The arrival of the "PLC" was revolutionary.
The Pilbara mine operators were very forward looking. They were early adopters of technology that would drive efficiency and allow the scale of operations that was unprecedented in Australia, or anywhere else in the world. The PLC based control systems installed were the largest in existence during the 70's and 80's. On several occasions we broke the programming software because we exceeded the allowances made by the developers. Granted, they always provided software updates/patches quickly.
My first brush with PLC's was with a Siemens which was installed at the car dumper in Dampier as part of an upgrade. Fault findimg on this was via a dedicated panel with a single line display. The system was housed in a Euro style card frame with power supply, CPU, memory, I/O cards and optional counter, timer and other function cards. This was, for the time, a very complex beast and a dog to fault find.
The 46Mtpa upgrade at Dampier in the mid 1970's saw a major revamp and extension. A new control tower, very similar to those at airports was built and one level housed multiple panels containing PLC equipment.
This was all Modicon, 184 gear utilising 200 series I/O.
The first SCADA system was also installed by Foxboro for this project. This consisted of a modified DEC PDP-11 computer with a serial connection to the PLC's.
Upstairs in the control room there were video status and alarm screens and a printer. In the day this was absolute cutting edge stuff. The computer was nicknamed "Claude" and could be a tad tempremental at times, especially so at month end reporting time.
The project also added a new stacker and an additional bucket wheel reclaimer, provided by IHI, both of which were equipped with Siemens PLC's.
The fines concentrator was added at Tom Price as part of the project and that also was all Modicon PLC's, including a 1084. This was a very rare beast. It effectively acted as a data concentrator for the other PLC's.
The Modicon "PLC" installation was a huge change.
A complete change in control philosophy. Out went all the ac control and in came 48vdc.
The level under the control room housed multiple panels containing PLC equipment.All the I/O for the plant was wired back to racks. All the PLC I/O cards were wired to terminals in the same racks and connected to the field wiring by jumper cables. Large 48vdc power supplies.
All the PLC equipment was supplied by Paklog, out of Sydney. They were the exclusive Modicon distributors.
There were multiple Modicon, 184 PLC's utilising 200 series with "true low" 10-60vdc I/O. These cards were used because NPN transistors were more common than PNP and cheaper.
These made fault finding for electricians more difficult as using a meter at an input point it read zero volts to ground for a point that was on. The card points sourced voltage, 48vdc, and when a field device was in the ON state the card voltage dropped to zero.
The PLC's had serial communications adapters to allow communications to the Foxboro computer.
PLC programming was done using a CRT terminal or a suitcase programming panel.
Modicon "PLC" installation.
An expansion of the facility brought PLC technology. In came 48vdc control power with "True Low". This gave the potential of 108vdc between the old relay system and the new PLC I/O.
The Stockpile Substation housed the new panels containing PLC equipment. Modicon, 184 PLC's utilising 200 series with "true low" 10-60vdc I/O. All the I/O for expansion was wired back to racks. All the PLC I/O cards were wired to terminals in the same racks and connected to the field wiring by jumper cables.
PLC programming was done using a CRT terminal or a suitcase programming panel.
This is a work in progress and will be expanded, time permitting.
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