197703 – Dawkins – Midland Control Centre

The recent commissioning of the above signalling project represented the final stage of Midland power signalling which began with the opening of the Midland Terminal on the 6th October, 1968. The power signalling at Midland Terminal at that time was operated from a small control panel in the Midland Station building whilst electro-mechanical signalling was operated from Box ‘A’ and mechanical signalling from Box ‘B’.

With the commissioning of Woodbridge Triangle in March 1970, all signalling and interlocking controlled by Midland Box ‘A’ was taken out of use and the Signal Box permanently closed. Extensive alterations were carried out at Midland Box ‘B’, a total of 32 points and signals being taken out of use. Alterations were also made to the signalling arrangements in the Midland Terminal area and the original control panel was replaced by a larger control panel. In addition to the signalling and interlocking associated with the Midland Terminal, this panel also controlled the signalling functions previously performed by Midland Box ‘A’, together with the new signalling on the Woodbridge Triangle.

The panel commissioned in 1970, like its predecessor, was of the individual key type. A notable feature of the installation was the use Type RR remote control equipment for the direct control and indication of signal functions on the Woodbridge Triangle, thereby obviating the need for satellite interlockings in that area together with their attendant relay rooms, control equipment and power supplies. The use of this frequency division multiplex system enabled the interlocking for the entire project to be accommodated in the relay room at Midland Terminal and drastically reduced the number of cable cores required between this central interlocking and the field locations at Woodbridge.

Another notable feature of the installation concerned gauge dis- crimination. A considerable portion of the track in the Midland-Woodbridge area was dual gauge and where narrow or standard gauge led out of dual gauge track it was necessary to ensure that signals reading over these routes could not remain cleared if oncoming trains did not correspond to the gauge of the route selected. This was achieved by means of gauge discrimination circuits.

The control panel in the Midland Station building was modified in October 1971 to include power signalling in the Lloyd Street area, but physical limitations in the Operating Room and relay room precluded any further developments to the signalling system. It therefore became necessary to consider a new control panel in a new building when the decision was later taken to integrate Bellevue at the eastern end, and Guildford and Bassendean at the western end of the present layout, into the signalling system. It was further decided that the panel should be designed to also accommodate the controls and indications incorporated at that time in the three independent C.T.C. panels in Perth.

That section of the new control panel which was comissioned in October 1975 controls all signalling in the Baseendean-Woodbridge-BeUevue area by means of a route setting system of the NX, or entrance-exit, type. This route setting system replaced the former Midland control panel and Midland Box ‘B’, also Bellevue Signal Box, Bassendean Signal Box and Guildford control panel. The type RR remote control system formerly operating Woodbridge Triangle signalling was retained and integrated into the new project, whilst a second RR system was incorporated to control the signalling at Bellevue. The revised signalling arrangements at Guildford and Bassendean necessitated the provision of new relay interlockings at both these centres, these satellite interlockings being controlled from Midland by means of a time division multiplex remote control system. The resignalling project was combined with major track alterations, extending from Bassendean to Bellevue, which were carried out in order to provide Up and Down dual gauge main lines throughout this section of line.

The completion of the Midland resignalling project represented Stage 1 of the new Midland Control Centre. Stage 2, involving transfer of control of the Armadale-Kwinana-Coolup C.T.C. System to Midland, followed in February 1976. This in turn was followed by transfer of control of the Bellevue-Avon Yard C.T.C. System to the Midland panel in June 1976. The fourth and final stage involves the control of the Forrestfield-Kwinana-Robb Jetty section by means of a route setting signalling system which wi11 replace the existing C.T.C. system when narrow gauge facilities are provided throughout this section of line.