4.                           Tags



WebAccess uses the concept of the “tag” to organize the information exchanged with

the PLC or automation device (the so-called database for the device). A “tag” is a unique identifier for a single piece of information read from the automation device.  WebAccess assigns additional qualities to the tag including description, alarms, alarm limits, addressing.  A WebAccess tag is a multi-dimensional object that describes a single piece of information read or written to the automation device. A tag can describe any measurement, output, bit, register or other value in a device.


The term “tag” has two sources of origin: one industrial and the other from software.


In industrial manufacturing plants, each instrument in a control room had a small metal “tag” attached to it, or on the panel beside it, that described the instrument or measurement usually with a seven digit alphanumeric code.


In software programs, especially many database software packages (Dbase4 is an example) the identifier of a row of information in the Database was the “tag name”.  Many HMI and SCADA software packages also use the term "tag" as an identifier of information read from automation device.


WebAccess provides a database for communications: a tag only needs to be defined once in the SCADA node that is connected to the automation device (PLC, RTU, etc.). All Clients access this tag using its tagname. This allows graphic displays that connect to that point to be used on all clients without modification.


WebAccess provides a set of communication “drivers” that enable engineers and technicians to easily establish communications to automation devices including PLCs, controllers, DCS, DDC systems, other software packages, recorders, RTUs, IO, smart transmitters and other automation hardware.


These communication “drivers” are implemented using fill-in-the-blank forms that are actually web pages that interact with the WebAccess Database.  No programming is required. The steps, in summary, are:


1.      Start Internet Explorer Web Browser

2.      Enter IP address of the Project Node

3.      Use WebAccess Configuration

4.      Open or Create a Project

5.      Configure a SCADA node (if it does not already exist)

6.      Configure a Comport for the SCADA Node (if it does not already exist)

7.      Configure a Device (if it does not already exist) 

8.      Add a Tag

9.      Select a Parameter that is close to the Tag

10.  Assign a unique Tagname, Address, conversion code,

11.  Optionally assign Alarms, Scaling, Engineering Units, Description and other features.


WebAccess drivers consist of the program that actually exchanges data with the device and a “database” which contains a description of what data the user wants to read and write to the device.


Before you can build an IO tag, you should have already built a SCADA Node, configured a Comport and configured a Device.


This section assumes you are already familiar with:


3.2SCADA Node Properties


3.3Communication Ports