Multimeter Basics

By Rageb Ahsan – Electrical Engineer

Classical AVOmeter

Classical AVOmeter

From the very name it’s clear that a multimeter is an instrument with several functions. A multimeter is used for measuring electrical parameters like voltage, current, ohm and some more. Once people used to call it an AVO meter from the first letters of the three major items of its concern.

For an electrician or an Electrical Engineer a multimeter is a very important tool. To start working regarding a new installation or maintenance an electrician has to be sanguine about the line voltage available. There is no way to confirm this without a meter. A voltmeter may serve the purpose. But in the next step he or she would require to measure a current flow. Then he will need an ampere meter also. At one time he would have to measure a circuit resistance. He will ask for an ohmmeter for that. So he would need three measuring instruments.

A multimeter would serve all the three purposes. It’s a compact, handy instrument and very much portable. Some brand products are so small; you can take it in your pocket even. However it’s such an instrument an electrician can’t think of an hour without it.

In addition to the measurement of above three parameters a multimeter is designed to test transistors.

Selecting Type and Range

As it’s manufactured to measure and test different items, it has got a selector switch to select for the desired one. A multimeter is designed to measure both A.C and D.C voltages. It has got different voltage ranges to choose. So for measuring a voltage you have to select the voltage type and range.

Similar the case is about measuring a resistance. You have to choose the range. Electrical current measurement is a bit tricky. The meter is to be connected in series for that. Otherwise you won’t get the measurement. Rather you would ruin the equipment.

Hence before measuring a voltage you must choose from A.C and D.C and at the same time you have to select a range. If you select a very high range your result will be less accurate. But you can change the range for accurate result. In case you select a range lower than actual, the meter may be damaged. So select the correct one or a higher one.

Before measuring a current flow you have to discontinue the circuit in which you like to measure the current and connect the meter in between to complete the circuit. If you connect the meter between two points having a potential difference, that will blow the safety fuse or even may damage the meter. So you should be very careful about it.

Resistance measurement is rather simple as you have to switch off the power or at least isolate the part of which you desire to measure the resistance. You may also detect continuity of a circuit with resistance measurement selected. This is a very useful thing for an electrician.

Some Words of Advice

Once multimeters were analog and a pointer moved to show the measured result. Now it’s digital and of course it’s much easier to read the value. A multimeter needs D.C. power for its functioning. Normally a battery is used for the purpose. As the battery gets discharged gradually it needs replacement. Replace the battery at proper time. Otherwise leakage of battery may damage the circuits of the meter itself.

Buy a good multimeter, use it properly, replace the battery at correct time and work safely.

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