Miniature draw wire sensor used in gearshift indicator system

When West Surrey Racing (WSR) needed a rapid solution to improve the gearshift indicator system on its FIA World Touring Car Championship BMW 320si, they chose MTA series cable-extension transducers from motorsports sensor specialists Variohm EuroSensor. The neat solution was delivered on the same day as the initial enquiry, in time to meet the deadline for FIA race approval, and easily installed and electrically interfaced to a simple dashboard display to indicate the selected gear from the gear stick position.

The compact miniature 'stringpot sensor' from Celesco was chosen for its installation simplicity and robustness. The 35mm diameter x 13mm thick sensor provided the distance measurement directly from the BMW's H-pattern 5-speed gearshift mechanism without the need to ensure precision alignment, with the integral spring loaded stainless steel cable simply connected to the gear stick. The IP55 rated aluminium housed unit was supplied on an optional mounting bracket that was fixed in a slightly offset position on the car chassis to ensure each gear position returned a different position reading.

WSR chose the smaller of two MTA models with a 75mm stroke and voltage divider (potentiometer) output powered from the car's 12 VDC supply. The high duty cycle conductive plastic potentiometer has an essentially infinite resolution and very long working life, and with a full stroke accuracy of better than +/-0.4 per cent and repeatability of +/-0.02 per cent, it provided more than adequate performance for the application.

With demanding applications in areas such as heavy construction equipment and agricultural machinery, the MTA series is well suited to the arduous environmental conditions that the BMW typically sees throughout a race.

WSR is based in Sunbury-on-Thames and in addition to its eBay-backed FIA WTCC BMW 320si race team, also competes in the British Touring Car Championship and provides R&D, CAD and engineering services throughout the motorsports industry that can accommodate anything from one-off performance prototypes to 'Limited Edition' production.

Variohm EuroSensor also supplies WSR with ride height position measurement solutions using its race proven ELPM series linear slimline linear position transducers. The compact rod-type ELPM provides stroke lengths up to 75mm in IP67 sealed housings.