Parameters are data used in a function block to perform calculations and logic. Some parameters are defined and unchangeable for certain function blocks. Some parameters default to a most common value but can be modified by the user or another function block. Others must be set by the user before executing the function block. Parameters that can be changed are called writeable parameters.
Parameters can be described by the type of information they provide to the function block:
Input parameters contain values from the operator, the field device, or other function blocks.
Output parameters are the output values generated by the function block or set by the operator or another function block.
Contained parameters are used only within the function block for calculation, logic, and status determination functions.
Mode-controlled parameters vary with the mode of the block.
Parameters can be dynamic, static, or non-volatile, depending on how they are restored after power failure:
Dynamic parameters are calculated by the block algorithm and do not need to be restored after power failure because the block recalculates the value.
Static parameters have a specific value that must be restored by a device for use after power failure.
Non-volatile parameters are written on a frequent basis and the last saved value (in most cases) is restored by a device after power failure.
Some parameters are extensible. That is, you can extend or increase the number of these parameters in a function block.
Some parameters are option bitstrings. They contain bit-encoded information that specify control strategy options, I/O value processing, status handling and processing, or the type of control logic used in the block.
Each parameter is transmitted in a certain data type format. This data can be transmitted between blocks for control, trending, alarming, and diagnostics.
The parameters visible in Control Studio may vary depending on level of configuration completed. For example, certain function blocks must be assigned to I/O before all the parameters are visible.