opc_connect - Connect an OPC Server
This function is to connect an OPC Server
opc_server_name='Matrikon.OPC.Simulation.1' opc_connect(opc_server_name)
Zhe Peng(pengzhe1113@gmail.com), Longhua Ma. Zhejiang Univ. China
opc_disconnect , opc_add_group , opc_add_item , opc_item_read , opc_item_write , opc_server_browse , opc_item_browse ,