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WATLOW Series 988 User’s Manual 7.1
Tuning, Manual Operation, Alarms and Error Codes, Chapter 7
Auto-tuning (Heat and/or Cool)
The Series 988 can automatically tune the PID parameters to fit the char-
acteristics of your particular thermal system.
Standard software units
(98_ A -_ _ _ _-_ _ _ _)
have 1 set of PID parame-
ters. Units with enhanced software (
98_ B -_ _ _ _-_ _ _ _)
and [AlgO] set
to [Pid2] (Global Menu) have two sets of PID parameters, PID A and PID
B. Only one PID set can be auto-tuned at a time. For information on tun-
ing a cascade system, see Chapter 8.
Before beginning the auto-tune sequence, make sure the [AtSP] parame-
ter located in the Global Menu is at the proper setting. This allows the
user to select the tuning set point as a percentage of the current control
set point. See Chapter 4 for more information on this parameter. The fig-
ure below uses the default setting, 90%, to define the auto-tuning process.
Once the auto-tune sequence has begun, the output 1 and output 2 pro-
portional band is set to 0 and the control goes into an on/off mode of con-
trol at the set point percentage determined by the [AtSP] parameter. The
displayed set point remains unchanged.
200°
Temperature
set point
100°
process
180°
auto-tune
begins
auto-tune
complete
90% of
set point
( [AtSP] default setting)
Auto-tuning at a set point of 200°F
Time
Figure 7.1 -
Auto-tuning
example.
˜
NOTE:
A useful reference
on tuning is
Tuning
of Industrial
Control Systems
by
Arman-do B.
Corripio, published
by the Instrument
Society of America.
Chapter 7 Tuning, Manual Operation,
Alarms and Error Codes
NOTE:
Auto-tune can be
initiated if [`rSp]
is set to [``on].
C7.wc 5/14/1999 8:54 AM Page 7.1