There is no limit to the number of SCADA nodes or Clients in a network (other than licensing requirements). Typically there is only one project node (the second would act as a backup database server or a redundant web server).
How you design your network will affect the overall performance of your system. Considerations include:
· Physical Location of Automation Devices including PLCs, Controllers, and Network Access points (Geography).
· Throughput required (i.e. SPEED of Display updates).
· SCAN time of Devices
· Network Characteristics (traffic, number of nodes)
· Number of users
· Device Driver
· The speed of the PLC or Device
· How many tags can be read in a single request from the PLC