Watlow Electric Revision 5 - Manual (Page 58)

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and the full scale adjusted to match the expected PV range. The graphics of the
Plot will show the effect of the PID tuning in real time.
The understanding of PID functions would be useful in tuning loops, but not
essential to a successful application of PID constants to a control loop.
8.2.1 INITIAL VALUES FOR PID LOOPS
The following values may initially be used for the PID constants. They
have been used for many applications and will serve as a starting point for
tuning the controller. If ANASOFT is used be sure the SYSTEM 32 control
is set for AUTO.
ON/OFF CONTROL
PB = Minimum PB
Gain = 510
Reset = 7.5 R/M Integral = 8 Sec.
Rate = 0 Min. Derivative = 0 Sec.
Output Filter = 4 Output Filter = 4
PROPORTIONAL BAND ONLY (P)
PB = 5% of SP Example SP = 450 PB = 22 Gain = 79 [J T/C]
Reset = .12 R/M
Integral = 500 Sec.
Rate = 0 Derivative = 0 Sec.
Output Filter = 4 Output Filter = 4
PB with Reset (PI)
PB = 10% of SP Example SP = 450 PB = 45 Gain = 39 [J T/C]
Reset = .5 R/M
Integral = 120 Sec.
Rate = 0 Derivative = 0 Sec.
Output Filter = 4 Output Filter = 4
PB with Reset with Rate (PID)
PB = 15% of SP Example SP = 450 PB = 67 Gain = 44 [K T/C]
Reset = 1 R/M
Integral = 60 Sec.
Rate = 0.2/Min. Derivative = 12 Sec.
Output Filter = 4 Output Filter = 4
WARNING: never set the reset above 3 R/M or integral below 20
seconds for proportional control as cycling will occur.
In controlling a process to a SP, process engineering must design the system
to allow the controller to be within it's control capability. In most processes,
the controller element is the fine control, while the process itself is the
course control. If all of the variables could be defined and precisely
controlled, when engineering a process, then a predetermined reset could be
used. When sizing control valves, electrical loads or whatever the final
element might be, the correct sizing will be one that allows the controller
output to be in the 40-60% of it's output when PV is stable at SP at mid-