West Control Solutions Pro-EC44 - Manual (Page 230)

Pro-EC44 2-Loop Graphical Profile Controller & Recorder
Pro-EC44 Product Manual - 59540-1 October 2013 Page 223
PD Control
Proportional and Derivative (PD) control combines proportional control with derivative action.
It is similar to PID control, but without Integral action.
Also refer to: Derivative; Integral; PID Control; Proportional Control and Tuning.
PI Control
Proportional and Integral Control (PI) combines proportional control with integral action. It is
similar to PID Control, but without derivative action. It is often used for modulating valves,
dampers or motor speed control, where derivative action can sometimes cause instability or
wear of mechanical components like valves, due to excessive movement.
Also refer to: Derivative; Integral; Modulating Valve; PID Control; Proportional Control;
Tuning and Valve Motor Control.
PID Control
Proportional Integral and Derivative control maintains accurate and stable levels in a process
(e.g. when controlling temperature or humidity etc). Proportional control avoids the oscillation
characteristic of on-off control by continuously adjusting the correcting variable output(s) to
keep the process variable stable. Integral action eliminates control deviation errors, and
Derivative action counters rapid process movements.
Also refer to: Control Action; Control Deviation; Control Enable; Control Type; Controller;
Correcting Variable; Derivative Action; Gain Scheduling; Integral Action; Manual Mode; On-
Off Control; PD Control; PI Control; PID Sets; Primary Proportional Band; Process Variable;
Secondary Proportional Band; Setpoint and Tuning.
PID Gain Sets
The instrument contains PID 5 sets for each control loop, allowing the instrument to be pre-
set for differing conditions. Each set has individual values for the proportional bands;
overlap/deadband; on-off differential and integral & derivative times.
These values are entered in the control configuration sub menu or via the automatic tuning.
The PID sets might be configured for different applications, or to allow for differing process or
load conditions that might occur in a single application. In these cases one set at a time
would
be selected as the “Active PID” set for that loop.
The PID sets are also used by the automatic gain scheduling feature.
Also refer to: Derivative Action; Gain Scheduling; Integral Action; On-Off Control; PID;
Primary Proportional Band; Secondary Proportional Band and Tuning.
PLC
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
The Pre-Tune facility artificially disturbs the process variable normal start-up pattern, so that
an approximation of the PID values can be made prior to the setpoint being reached. During
pre-tune, the controller outputs full primary power until the process value
reaches the “tuning
point”. With Standard Pre-Tune this is halfway to the setpoint, but an alternative method
allows the user to specify the process value to tune at. Pre-tune can be selected from the
automatic tuning menu and will automatically disengage once complete.