Feedback control is the principle behind nearly every automatic loop in a plant: measure the result, compare it to the goal, and correct based on the difference. It is reactive by design - it responds to error that has already shown up in the measurement. This guide explains how feedback control works, why it is called negative feedback, and how it contrasts with feedforward control.
Feedback Control in one line: Feedback control is a closed-loop strategy that measures a process variable, compares it to the setpoint, and adjusts an output to reduce the error - correcting the process after a deviation has been measured.
In a feedback loop the controller continuously subtracts the measured process variable from the setpoint to get an error, then drives its output to shrink that error toward zero. This is called negative feedback because the correction opposes the deviation: if level rises above setpoint, the controller acts to bring it back down. PID is the most common algorithm used to compute that correction.
The defining trait of feedback control is that it is reactive - it cannot act until a disturbance has actually moved the process variable. That makes it robust and general-purpose: it does not need a model of every disturbance, because it simply responds to whatever error appears. The trade-off is that some deviation must occur before the controller can respond to it.
Feedforward control is the complement to feedback. Instead of waiting for error, a feedforward scheme measures a known disturbance and pre-emptively adjusts the output before the process variable moves - for example, boosting heater output the moment cold feed flow increases, rather than waiting for the temperature to sag. Feedforward is proactive but needs a good model of the disturbance and cannot catch unmeasured upsets.
In real oil-and-gas control schemes the two are combined: feedforward handles a large, measurable disturbance quickly, while feedback trims out the residual error and everything the feedforward model missed. Feedback remains the foundation because it corrects for anything, measured or not.
Because the controller's correction opposes the deviation. When the process variable rises above setpoint, the controller acts to bring it back down, and vice versa - the response is negative relative to the error.
Feedback control reacts to error after it appears in the measurement. Feedforward control measures a known disturbance and adjusts the output before the process variable moves. The two are often combined for fast, accurate control.
Effectively yes. Feedback control relies on measuring the result and feeding it back to the controller, which is exactly what makes a loop closed-loop. The terms are used interchangeably in most process contexts.
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