Field instruments are devices that measures a physical quantity such as flow, temperature, level, distance, angle, or pressure. Instruments are often part of a control system in refineries, factories, and vehicles. The control of processes is one of the main branches of applied instrumentation. Instruments attached to a control system may provide signals used to operate solenoids, valves, regulators, circuit breakers or relays.etc. These devices control a desired output variable, and provide either remote or automated control capabilities.