APPLICATION STORY

          
 

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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