I'am using plc fatek fbs 40 ma i'am using usb-to- com adapter and rs232 cable the cable and usb adapter programed the plc without any problem and the simulation work and rx tx led light in plc but if relay or cantactor switch on and off the connection between plc and pc is faild and the connection not connect again else remove usb adapter and connect again
I see that you have already asked this question in a different thread as seen here http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/Serial-fatek-plc/m-p/3592551. I'm happy to help, but it looks like another person has already responded in the other forum to assist you. Please only make one post for your issues, it makes it easier for us and others to track if all the information is in one thread.
I'm sure that this is more electrical, then software issue. Most probably while turn on contactor, your usb hub to which converter is connected, looses power, and then device is disconnected from the system; or something like that.
