Transducers in use on The BA London Eye

The British Airways London Eye is a high profile attraction on the bank of the Thames, offering a unique visitor experience. Cable extension transducers supplied by Graham & White Instruments, are being used in an innovative application to monitor vital aspects of the operation.

The engineering design and production of this triangulated steel tube structure had to take into account numerous critical factors such as fatigue, wind speed, thermal effects, manufacturing tolerances etc. All variables when factored into the final design were to produce a structure which was above all safe, reliable, gave easy passenger access, and with back-up systems for reliability and safety.

Two variables requiring constant monitoring are the rotational eccentricity of the wheel in both vertical and horizontal directions. Both are critical to the safe and correct positioning of the passenger platform in relation to the 32 Capsules, each of which could be in a slightly different position, with the wheel constantly moving at a 250mm per second load/unload speed.

WGH Transportation Engineering were charged with designing this element of the project, and chose the WS-10-500 cable extension transducers which offered a cost effective reliable and robust engineering solution to monitoring these two variables.

The transducer is housed in a compact rugged IP65 body containing a drum on which is wound a flexible steel cable, a tensator constant torque motor, and a potentiometer. The cable is attached to the moving element, and the body fixed to a stationary surface. As the element moves in relation to the transducer body the cable is drawn from the drum, thus rotating it, and driving the multiturn potentiometer. The tensator motor maintains a constant force during extraction and provides the “Pull” to return the cable. An applied voltage on the potentiometer provides the variable output signal which is linear and proportional to movement.

Duplicate pairs of Transducers are used to monitor the horizontal and vertical movement of pantograph type power collector arms registered on the wheel rim. This displacement information enables the platform control system to respond to positional changes of the wheel.

The passenger platform, curved on a 65m radius, is constructed using 18 “fingers”. Each can be individually adjusted in the horizontal direction, while the whole platform can be raised or lowered by 10 electrically driven jacks, as determined by the corrective signals generated from the rim monitor.

Servo motor drives move the fingers in and out from the platform edge, and each employs a WS-10-500 transducer to monitor the movement. This gives a cross check between the servo motor and absolute position, thus verifying the finger movement. This ensures that the platform is positioned correctly in relation to each capsule, ensuring safe entrance and exit for the passengers, and with fail safe monitoring.

For more information, please contact:

Graham & White Instruments Ltd. 135 Hatfield Road, St Albans. AL1 4LZ. UK.
Tel: +44(0) 1727-861110 Fax: +44(0) 1727-844272

January 2000 - Ref: 9252


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