5.                           Advanced Block, Parameter & Tag Configuration


The information in this chapter is especially important to know when configuring customized parameters and blocks.

There are several types of Templates in WebAccess including: Parameters, Blocks, Faceplates and Block Detail Displays. Some computer-types might call these “object-classes”. Essentially, a template is a starting point that allows a novice user to implement a communication database and graphics with minimum knowledge.

These Templates also act as Productivity Tools enabling Advanced Users to reduce the Time, Effort and Costs to implement a large automation Project.

The first and most common Templates in WebAccess are Parameters. Each driver, comes with a library of “Parameters” that specify communication to data in automation devices. Typically, each data type or register type in the PLC or Device has a parameter defined for it. Each parameter specifies a typical address. A user, totally unfamiliar with the addressing scheme or register naming in a PLC can pick a Parameter from a pull down menu, assign a tag name and Voila! A Tag is completely defined, including the address.

The next most common Templates in WebAccess are Blocks. A block is a group of parameters that are associated with a single tagname. Whereas a Parameter is most commonly used for a single register in a PLC, a Block is most commonly used for a PID controller in a PLC, controller or DCS.

The Parameter or Block-Type act as templates for creating Tags and Blocks. The template is created before actually creating the communication object, i.e. the tag and block.

An IO Block is a group or “block” of parameters read or written from the field automation 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 of the controllers have the identical set of values read and written.  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.

A block can consist of any user defined grouping of parameters form the same communication device (i.e. the same PLC, controller, RTU, etc.).

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.

Blocks are also used to minimize graphic requirements. For example, a block might be created for each of six types of RTUs used in a facility. Each RTU consists of 20 or more measurements and outputs. All 200 RTUs can be viewed from just six displays. As site personnel add additional RTUs, no additional graphics are needed. Overview Group Displays and Faceplate Group Displays are system template displays supplied with every WebAccess system. They allow data from Blocks to be displayed without any graphics building.

The Block Detail Display is another Template. One display can be used to view any Block of the same type. Typically, this is used in PID loop controllers where any PID block can be viewed with this display. A large amount of data (usually all relevant IO) are placed on this display, hence the origin of the name ‘Block Detail”.

Faceplates are similar in concept to Block Detail Display, however they are incorporated into other process graphics and mixed with non-related data. A user selects a faceplate from a menu while building a process graphic.

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