Remote Q factor measurement system for a ATS coil using digital phase locked loop

For safety reasons, the ATS (automatic train stop) system is used, which is a kind of communication system with a feedback amplifier and a transformer on the train and wayside coils. The coils are highly resonant LC circuits, and also have very high Q (quality) factors. The Q factors of wayside ATS coils have to be maintained high enough for the amplifier to operate reliably. In this paper, a novel Q measurement system is proposed. The system measures the resonant frequency and the bandwidth of the ATS coils, by controlling the phase difference between the transformer and the coil using a digital PLL (phase locked loop). The overall configuration and algorithms of the proposed system and the digital PLL control schemes are presented in detail. Experimental waveforms are shown to verify the system performance