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Zachary Piper IRSE Student Member B.Eng Electrical

Ansaldo Signal Union Switch and Signal Pty. Ltd.

Traditional means of vital train detection used on railways are unable to be applied to the KL Monorail, which runs on pneumatic tyres, therefore an alternate means of detection is required. The TDS (Train Detection System) used on the monorail was adapted from a platform door alignment system designed specifically for the driverless Copenhagen Metro by US&S Inc.

The TDS used on the KL Monorail utilizes AFO-IIC (Audio Frequency Overlay) equipment that is typically employed as a track circuit which is superimposed over other types of track circuits. The AFO system consists of a transmitter (Tx) and receiver (Rx). The Tx units produce a amplitude modulated waveform at a particular frequency to which the Rx unit is tuned and will respond to. The units used on the monorail have been specially modified to increase the output from the transmitters and the sensitivity of the receivers. This includes additional impedance matching components to optimize energy transfer between the coil antennae that are connected to their output/inputs.

This TDS comprises a transmitter unit and antenna which attaches below the vehicle skirting at the front and rear of the train. This couples with a fixed antenna mounted on the side of the monorail beam which is connected to a receiver. When trains pass over the fixed wayside antennae the receivers detect the AM waveform from the trains and indicate to the Processor Based Interlocking. The PBI uses these indications to count trains in and out of track sections, in a similar fashion to an axle counter, so the track section occupancy status is always known.

Because the equipment has never been applied this way before, all parameters that affect the overall performance of the TDS had firstly to be identified and then tested in the factory and field to establish the installation parameters of the system. Specific issues included: vital input processing of the PBI, positioning of both onboard and the wayside antennae, wayside cabling effects upon received voltage. All items were carefully tested to determine the maximum train speed under which the TDS could reliably detect.

A maximum running speed over detection points of 45Km/h was achieved by the TDS. A higher running speed sort by the client at a site of a future station saw an increased detectable speed of 65Km/h by modifying the interface between the AFO and the PBI.