Question on S7 PLC, OPC and visual basic


Thread Starter


I am newbie. In our plant used S7 CPU 319-3 PN/DP and HMI (writing on Visual basic). There is OPC (delta logic) server in HMI. Problem is that some data are in HMI are not same as HMI and when changed the parameter then it is not changing in PLC and vice versa.

Could anyone tell me how visual basic program exchange data with PLC. or How the way of the solving the problem? or Is it hardware or software issue ?

Thank you
OK, I'm going to assume you are looking for a basic overview and some simple troubleshooting steps, rather than a detailed explanation about VB programming.

The VB Program talks to the OPC server. The OPC Server in turn talks to the PLC. So the VB program never communicates directly to the PLC.

You need to use a third party OPC client to check whether the Data in the OPC server matches the PLC and / or the HMI. This will tell you where the problem lies.

Use google to find an OPC explorer if you don't already have one. There are plenty of free ones available. The Matrikon OPC explorer is as good as any.

If you want more help than this you are going to have to give us more information about what sort of HMI you have, where this VB program exists, how often it happens etc, and a better description of what is wrong.