March 2004

Multimeters

How to use them

March 2004

The Multimeter

We have black and yellow ones – the black ones are the ‘newest’…

Some of the yellow ones have ‘use only as an ammeter’ written on them… look at such advice!

March 2004

‘COM’

• Always start by putting a wire into the ‘com’ connection – this is common to its use as a voltmeter and ammeter.

March 2004

Use as an ammeter

• You already have one wire in the ‘com’. You need to put another wire in the terminal with ’10A’ on it

• Then turn the dial to 10A

March 2004

Ammeter• The ammeter is placed in series in a circuit –

never put it in parallel – it is of such low resistance that it will cause a short circuit and could make your power pack ‘blow’ or a battery get very hot!

• You have to make a gap in your circuit to add it in. Put it next to the component you wish to investigate.

• It tells you the rate at which the charge is moving through your component (how fast the charge is moving)

• A ‘typical’ low current is 0.1A• A high current is anything more than 1A – 5A

will make the wires smell and/or melt!

March 2004

Use as a voltmeter

• You already have one wire in the ‘com’. You need to put another wire in the terminal with a V on it

• Then turn the dial to 20V

March 2004

Voltmeter

• The voltmeter is placed in parallel around the component you are investigating. Never put it in series – it has such a high resistance it will cut the flow of current down to a trickle!

• It tells you the potential difference across the component – the ‘electrical slope’ that makes charge move through it.

• It is always the last part of a circuit that you wire up and can be added or removed without changing the action of the circuit itself.

March 2004

Always turn the dial ‘off’ after use

• These multimeters operate on 9V batteries.

• They are expensive to run all day and night!

• Make sure they are ‘off’ when you are not using them