Distance pulse generator
Odometer pulse generator (TIG, for English wheel impulse generator ) are robust sensors which are used in the railway system, the rotation of the axles of railway vehicles to be detected. In particular locomotives have many sub-systems separate from other components normally electrically isolated need speed signals. These include the odometry (distance measurement), sliding , skidding and rolling protection , door security and others.
A distinction is made between bearingless and self-bearing encoders.
functionality
The sensors work with optical light barriers , magnetic Hall or (earlier) wigand sensors or as a generator as a tachometer generator or resolver . An evaluation unit determines from the wheel diameter, the pitch of the encoder, and the counted pulses or the pulse frequency , the driven distance or the speed . Several sensors on one coding disk - this is the rule for encoders with internal bearings - supply independent systems or allow the direction of rotation to be determined. A stable phase reference is necessary for this.
Bearingless encoders
In the case of encoders without bearings, a coding disk is located on the axle of a wheel set . Since this moves on bad tracks in its warehouse, the distance between the coding disk and the mostly magnetic pick-up must be correspondingly large. The resolution (number of pulses per revolution) is therefore limited to a small value. Where that's acceptable, that's a robust solution. Such bearingless encoders can be found on almost every wheel set of a rail vehicle. They are mainly used for anti-skid protection.
For the traction control of electrically or diesel-electrically driven rail vehicles, there are higher requirements for the resolution of the sensors in order to enable fast slip control. One solution is to position the encoder on the drive shaft of a gearbox that is usually present. In the case of a hollow shaft drive , however, the elasticity between the gear unit and the wheelset interferes. A more direct detection of the slip is possible with optical encoders.
Encoders stored in-house
Sensors with a high number of pulses (mainly optical ) have their own axis. The coding disk and sensor can be housed in a stable, water and dust-proof housing that is flanged onto the bearing cover of the wheel set - to compensate for bearing play with a coupling.
Measurement error
The distance measurement with the TIG can be grossly falsified by sliding or skidding the relevant axis. The occurrence of such slip events can be recognized from the dynamic behavior, but the error can only be partially corrected by interpolation. Therefore, when used in safety-critical systems such as LZB or ETCS (as part of ETCS odometry ), additional sensors with a different measuring principle are used, often Doppler radar sensors .
The fact that the diameter of the wearing wheels is not exactly known also gives rise to uncertainties that increase with the distance traveled. A regular comparison of the TIG information with a reference , e.g. B. Eurobalises is therefore necessary.
Monitoring functions are common in order to be able to distinguish cable break from standstill or a blocked brake.
swell
- ↑ Deuta-Werke view of the flange side