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Self-Tune
Continuously optimises tuning while a controller is operating. It uses a pattern recognition
algorithm, which monitors the process error (deviation signal). The diagram shows a typical
temperature application involving a process start up, setpoint change and load disturbance.
The deviation signal is shown shaded and overshoots have been exaggerated for clarity.
The Self-Tune algorithm observes one complete deviation oscillation before calculating a set
of PID values. Successive deviation oscillation causes values to be recalculated so that the
controller rapidly converges on optimal control. When the controller is switched off, the final
PID terms remain stored in the controller's non-volatile memory, and are used as starting
values at the next switch on. The stored values may not always be valid, if for instance the
controller is brand new or the application has been changed. In these cases the user can
utilise Pre-Tune to establish new initial values.
Use of continuous self-tuning is not always appropriate for applications which are frequently
subjected to artificial load disturbances, for example where an oven door is likely to be
frequently left open for extended periods of time. Self-Tune cannot be engaged if a controller
is set for On-Off Control.
Also refer to On-Off Control, Pre-Tune, PID, and Tuning.
Serial Communications Option
An feature that allows other devices such as PC's, PLC's or a master controller to read or
change an instruments parameters via an RS485 Serial link. Full details can be found in the
Serial Communications sections of this manual.
Also refer to Controller, Indicator, Master & Slave, Limit Controller and PLC
Setpoint
The target value at which a controller will attempt to maintain the process variable by
adjusting its power output level. Controllers can have either one or two setpoints. These can
be one or two local internal setpoints ( :- or :-2 and :-3 ), or one local internal setpoint
( +:- ) and one externally adjusted remote ( 0:- ) setpoint, if a Remote Setpoint module is
fitted. The value of the setpoints can be adjusted between the Setpoint Upper Limit and
Setpoint Lower Limits. The active setpoint is defined by the status of the Setpoint Select
parameter or a digital input.
Also refer to Limit Setpoint, Process Variable, Remote Setpoint, Scale Range Lower Limit,
Setpoint Lower Limit, Setpoint Upper Limit and Setpoint Select
59305, Issue 5 – March 2005
- DIN Controllers & Indicators - Product Manual
Setpoint 2
Setpoint 1
Figure 45.
Load Disturbance
Setpoint Change
Self-Tune Operation
Glossary
Type: Controller Tuning Definition
Time
Type: General Definition
Type: Controller Definition
Page 125
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