Baumer has been acting as a reliable partner for many years Rail technology, Long-lasting and economical standard sensors with industry-standard qualification and customer-oriented new developments for all conceivable sensor applications in rail technology belong today to the broad product range. Without a multitude of different sensors, safety and comfort can not be guaranteed with rail vehicles.
In the drive system and bogie of the chassis of rail vehicles, for example, sensors detect the speed of the engine, transmission and axle and measure pressures in the brake system. Ultrasonic sensors reliably detect the distance to the platform for the optimum extension path of the treadmill. Inductive sensors signal end position, z. B. in the boarding and on the window locks. In the coupling systems hydraulic and pneumatic pressures are measured and the coupling processes are monitored. Of course, the air conditioners also need sensors and gauges. In addition, all relevant measured values must be visualized in the driver's cab.
Sensor technology for Drive system and chassis
Today, anti-slip protection, traction control and train protection systems play a key role in rail safety. Eg the European one Train control system ETCS (European Train Control System). For this purpose, the angle of rotation and the number of revolutions in the drive system and bogie of the chassis must be recorded at many relevant points. Specially developed for tough use in the bogie Multi-channel pulse generator BMIV This provides good conditions for this: Up to 12 channels in four galvanically isolated blocks allow the determination of the wheelset speed simultaneously in several systems, even with different pulse numbers. Function control signals ensure maximum safety - the sensor also sends signals when the train is stationary. These "signs of life" ensure that, for example, a cable break is detected as quickly as possible.
Sensing principles for harsh environmental conditions
Under harsh operating conditions, the question arises of the suitable scanning technology. Here, the proven "Magres" principle offers good conditions. In contrast to all other detection principles, this magnetic scanning is completely insensitive to the loads occurring in train traffic such as vibrations, shocks, dirt, oils, fats, splashing water, condensation, severe temperature fluctuations as well as foreign magnetic fields. The pulse generators comply with the railway standards and are also suitable for the European train control system ETCS with SIL-2 assessment.
Also with magnetic scanning work the Rotary encoder of the "HDmag" series, The magnetic hollow shaft encoders with an inner diameter of up to 740 mm can be mounted directly on the motor hub. Due to their axially very narrow design and the omission of the torque arm they only need very little space on the shaft. Thanks to the signal processing integrated in the scanning head, rectangular signals (HTL or TTL) or sin / cos signals can be generated. The electronics of the sensor head are completely encapsulated to protect against dirt, shock and vibration.
Also suitable for use with rail vehicles are sensors that scan ferromagnetic gears using the Hall principle. To the tasks of the non-contact Hall sensor MTRM 16 include, for example, the speed detection for anti-skid and speed control and the direction of rotation detection. Depending on the version, it is suitable for gear sizes up to module 3 and can be used at temperatures from -40 ° to + 120 ° C. The sensor is also shock and vibration resistant and housed in a completely enclosed, rugged metal housing. Thanks to switching frequencies of up to 20 kHz, the MTRM 16 can reliably detect the speed of high-speed gears.
Another example of safety-related sensor technology on rail vehicles is the Incremental encoder FOG 9who has already proven its reliability on the world's most powerful four-axle diesel-hydraulic locomotive: Vossloh's MaK 2000-4 BB with its 2700 kW is able to drive with a 2,8 t hitch even on an 745% slope. Among other things, an optimized anti-skid protection, which detects the slip at the friction limit of the wheels, contributes to this performance. The speed measurement required for this purpose is taken care of by the heavy-duty incremental encoder, which is mounted directly on the unsprung axle with its Euro flange B10. The short design and the massive aluminum housing with two-sided support of the stainless steel shaft offer high vibration and shock resistance. High-voltage power transistors ensure that the square-wave signals are transmitted without interference even over longer distances.
Pressure measurement in railway applications
An important field of application for sensors in railway engineering is pressure measurement. The spectrum ranges from the brake system via the overhead line pantographs and the cooling systems of traction vehicles to shock absorbers or air conditioning systems. Due to the inevitable vibrations during the ride, the pressure gauges used must be extremely robust. The pressure transmitter PBSR was developed for extreme loads. It monitors the pressure in the brake system of various high-speed trains and is suitable for pneumatic and hydraulic brake control as well as for cooling circuits. Robust pressure transmitters EF6 are also used in the high voltage range for pressure monitoring of the current collector (pantograph).
For heavy load applications in rail vehicles, eg. B. to monitor the hydraulic pressure of parking brakes on trains, the pressure gauge MEX3 is suitable. The instrument, made of stainless steel, was housed in an aluminum housing with a polycarbonate viewing window, especially for use in harsh environments. The MFE series, which was also developed specifically for railway applications, is mainly used in on-board applications. The scale illumination ensures good readability in the cab.
In the cooling systems of the power supply system, within air conditioning systems or in the brake systems, eg. As trams is often the pressure switch CPX / PFX used. It was developed for a temperature range of -40 ° to + 150 ° C and can be easily adapted to individual needs. For example, the pressure switch has already been designed for increased operating voltages up to 130 V. However, many other pressure and level sensors suitable for railway applications can also be adapted to individual application requirements. Regardless of whether it is for air conditioning systems, waste water tanks or toilet functions, there is a suitable sensor solution for every application.
Safety at footboard, door, window and toilet
In rail vehicles, however, inductive and capacitive sensors have many applications. For a comfortable and safe entry, for example, a minimum gap between platform edge and car is required. The correct end position of the access aid can be monitored with inductive sensors. The durable and reliable sensors are also suitable for locking the doors and windows. They are available in cylindrical and parallelepiped designs and, depending on the design, are suitable for switching distances up to 20 mm. Just like all other sensors, they are also "put through their paces" and designed for years of reliable operation. This is a criterion that should not be underestimated for rail technology because modern railcars and trains are designed for long operating times of up to 30 years. With an MTTF of over 100 years, the inductive sensors in stainless steel housing meet the high demands. Its wide operating temperature range of -40 ° to + 100 ° C contributes to the reliable operation of rail vehicles.
The Capacitive level sensor CFAK 12 finds application in railway toilets. Here, on the one hand, it serves as overflow protection when the toilet is blocked and the water level rises. On the other hand, it ensures by the successful hiding of suspended matter, toilet paper and cleaning agents, that the rinse usually always works reliably. Thanks to its special housing shape and the smooth plastic surface, dirt particles adhere very poorly, which considerably reduces the cleaning effort. In addition, the sensor is extremely resistant to cleaning agents.
The author Steffen Günther is Head of Product Marketing Management at Baumer GmbH