Analogue multimeters

Analogue meters take a little power from the circuit under test to operate their pointer. They must have a high sensitivity of at least 20kohm/V or they may upset the circuit under test and give an incorrect reading. See the section below on sensitivity for more details.

Batteries inside the meter provide power for the resistance ranges, they will last several years but you should avoid leaving the meter set to a resistance range in case the leads touch accidentally and run the battery flat.

Typical ranges for analogue multimeters like the one illustrated:
(the voltage and current values given are the maximum reading on each range)

* 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 meter.
* AC Current: None. (You are unlikely to need to measure this).
* Resistance: 20ohm, 200ohm, 2kohm, 20kohm, 200kohm.
These resistance values are in the middle of the scale for each range.

It is a good idea to leave an analogue multimeter set to a DC voltage range such as 10V when not in use. It is less likely to be damaged by careless use on this range, and there is a good chance that it will be the range you need to use next anyway!

Sensitivity of an analogue multimeter
Multimeters must have a high sensitivity of at least 20kohm/V otherwise their resistance on DC voltage ranges may be too low to avoid upsetting the circuit under test and giving an incorrect reading. To obtain valid readings the meter resistance should be at least 10 times the circuit resistance (take this to be the highest resistor value near where the meter is connected). You can increase the meter resistance by selecting a higher voltage range, but this may give a reading which is too small to read accurately!

On any DC voltage range:
Analogue Meter Resistance = Sensitivity × Max. reading of range
e.g. a meter with 20kohm/V sensitivity on its 10V range has a resistance of 20kohm/V × 10V = 200kohm.