PZB90

PZB or Indusi is an intermittent cab signalling system and train protection system used in Germany, Austria, Slovenia, Croatia, Romania, Israel, on two lines in Hungary on one line in Canada.

Developed in Germany the historic short name Indusi was derived from German Induktive Zugsicherung ("inductive train protection"). Later generations of the system were named PZB highlighting that the PZB/Indusi system is a family of intermittent train control systems in comparison with the continuous train control systems including the German LZB (short from German Linienzugbeeinflussung, literally "linear train influencing") that was introduced at the time. The term PZB is short from German Punktförmige Zugbeeinflussung, literally "punctiform train influencing", translated as "intermittent train protection" or officially "intermittent automatic train running control"

Originally Indusi provided warnings and enforced braking only if the warning was not acknowledged (similar to traditional automatic train stop). The later PZB systems provide more enforcement relying on a train computer.

Experiments with magnetic induction for a train protection system can be traced back as early as 1908. All of the early prototypes did require track-side electricity supply which was not available however in the widespread mechanical interlocking stations. Parallel investigations did look at optical recognition equipment (German "Optische Zugsicherung" / OPSI) which was dumped however on the base of instability due to dirt and dust on the lenses.

Since 1931 the development concentrated on an inductive train protection system (INDUSI) that did not require electricity. In a parallel development Switzerland started to introduce the Integra-Signum system based on magnets since 1933 which is based on similar ideas. The Swiss system did not use a resonance frequency but a static magnetization which can only be detected as a signal when the train is moving fast enough. While the frequency induction is superior the German system did need to install frequency generators on the locomotive which has been a demanding endeavour at the time of steam engines being the predominant locomotive types. The Indusi system was deployed in Germany since 1934 and the system spread to Austria and countries of the historic Austro-Hungarian Empire which share a common root with Germany in terms of rail transport history during the German Customs Union.

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