Multimeter- Principle and operation

In the electronics lab, a common piece of test equipment is the multimeter, in which different kinds of meters are combined into a single unit. The volt-ohm-milliammeter (VOM) is the most often used. As its name implies, it combines voltage, resistance and current measuring capabilities.

 You should not have too much trouble envisioning how a single milliammeter can be used for measuring voltage, current and resistance. The preceding discussions for measurements of these quantities have all included methods in which a current meter can be used to measure the intended quantity.

   Commercially available multimeters have certain limits in the values they can measure. The maximum voltage is around 1000 V; larger voltages require special leads and heavily insulated wires, as well as other safety precautions. The maximum current that a common VOM can measure is about 1 A. The maximum resistance is on the order of several mega ohms or tens of mega ohms. The lower limit of resistance indication is about an ohm.