Section 8 Operation Examples Single Loop Automatic Operation with Feedforward
3BUR002418-600 A 199
Single Loop Automatic Operation with Feedforward
Feedforward control is a strategy used to compensate for disturbances in a system
before they affect the controlled process variable. A feedforward control system
measures a disturbance variable, predicts its effect on the process, and applies
corrective action to cancel the effect of the disturbance. A block diagram of
feedforward control type of system is shown in Figure 84.
Feedforward control system provides a combination of feedforward and feedback
control. Feedback provides its normal function of holding the process at the
setpoint. Feedforward helps the feedback function by modifying the control output
as required to cancel the effect of variations in the disturbance variable. The
feedforward input (set up as a percent of output) is multiplied by a constant (gain),
and a bias value (%) is added to or subtracted from the signal. The gain and bias
values are tunable. The feedforward function can be configured to either add the
signal to the control output or multiply the output by the signal.
Figure 84. Block Diagram of feedforward control system
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