can anyone tell me the cheapest adapter to monitor a modbus+ plc with a laptop?

 

The best way I have found is to install a Bridge from ethernet to MB+. First you install a computer on your MB+ network with a SA85 MB+ adapter and a connection to your eithernet LAN. By installing a WinConX Virutal MBX driver on that machine you can set up any computer on your ethernet network to communicate using a Virtual MB+ connection to the MB+ network. It looks just like a local MB+ connection on the computer you are programming with. This does require you to have a SA85 card, but you only need one. Also you need to be on a LAN and it does not help if you want to program right at the PLC