Applies To:
  • CitectSCADA
Summary:
I have a CitectSCADA project with approximately 60000 tags defined, using the latest S7NT driver V2.05.04.000 via 100MB/s LAN. I am also using the Siemens Softnet S7 V6 Simatic NET software. If I display a page, the time it takes for CitectSCADA to display the page is around 6 - 8s. Why does it takes so long for CitectSCADA to display the page for an Ethernet based driver? 

Solution:
Normally CitectSCADA will not display a page until all requests for information on that page have been satisfied. Thus for example, if it takes 100ms for a response from the S7 PLC and if it takes 40 requests to update the page, then the page will not be displayed any faster than 4s.

To increase the performance of the CitectSCADA/PLC system (Citect/S7 driver/Siemens Softnet S7 V6), normally it is recommended that Citect projects be configured to use 1 CitectSCADA port per I/O Device when using the S7NT driver. Thus, CitectSCADA can send multiple requests to the Siemens Softnet S7 API at the same time to increase throughput. This will generally provide an improvement in page update time. Using 1 port per I/O Device is normally not a problem since Siemens Softnet V6 can supports up to 10 connections. It can however support up to 64 PLC's shared amongst these 10 connections.

However, the Siemens Softnet S7 API has a limitation. It can process 2 simultaneous commands from a single external connection. This means that whilst the S7NT driver can send multiple commands to the S7 PLC, it can only send 2 requests to the Siemens Softnet S7 API at a time. Sending more than 2 requests to the Siemens Softnet S7 API will result in errors 0x227A being returned to CitectSCADA.

The S7NT driver V20505000 has been coded to only send 2 requests to the Siemens Softnet S7 API for each port configured in CitectSCADA.

 
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