Custom Search

1-24 shown in figure 1-24(C). The range of the meter is now 10 milliamperes and it is possible to read the meter indication of 5 milliamperes with the greatest degree of accuracy. Since the current indicated is equal to (or greater than) the next range of the ammeter (5 milliamperes), the meter should NOT be switched to the next range. AMMETER SAFETY PRECAUTIONS When you use an ammeter, certain precautions must be observed to prevent injury to yourself or others and to prevent damage to the ammeter or the equipment on which you are working. The following list contains the MINIMUM precautions to observe when using an ammeter. Ammeters must always be connected in series with the circuit under test. Always start with the highest range of an ammeter. Deenergize and discharge the circuit completely before you connect or disconnect the ammeter. In dc ammeters, observe the proper circuit polarity to prevent the meter from being damaged. Never use a dc ammeter to measure ac. Observe the general safety precautions of electrical and electronic devices. Q26.     Why should you use the highest range of an ammeter for the initial measurement? Q27.     What range of an ammeter is selected for the final measurement? Q28.     List the six safety precautions for the use of ammeters. Q29.     Why will an ammeter be damaged if connected in parallel with the circuit to be measured? VOLTMETERS All the meter movements discussed so far react to current, and you have been shown how ammeters are constructed from those meter movements. It is often necessary to measure circuit properties other than current. Voltage measurement, for example, is accomplished with a VOLTMETER. VOLTMETERS CONNECTED IN PARALLEL While ammeters are always connected in series, voltmeters are always connected in parallel. Figure 1-25 (and the following figures) use resistors to represent the voltmeter movement. Since a meter movement can be considered as a resistor, the concepts illustrated are true for voltmeters as well as resistors. For simplicity, dc circuits are shown, but the principles apply to both ac and dc voltmeters.