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Chemical Engineering vocabulary · Process Control and Instrumentation

Control loop

Meaning in chemical engineering, with examples

nounCommon term

In chemical engineering, control loop means: A set of parts that work together to hold one process variable at its setpoint: a sensor and transmitter, a controller and a final element such as a control valve.

In Turkish: kontrol döngüsü, kontrol çevrimi

How it is used

Used by control engineers, operators and instrument technicians. Loops are tuned, checked, put in auto or manual and closed or opened. On P&IDs each loop has a tag number, for example TIC-101 for a temperature indicating controller.

Example sentences

  1. Half of the control loops on this unit are running in manual, which is a bad sign.

  2. Do a loop check on the new pressure control loop before start-up.

Common collocations

  • control loop tuning
  • loop check
  • closed loop
  • open loop
  • cascade loop
  • PID controllerThe most common type of process controller. It sets its output from three terms: proportional (the present error), integral (past error) and derivative (how fast the error is changing).
  • feedback controlA control method that measures the process variable, compares it with the setpoint and adjusts the output, usually a valve, to correct the difference.
  • setpointThe target value that a controller tries to hold, such as a temperature of 85 °C or a tank level of 60%.
  • transmitterA field instrument that measures a value such as pressure, temperature, level or flow and sends it as an electrical signal, often 4–20 mA, to the control system.
  • control valveAn automatic valve that opens and closes in small steps on a signal from a controller, so that flow, pressure, level or temperature stays at the setpoint.

More terms: Process Control and Instrumentation

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