Champaran HumSafar Express : इन अजनबी सी राहों में, जो तू मेरा हमसफ़र हो जाये, बीत जाए पल भर में ये वक़्त, और हसीन सफ़र हो जाये. - Piyush Singh

Stands for Distributive Power Wireless Control System
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This system was mostly invented for use in Python Rakes. Usually a python rake has the following CC -- LOCO Rake 1 Loco Rake 2. The 1st loco and the 2nd loco will communicate wirelessly via Radio Frequency. The radio frequency devices fitted in both locos will get synchronized, so when the lead loco will apply brake or increase notch or when release MR or brake pressure or any other activities , then these will be also effective in the trailing loco.
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If locos are MUed Together then also these activities can be done by the lead loco and the effects will be reflected on the rear loco.
But to do with through radio frequency, DPWCS is used.
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I may not be completely correct, but this is the general logic behind.
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The rusty box just above the cab door is the DPWCS device