WEST P4100 - Pid; PLC Type: General Definition; Pre-Tune

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- DIN Controllers & Indicators - Product Manual
59305, Issue 5 – March 2005 Glossary Page 119
PID Type: Controller Definition
This stands for Proportional Integral and Derivative. A control method that accurately
maintains the desired level in a process (e.g. controlling a temperature). It avoids the
oscillation characteristic of On-Off control by continuously adjusting the power output level to
keep the process variable stable at the desired target setpoint.
Also refer to Automatic Reset, Controller, On-Off Control, Primary Proportional Band,
Process Variable, Rate, Secondary Proportional Band, Setpoint and Tuning
PLC Type: General Definition
This stands for Programmable Logic Controller. A microprocessor based device used in
machine control. It is particularly suited to sequential control applications, and uses “Ladder
Logic” programming techniques. Some PLC’s are capable of basic PID control, but tend to
be expensive and often give inferior levels of control.
Also refer to PID.
Pre-Tune Type: Controller Definition
The Pre-Tune facility artificially disturbs the start-up pattern so that a first approximation of
the PID values can be made prior to the setpoint being reached. During Pre-Tune, the
controller demands full power until the process value has moved approximately halfway to
the setpoint. At that point, power is removed, thereby introducing an oscillation. Once the
oscillation peak has passed, the Pre-Tune algorithm calculates an approximation of the
optimum PID tuning terms proportional band(s), automatic reset and rate. The process is
shown in the diagram below.
When Pre-Tune is completed, the PID control output power is applied using the calculated
values. Pre-Tune limits the possibility of setpoint overshoot when the controller is new or the
application has been changed. As a single-shot operation, it will automatically disengage
once complete, but can be configured to run at every power up using the Auto Pre-Tune
function. Pre-Tune will not engage if either primary or secondary outputs on a controller are
set for On-Off control, during setpoint ramping or if the process variable is less than 5% of
the input span from the setpoint.