Re: Proximity Switches

From:         ehahn@mallard.mitre.org (Ed Hahn)
Organization: The MITRE Corporation
Date:         27 Jun 96 12:56:53 
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In article <airliners.1996.1046@ohare.Chicago.COM> Al Hrovat <ahrovat@cfsmo.honeywell.com> writes:

ah> I understand that modern aircraft use a magnetic sensor called a
ah> proximity switch to determine the position of landing gear, doors,
ah> etc.  Does anyone know why this arrangement is used instead of a
ah> simple mechanical switch?  Are the magnetic pick-offs more
ah> reliable than a simple switch?

The prox switches (in theory) are much more reliable than the older
mechanical switches, as they are sealed from the environment and need
no adjustment to ensure proper operation.  (As opposed to a mechnical
switch which must be adjusted to ensure that the switch reads "closed"
at the appropriate location in the mechnical travel, depending on the
application.)

The principle of operation is very simple; the magnetic pickup can
sense an change in inductive impedance when the appropriate metal is
touching the surface over the pickup.

This method is actually quite analagous to the turn-lane sensor loops
which are buried in the roadway and tell the traffic light controller
that a car is at the intersection.

ed

--------   Ed Hahn | ehahn@mitre.org | (703) 883-5988   --------
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.