First Steps in Using a Multimeter
Part 2: Measuring Current
Created on: 9 August 2012
Before measuring current, the positive (red) lead of the multimeter must usually be unplugged from it's normal connector in the multimeter and then plugged into a separate connector in the multimeter that is marked A or mA. This is not always the case, some cheaper meters may have the volts, mill-amps and ohms on one connector and amps on a separate connector.
In this video, two different multimeters are used to measure current in the same circuit. The first multimeter is a cheap one that does not require the red lead to be plugged into a separate connector when measuring mill-amps (mA). The second meter does require the red lead to be plugged into a separate connector to measure mill-amps.
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The Circuit Under Test
The circuit in the video in which current is being measured is a simple LED circuit that consists of a LED in series with a resistor. This circuit is the same circuit that is used in tutorial 1.
It is very important to realise that when a multimeter is set to the amps or mill-maps scale, and the red lead plugged into the correct socket in the multimeter, that the two leads of the multimeter are now like a single piece of wire. Touching the leads to the two terminals of a battery must never be done as this will short out the battery and is the same as taking a single piece of wire and connecting it across the battery terminals.
In the same way, when the multimeter is set to amps or milli-amps range, it must not be used to measure across any component in a circuit. This would be the same as shorting the component out with a piece of wire.
Taking a Current Measurement
To measure the current flowing in a circuit, the circuit must be broken and the multimeter inserted in the break to then complete the circuit again. In this way the multimeter in current mode forms part of the circuit.
In the video, the current flows from the battery terminal through the multimeter, then through the LED, through the resistor and back to the opposite battery terminal.
Series and Parallel Measurement
The multimeter on the current setting (which makes it into an ammeter) is said to be connected in series in the circuit.
Voltage measurements are made in parallel or across a battery or component in a circuit.