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Entry type: FAQ Entry ID: 109755846, Entry date: 02/22/2018

What are the system limits of the OPC UA Server with S7-1500 with firmware V2.0.x and V2.1.x?

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The following tables give you the system limits of the OPC UA Server with S7-1500 CPUs, ET 200 CPUs, Software Controllers and Open Controllers.


Table 1 shows the system limits of the OPC UA Server with S7-1500 with firmware V2.0.x and V2.1.x:

Property CPU
1510, 1511, 1512, 1513 1515, 1516, 1505S 1517, 1518, 1507S 
Maximum number of subscriptions with more than 1000 monitored elements per subscription over all sessions1010


Maximum number of subscriptions with a maximum of 1000 monitored elements per subscription over all sessions

Maximum number of subscriptions per session202020
Possible sampling intervals100ms, 250ms, 500ms, 1000ms, 2500ms, 5000ms100ms, 250ms, 500ms, 1000ms, 2500ms, 5000ms50ms, 100ms, 250ms, 500ms, 1000ms, 2500ms, 5000ms
Smallest possible Send interval500ms200ms50ms
Maximum number of sessions324864

Table 1


  • The number of 10,000 elements per subscription is always the maximum.
  • A subscription with a maximum of 1000 elements cannot be converted into a subscription with more than 1000 elements.
  • With regard to performance, it does not matter over how many subscriptions the number of elements is distributed.
    • Variant A: Large number of subscriptions with small number of elements.
    • Variant B: Small number of subscriptions and large number of elements.
    • The difference is the larger main memory requirement in Variant A.
  • If more elements are specified in the table above than registered in a subscription, the status code "BadTooManyMonitoredItems" is returned in the OPC UA client. In this case the client should attempt to register the remaining elements via another subscription.
  • If the maximum quantity framework of the server is exceeded, the status message "BadOutOfMemory" is sent to the OPC UA client.
  • Independent of the system limits mentioned above it is recommended not to exceed the number of elements to be monitored specified in Table 2 as overall quantity framework of the server.

Property CPU 

1510, 1511, 1511C,

1513, 1505S 

1515, 1516  1517, 1518, 1507S 
* Recommended maximum number of elements over all subscriptions10002000 10000

Table 2

* These recommendations are based on a user program with the following conditions:

  • Only OPC UA communication (no other communication, like TCP, for example, is executed).
  • 1 second sampling and Send interval.
  • No OBs with priority greater than 15 (this means no interruption of the communication through OB processing).
  • 50% maximum communication load

  • Data type of the elements: WSTRING

Note on the versions V2.5 and higher
The system limits described above no longer apply to firmware V2.5 and higher.

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