22
The proportional action is set through the setup procedure as
“Deviation” in percent of full scale of the selected range.
Each setpoint has a selectable deviation: D1 for setpoint1
and D2 for setpoint2.
Two further parameters must be provided for both setpoints:
Ti = Kp/Ki, reset time, measured in minutes
Td = Kd/Kp, rate time, measured in minutes.
Ti1 and Td1 will be the reset time and rate time for setpoint1,
while Ti2 and Td2 will be the reset time and the rate time for
setpoint2.
TUNING A PID CONTROLLER
The proportional, integrative, derivative terms must be tuned,
i.e. adjusted to a particular process. Since the process vari-
ables are not typically known, a “trial and error” tuning
procedure must be applied to get the best possible control for
the particular process. The target is to achieve a fast response
time and a small overshoot.
Many tuning procedures are available and can be applied
to the EC/TDS controllers. A simple and profitable procedure
is reported in this manual and can be used in almost all
applications.
The user can vary five different parameters, i.e. the setpoint
(S1 or S2), the deviation (D1 or D2), the reset time, the rate
time and the proportional control mode period T
c
(from 1 to
30 minutes).
Note User can disable the derivative and/or integrative action (for
P or PI controllers) by setting Td = 0 and/or Ti = MAX (Ti)
respectively through the setup procedure.
