On 17-Dec-2003, "Michael 182" wrote:

How does an electronic altimeter work? Is there some kind of pressure
sensor?


Yes. The sensing element is in essence a solid-state strain gauge that
detects atmospheric pressure. This is similar to the mechanisms used in
many blind encoders. The Casio watch and similar electronic altimeters
include means for correcting for variations in barometric pressure.
(However, in the case of the Casio the adjustment is unfortunately not in
terms of sea level pressure but is rather just a means to adjust the
altitude readout. For aviation use you set it on the ground to the airport
elevation and adjust it in flight by setting it against the airplane's
altimeter.

While there are some very sophisticated piezoelectric pressure sensors that
allow for an electronic altimeter to be as sensitive as the good old
expanding bellows mechanical kind, the inexpensive strain gauge mechanism is
not quite as good. Adequate for blind encoding or an altitude watch where
required resolution is on the order of 50-100 feet, but not good enough for
use on an instrument approach to low minimums.
______
Elliott Drucker