Points to Pay Attention to When Selecting and Using Ammeters and Voltmeters
The measurement mechanism of ammeter and voltmeter is basically the same, but the connection in the measurement circuit is different. Therefore, the following points should be paid attention to when selecting and using ammeters and voltmeters.
1. Choice of type. When the measured value is DC, the DC meter should be selected, that is, the instrument of the magnetoelectric system measuring mechanism. When the measured is AC, attention should be paid to its waveform and frequency. If it is a sine wave, you only need to measure the effective value to convert it to other values (such as maximum value, average value, etc.), and you can use any kind of AC meter; if it is a non-sine wave, you should distinguish what needs to be measured Value, the effective value can choose the instrument of the magnetic system or the ferromagnetic electric system measuring mechanism, and the average value can choose the instrument of the rectifying system measuring mechanism. The instrumentation of the measuring mechanism of the electric system is often used for the precise measurement of alternating current and voltage.
2. Choice of accuracy. Because the higher the accuracy of the instrument, the more expensive it is, and the more difficult it is to maintain. Moreover, if other conditions are improperly matched, even a high-accuracy instrument may not be able to obtain accurate measurement results. Therefore, do not choose a high-accuracy instrument when the instrument with low accuracy can meet the measurement requirements. Usually, instruments of level 0.1 and level 0.2 are selected as standard meters; instruments of level 0.5 and level 1.0 are used for laboratory measurement; instruments below level 1.5 are generally selected for engineering measurement.
⒊ The choice of measuring range. In order to give full play to the role of the accuracy of the instrument, it is also necessary to choose a reasonable meter limit according to the size of the measured instrument. If it is not selected properly, the measurement error will be large. Generally, the indication of the instrument to be measured is greater than 1/2~2/3 of the maximum range of the instrument, but cannot exceed its maximum range.
4. Selection of internal resistance. When selecting an instrument, the internal resistance of the instrument should also be selected according to the measured impedance, otherwise it will cause a large measurement error. Because the size of the internal resistance reflects the power consumption of the instrument itself, when measuring current, an ammeter with as small an internal resistance as possible should be selected; when measuring voltage, a voltmeter with as large an internal resistance as possible should be selected.
