12. Troubleshooting

12.1. OPC UA Communication Troubleshooting

Runtime error: Cannot connect to this OPC Server

If upon starting the simulation the above error shows up, navigate to External Signal Configuration in the Automation tab. The connection status of the OPC Server has to be ‘connceted’. If the status is ‘connected’, click OK and try running the simulation again. If the status is ‘unknown’, click on Refresh Server Status. This may change the status back to ‘connected’ and the simulation will then run.

Green tick is missing; cannot choose external variables in External Signal Configuration

If this is the case, close all open assemblies and restart Siemens NX.

OPC UA communication connected but variables do not get updated during the simulation #1

If the OPC UA communication is succesful and mapping is done correctly, but the variables do not get updated through OPC UA in either direction (i.e., both inputs and outputs do not respond), then a certain part or sub-assembly is causing this problem. The solution is to start rebuilding the current main assembly in a new file and adding each part one by one, testing the OPC UA connection after adding each part. This way, you will be able to spot the part and/or assembly that is causing the communication issue.

If the cause of the issue is a sub-assembly, create a new sub-assembly with a different name and import all parts of the old sub-assembly in. Use the new assembly instead of the old one. This should allow the communication to function.

If the cause of the problem is a part, reconstruct the part in a new file and use the new part (copying the old part in a new file does not resolve the problem).

OPC UA communication connected but variables do not get updated during the simulation #2

If the OPC UA communication was running perfectly but all of a sudden the variables stop responding, this may be caused by running a simulation only on a sub-assembly or part level. Undoing the past 3 steps and reselecting the main assembly then running the simulation will undo this problem.

Siemens NX MCD offers the possibility to run simulations on the sub-assembly or part level. This is helpful to see how only one part will be simulated without simulating the entire assembly. However, it is recommended to run the simulation only on main assembly level because of this OPC UA communication bug.

Only some variables are updated through OPC UA

This issue occurs when communicating with a PLC program over OPC UA.

In case the OPC UA communication seems to function with only some variables and with other variables it seems to be down, make sure that the variables being transfered over OPC UA are declared in a function block in the PLC program and not mapped directly to a PLC I/O module.

12.2. PLCSIM Advanced V2.0 Troubleshooting

PLC Instance cannot be started: licence could not be found

If the simulation instance of a PLC does not run, open PLCSIM Advanced as an administrator and try again.