Manual

Page 9
PROGRAMMING AND OPERATION FOR PID
Theory of Operation
The PID method of control is based on the individual tuning of proportional
band values, integral time values, and derivative time values to help a unit
automatically compensate for changes in a control system. The
proportional band is the range around the set point in which the control’s
proportioning takes place. The control increases or decreases the output
proportionately to the process temperature’s deviation from the set point.
The integral time eliminates undershoot and overshoot of the set point by
adjusting the proportioning control based on the amount of deviation from
the set point during steady state operation. The derivative time eliminates
undershoot and overshoot by adjusting the proportioning control based on
the rate of rise or fall of the process temperature. The integral deviation
offset correction (ioFn) improves the speed in which the process value
reaches the set point value. If this parameter is set to zero, the output will
be zero when the process value is equal to the set point value. If the
integral time parameter is used only to eliminate steady state error, it may
take a long time to reach the set point because it needs time to
accumulate the error. This parameter defines the default output level on
start up. When the integral time is set at 0, then the proportional derivative
offset correction (PdoF) would replace the integral deviation offset
correction, but serves the same function.
Program Set Up
In order to use the PID function in the C series controllers, the Control
Mode will have to be set to PID in the Initial Setting Menu. After changing
the Control Mode, the PID parameters can be accessed in the Regulation
Menu. The PID parameters can either be programmed manually or they
can be set by the controller using the auto tune function. The auto tune
will use trial and error to tune the PID parameters to give the control the
most precise control. Since the time to accurately tune the control may
differ depending on the process, the controller can also be manually tuned
to known PID values prior to running auto tune. The Run/Stop parameter
must be set to run in order to start auto tuning.