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pmm5111a0600p_01
Check that the Setpoint Upper Limit (
) and Setpoint Lower Limit (
) are set to safe levels
for the process. Adjust if required
Select ON-OFF control (
=0)
Switch on the process. The process variable will
oscillate about the setpoint.
T
t
P
PV
SV
Record the Peak-to-Peak variation (P) of the first cycle (i.e. the difference between the highest value of the
first overshoot and the lowest value of the first undershoot), and the time period of the oscillation (T) in
minutes:
Primary Proportional Band (P):
x100
Integral Time Constant (I):
= T [min]
Derivative Time Constant (D):
= T/6 [min]
In Set-up Mode select PID parameters in accordance to the calculation using the formula above.
Dual Control Tuning (PID with Primary and Secondary Outputs) – cooling and heating
In Configuration mode select Dual control type
Primary and Secondary control
Select Setpoint Value of Primary output as described above.
Set
to the same value as
and monitor the operation of the controller in dual control
mode.
If there is a tendency to oscillate as the control passes into the Secondary Proportional Band, increase
the value of
.
If the process appears to be over-damped in the region of the Secondary Proportional Band, decrease
the value of
.
When the PID tuning values have been determined, if there is a kick to the process variable as control
passes from one output to the other, set the Overlap/Deadband
parameter to a positive value to
introduce some overlap.
Adjust this value by trial and error until satisfactory results are obtained.
10.6
M
ANUAL
F
INE
T
UNING OF
PID
PARAMETERS
Adjustment of Cycle Time (
) parameter (in Set-up Mode) is provided for each time proportioning
control output. Take into consideration that a shorter cycle time gives more accurate control but
electromechanical components such as relays have a reduced life span.
Increase the width of the proportional band if the process overshoots or oscillates excessively.
Decrease the width of the proportional band if the process responds slowly or fails to reach setpoint.
Increase the automatic reset (
) (Integral Time Constant) until the process becomes unstable,
and then decrease until stability has been restored.
Modify Integrate Time to between 10-25% of the previous value. If the process overshoots or oscillates
excessively, decrease its value.
After making all other adjustments, if an offset exists between the setpoint and the process variable use
the Bias
(manual reset) to eliminate the error. When PV is below SV use a larger bias value,
when PV is above SV use a smaller bias value.
