HMI OPC client cannot show Negative values


Thread Starter


My Cimplicity HMI with OPC client is connected with Siemens PLC with Siemens OPC server. I can read 0 and positive values, but the negative values are not read on Cimplicity. Why?

Siemens PLC is S7-314 and the OPC Server is Siemens Simatic NET S7/SR-OPC-Server V2.2 Build 1381.

Steve Myres, PE

Is the display interpreting them as unsigned integer rather than signed integer? If this were happening with a 16-bit integer, for example, -10000 might display as 55,535. Or, is the absolute value correct, as in -10000 shows as 10000? In this case, the HMI would be ignoring the sign bit.

Donald Pittendrigh

Hi All

Have the same problem with InTouch, the Siemens OPC scout shows the values correctly as negative, I couldn't be bothered and changed all the tags to real numbers, the OPC was so fast anyway and the numbers in the scada didn't suffer from the improved accuracy. Now I only use reals, even in the PLC program.

Donald Pittendrigh