Sensors & transducers With precision and reliability to the top


Tacho generators in drives of mountain railways and ski lifts are exposed to enormous strain. Nevertheless, they must perform for precise and reliable speed measurement. This is why manufacturers rely on HeavyDuty solutions from Baumer Hübner. What does it take for a tacho generator to withstand the rough conditions on snow-covered mountains?


2,964 metres. At a speed of 10 metres per second, the trip takes about seven and a half minutes, powered by two electric motors of 500 kW. In the driver’s cab, control of the current motor status - slow, idle, forward, reverse, accelerate, high-speed and brake - requires a high level of accuracy and reliability by the speed control system. After all, passenger comfort and safety are first. However, the components in mountain railways


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are exposed to harsh conditions: Wind, rain and snow shape the ambience, temperatures range from double-digit minus degrees in winter to high plus degrees in summer. A perfect application example for the HeavyDuty tacho generators from Baumer Hübner, particularly the analogue tacho generator TDP 0.2 LT which is a robust and precise speed sensor variant.


HeavyDuTy as eNcompassiNg performaNce promise To Baumer Hübner, HeavyDuty is much more than thick-walled housings and corrosion protection. HeavyDuty is the encompassing promise of never letting users down thanks to reliable performance for many years. A prerequisite particularly in mountain railway applications. To ensure this, some specific criteria must be met: Mechanical robustness of course is key. Tacho


generators in mountain railway drives must withstand shocks, vibration and other impacts the rotating shaft is exposed to for many years, without losing any of their functionalities. After all, product exchange is expensive, not because of tacho pricing but because of installation in places difficult to access and system downtime during exchange. Robust housings with solid walls are a good start, so TDP 0.2 LT comes in a die-cast aluminium housing and with stainless steel shaft. But also the interior must be protected against shocks and vibration. TDP 0.2 LT with bearings at both shaft ends is capable of enduring high radial and axial shaft load. HeavyDuty tacho generators must withstand dust,


dirt and moisture which requires a sufficient level of tightness. For this reason, the HeavyDuty housing is well sealed, especially at critical, neuralgic points – shaft and electrical connections. In addition, appropriate materials and coatings protect against corrosion by salt water or chemicals. Tacho generators do not integrate electronics and


therefore are extremely durable against harmful impacts by electromagnetic fields. So, nothing stands in the way


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HigH-precisioN TacHomeTer volTage THrougHouT THe eNTire speeD raNge The conventional combination of copper commutator and graphite brushes in tacho generators has long been outdated. The copper oxide layers on the commutator cause irregular transition resistance and thus high ripple in tachometer voltage, so low speed would not be accurately detected. However, graphite with good sliding properties ensures a long brush service life. The combination of copper commutator and silver graphite brushes is much more appropriate for low speed detection, since precious metal brushes apply a highly conductive “patina” to the commutator. However, this solution is sensitive to adverse ambient conditions such as oil, grease or air containing sulphur and salt. Under such conditions no patina would build up and the said good transmission properties would be lost over the entire speed range. In addition, there is increased wear because the metal-containing


February 2021 Instrumentation Monthly


or many years, the cable railway traveling in the Tyrolean Alps to the top of Zugspitze has been carrying hundreds of people to an altitude of


for routing live, unshielded cables nearby. Furthermore, shaft currents induced by voltage differences might burn the bearing lubrication which results into bearing destruction. The electrically insulated interior of HeavyDuty tacho generators is therefore well protected against such harmful influences. Last but not least, precision is another valuable


virtue of these HeavyDuty heavy weights. Tacho generators must deliver reliable signals at all times to ensure precise drive control and regulation. Based on the speed information, the controller can identify any drive speed deviation and will intervene. HeavyDuty tacho generators in heavy vehicles such as mountain railways must be as precise as smaller speed sensors. It is not without reason that TDP 0.2 LT is field-tested and extremely reliable. It delivers a 60V output signal already at 1,000 rpm; at the maximum operating speed of 10,000 rpm the controller is even provided with up to 600V.


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