I'm investigating an issue that has been reported on site and am looking for some info/insight. We have a system using a S7-1500 F PLC and running a Unified Comfort Panel. The HMI is located in a control room and the PLC is in a different room with the machinery. There is a requirement during maintenance/troubleshooting for an engineer to go up into the machinery room and they need access to the HMI. To get around this we have installed a remote access gateway with the PLC which provides a wifi signal that the engineer can connect to to get on the network (all securely protected). We have then provided a tablet that can connect to this remote gateway and access the runtime via a browser (ip address). This works well, however naturally if the engineer walks too far away from the access point then the signal drops out on the tablet and they lose connection to the runtime. In this instance it appears to cause a PLC stop and shuts down the system. If the system is stationary then it is an inconvenience as the system must be restarted (which takes up to a few mins) but if the machinery is moving and then performs an emergency stop then it can cause a lot of mechanical stress. The e-stop is meant to be a last resort stop and not something that should be frequently occurring so we're looking at how we can avoid it.

Does anyone know why this might occur? I don't have access to the program currently so am curious if this is something that was written by the PLC engineer or whether it's by design from Siemens. The physical HMI panel on the network is still connected, the tablet is just another instance of the runtime right? Can a timeout delay be incorporated that will allow the tablet to cut out temporarily e.g. allow 10s of connection loss before causing a stop?

We also want to look at using signal boosters to improve the signal for the tablet but inevitably we will still get a signal dropout at some point.