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4.0 PID Control Block, Fieldbus Foundation
4.1 Introduction:
PR5350 is fitted with a PID Control Block which can only be used in Fieldbus Foundation in-
stallations. 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 excep-
tion 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.
