SU60764A1 - Device for measuring AC frequency - Google Patents

Description

Device for measuring the frequency of alternating current. This is based on the use of a skin effect phenomenon, which consists in the fact that the active resistance of the conductor is proportional to the change in the frequency of the current flowing through the conductor. Devices of this type usually do not provide sufficient accuracy. In the described device, this disadvantage is eliminated. This is achieved by using two conductors of the same cross section, included in a common circuit, the shape of which is chosen in such a way that the resistance of one conductor hardly changes when the frequency of the flowing current changes, and the resistance of the other considerably depends on the frequency. Frequency is determined by comparing the resistances of conductors by conventional methods used in electrical measurement techniques.

FIG. 1-6 depict various possible impedance measurement schemes for the -comparable conductors. One of the conductors is made in the form of a thin-walled tube 1, and the second in the form of a flat cylinder 2.

The simplest way to measure frequency is to determine the temperature difference on the surface of said conductors when heated by their measured high frequency alternating current (Fig. 1-3). In this case, the resistances 1 n 2 can be connected to the current circuit in series (Fig. 1) or in parallel (Fig. 2), where the alternating current of the measured frequency is supplied to points 5.

Thermocouples 4 and 5 (Figs. 1 and 2) mounted on the surface of both conductors can be used to measure the heating temperature. Thus, the measurement process is reduced to measuring the difference or the ratio of the thermoelectromotive forces of both thermocouples, which can be carried out by conventional methods known in electrical engineering. For this purpose, for example, can be used

No. 60764

a magnetoelectric device 7 (Fig. 1-2) of the ratiometric type, or a conventional measuring device (Fig. 3), on the clamps: of which the difference in voltages of both thermocouples is directly applied. For the pre-fitting of the circuit, two adjustable resistances of 8-л 9 serve. For measurement, the usual bridge circuit can also be used (Fig. 4 and 5). Resistances 8 and 9 (Fig. 4) are common resistors. -The size of them is chosen to balance the bridge at a constant current.

When powered by an alternating current bridge, the balance of the bridge is disturbed. By the deviation of the arrow of the magnetoelectric device (galvanometer) 7, included in the diagonal of the bridge through the rectifier 10; determine the frequency of the supply current. The instrument can be calibrated directly at the values of the measured frequency.

To increase the sensitivity of the circuit, not one but two resistances (Fig. 5) can be included in it, changing its value depending on the frequency, resistance 1 -k 9 and two resistances whose magnitudes depend little on the current frequency ( resistance

2 and 8). :,

In the diagrams of FIG. 4 and 5, the resistance of the compared conductors is measured directly.

It is also possible to measure the voltage drops on the resistors (conductor) / and 2 being compared, which are connected to the AC circuit in series (Fig. 6). For this purpose, points 12–13 and 13–14 at opposite ends of each of the resistances (conductors) Y and 2 are connected to one of the windings of the differential magnetoelectric device 7, which, as well as. in the cases described above, can be switched on via rectifier 10.

Other various switching schemes are possible, which in all cases will be based on measuring the difference in resistance of both resistances (conductors) 1 and 2.

The device can be used as a frequency relay, for which it is necessary to use a device with contacts instead of a magnetoelectric device 7 with a scale.

The subject matter of the invention.

Claims (3)

1. A device for measuring the frequency of an alternating current, based on the use of a skin effect that causes a change in the active resistance of a conductor depending on the frequency of the flowing current, characterized in that, two connected in series or in parallel are used to determine the change in frequency by the redistribution of currents in both conductors a conductor, the shape and material of which are chosen in such a way that their resistance varies differently with changes in the frequency of the current flowing through them. 2: The form of the device according to claim 1, characterized by the use of thermocouples installed on the surface of both conductors and connected differentially to the measuring device circuit, in order to determine the frequency by the temperature difference between the surface heating of both conductors by the measured current. 3. The form of the device according to claim 1, characterized in that, in order to determine the frequency by changing the ratio of the voltage drops on both series-connected conductors, their ends are directly connected to the windings of the differential measuring device.