On leaving the Pilbara in 1980 I joined the Agnew Clough operation at Wundowie in Western Australia.
This was an eye opener. Up on the hill was the brand new, still to be commissioned "Coates Vanadium Plant".
Down on the flat was "Wundowie Iron and Steel".
This was a case of chalk and cheese.
The Vanadium plant was state-of-the-art. Iron & Steel was locked into the 1940's. For me it was like a time-warp.
I was employed in the Vanadium plant. It had a large fence around it to keep the others out.

The plant was owned by the Agnew Clough Joint Venture and designed and built by Minproc, a local Perth company.
The plant was built to process ore from a small vanadium deposit near Wundowie. The deposit was in magnetite and was approx 0.5% V2O5. Extraction was always going to be difficult with 99.5% waste product.
The plant had a large storage bin, then a conveying and crushing plant designed to provide feed to a three stage vertical fluid bed calciner. The calciner product was fed into a leaching circuit, then to a filtration circuit to produce Ammonium metavanadate powder.
This was converted to vanadium pentoxide and then fed into a small gas fired furnace. The molten product dropped onto a stainless steel cooling conveyor to produce the final vanadium product which looked a lot like welding slag. The product was moved into containers for export shipment.

Unfortunately there were huge problems with the plant. The process worked but the ongoing problems with the fluid bed system, dust control, the low recovery rate finally made the project non-viable and it closed down.

A two level control building had a control room upstairs. The level under the control room housed multiple panels containing PLC and DCS equipment.

Digital control and logic was all in Struthers Dunn PLC's. Analog control was done by Honeywell TDC DCS equipment. The operator interface was by Honeywell TDC 2000.

There were ten PLC's mounted direct on the walls. All the PLC I/O cards were wired to marshalling terminals in panels on the walls above and connected to the field wiring by jumper cables.
The PLC's were all Struthers-Dunn. These were stand-alone units with CPU, memory and plugin I/O cards. The output cards were fused, but still regularly blew transistor outputs. The cards used discrete components and could be repaired if skilled enough.
Programming was in relay ladder and done in the programmer. This was then written to eeprom on the programmer. To update, the PLC was powered down and the program eeprom replaced with the new one and the system powered up again.
The program was an interesting concept because the PLC could be run by the program in the programming panel for testing, before writing to the eeprom. The eeprom's were erased under uv light and could then be re-used.

We had a lot of trouble with reliability which caused havoc with the fluid bed system. If anything caused it to shut down, getting it back running and stable was a process taking an hour, or a day, depending on how long it was down for.
Particular PLC locations were more susceptible to failures, most likely from external interference, but we could never isolate the cause.

We eventually replaced two of the PLC's with a shiny new Modicon 584A. This was the first installed in W.A. and had solid state memory, rather than the ferrite core of the previous versions. It went into a new cabinet fitted with 500 series remote I/O and one remote 200 series rack. The 500 series was for drive control and the 200 series for interface to the Honeywell TDC with analog I/O.
Thie addition greatly improved reliability and control functionality.
PLC programming was done using a CRT programming panel.

Honeywell TDC 2000

This DCS was designed, specified, supplied and programmed by Honeywell.
This allowed them , as the experts in that field, to oversell the hardware by a huge amount and complicate the programming which contributed to the unreliability of the entire system.
I had never seen a TDC system before, but had to quickly learn how it all worked or be totally at the mercy of the mighty Honeywell machine, which had the ear of the plant manager.