The ammeter is an instrument used to measure electrical current. To measure the current flowing through some point of a circuit, the circuit must be broken open at that point and the ammeter inserted so that the current to be measured actually flows through the meter too. (Note: Turn off the power before inserting the ammeter, then restore the power to make the current reading.) To reiterate: to measure the current flowing through a circuit element, the circuit must be opened and the ammeter put in series with it. See the top two circuits of Fig. 4 for examples of correct ammeter placement
Most meters have a number of possible settings for the maximum possible current that can be measured; for example: 2 A, 200 mA, 20 mA, 2 mA. You should always start by turning the setting to the highest possible rating (for example, 2 A). When the meter is finally situated in the circuit to take the reading, and the power is turned on to the circuit, the sensitivity of the ammeter may be increased by changing to progressively lower ranges. It is important not to overshoot the maximum value that can be read. For example, if the current is about 75 mA, then the ammeter would be set to the 200 mA scale for the most accurate reading; setting to the 20 mA scale would overload the ammeter and most likely open its internal fuse. Golden rule of multimeters: Return to voltmeter mode immediately after use as an ammeter is completed
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