Liseberg in Gothenburg, Sweden has the biggest amusement park in the Nordic Countries. One attraction is the Lisebergs Tower, which is 116 meters tall. This has a glass-sided elevator cabin in which up to 80 persons can travel to near the top where it rotates about its own axis so that they can see Gothenberg below. An old relay-based control system needed to be replaced and for safe and effective control a major challenge was to organize communications with the elevator cabin.
The solution was to use wireless PROFINET. One wireless access point (WAP) is placed in the elevator cage, around which a 'leaking antenna' cable is located. Another 'leaking antenna' is placed vertically on the outside of the tower so there is always a data connection with the elevator cabin. The antenna cables each have one client connected - one 90 meters up in the machine-room, the other in the cabin. From the top client a fiber optic cable runs down to the control system located underneath the tower. From there it goes to the main Liseberg network. Most of the drives are connected via PROFIBUS and PROFINET in nine cabinet locations. Failsafe signals are transferred via PROFINET too. Since all drives and HMI devices are integrated in the same system all nodes in the system can be accessed from any location. The control system knows the exact target position of the elevator and also the velocities to run. The PLC calculates the deceleration ramps while fixed sensors check the elevator's position. The monitor system is double redundant: one system controls the positions and one watches the position monitoring system. Faster operating speeds and softer decelerations are now possible.
Using wireless PROFINET with a double redundant monitoring system solves all problems at once, say staff at Liseberg. Communications with the elevator cabins is well organized and, further, the level of safety they now have with PROFIBUS and PROFINET is far superior to that of previous systems.