S7-200 test for network connectivity

Hi Hi,
I'm using an S7-200 PLC which is connected to a Wonderware InTouch 9.5 HMI. The PLC is being used to control the level in a tank. If the HMI is in start up mode and the HMI PC somehow fails or shuts down and the tank is in start up mode the tank will continue to full. I'm using the TCP/IP protocol to communicate the HMI to the PLC. I need to figure out a way in which the PLC can test for network communication so that in the event that this communication goes down the PLC can go into a shutdown mode and stop fulling the tank. How can i implement this in the ladder logic?

One method would be to use a PLC register (tag) that the PLC slowly decrements. The HMI would set this value to some number periodically. At zero the PLC would stop. The HMI should only need to run such a script when you're in "startup mode".

Other various "heartbeat" schemes work on a similar concept.

Thankx a whole lot. I'm looking into it at the moment

PLC not reading HMI input

Hi, I wrote the code for the plc and i configured the HMI and the TopServer communication module. The code however does not turn of my tank system when the pc shuts down. I believe this is beacuse the plc is not reading the input from the HMI. Can you please tell me how i can check to see if the PLC is reading the HMI input.

Thank you