / amplifier 5, rectified by valve 10, is used as in the device of FIG. 1 to further power the thermocouple (resistance) heater 2.

In some cases, especially when measuring DC power or low frequency power, it is desirable to electrically separate the auxiliary current circuit from the value of the measured current. To do this, heaters and heat resistance heaters should be made of separate insulated wires // and 12, one of which is included in the measured circuit, and the other in a compensating current circuit ((phi1- 3))

Claims (4)

1. A method for measuring power in AC circuits using a quadratic detection power meter, in which two thermal converters are applied, the heaters of which are supplied, respectively, the sum and difference of the current and voltage of the controlled circuit, and the thermocouple circuit is connected to the thermocouple (or resistance) circuit. the difference between them e. d. a device, characterized in that, in order to improve the measurement accuracy, the deviation of the measuring device is compensated by applying an additional direct current to one of the heaters, which has a lower temperature / tour, and the measured power is determined from the value of the compensation current. 2. A device for carrying out the method according to claim 1, in which heated thermocouples are used as thermal converters, differing in that in order to automatically compensate for differences e. d. thermocouples, the latter are connected to the input of an electronic amplifier, the current at the output of which is used to add power to one of the heaters in such a way that an increase in current occurs until complete compensation is e. d. thermocouple 3. A device for carrying out the method of claim 1, wherein heating resistors are used as thermal converters, characterized in that said resistances serve as shoulders of an alternating current bridge, the rectified current in the output diagonal of which is fed into the circuit of one of the heaters of the device. 4. In the device according to claim 2, use a heater composed of separate wires isolated from one another, one of which is included in the measured circuit and the other for supplying a compensating current.