Keywords : Leonard+Bauer, speed sensor, GEL247, temperature, Hall effect overview On rail vehicles, the stability of the vehicle system largely depends on the reliability and accuracy of the acquired speed signals, which include the current speed value and the change in speed. Speed ​​signal acquisition is involved in locomotive traction control, wheel slip protection, train control, and door control. We can see that this task is performed by numerous speed sensors in various rail vehicles. In the past, speed sensors were often unstable and prone to failure, frequently causing vehicle accidents. The main reason was that early sensors were primarily analog, and the digital sensors used at the time were also of poor quality. The main reason for these speed sensor problems was the extremely harsh environment in which rail vehicles operate. After years of research and practical experience, the German company Leonard+Bauer has developed a high-quality, multi-functional speed sensor with very stable performance, widely used in the harsh working conditions of the rail train industry. Bearingless Speed ​​Sensor Although some rail trains do not use sensors, most locomotive control systems require speed sensors. The most commonly used type of speed sensor is the dual-channel speed sensor (Figures 1 and 2). This sensor directly scans the gears on the locomotive motor shaft or reducer, therefore, the sensor itself does not require bearings. The target measuring gear can be custom-made according to user requirements or utilize existing measuring gears in the equipment. This speed sensor utilizes the magnetic field modulation principle (Figure 3) and is suitable for measuring ferromagnetic wheels with a module of 1 and a module of 3.5. The shape of the teeth of the measured gear is also an important factor, as this speed sensor can measure square-toothed gears and gears with involute teeth. Depending on the diameter and number of teeth of the measuring wheel, the resolution of this speed sensor ranges from 60 pulses per revolution to 300 pulses per revolution, which meets the requirements of general locomotive motor drives. This type of speed sensor typically consists of two Hall sensors, a permanent magnet, and a signal processing circuit. When the speed sensor scans the rotating gear, the magnetic field of the permanent magnet changes. The change in the magnetic field is recorded by the Hall sensors, converted into a square wave in the comparison stage of the circuit, and amplified in the drive stage. However, the performance of the Hall sensor is greatly affected by temperature. Therefore, the factors determining the sensitivity and phase difference of a speed sensor are not only the gear mounting air gap, but also temperature. Temperature significantly reduces the maximum permissible air gap between the sensor and the gear. At room temperature, a standard module 2 measuring gear can achieve a mounting air gap of 2-3 mm, but when the required temperature range is -40°C to +120°C, the maximum permissible air gap drops to 1.3 mm. We typically require our measuring gears to have both high resolution and small size, thus necessitating a smaller maximum air gap. The maximum permissible air gap range for a high-resolution module 1 pinion is 0.5-0.8 mm. For design engineers, a smaller required mounting air gap for the speed sensor places higher demands on the overall equipment design. A smaller permissible air gap range limits the mechanical mounting tolerances of the measured motor housing and the permissible error range of the measuring gear for the output signal. Therefore, locomotive motor manufacturers and operators prefer speed sensors with a larger mounting air gap range. In actual operation, the amplitude of the speed sensor output signal decreases rapidly as the mounting air gap increases (as shown in Figure 4). Sensor manufacturers need to compensate for the signal amplitude as much as possible, and also compensate for the phase difference accordingly. The common practice is to measure the sensor's operating temperature and compensate for the phase difference based on this temperature information—this is what we usually call temperature compensation. However, this approach has two drawbacks: first, the signal phase difference and temperature are not linearly related; second, not every sensor has the same phase difference. Therefore, the temperature adaptability of traditional sensors needs improvement. The new generation of Lenord+Bauer speed sensors has found a new method to address the shortcomings of traditional sensors. It uses an integrated signal processor to adjust the signal amplitude and phase difference, thereby increasing the sensor's mounting air gap to approximately twice its original size. Using this sensor, for measuring gears with a module of 1, the mounting air gap can reach 1.4 mm, which is larger than the mounting air gap for measuring gears with a module of 2 using traditional sensors. For the new generation of sensors, the mounting air gap for gears with a module of 2 can reach 2.2 mm. At the same time, the new generation of sensors significantly improves signal quality. Faced with the same air gap fluctuations and temperature changes, the new sensor exhibits three times the stability of duty cycle and phase shift in both channels compared to the traditional sensor. Furthermore, although the new sensor's circuitry is more complex, its MTBF value is higher than that of the traditional sensor. The new sensor not only provides higher signal accuracy but also better signal availability. This new sensor has a similar appearance to the traditional sensor (as shown in Figure 5) and can be applied to all vehicles currently in use.