Wika T53 Uživatelský manuál stáhnout pdf (Strana 31)

4.0 PID Control Block, Fieldbus Foundation

4.1 Introduction:

T53 is fitted with a PID Control Block which can only be used in Fieldbus Foundation installa

tions. The PID Block is constructed according to standard specifications outlined in Fieldbus

Foundation and producer specific parameters have not been added. Please notice that the

PID function is not specified in the Profibus Nutzerorganisation and thus cannot be used in

Profibus installations.

4.2 Overview

The PID block is key to many control schemes and is used almost universally, with the ex

ception of PD, which is used when the process itself does the integration. As long as an error

exists, the PID function will integrate the error, which moves the output in a direction to cor

rect the error. PID blocks may be cascaded when the difference in process time constants of

a primary and secondary process measurement makes it necessary or desirable.

4.3 Schematic:

4.4 Description

The Process Value to be controlled is connected to the IN input. This value is passed through

a filter whose time constant is PV_FTIME. The value is then shown as the PV, which is used

in conjunction with the SP in the PID algorithm. A PID will not integrate if the limit status of IN

is constant. A full PV and DV alarm sub-function is provided. The PV has a status, although it

is a Contained parameter.

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Wika T53 Uživatelský manuál Strana 31