5.2        Parameters

Beginning Engineers and Technicians usually do not need to build parameters.  WebAccess comes with a set of default parameters for your device driver. Someone from the WebAccess engineering department already created some parameters for you to use that are typical for your device.

Parameters as a Productivity Tool

Parameters are used by Advanced Users to create productivity objects to increase the efficiency of building an automation project.

The simplest productivity object is to copy or edited a default parameter to act as better template for creating tags. For example, if all of your addresses begin with a higher number than the default parameter uses, you can edit the default parameter to save typing.

Another use of parameters is to develop some project standards that help other users who are assisting you.  You might define a FLOW parameter with a starting address for flow transmitters inputs, plus engineering units, typical span high and low, and conversion codes used with Flow measurements.  Then tell the user to create new Flow measurement tags using that parameter as a starting point.

Parameters are also a way to create a custom Point Detail display.  If you create a Point Detail Display named after the parameter used to create a tag, this user built point detail will be called up (in stead of the default point detail display).

Blocks are the biggest Productivity Tool

Blocks are the most effective use of parameters to increase the productivity and save time in building a large automation project or a series of projects that are repeated.

The classic example of the use of Blocks in large automation projects is to create a block for use with the each controller type in your project.  First, parameters would be built that reflect Setpoint, Measurement, Output, Auto/Manual, Remote Local, Tuning parameters, etc.  Next, these parameter would be assembled into a block type.  This block type could be used as a template to create hundreds of Controller Blocks in your project.

For Blocks to work well, the addressing in each controller must be similar with some predictable offset or pattern.

Parameters are the elements in a Block

Users and operators will referenced the elements in a block by appending the parameter name to the Block Tag name: Blockname:parameter . You should pick a parameter name that will be meaningful to ordinary users and operators. 

For example, a Foxboro 761 device:

TIC101:SP for the setpoint of a Temperature controller,
TIC101:MEAS for the measurement,
TIC101:OUTP for the output of the primary controller
TIC101:OUTS for the output of the secondary controller
TIC101:AM for the auto manual state
TIC101:RL for the remote local state
TIC101:PB for the proportional band tuning constant
TIC101:INT for the integral tuning constant
There are probably 50 more parameters in a Foxboro 761 controller.

The real working creating a block is to create the parameters that will be grouped into the block. Once you create a block, you cannot change the parameter name without re-creating both the block-type and the block. 

Notice that the parameter names are limited to 7 characters.  In addition, parameter names can be used again in a different device type (for example you could have a SP parameter in all device types).  However, a parameter name must be unique within a device type.