You can use the auto-tuning program for new process
es
or directly
set the appropriate values for PB, TI & TD according to
historical
data
for the repeated systems. If the control behavior is still
inadequate, then use manual tuning to improve the control. See
section 3-12 for manual tuning.
CPB Programming : The cooling proportional band is measured by %
of PB with range 50~300. Initially set 100% for CPB and examine the
cooling effect. If cooling action should be enhanced then decrease
CPB, if cooling action is too strong then increase CPB. The value of
CPB is related to PB and its value remains unchanged throughout the
auto-tuning procedures.
Adjustment of CPB is related to the cooling media used.
If
air is used
as
the
cooling
media, adjust CPB t
o
100%.
If
oil is used as cooling
media, adjust CPB t
o
125%. For water
,
adjust CPB t
o
250%.
DB Programming: Adjustment of DB is dependent on the system
requirements. If more positive value of DB ( greater dead band ) is
used, an unwanted cooling action can be avoided but an excessive
overshoot over the set point will occur. If more negative value of DB (
greater overlap ) is used, an excessive overshoot over the set point
can be minimized but an unwanted cooling action will occur. It is
adjustable in the range -36.0% to 36.0 % of PB. A negative DB value
shows an overlap area over which both outputs are active. A positive
DB value shows a dead band area over which neither output is active.
Output 2 ON-OFF Control (Alarm function):
O
utput 2 can also be
configured as
an
alarm. There are 4 kinds of alarm functions
that can
be selected for output 2
;
these are: DE.HI (deviation high alarm ),
DE.LO (deviation low alarm ), PV.HI (process high alarm ) and PV.LO
( process low alarm ). Refer to Figure 3.3 and Figure 3.4 for the
description of deviation alarm and process alarm.
35
