PZB, or Indusi, is an intermittent cab signalling system and train protection system used in Germany, Austria, Slovenia, Croatia, Romania, Israel, Serbia, on two lines in Hungary, on the Tyne and Wear Metro in the UK, and formerly on the Trillium Line in Canada.
Developed in Germany, the historic short name Indusi was derived from German ("inductive train protection"). Later generations of the system were named PZB (short for German , literally "punctiform train influencing", translated as "intermittent train protection" or officially "intermittent automatic train running control"),Ernst, Dr.-Ing. Richard (1989). Wörterbuch der Industriellen Technik (5th ed.). Wiesbaden: Oscar Brandstetter, p. 802. . highlighting that the PZB/Indusi system is a family of intermittent train control systems, in comparison with the continuous train control systems including LZB (German , literally "linear train influencing") that were introduced at the time.
Originally, Indusi provided warnings and enforced braking only if the warning was not acknowledged (similar to a traditional automatic train stop). The later PZB systems provide more enforcement, relying on an onboard computer.
History Experiments with magnetic induction for a train protection system can be traced back as early as 1908. All of the early prototypes required track-side electricity supply, however, which was not available in the mechanical interlocking stations widespread at the time. Parallel investigations looked at optical recognition equipment (German / OPSI); this was however not developed further on the basis 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 in 1933, 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 method was considered superior, the German system needed the installation of frequency generators on the locomotive which was a demanding endeavour at the time of steam engines being the predominant locomotive type. The Indusi system was deployed in Germany in 1934, and the system spread to Austria and countries of the historic Austro-Hungarian Empire, which shared a common root with Germany in terms of rail transport history during the German Customs Union.
I 34 The original Indusi system was deployed in Germany in 1934 – it was not called by that name, however (using the full title ) and the shorthand "I 34" is a retrospective designation as well. The initial tests only used a train stop function (the 2000 Hz signal in later revisions) – by the end of 1934 there were already 165 locomotives equipped with the Indusi detectors and 4500 km of track were secured with inductors. At the end of WWII the system was not functional anymore and in 1944 the equipment of 870 locomotives and the Indusi signals on 6700 km of track were officially switched off.
During 1947 the Indusi resonators of the locomotives were re-enabled together with a network of 1180 km of track in western occupied zones.
I 54 The Deutsche Bundesbahn started an effort to standardize the function of a modern Indusi system leading to the Indusi I 54 specification in 1954. This included a new frequency generator that did not require three motors but only a single transistor frequency generator with a downstream audio crossover to emit the three frequencies in parallel.
I 60 Minor improvements in the 1960s led to the Indusi I 60 system. When a 1000 Hz inductor was encountered, the driver had to acknowledge the caution signal within four seconds. Additionally, a countdown was started to check whether the train had slowed to a specified speed within a specified time frame. Depending on the type of train the locomotive was hauling, the system could be manually switched between three modes of operation: freight train, low speed and high speed passenger train. In each mode, the system calculated a different speed curve based on the maximum allowable speed and braking characteristics of the train.
The original I 60 system proved insufficient in a number of situations, so it saw multiple revisions that finally led to the revised standard I 60R.
I 60R With the introduction of (LZB) by Deutsche Bundesbahn the locomotives were equipped with a microprocessor-based LZB/I 80 train protection system. It was able to pick up the Indusi signals since 1980. The experience with this system led to the development of the Indusi I 60R system that required microprocessors in all locomotives. Instead of checking certain speeds at certain points in time, the new system continuously checked a curve of speed against time. If the train was faster than the curve allowed, a stop could be enforced at any time.
PZ80 The PZ80 is an independent development of GDR based company Geräte- und Reglerwerk Teltow. There was a need for efficient train protection systems by the Deutsche Reichsbahn. They wanted to gain independence from the technically obsolete I 60 supply by the West-German Siemens manufacturer and replacement imports of the Romanian I 60 Icret. The PZ80 supported all Indusi 60 modes enhanced with a number of new modes including speed control in steps of 10 km/h, continuous braking curves and a restrictive mode. In 1990 the developer was sold by the Treuhand institution to Siemens. So this system was the foundation of the upcoming PZB90 system.
PZB90 PZB90 is a new version, deployed in the mid-1990s. It features a new 'restrictive mode' as the result of two accidents. In both cases a had train stopped at a station as intended. Then the train accelerated again, despite the signal still showing red. When the train reached the exit signal, its speed was sufficient to crash into another train despite the automatic braking enforced by the 2000 Hz inductor.
