Apr 102013
 

Multimeter is very useful test instrument. It can be easily and quickly set to be a voltmeter, ammeter or an ohmmeter just by operating a multi-position switch on it. They have several settings (known as ranges) for each type of meter and the choice of Alternative Current (AC) or Direct Current (DC). Some multimeters have features such as transistor testing, continuity testing and ranges for measuring capacitance and frequency.

How to choose a multimeter?

While choosing a multimeter, we have to go through all the features of a multimeter. A digital multimeter is the best choice if we are buying a multimeter. If we are buying an analog multimeter, we must make sure that it has high sensitivity of 20 K/V or greater on DC voltage ranges, anything less is not suitable for electronics. The sensitivity is normally marked in a corner of the scale. The lower value of Alternating Current (AC) should be ignored and the higher value of Direct Current (DC) should also be ignored.

Types of Multimeters

There are generally two types of multimeters. They are listed below with their descriptions:

1. Digital Multimeters: Analog multimeters are those multimeters which work on the digital principle. These digital multimetermultimeters contain a battery to power the display so they use virtually no power from the circuit which is under test. This means that on their Direct Current (DC) voltage ranges, they have a very high resistance (also referred to as input impedance) of 1M or more. It is usually 10M. Typical ranges for digital multimters are listed below:

– DC voltage: 200mV, 2000mV, 20V, 200V, 600V.AC voltage: 200V, 600V.
– DC current: 200µA, 2000µA, 20mA, 200mA, 10A*.
*The 10A range is usually unfused and connected through a special socket.
– AC current: None (It is not necessary to measure AC current.)
– Resistance: 200, 2000, 20K, 200K, 2000K, Diode Test.

Digital meters have a special diode test setting because their resistance ranges cannot be used to test diodes and other semiconductors.

Note: The values given above are the maximum readings on each range.

2.  Analog Multimeters: Analog multimeters take a little power from the circuit under test to operate their pointers. These multimeters work onanalog multimeter the analog principle. They must have a high sensitivity of at least 20K/V or they may upset the circuit under test and give an incorrect reading.Batteries inside the meter provide power for the resistance ranges and they will last for several years. But we should avoid leaving the multimeter set to a resistance range, in case the leads touch accidentally and they run the battery flat.The typical ranges for analog multimeters are listed below:

– DC voltage: 0.5V, 2.5V, 10V, 50V, 250V, 1000V.
– AC voltage: 10V, 50V, 250V, 1000V.
– DC current: 50µA, 2.5mA, 25mA, 250mA. (A high current range is often missing from this type of multimeter.)
– AC current: None (It is not necessary to measure AC current.)
– Resistance: 20, 200, 2K, 20K, 200K. These resistance values are in the middle of the scale for each range.

Note: The values given above are the maximum readings on each range.