GPS-X Technical Reference

349 Tools Object
The following parameters are accessed by clicking on the More... button in the Control
Variable form. Only the parameters in the Controller Set up sub-section are discussed
here. For a discussion on the Controller Tuning sub-section see Tuning PID
Controllers.
Controller form (Full Position / Velocity): This parameter is used to specify
which form of the PID controller equation is used (position or velocity). The
default velocity form is recommended because it has built-in protection against
integral windup.
Controller type (P / PI / PID): This parameter specifies the modes to be used in
the PID controller. Using the PI option is recommended in most cases. When
using the P option, the offset between the controlled variable and the setpoint
cannot be completely eliminated.
Control variable with label: This is the cryptic variable name for the controlled
variable including the appended stream label.
Controller sampling time: This is the length of time between controller
executions. If this parameter is too large the control performance will be poor and
possibly unstable.
Proportional gain: This is the controller tuning constant, K c.
Integral time: This is the controller tuning constant, T I.
Derivative time: This is the controller tuning constant, T D.
Controller effect on controlled var - direct (ON - OFF): Since the value of the
proportional gain in GPS-X must be positive, this parameter controls
the `direction' of the controller. If a positive step in the manipulated variable
results in a positive change in the controlled variable (at steady-state), i.e. the
process gain is positive, then this parameter should be ON (e.g. an increase in air
flow causes an increase in DO). Otherwise, it should be OFF (e.g. an increase in
wastage rate causes a decrease in MLSS concentration).
Derivative kick protection (ON - OFF): When this setting is ON the
manipulated variable is prevented from making large jumps in response to
setpoint changes. This parameter is only applicable when the controller type is
set to PID.
Derivative filtering (ON - OFF): The derivative filter is used to filter the signal
fed to the derivative mode of the PID controller.
Cutoff frequency: This is the derivative filter's corner frequency (i.e. reciprocal
of its time constant).
GPS-X Technical Reference