Re: Proximity Switches

From:         Chris Hall <>
Organization: Airborne Display Limited
Date:         27 Jun 96 12:56:54 
References:   1
Followups:    1
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In article <airliners.1996.1046@ohare.Chicago.COM>, Al Hrovat
<> writes
>I understand that modern aircraft use a magnetic sensor called a proximity
>switch to determine the position of landing gear, doors, etc.  Does anyone
>know why this arrangement is used instead of a simple mechanical switch?
>Are the magnetic pick-offs more reliable than a simple switch?

The advantages of a proximity switch over a normal micro switch are
many, but the most important advantage is that they are absolutely
sealed against the environment.

Wheel wells are dirty places, and mechanical switches pick up their
share of the muck flying around. Eventually, seals fail and the switch

A magnetic reed switch also has a longer operating life than a
mechanical switch. The life of the reed can be measured in millions of
operations before it is likely to fail.
Chris Hall