In any process activity involving the measurement of process variables like pressure, flow and level of gas, steam or fluid and temperature of static and dynamic elements, transmitters are used. These measurements are extremely critical for satisfactory and trouble free operation of a plant. The transmitter converts these physical parameters to electrical signals which are further fed into the plant DA S or DM. Since the transmitters are housed in the fields near the source of origin of signal, special provision for their mounting has to be provided. As per the field location, the transmitters and related equipment may be housed in racks or in enclosures.

Enclosures are cubicles which, besides providing proper support for mounting of local instruments, provide protection against ingress of dust and water. These are put in places where the presence of moisture and impurities may impede the proper functioning of the equipment On the other hand, racks are free standing structures for supporting local instruments. These are placed at locations where the atmosphere is clean and free from impurities.