The new restrictive mode limits speeds after a train stopped before reaching a red signal. Currently, trains are limited to 45 km/h when stopping after an active 1000 Hz inductor or to 25 km/h when stopping after an active 500 Hz inductor.
Software 1.6 The software update of PZB90 to version 1.6 had important changes to the braking curves: for most train types the target speed was lowered while allowing a longer time interval. This is a change on the old Indusi specification that had fixed intervals. The new software version can use uneven times – for example train type O must have 85 km/h after 23 seconds which had been previously specified as 95 km/h after 20 seconds. The new braking curves have been found by extensive simulation to get a better tradeoff between security and efficiency so that train operation is optimized.
Another change is bound to the alert functions – when a restrictive mode is extended by another 1000 Hz it does not activate the cab signal if a previous warning signal had been acknowledged. When starting from a halted position many restrictive modes could be released ("PZB frei" button) as they had been purely based on time – since version 1.6 the actual section length is controlled where the PZB restrictive mode can not be released. This led to some changes in railway stations with moving 1000 Hz inductors.
Software 2.0 The software update of PZB90 to version 2.0 changed some corner cases of the train control – previously it had been possible to lift any restrictive mode by changing the reverser from forward to reverse and back to forward. From version 2.0 on it will remember the enforced speed restriction. Another change was a malfunction when the train had been halted directly over an inductor that could only be released by using the fault reset which however would also drop all speed restrictions from external signaling.
Function
Locomotives and multiple unit cars with operating cabs are equipped with onboard transmitter coils with the superimposed frequencies 500 Hz, 1000 Hz and 2000 Hz. Passive tuned inductors (RLC circuits) are situated at appropriate trackside locations; each inductor resonates at one of the three frequencies, depending on its location. When the leading end of the train passes over one of the trackside inductors, the inductor's presence is detected by the onboard equipment through a change in magnetic flux. This activates the appropriate onboard circuit and triggers whatever action is required based on the location (e.g., an audible/visual warning, enforced speed limit, or enforced stop).
The three frequencies have different meanings to the train:
1000-Hz speed limiter Warning that the distant signal being passed shows "caution", drop of speed required. Driver has to confirm that they have seen the "caution" aspect by pressing a button; failure to do so within a few seconds results in a forced stop.
The 1000 Hz is active along with a yellow signal on a distant signal before a main signal, or on a main signal combined with a distant option for the following main signal, or it is active before a railroad crossing.
The train driver has to acknowledge the cab signaling within 4 seconds (2.5 seconds on trains with an MVB electronic bus) by hitting a button – this is called vigilance test (German "Wachsamkeitskontrolle"). Failing to do so will result in an emergency stop.
After acknowledging the warning signal the train has to stay below the braking curve (German "Bremskurve") – fast trains may travel up to 165 km/h and they must reduce the speed to below 85 km/h after 23 seconds. Note that the operation of high speed trains beyond 165 km/h is not based on visual wayside signals or PZB inductors (using LZB or European Train Control System cab-signalling instead in Germany).
The train cannot be released from the speed restrictions within 700 m after the 1000 Hz activation. After that point the train driver may hit a release button (German ). In later generations the enforced speed limit was extended to 1250 m and the 700 m point is only relevant for the 500 Hz inductor.
The monitored speed (German ) depends on the train type which is in direct relation to the mass and braking capability – the quotient of these is given in braking percent (German ). If the train speed drops below a switch speed (German ) the restricted mode is activated – this includes a constant maximum speed of 45 km/h up to the 500 Hz inductor which lowers the speed even further during the restricted speed control (German ).
PZB-90-train type maximum speed Vü1 restricted speed Vü2 switch speed Vum O (higher) over 110 from 165 km/h to 85 km/hwithin 23 s constant 45 km/h constant 10 km/h M (medium) 66 to 110 from 125 km/h to 70 km/hwithin 29 s constant 45 km/h constant 10 km/h U (lower) below 66 from 105 km/h to 55 km/hwithin 38 s constant 45 km/h constant 10 km/h
500-Hz speed limiter Immediate maximum speed (Vmax) as well as further drop of speed are enforced.
The 500 Hz inductor can be found shortly before a main signal which actives a speed control for next 250 m. This will extend the braking curve Vü1 from the 1000 Hz up to the main signal. The restricted mode after a 1000 Hz is followed by a braking curve Vü2 to reduce the speed up to the main signal. While the switch speed was at 10 km/h after the 1000 Hz speed limiter (reflecting a full stop of the train) it does now follow braking curve being again no more than 10 km/h at the position of the main signal. The actual braking curves depend again on the train type (which is based on the braking percent the train driver has calculated).