In 2009 a large section of the Fonterra Waitoa site ethernet network infrastructure was upgraded, with installation of a fibre-optic ring and layer 3 network switches. This upgrade required changes to PLC and HMI IP addresses, and to PLC messaging parameters for communications to the affected PLCs. This portion of the project was awarded to Tait Controls.
A list of site PLCs was prepared – 76 in all mostly Allen Bradley with a mix of PLC-5/250s, SLCs, and ControlLogix. Communications parameters for each PLC were determined – DH+ links and node numbers, and Ethernet addresses for PLC-PLC messaging and PLC-HMI connections.
Details of more than 500 PLC-PLC messages were extracted from the program code, and a matrix showing PLC inter-connectivity produced. Each message was examined and a list of changes prepared by area, together with new routing tables for each of the 8 gateway racks. Relevant HMI systems were examined and PC addresses noted. PLC communication drivers were checked, with more than 100 identified for change.
Critical communications were identified, and acceptable down time agreed before the change-over began. Implementation and checking was carried out alongside hardware changes, and took place during normal working hours, over a three day period, without incident.