SU454494A1 - Digital Active Power Micrometer - Google Patents

Description

one

This invention relates to electrical measuring technology.

Digital wattmeters of active power are known, including amplifiers, a shunt, an electrometer, a photo amplifier controlled by a moving electrode of an electrometer, voltage - frequency and frequency - current converters, a reversible counter, a display unit and a control unit.

The proposed active power microwatmeter differs from the known ones in that the outputs of the amplifiers are connected to stationary electrodes, the movable electrode of which is connected to the output of the frequency-current converter, the inputs of the amplifiers are connected via a switch to the load and shunt, and a switch is connected parallel to the shunt.

This improves the accuracy of the device.

The drawing shows the scheme of the proposed microwattmeter.

The circuit contains stationary electrodes 1 and 2 of the electrometer; capacitors 3, 4, 5; amplifiers 6 and 7 AC; keys 8 and 9, load 10; Shchuit 11; resistors 12 and 13; sources 14 and 15 of the reference voltage; movable electrode 16 electrometer; analog-to-digital converter 17; photo booster 18 dc; voltage converter 19 is frequency; 20 ch2 converter

stota - current; reversible counter 21; digital display unit 22; control unit 23; feedback resistor 24. As can be seen from the device diagram, the moving electrodes 1, 2 of the electrometer are connected via capacitors 3, 4, amplifiers 6 and 7 of alternating current and switches 8 and 9 to load 10 and shunt 11, and through resistors 12 and 13 and sources 14 and 15 of the reference voltage wives - to

common bus amplifiers 6 and 7.

The movable electrode 16 of the electrometer is connected to the output of an analog-to-digital converter 17, consisting of a DC photoamplifier controlled by a movable

electrode, voltage converter - frequency, frequency-current converter, reversible counter, digital display unit and control unit 23, and through feedback resistor 24 and capacitor 5 - with common

the thickness of the amplifiers 6 and 7.

The operation of the device is as follows.

The torque that occurs in an electrometer under the action of applied AC voltages,

Zhzr K, and - K, Ul,

where / Kz Kz are the electrometer constants; Ui, C / 2 - the voltage at the output of the amplifiers b and 7 of the alternating current, automatically balanced by the compensating moment of the feedback

M, 2t / on oc (Kg - K,) Ul (Kg K,},

where f / on is the constant voltage of the reference source 14 and 15,

Uoc is a constant feedback voltage.

The measurement is divided into four cycles. In the first cycle, the keys 8 and 9 are in position I, and the total voltage from load 10 and shunt 11 is fed to the input of amplifier 6, and the voltage from shunt 11 to the input of amplifier 7. In the second cycle, key 8 is switched to position II . In doing so, the input circuits of the amplifiers 6 and 7 are interchanged. In the third cycle, the key 9 is transferred to position II and the voltage from the load 10 is fed to the input of the amplifier 7, and the input of the amplifier 6 is connected to the total thickness. In the fourth cycle, the key 8 is switched to the position I, the input of the amplifier 7 is connected to the common bus, and the input of the amplifier 6 is connected with a load of 10.

Since in the steady state mode in each of the cycles we can assume that

Zhvr - A4, then, - Zhvr, + vr, - L / VR4 1: ZHK.-Zhk, + F ", - F".,

and when you consider that

OS KocKn-f,

where Kp is the frequency converter factor 20, the frequency is the current, / is the frequency, and the number of pulses counted in each cycle by a reversible counter over time

d,,

 W.P,

5 where

  N, -N, + N,

/ Su - amplifier gain,

Rm is the shunt resistance, P is the measured power.

Thus, if the reversible counter operates in the summation mode in the first and third cycles and in the subtraction mode in the second and fourth cycles, then the recorded number of pulses is proportional to the active power measured in the load. The synchronous operation of the keys of the reversible counter and the digital display unit is carried out with the number of the control unit.

Subject invention

Digital active power microvatmeter, containing amplifiers, shunt, electrometer, photo amplifier controlled by a movable electrode of the electrometer, voltage - frequency and frequency - current converters, reversible counter, display unit and control unit, characterized in that, to improve accuracy, the outputs amplifiers are connected to the stationary electrodes of an electrometer, the movable electrode of which is connected to the output of a frequency-current converter, the inputs of the amplifiers are connected via switches to a load and a shunt, and parallel to the shunt It included key.