Measurement of Electrical Measurements
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MEASUREMENT OF ELECTRICAL MEASUREMENTS
A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. The most basic instruments include an ammeter, voltmeter, and ohmmeter.
: 1. Current intensity – ammeter An ammeter is an instrument which is used to measure the flow of an electric current in a circuit. The ammeter must be connected in series with the resistor. Ammeters must have a LOW resistance. (All the current flowing in the circuit must pass through the ammeter. As meters are not supposed to alter the behaviour of the circuit, or at least not significantly, the ammeter must have a very LOW resistance).
Diagrams A and B below show a circuit before and after connecting an ammeter.
A B
2. Voltage – voltmeter A voltmeter is an instrument used for measuring the voltage between two points in an electric circuit. To measure the voltage, the circuit is not changed: the voltmeter is connected in parallel. Voltmeters must have a HIGH resistance. (This time, you do not need to break the circuit. The voltmeter is connected in parallel, so it should take as little current from the circuit as possible. In other words, a voltmeter should have a very HIGH resistance). Voltage measurements are used much more often than current measurements. Diagram C shows the same circuit after connecting a voltmeter:
A C
3. Resistance – ohmmeter
An ohmmeter is an instrument used to measure the resistance of a particular component of an electric circuit.
A D
To measure resistance, the component must be removed from the circuit.
If you want to measure the resistance of a particular component, you must take it out of the circuit and test it separately, as shown in diagram D.