Industrial Instrumentation Terms

Industrial Instrumentation and Control Systems have their own unique terms and standards that are used. Some of them include:

Process: This is the physical system we measure or control for example: Steam Boiler, Oil Refinery, Power Generating Unit etc. 

Process Variable or PV: The specific quantity we are measuring in a process e.g. Flow, PH, Temperature, Pressure, Level etc. 

Primary Sensing Element: This is a device that directly senses the process variable and translates the sensed quantity into an analog representation (electrical voltage, current, resistance, motion etc.) These elements maybe like Thermocouple, Thermistor, Accelerometer etc. 

Set point: This is the value at which we desire the process variable to be maintained at. 

Transducer: This is the device that converts one standardized instrumentation signal into another standardized instrumentation signal. It may also perform some processing of the signal. Some of these includes: I/P converter (converts 4-20 mA electric signal into 3-15 PSI pneumatic signal). 

Transmitter: A device that translates the signal produced by a primary sensing element into a standardized instrumentation signal such as 3-15 PSI air pressure, 4-20 mA DC electric current, etc. which can then be conveyed to an indicating device, a controlling device or both. 

Automatic Mode: When the controller generates an output signal based on the relationship of the process variable (PV) to the set point (SP). 

Manual Mode: When the controller's decision-making ability is bypassed to let a human operator directly determine the output signal sent to the final control element. 

Final Control Element: A device that receives the signal from a controller to directly influence the process e.g. a control valve. 

Manipulated Variable: This is the signal commanding (manipulating) the final control element to influence the process. 

Controller: A device that receives a process variable (PV) signal from a primary sensing element or transmitter, compares that signal to the desired value for the process variable (called the set-point), and calculates an appropriate output signal value to be sent to a final control element, such as a control valve.

 

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The above are some of the Key but very basic terms that any Instrumentation Professional should be well versed with.

You can also read: Basic Introduction to Industrial Instrumentation