Any choice of ammeter

The measuring mechanism of ammeter and voltmeter is basically the same, but the connection in the measuring circuit is different. Therefore, in the selection and use of ammeter and voltmeter should pay attention to the following points.

1. Type selection. When DC is measured, DC meter should be selected, that is, the instrument of magnetoelectric measuring mechanism. When the measured signal is AC, attention should be paid to its waveform and frequency. If it is a sine wave, it can be converted to other values (such as large value, average value, etc.) by measuring the effective value, and any kind of AC meter can be used; If it is a non sinusoidal wave, the value to be measured should be distinguished. The effective value can be the instrument of magnetic or ferroelectric measuring mechanism, and the average value can be the instrument of rectifier measuring mechanism. The instruments of electric measuring mechanism are often used for the precise measurement of AC current and voltage.

2. Selection of accuracy. Because the higher the accuracy of the instrument, the more expensive the price, maintenance is more difficult. Moreover, if other conditions are not matched properly, no matter how high the accuracy level of the instrument, it may not be able to get accurate measurement results. Therefore, in the case that the instrument with low accuracy can meet the measurement requirements, the instrument with high accuracy should not be selected. Generally, class 0.1 and class 0.2 instruments are selected as standard tables; Class 0.5 and 1.0 instruments are used for laboratory measurement; Instruments below grade 1.5 are generally used for engineering survey.

3. Selection of measuring range. In order to give full play to the accuracy of the instrument, it is necessary to reasonably select the measuring limit of the instrument according to the measured size. If it is not selected properly, the measurement error will be very large. Generally, the indication of the instrument to be measured is more than 1 / 2 ~ 2 / 3 of the large range of the instrument, but not more than its large range.

4. Selection of internal resistance. When selecting the instrument, the internal resistance of the instrument should also be selected according to the measured impedance, otherwise it will bring large measurement error. Because the internal resistance reflects the power consumption of the instrument itself, the ammeter with the smallest internal resistance should be selected when measuring the current; When measuring the voltage, the voltmeter with the largest internal resistance should be selected.