by BASIC DEFINITIONS ON INSTRUMENTATION
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Instrumentation uses a lot of words which need to be explained.
Before we can talk about instrumentation and process control you
need to understand the following words.
• Instrument -
Any device for measuring, indicating, controlling, recording and
adjusting a physical or chemical property e.g. flow, pressure,
acidity, weight, gas concentration, etc.
• Instrumentation -
A complete set of instruments used to control a process,
e.g. refining, oil/gas production, LNG, LPG, etc.
• Indicator -
A device which shows a measured value to the operator.
• Recorder -
A device which continuously records measurements, either
electronically or on an ink chart. It is used to show production
figures, etc.
• Process Loop -
A group of instruments used to control a single process variable
e.g. pressure, flow, level, etc.
• Process -
The operator's word for a manufacturing unit e.g., refining, liquefying gas, etc.
• Measured Variable or Process Variable
(MV) The value of the property being controlled by a single
process loop e.g. pressure, flow, level, etc.
• Desired Value or Set Point (SP)
The value required by the operator.
• Error Signal (ES)
The difference between the measured variable and the set point
should be zero for good control.
• Controller -
A device, either pneumatic or electrical / electronic, which adjusts the error signal to zero.
• Correcting Unit -
(Final Control Element) A device which works on the command of
the controller. It is used to adjust the measured value to obtain
a zero error signal, e.g. control valve, etc.
• Transmission -
A method of standardising signals sent from various parts of the plant.
• Transmitter -
A device which takes a measurement and changes it into a standard signal.
• Transducer -
A device which changes one form of energy to
another; particularly from electrical to pneumatic.
