Watlow PPC-2000 - Manual (Page 115)

PPC-2000 User’s Guide Chapter 3: Operating with AnaWin 3
Doc.# 30002-00 Rev 2.3 Watlow Anafaze 91
The PPC-2000 provides two methods for coordinating a heat
and a cool output driven by a single channel. The Control Type
parameter offers two choices PID1 and PID2. Table 3.1
describes these two algorithms.
Table 3.1 Control Types PID1 and PID2
PID1
Only the heat output or the cool output is on at
any instant in time. The spread parameter pro-
vides a minimum switching hysteresis between
the two outputs. The channel will not switch
from heating to cooling until the heat integral
sum has dropped to zero, which is to say until
the process variable has been above set point
for some amount of time.
When the spread is set to zero, however, the
channel switches from heat to cool depending
on the PID calculation only, regardless of
whether the process variable is above the set
point.
PID2
When a channel uses the PID2 control type, the
cool output will come on whenever the process
variable is above the set point by more than the
spread setting. The cool output remains on until
the process variable drops to the set point. The
heat output operates as it would if the cool out-
put were not enabled. This algorithm was devel-
oped for plastic extruders, but may be of benefit
whenever a load is typically heated but occa-
sionally needs cooling.