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Entry type: FAQ Entry ID: 109763090, Entry date: 03/05/2019
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What is the meaning of the OPC UA status code "GoodOverload"?

  • Entry
  • Associated product(s)
With firmware V2.5 and higher of SIMATIC S7-1500, when using subscriptions the OPC UA server can transmit the status code "GoodOverload" when there is an overload of the CPU during sampling.

With an OPC UA subscription on different items (variables) the OPC UA server of the SIMATIC S7-1500 has to check the items for value change at predefined intervals (sampling intervals). This check, the so-called "Sampling", needs a certain time that is independent of the number and data type of the items. After the sampling has been completed and a publishing job is there, the server sends the items to the client.
 


Fig. 1

If there are too many items in the queue, an "Overload" of the communication stack might occur, the CPU cannot check all the items in the specified sampling interval and therefore has to jump to the next sampling job. In this case the CPU sends the status code "GoodOverload" (0x002F0000) per item even though the items have not been checked. The meaning of the status code according to IEC 61131-3 is: "Sampling has slowed down due to resource limitations"
 


Fig. 2

Note
Even if in the case of an overload no values of the subscription are transferred, the sending of the "GoodOverload" status generates a communication load in the network and on the CPU.

Remedy
Reduce the number of items to be monitored or increase the sampling interval.
Possible sampling intervals of a SIMATIC S7-1500:

  • 50ms (only CPU 517/1518)
  • 100ms
  • 250ms
  • 500ms
  • 1000ms
  • 2500ms
  • 5000ms
 

Additional Keywords
OPCUA, Status_Code, Good_Overload, Good Overload, OPC-UA, OPC-UA subscription

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