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WATLOW Series 988 User’s Manual 9.9
Enhanced Software Features, Chapter 9
Enhanced Software
TLTL
WW
WW
AA
PROCESS
L1 L2 L3 L4
DEV
% OUT
DISPLAY
MODE
AUTO
MAN
SERIES 988
input 1
input 2
output 1
output 2
chiller
limit
sensor
heater
Test Chamber
temperature
sensor
pressure
switch
limit
Sample Application
A test engineer needs to control the temperature in a test chamber that
can be operated at normal atmosphere or under vacuum conditions. If he
tunes the controller for normal atmospheric conditions, when he reaches
the portion of his test that requires a vacuum, he must stop the test and
enter new PID parameters to maintain stable temperatures. The system
characteristics are so very different, that one set of PIDs will not give satis-
factory results under both normal and vacuum conditions.
The Series 988 solves this problem with the dual PID option. Auto-tuning
PID A under normal atmospheric conditions, then auto-tuning PID B
under vacuum conditions, establishes PID values for two sets of system
characteristics. A pressure switch connected to the event input tells the
controller when to switch between PID A and PID B, eliminating the need
to change PID values manually.
Figure 9.9 - Test
chamber controlled
with dual PID sets.