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