WebAccess only requires that the customer pay for the SCADA node License and install a hardkey on the SCADA node. The Client and Project nodes are licensed at no charge. The Building Energy Management System (BEMS) is an option that requires an additional license (and hard key) for the Project Node
The SCADA node communicates in real-time with PLCs and automation equipment.
Clients communicate with the SCADA nodes over the Internet or an intranet to display real-time data.
The Project Node is the configuration, engineering tool, central database server and Web Server. Clients communicate with the Project Node over the Internet or an Intranet to build graphics, configure communications (tags) and download configurations to the SCADA nodes. The Project Node also provides the initial connection between Clients and SCADA nodes.
Most customers will need only one project node. Only one project node is required, but two project nodes enable a backup project node to be used as either a "hot standby" or "off-line development" node. Engineers and technicians can install multiple copies of Project Node software on laptops and PCs for off-line development.
A customer can have hundreds of clients if he wishes. In the standard, full-feature version of WebAccess, there is not charge for the clients. The number of Clients can be limited by the specific SCADA node license purchased. The Client-Plug-in is distributed for free (without charge). Only the SCADA node needs a Hardkey. There is no Hardkey required for the Client or Project Node.
For example, a user has 20,000 tags on one SCADA node and 19 client workstations. He needs only one Hardkey (and one 20,00 tag license for the SCADA node). His 19 Clients can view the one SCADA node over an Intranet or Internet using a Web Browser and the Client Plug-in (or Thin Client).
The reason the Hardkey must be on the SCADA node is to protect the software license and prevent people from using the software without paying for it. We charge for the SCADA node. One SCADA node = one Hardkey = one license.
A SCADA node is always just one computer. You can have multiple SCADA nodes in a Project. Each SCADA node must have a license and a Hardkey.
The SCADA node usually connects directly to the PLC or Controller. The Clients do not directly connect to the PLC or Controller. The Clients connect to the SCADA node to get data.
How many SCADA nodes are required depends on the physical layout of the plant, reliability and through put issues.
For example, there are 10 PLCs and about 100 tags to be read on each. If the 10 PLCs are spread far apart, so far that they could not connect to the same SCADA node, then 10 SCADA nodes are probably required. If the PLCs are far apart (geographically) then the customer would need 10 separate SCADA nodes, each with a 150 tag license (there is no 100 tag license) or a mix of 150 point and 300 point licenses if it were not exactly 100 Tags at each location. If the 10 PLCs are close enough to connect to a single PC, then a single SCADA node, with one 1200 Tag license would work.