Monthly Archive: September 2007

Sep
24

Feedforward Techniques – Part 4

One of the simplest and easiest techniques to evaluate and implement is set point feed forward. The maximum feedforward gain is the inverse of the process gain. You just need to make sure the process gain is converted to the same units used for the feedforward gain and only a fraction of the maximum is …

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Sep
18

Feedforward Techniques – Part 3

In many of the plants I worked in the production capacity had been increased over the years by a series of debottlenecking projects. Unfortunately the surge tanks volumes were not increased probably because of a lack of understanding of dynamics. Consequently, unit operations upstream and downstream of the surge tank had to be decreased because …

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Sep
08

Feedforward Techniques – Part 2

Maybe I have just been unlucky or maybe the plants I worked in were as stressed as the typical project schedule these days but often for column temperature, boiler level control, and neutralizer pH, feedforward control didn’t live up to expectations. The problem was abusive unmeasured disturbances. The feedforward signal is often flow, which doesn’t …

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Sep
04

Feedforward Techniques – Part 1

When does feedforward control do more harm than good? Are there smart techniques to deal with these situations so feedforward is not permanently disabled in a PID controller? If the feedforward correction arrives too soon, there can be an inverse response where the initial reaction seen in the controlled variable is in the opposite direction …

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