instrumentation

Instrumentation is an electrical or pneumatic device placed in the field to provide measurement and/or control capabilities for the system.

The simplest measurement instrumentation device is a thermistor. A thermistor is very similar to a typical resistor, except that it greatly varies its resistance depending on its temperature. Therefore this device can easily be used for measurement of temperature in the field. Other temperature-sensitive devices include RTDs, which also change resistance depending on temperature, and thermocouples, which produce a varying voltage when subjected to heat.

Control instrumentation includes devices such as solenoids, Electrically Operated Valves, breakers, relays, etc. These devices are able to change a field parameter, and provide remote control capabilities.

Transmitters are devices which produce an analog signal, usually in the form of a 4-20 mA electrical current signal, although many other options are possible using voltage, frequency, or pressure. This signal can be used to directly control other instruments, or sent to a PLC, DCS, SCADA system or other type of computerized controller, where it can be interpreted into readable values, or used to control other devices and processes in the system.

Instrumentation plays a significant role in both gathering information from the field and changing the field parameters, and as such are a key part of control loops.