Function blocks are smart devices that hold control software on fieldbus instruments. These smart devices or microprocessors enable Foundation Fieldbus and Profibus PA instruments to perform control functions independently of a DCS. There are many types of function blocks. Each function block has a specific purpose. Smart Instrumentation provides a set of the most common function blocks, with properties defined by Fieldbus Foundation. You cannot delete these shipped function blocks or rename them, but you can modify their definitions if needed. You can, however, create your own user-defined function blocks for both Fieldbus Foundation and Profibus PA instruments. You can modify and delete these function blocks as you need.
Function blocks are associated with particular instrument types. When creating a new instrument based on an instrument type that has been associated with a function block, the software creates that instrument and automatically associates it with the function block have been set for pertinent instrument type. The software allows you to associate multiple function blocks with a single instrument type. For example, a basic flow transmitter will have one AI (analog input) block associated with it. However, a similar instrument may be used to measure also pressure and temperature (required for gas flow compensation), and may be further equipped with one or more alarm functions. An AI function block is required for each additional process measurement and an AA (analog alarm) block for each alarm function. You can also associate existing instruments with function blocks, or modify associations as needed.
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You cannot create virtual tags for an instrument that is not associated with at least one function block.
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A number of Foundation Fieldbus and Profibus PA function blocks are shipped with the software. You cannot add, delete or modify any of them. You can see all the available function block types on the Function Block – Instrument Type Association dialog (for details, see Associate Function Blocks with Instrument Types.