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[Luyben] Process Mod.. - Student subdomain for University of Bath

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DESIGN OF CONTROLLERS FOR MULTIVARIABLE PROCESSES 605<br />

OR<br />

0<br />

,/--<br />

- -<br />

x3<br />

- 25 ~<br />

\ /<br />

\ /<br />

l-’<br />

I I I I I I<br />

0 20 40 60<br />

Time, min<br />

FIGURE 17.2<br />

Ogunnaike and Ray column: BLT and empirical tuning.<br />

value <strong>of</strong> F and still satisfies the + 2N maximum closedloop log modulus criterion<br />

(see the paper by Monica, Yu, and <strong>Luyben</strong> in IEC Research, Vol. 27, 1988, p.<br />

969).<br />

17.6 LOAD REJECTION PERFORMANCE<br />

In most chemical processes the principal control problem is load rejection. We<br />

want a control system that can keep the controlled variables at or near their<br />

setpoints in the face <strong>of</strong> load disturbances. Thus the closedloop regulator transfer<br />

function is the most important.<br />

The ideal closedloop relationship between the controlled variable and the<br />

load is zero. Of course this can never be achieved, but the smaller the magnitude

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