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Proportional action can be set by means of the Proportional Band (PB). Proportional Band
is expressed in percentage of the input range and is related to Kp according to the following:
Kp = 100/PB.
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 variables 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).
Error
0
Proportional Band
Controller
output
