Unication Messenger m90 Manual de usuario descargar pdf (Pagina 242)

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U90 Ladder Software Manual

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Inside the PID Function

The PID function is based on 3 actions, Proportional, Integral, and Derivative. The PID

output is the combined output of all 3 actions.

All of the PID functions are activated by changes in the process Error, the difference

between the Process Value and the process Set Point value (E = SP – PV).

Proportional Band

The proportional band is a range defined around the Set Point. It is expressed as a

percentage of the total Process Value (PV). When the PV is within this range, the PID

function is active.

Note that the proportional band may exceed 100%. In this case, PID control is applied over

the entire system range.

Proportional Action

Proportional action begins after the PV enters the proportional band; at this point, the Error

is 100%. The action outputs a value that is in direct linear proportion to the size of the

Error value.

A broad proportional band causes a more gradual initial response from the controller.

Typically, Set Point overshoot is low; but when the system stabilizes, oscillations around

the Set Point tend to be greater.

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Unication Messenger m90 Manual de usuario Pagina 242

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