West Control Solutions N8100 - Manual (Page 24)

2.3 OPERATOR MODE DISPLAYS
Once the complete cycle of Set Up Mode parameters has been displayed, the
user may then step through the Operator Mode displays (see Subsection 1.2),
making adjustments where required, before re-starting the Set Up Mode
parameter cycle, as shown in Table 2-1.
2.4 TUNING THE CONTROLLER MANUALLY
2.4.1 Controllers Fitted with Output 1 Only
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. Set the setpoint to the normal operating process value (or to a lower
value if overshoot beyond this value is likely to cause damage).
2. Select ON/OFF Control (i.e. set Pb1 = 0).
3. Switch on the process. The process variable will oscillate about the
setpoint. Note (a) The peak-to-peak variation (P) of the first cycle i.e. the
difference between the highest value of the first overshoot and the lowest
value of the first undershoot, and (b)tThe cycle time (T) of this oscillation in
minutes (see Figure 2-4)
4. The control parameters should then be set as follows:
=
P
ScaleRange
x 100
= T minutes
=
T
6
minutes
NOTE: After setting up the parameters, set the Controller to Operator Mode
(see Subsection 2.6) to prevent unauthorised adjustment to the values.
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