Echelon LonPoint Application and Plug-In - Manual (Page 92)

9-8 PID Controller Functional Block
Bias Sets the controlled variable output for a P-only
controller when there is zero error. This is only used if
the integral (I) term is 0.
Deadband When the difference between the setpoint and the
process variable is less than this value, no controlled
variable adjustment is made. The process variable is
considered close enough. Deadband may be used to
reduce actuator wear.
Cascade Causes the controlled variable to react more strongly to
changes in the setpoint for the PI and PID
configurations. If you need to track setpoint changes
quickly, turn Cascade on. If you want good response to
load disturbances and setpoint response is less
important, turn Cascade off.
This is option is called Cascade because when PID
controllers are in a cascaded configuration, with the
outer PID's controlled variable feeding the inner
controller's setpoint, setpoint changes to the inner
controller are as important as process disturbances.
Make sure to turn Cascade on for the inner controller in
a cascade arrangement.
When this option is set, two changes are made to the
control algorithm: The setpoint value is not used when
proportional contribution is calculated and the
derivative contribution is given by d/dt(error)
instead of d/dt(PV).
Reverse Acting Process Specifies whether or not the process is reversing. If an
increase to the controlled variable causes the process
variable to decrease, then the process is considered to be
reversing. The process includes the sensors and
actuators. A simple open-loop test can be made to
determine how to set this property. Put the controller in
override and wait for the process variable to stabilize,
then increase the override value. If the process variable
decreases, the process is reversing.
See LonPoint PID Controller Tuning, later in this chapter, for more information on
setting these values.