Introduction to Measuring Mechanism Used by AC Ammeter
The non-sinusoidal waveform has little effect on the electromagnetic system, electric system, and thermoelectric ammeter. Rectifying ammeters are limited to sinusoidal waveforms, and digital ammeters have similar limitations. In the power system, a converter ammeter can be used to measure non-sinusoidal current. When measuring large current, it must be used with a special shunt. When measuring large currents, it must be used with current transformers.
The AC ammeter mainly adopts the measuring mechanism of the electromagnetic system ammeter, the electric system ammeter and the rectifier type ammeter. The minimum measuring range of the measuring mechanism of the electromagnetic system is about tens of milliamperes. In order to increase the measuring range, the number of turns of the coil should be reduced proportionally and the wire should be thickened. When the ammeter is composed of an electric system measuring mechanism, the moving coil and the static coil are connected in parallel, and the minimum range is about tens of milliamperes. In order to increase the range, the number of turns of the static coil should be reduced, and the wire should be thickened, or the two static coils should be connected in parallel instead of series, then the range of the ammeter will be doubled. When measuring alternating current with a rectifying ammeter, the ammeter reading is correct only when the alternating current is a sinusoidal waveform. A shunt can also be used to extend the measuring range. In addition, high-frequency currents can also be measured with thermoelectric meters. Most of the large-range AC ammeters used in power systems are 5A or 1A electromagnetic ammeters, and are equipped with current transformers with appropriate current transformation ratios.
