The Benefits of Feed Forward Control

FF-+-FB-Control1 By nature most people are reactive when it comes to dealing with life’s big expenditures.  Think of happy occasions such as graduations and weddings.  Then consider more somber milestones like retirement.  By most accounts the average worker is wholly unprepared to absorb the costs linked to these and other of life’s events.  Even though the timing and amount of those costs can be forecasted, the typical approach to saving for the future isn’t up to the task.  Face it: As a species we’re wired to be reactive!

The PID controller is similarly reactive.  While the PID is programmed to address variability within a process from slight to severe it lacks the ability to enact the necessary adjustments proactively.  Indeed, a feedback controller has no sense of upstream activity until a given upset hits and is computed by the PID in the form of Error.  What’s more, the controller’s response is limited to the amount of Error that’s computed – it’s not based on additional Error that’s known to be on its way.

Feed Forward Control is an advanced control scheme that is well-suited for processes which are routinely affected by a known upstream source of disturbances.  With an accurate model of the disturbance the Feed Forward architecture enables proactive adjustments.  Those adjustments deliver an appropriate response at the appropriate time, and they are thereby able to minimize the negative effects of the disturbance.  They may even blunt the disturbance altogether and eliminate any negative effects.

Following are a few specific ways that Feed Forward Control can benefit your process:

Defined

Feed Forward is an ideal control scheme when there is a known or defined source of routine disturbances.  Feed Forward is able to key in on the source, and by modeling the range of disturbances emanating from that source Feed Forward Control can prepare an appropriate response.

Proactive

Whereas PID Control is reactive, Feed Forward Control is proactive.  Once an upstream disturbance is identified Feed Forward immediately seizes the initiative and prescribes an appropriate change. It is Feed Forward’s proactive nature that either minimizes or eliminates the negative effects of a known disturbance.

Measured

Since the PID responds to Error it is always catching up as the effects of a disturbance steadily build over time.  In contrast Feed Forward’s use of a disturbance model allows it to assess the full magnitude of the disturbance and to implement an appropriate countermeasure.

Timely

The value of Feed Forward’s timeliness shouldn’t be underestimated.  If Feed Forward Control simply delivered a countermeasure as soon as the disturbance was identified, then it might do more harm to the process.  Fortunately it is designed to deliver the countermeasure as the disturbance hits the process, essentially nullifying the negative effects of the disturbance.

If these benefits address problems that you experience in your facility, then Feed Forward may be the right regulatory control solution for you. While Feed Forward does involve additional instrumentation and engineering costs, it typically pays for itself quickly when deployed under the right circumstances.

These resources offer related content:

Iconic-Mark_Inverted-Color

How Does Loop Monitoring Help with Root-Cause Analysis?

For most individuals, a house is the most expensive asset that they’ll ever purchase. And while living there a homeowner can expect a significant problem or two to arise whether that problem involves a leaky roof, termite damage, or some other costly issue. A downside...

Why is Zeigler-Nichols the Wrong Choice for Your PID Controllers?

PID Control Loops Have Specific Purposes and Unique Attributes.  'One Size Fits All' Approaches to Tuning May Be a Recipe for Failure.    In 1909 Henry Ford famously offered customers any color of his Model T automobile as long as their choice was black. Ford's...
training-2-workshop-exercises

The Power of the Hear-See-Do Learning Method

There is an old proverb that goes: “If you test a fish on how well it climbs a tree, it will think it’s a failure.” While this proverb is often used in relation to traditional K-12 education, it stands true in just about any educational...

Still looking for more?

Now that you’ve gotten the basics, connect with our team to learn how our people, processes and technologies can help you optimize.