EXCEL CARE CONTROL ICONS ALPHABETIC REFERENCE
195 74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
PID Controller
P3 Proportional band Xp
P4 Derivative time Tv (in seconds).
P5 Integral action time Tn (in seconds). If you set Integral action time to zero in the
internal parameters dialog box, software sets the P4 parameter to 1,000,000. A
number this large effectively disables the integral term.
P6 Minimum output (in percent)
P7 Maximum output (in percent)
P8 Reference variable (W) if entered as a parameter (not connected to a point)
P Controller To use only the proportional term of the PID controller, set Derivative time and
Integral action time to zero. Set the Proportional band value to indicate how large
the deviation must be to cover the entire positioning range. The following diagram
illustrates the proportional band:
For example, to control a mixing valve that can be open only between 25 and 75
percent (Minimum output and Maximum output), you can set the internal parameters
as follows:
Proportional band range 25 (deviation across the range)
Minimum limit 25 percent
Maximum limit 75 percent
Software calculates the proportional band according to the following formula:
The operating point of the PID controller is at 50 percent, that is, PID output is 50
percent when the controlled variable is equal to the reference variable.
PI Controller To use the proportional and integral terms of the PID controller, set Derivative time
to zero. Input the other parameters as explained for the P Controller.
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