West Control Solutions N8100 - Manual (Page 25)

2.4.2 Controllers Fitted with Output 1 and Output 2
Before starting to tune the Controller to the load, check that the Setpoint High and
Low Limits (SPhi and SPLo) are set to safe levels - see Subsections 2.2.12 and
2.2.13.
The following simple technique may be used to determine values for proportional
band (Pb1), derivative time constant (rAtE) and integral time constant (rSEt).
NOTE: This technique is suitable only for processes which are not harmed by
large fluctuations in the process variable. It provides an acceptable basis
from which to start fine tuning for a wide range of processes.
1. Tune the Controller using Output 1 only as described in Subsection 2.4.1.
2. Set Pb2 to the same value as Pb1 and monitor the operation of the
Controller in dual output mode. If there is a tendency to oscillate as control
passes into the Output 2 proportional band, increase the value of Pb2. If
the process appears to be over-damped in the region of the Output 2
proportional band, decrease the value of Pb2.
3. When values of proportional bands, integral time constant and derivative
time constant have been determined for tuning, if there is a “kick” as
control passes from one output to the other, set OL to a positive value to
introduce some overlap. Adjust the value of OL by trial and error until
satisfied.
2.5 SELF-TUNE AND PRE-TUNE FACILITIES
Once the Controller has been manually tuned, the Self-Tune and Pre-Tune
facilities may be used in Operator Mode to enhance further the response of the
Controller (see Subsections 1.9 and 1.8 respectively).
O054-2 2-14
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Figure 2-4 Manual Tuning Parameters - Output 1 only