After the Expansion Project 2x was completed in 2003 WAGTEC Engineers found themselves involved at DBCT again for Expansion 6x project. This project mainly involved replacing the legacy AB PLC5 and Honeywell systems with the newer AB ControlLogix PLC's and Rockwell SCADA. WAGTEC Engineers were involved in the re-write of all Yard Machine code to a common format and standard.
Each of the site's Yard Machines was programmed by different subcontractors over the years, and although they performed similar functions, the code implemented to do this was vastly different between the machines. If a change to machine operation was required, then each machine had to be programmed separately. DBCT came up with new State Machine diagrams outlining the common machine functions (e.g. Bench Stack, Auto-Relocate, Auto-Reclaim) with the idea being that these high level state machines could be used in every Yard Machine, with interface blocks to attached to each yard machine's different IO.
Standard Control blocks were developed along with standard Alarm and Sequencing blocks. Utilizing the new features of AB ControlLogix User Defined Templates and Programming Blocks the code was written around the new State Diagrams. The Original PLC5 PLC was left in place, however code was implemented in the PLC5 which allowed the new ControlLogix PLC control over the IO by toggling a bit. This enabled the new State Machine logic to be tested in parallel with the old PLC5 code. IO Trends of machine operation were taken whilst under both control systems and analyzed - obviously when the ControlLogix trend didn't line up with the PLC5 trend there was a programming problem!. By having the 'dual control' arrangement, if a problem surfaced with the new logic the machine could be returned to an operating state immediately instead of holding up production.
Until late 2003 the Darymple Bay Coal Terminal has been running under the control of a Digital PDP-11 system which was installed in the early 1970's. This tape drive system ran the plant sequencing flawlessly over these years, which goes to show that the reliability and scaleability of the original installation was incredible even in today's terms.
Resources to look after the legacy system were becoming thin on the ground, and parts were next to impossible to find. As a result, DBCT put together a plan to replace the PDP11 system with something more modern.
The PDP-11 handled job control from the MIMS system, taking train data and starting up conveyors and yard machines in sequence to transport coal from the rail loadout areas to the stockpiles, and from the stockpiles to the outloading Shiploaders. Information was relayed to the site's 20 AB PLC5's via 232/485 communications which ran at a baud rate of 9600bps. The PDP-11 system also took care of anti-collision for the site's 7 yard machines.
The PDP-11 'C' based source code was reverse-engineered and programmed into a AB ControlLogix PLC dubbed the 'Gateway PLC'. The Honeywell Plantscape 320 SCADA package was modified to transfer job control to the Gateway PLC which then sequenced inloading and outloading streams to the other site PLC's. Replacing the entire PDP-11 code was done in stages with minimal plant downtime.