ABSTRACT
This chapter covers both analogue and digital instruments. Analogue instruments gets supersede by digital instruments, which is easy to read, mechanically robust and less expensive. The chapter deals with moving-coil instrument, described as 'polarised' instruments, the most common type of meter employed by precision analogue instruments such as ammeters, voltmeters, ohmmeters, and multimeters. The moving coil is connected to the external circuit via a pair of coiled hairsprings, located at opposite ends of the coil. Their function is to control the movement of the coil, and to restore the coil and pointer back to their rest position when there is no current flowing around the coil. The chapter determines the value of the shunt resistance, required to convert a moving-coil instrument to circuit current and the value of the multiplier resistance, required to convert a moving-coil instrument to potential difference. Also, the 'sensitivity' of a moving-coil instrument indicates the value of current required for the instrument to achieve full-scale deflection.
