Pro-EC44 2-Loop Graphical Profile Controller & Recorder
Pro-EC44 Product Manual - 59540-2 September 2014
Page 99
19 Controller Tuning
PID Sets & Gain Scheduling
Up to 5 sets of PID tuning terms can be entered for each control loop, allowing the
instrument to be pre-set for differing conditions. Each set has individual values for the
following parameters: Primary Proportional Band; Secondary Proportional Band; On-Off
Differential; Integral Time; Derivative time; Overlap/Deadband.
The parameter values can be entered in the control configuration sub menu (
page 50
), but
also see Automatic Tuning below for automatic tuning of the PID sets.
The PID sets might be configured for different applications, or to allow for differing process or
load conditions that might occur in a single application. In this case one set at a time would
be selected as the “Active PID” set for that loop.
Alternatively, if the process conditions change significantly during use (e.g. if it is partially
exothermic as the temperature rises) Gain Scheduling can be employed.
Gain scheduling ‘bumplessly’ switches PID sets automatically at successively higher setpoint
or process values, giving optimal control across a wide range of process conditions. This is
explained in the diagram below.
PID set 1 is used from the
scaled input lower limit until the
“breakpoint” for set 2 is passed
and that set becomes active.
Set 2 is then used until the
breakpoint for Set 3 is reached
etc.
If any breakpoint is set to OFF,
the subsequent PID sets are
not used.
The final set continues from the
last breakpoint to the scaled
input upper limit.
Gain Scheduling breakpoints can be selected to switch PID sets with a change in the current
setpoint value, or the current process value.
Note:
ON/OFF control is possible with the individual PID sets but cannot be used
with gain scheduling. On/off control is replaced with the default proportional band
if gain scheduling is turned on.
If the a change to the scale lower or upper limits forces any of the breakpoints out of bounds,
all breakpoints will be turned off and the instruments uses the default PID set 1.
PID Set 1
PID Set 2
PID Set 3
PID Set 4
PID Set 5
PV or SP
Scale Upper Limit
Scale Lower Limit
B
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