16
…6
TUNING LEVEL
…6.1
Introduction to Self-tuning
Information. 'At Set Point' self-tuning automatically calculates the P.I.D. terms based
on the process reaction during a self-tuning cycle. The controller output is
manipulated to give six process oscillations which are used to determine the tuning
parameters.
Fig. 6.2 'At Set Point' Self-tuning
Information.
On initial conditions:
•
'Start-up' Tuning
– the controller is placed in the Manual control mode with the control
output value set to give a stable process variable at least 10% of the engineering range
below the control set point.
•
'At Set Point' Tuning
– may be initialized in the automatic mode but the process variable
must be close to the required set point and stable. The control output must also be
stable. However, for best results the Manual control mode can be used to stabilize the
output and the process value. The output must be adjusted slowly to allow process
response to the change, to bring the process variable to the required control set point.
The closer the process is to the set point, the more effective the self-tuning cycle.
6.2
Self-tuning Page
SELF
– – – – – –
– – – – – –
Error
No
Error
tUNE
Self-tune High Limit
Self-tune Low Limit
Hysteresis
Band
Hysteresis
Value
Output Step
Values at
Start of
Execution
Controller Output
Time
Signal Noise
Page Header – Self-tune.
Note. This page is not displayed if the Profile Function is
'ON' or
Control Type
is set to '
bNdLSS
'
Error and Diagnostic Messages
If there are errors during self-tune, flashing error and
diagnostic messages are displayed. To clear message,
press the
switch – see Table 6.1.
Continued on next page
