Figure 1.12 Project Node is a central database and Configuration Tool
The Project Node consists of four elements:
1. The Configuration Tool - The Project Node software is a collection of ASP (Active Server Pages) organized into a Web Site. These ASP pages act as the Configuration Tool enabling ordinary web browsers to configure a WebAccess project.
2. A Centralized Database of the configuration of each SCADA node in the project. A copy of all graphics files, scripts and other components is kept on the Project node. Editing of the Tag Database or editing a graphic requires a connection to the Project Node. The Database and Graphic files are physically located on the Project Node. Changes to the database or graphic are not seen on the SCADA nodes until the changes are "Downloaded" to the SCADA nodes. Optionally, real-time data logging to a central ODBC compliant database (Access or SQL SERVER) is used to record data from all SCADA nodes in the system.
3. Central Historical Data Log - The Project Node also keeps a central database of all logged real-time data (now its considered Historical). This is similar to the data displayed on Real-time and Historical Trends (i.e. Data Log Trends). Users can extract this data using Scheduled Reports and the System Log queries for the Tools menu in VIEW. Data from all SCADA nodes can be recorded to the central ODBC logs. The default database is Microsoft Access, although Clients do not need Access to view the data, they can use their Web Browser and copy and paste data to EXCEL, Word, and other office applications.
4. Web Server - A standard ASP enabled Web Server is used. This is the standard web server supplied with Windows Server 2003, 2000, Vista (Business or Ultimate) or XP Professional: IIS (Internet Information Server) with the WWW publishing Service.
Windows 2000 Professional and Windows XP professional can support up to 10 simultaneous connections.
Windows 2000 Server or Server 2003 versions can support an unlimited number of connections.
A connection to the Web Server / Project Node is only needed for:
· Configuration (Project Manager)
· DRAW
· The initial connection between a Client and the SCADA node (VIEW)
· When the refresh button is pressed on the Client (VIEW)
· A Thin Client connection
· Data logging to central ODBC database
· Viewing the central ODBC Logs
· Viewing, Changing or downloading the Scheduler
· Viewing Scheduled Reports
Note- ViewDAQ never requires a connection to the Web Server. In addition, the SCADA node "Kernel" will start without any connection to the Web Server.
The number of simultaneous connections required by the Project Node can be much less than the number of Clients connected to SCADA nodes. Web Browser Clients, using the plug-in, are redirected to the SCADA node and the connection with the Project Node is dropped until the user either presses the Refresh button (not usually done) or opens a new web browser window to make a new connection to WebAccess.
Only Thin Clients, Configuration (Project Manager) and DRAW require a continuous connection with the Project Node.
The WWW Service (Web Server) must be installed. WebAccess supports Anonymous Access, Authenticated Access (NT Authentication or Integrated Windows authentication), Secure Communications including Certificates, Secure Sockets and Virtual Private Networks (VPN).