What is the functioning, use, construction and working of Electronic multimeter?

It is a very versatile meter in laboratories because it can be used for many purposes. Some of its functions are DC and AC current and voltage measurement and resistance of resistors used in electronic circuits. The solid state version is described here in oncoming discussion. Following components are constituent parts of a multi-meter.

·         A balance bridge DC amplifier and PMMC indicator

·         A range switch which is an attenuator to limit the value of input voltage to the desired one.

·         A rectifier on order to convert AC to  equivalent DC value

·         An internal battery and additional circuitry for the measurement of resistance.

·         A function Switch to reset various measurement functions for the instrument like current, voltage and resistance.

Along with this all the instruments has a built in power supply for the purpose of performing operation on power mains and many cases one or more than one batteries for operation as portable test instrument. Here is figure that is capable of showing all the part that has been discussed about in our discussion so far.

Balanced DC amplifier

 

This figure shows the schematic diagram of a balanced bridge DC amplifier that uses two field effect transistors (FETs). These two FETs are reasonably matched with each other on the basis of current gain this done to ensure thermal stability in the circuitry. The upper arm of the bridge is formed with the help of two FETs the source resistors R1 and R2 together with zero adjustment of resistor R3 form the lower bridge. The PMMC instrument is connected between the source terminals of FETs. These two FETs represent two opposite end of the bridge. In case of no input signal applied to the gate terminal of FETs they remain to be at the zero potential or ground potential. In this case in ideal situation there should be no current flowing through the meter. But due to presence of some miss matches between the FETs and also due to some differences in values of resistor a current does flows. This unwanted current can be reduced to zero with the help of a grounded variable resistor.