4.1.2   Blocks

An IO Block is a group or “block” of parameters from the field device that are associated with a single tagname. The most common usage is with a PID Controller: the Measurement parameter, the Setpoint parameter, the Auto/Manual status, the output, alarms and tuning parameters are all referenced using the same tagname (for example LIC101). The Setpoint, measurement, output, alarms and tuning parameters are referred to as “parameters”. Each parameter can be of a different type: analog, digital or text. To reference the measurement value of a Foxboro 761 controller configured as a Block, the syntax is LIC101:MEAS. Similarly, the Setpoint is LIC101:SP.

Blocks allow a large number of tags to be built by specifying a single name and addressing offset.  Blocks also enable the use of the Block Detail Display, which is a template type display: a single display that can be used to view all blocks of the same Block Type. 

For example, a large office tower has 200 VAV controllers each with 25 parameters, all identical.  A VAV block is configured and used to rapidly implement the communications to these devices. Further, only a single display (a Block Detail Display) is needed to view all 200 VAVs.  Further, as new VAV controllers are added, no additional display building is needed.

Many WebAccess drivers come with pre-built Blocks and Block Detail Displays.  Engineers and Technicians can create new Blocks using WebAccess Configuration and can create new Block Detail Displays using WebAccess DRAW.

The software license control file limits the number of IO Blocks.  Each Parameter counts as a Tag.