page_title: Track circuit
section_title: Data Pickup Unit
hierarchical_section_title: Track circuit / Principles and operation / CSEE UM71 / Data Pickup Unit
caption_attribution_description: English: Track Circuit Jointless DPU CSEE End View
context_page_description: A track circuit is a simple electrical device used to detect the presence or absence of a train on rail tracks, used to inform signallers and control relevant signals.
context_section_description: A jointless track circuit such as the CSEE can be divided with a data pickup unit (DPU), which is cheaper than splitting it into two track circuits. A DPU avoids the need to change the frequency of a whole series of track circuits in a cascade. The DPU consists of a tuned coil which detects the presence or absence of current in the adjacent rail and picks up or drops a relay accordingly. One use of DPUs is for timing circuits. Each track circuit frequency has its own DPU tuned to that frequency. DPUs can be located almost anywhere; they overcome the limitation that jointless tracks have a minimum length.
caption: Data Pickup Unit CSEE; end view
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