What is Process Instrumentation?

Instrumentation is the variety of measuring instruments to monitor and control a process. It is the art and science of measurement and control of process variables within a production, laboratory, or manufacturing area. An instrument is a device that measures a physical quantity such as flow, temperature, level, distance, angle, or pressure. Instruments may be as simple as direct reading thermometers or may be complex multi-variable process analyzers. 

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. Instrumentation can also refer to handheld devices that measure some desired variable. Diverse handheld instrumentation is common in laboratories, but can be found in the household as well. For example, a smoke detector is a common instrument found in most western homes.

Instruments attached to a control system may provide signals used to operate solenoids, valves, regulators, circuit breakers, or relays. These devices control a desired output variable, and provide either remote or automated control capabilities. These are often referred to as final control elements when controlled remotely or by a control system. A transmitter is a device that produces an output signal, often in the form of a 4 20 mA electrical current signal, although many other options using voltage, frequency, pressure, or Ethernet are possible.

This signal can be used for informational purposes, or it can be sent to a PLC, DCS, SCADA system, Lab VIEW or other type of computerized controller, where it can be interpreted into readable values and used to control other devices and processes in the system. Control 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.

Importance of process parameters: 

 Process Parameters (also called a process variable) are certain measures that refer to status of the process (their values indicate whether the process meets the plan or it needs adjustment). In order to obtain effective execution of the process its parameters should stay under continuous control.

The simplest examples of parameters you can find in a manufacturing process are pressure, temperature, and chemical composition – anyone of these may have its desired value that is called a set-point that regulates proper functioning of process elements and operations, while if a parameter deviates from its set-point (goes beyond the acceptable level of variance), then probably a process tends to fail, hence special automatics or human operators should intrude into this process to adjust it and prevent upset.

The Process Variables used in instrumentation are:

 Flow - Defined as volume per unit of time at specified temperature and pressure conditions, is generally measured by positive-displacement or rate meters. Units: kg / hr., litter / min, gallon / min, m3 / hr., Nm3 / hr. (gases)

 Pressure - Force acting per unit Area. P = F/A. Units: bar, Pascal, kg / cm2, lb. / in2.

 Temperature - It is the degree of hotness or coldness of a body. Units: Degree Centigrade, Degree Fahrenheit, Degree Kelvin, Degree Rankin.

 Level - Different between two heights. Units: Meters, mm, cm, percentage.