Glossary - P

Packet The sequence of bits used to encode the instructions upon which a decoder operates. Pantograph A current pickup device for electric locomotives and cars. Piggyback The movement of truck trailers on flatcars. Also called trailer-on-flatcar (TOFC). Platform A loading dock for freight or passengers. A high platform is even with the car floor, while a low platform may be at any height below floor level. Points The two connected short rails in a turnout that move to change a train's route. Portal An entrance to a tunnel or the framing at the ends of a truss bridge. Power district An area of the layout connected directly to its own booster, electrically isolated from any other boosters or power districts. Power pack (or supply) A model railroad control device containing, at the minimum, a transformer and rectifier to reduce 120-volt AC house current to a lower DC voltage for running model trains. Profile A scale drawing which shows the grade alignment for a section of main track. Programming track A short piece of track electrically separated from the main trackage. It is used to program any CV, including the decoder's address. CVs may also be read back to the cab from a decoder on the programming track. Prototype The real, full-sized object after which a scale model is made. Pull the pin Operate the uncoupling lever. Pullman A sleeping car or parlor car operated by the Pullman Co.; by extension, any sleeping car. Pulse width modulation (PWM) Used to control the speed of a DC motor by applying pulses of a constant voltage of varying width. The wider the pulses, the faster the motor turns. This is the method of motor control used by DCC decoders. Puzzle switch A slang term referring to the special track components, including single or double slip switches used in extremely congested areas.

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