Applies To:
  • CitectSCADA 5.xx
  • CitectHMI 5.xx
Summary:
I have a CitectSCADA OPC Client attempting to read REAL values from a Siemens S7 PLC via the Siemens OPC Server. The data that comes back through doesn't look correct though. Small numbers come back as impossibly large values etc.

My variable tag in CitectSCADA has the following format:

Tag Name: Speed

Data Type: REAL

Address: S7:[Area1]DB132,DWORD40,1

I have confirmed in my PLC program that the datablock and offset is correct, but I don't see the correct value returned in CitectSCADA.

 

Solution:
The problem is in the address field of your variable tag. The use of DWORD in the address field indicates to the OPC Server that you require a 32 Bit UINT, instead of a REAL variable. The format for these two datatypes is different, and hence the incorrect value is returned to CitectSCADA.

The correct REAL address in this case would be as follows:

Address: S7:[Area1]DB132,REAL40,1

 
Keywords:
OPC, REAL, S7 

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