Transrapid in Shanghai - continued
Like two arms, the supports mounted on the body of the vehicle grasp around the lateral guidance rails. Supported and propelled by a magnetic field, the Transrapid does not roll on wheels, it hovers. Electronically controlled support magnets are located on the support arms underneath the vehicle and cause it to hover by pulling it up to stator magnets, while guidance magnets keep the train on track. An travelling electromagnetic field along the guideway provides the propulsion system of the Transrapid. The key to the stability of the magnetic levitation system depends on maintaining the correct distance between the support magnet and stator pack, as well as between the guidance magnet and the guidance rail (see illustration below). The gap between the magnets and the guideway is precisely monitored by the control system, which make it possible to detect even the smallest inaccuracies in the position of the guideway components.
The Guideway Monitoring System monitors the guideway of the Transrapid while it is in transit. The centralized control system together with inductive gap sensors, which are integrated in the levitation magnets, monitor the clearance between stator and support magnet, as well as between the guidance rail and guidance magnet. Depending on the gap widths detected, specific signals are transmitted which indicate the position accuracy, or inaccuracy, of the guideway components. In turn, magnetic regulation units can adjust the magnets, which then correct the gap widths.
For reasons of safety and maintenance, it is also important to be able to locate changes or damages in guideway. Therefore, positioning signals are used and recorded during the entire ride. In the GMS, this location data is recorded and compared online to predetermined set values, via a CAN interface which connects the GMS and the central vehicle diagnosis system.
There are GMS systems in two of three Transrapid maglevs, which are currently in operation in Shanghai. During every trip and at every speed, measurements are recorded automatically. A system consists of one processor each for support and guidance. As soon as the train is activated, the system switches on and operates fully automatically.
