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Advanced Control

Fuzzy Logic Tuning by controlnovice
Posted: 26 Oct 05

DeltaV's Fuzzy Logic Controller (FLC) has three tuning parameters.  I'm not sure about other manufacturers.  They are:

% Error
% Change in Error
% Output

% Error:  Very similar to P in PID.  It looks at the error between setpoint and actual value.  The parameter is in % of full scale of your process value.

% Change in error:  How fast the process is approaching setpoint.  This is also in % of full scale of your process value.

% Output:  When the process value differs more than the "% Error" and the process value is heading in the 'wrong' direction (away from setpoint) by more than the "% change in error", then the output will change by the amount in this parameter.  But, if the % Error or the %change in error is below the set parameters, the the fuzzy logic kicks in to determine how much and which direction the output will go.

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