West Control Solutions N6600 - Manual (Page 34)

3.4 TUNING THE CONTROLLER MANUALLY
3.4.1 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 3.2.12 and
3.2.13.
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 for use only with 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. Under these conditions, the process variable will
oscillate about the setpoint and the following parameter values should be
noted:
(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 - see Figure 3-4)
(b) The cycle time (T) of this oscillation in minutes (see Figure 3-4)
4. The control parameters should then be set at follows:
=
P
ScaleRange
X 100
= T minutes
=
T
6
minutes
NOTE: After setting up the parameters, set the Controller to Operator
Mode (see Subsection 3.6) to prevent unauthorised adjustment to
the values.
3-18 O075-3
PM-0075