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Peter Hollings wrote, in [9616],-

"I think electronics has opened up better and cheaper solutions than
contemplated by Vannevar Bush.  Here is a project in the field of robotics
from a few years back that addresses a similar problem of maintaining
vertical orientation: http://www.dprg.org/projects/2003-01a/ . A Google
search for "integrated circuit accelerometer" turns up a large number
interesting and relatively inexpensive devices. Similarly, there are
compasses, etc. In fact, I believe a whole Sextant might be automated and
probably the military has done so."

Response from George-

I have severe doubts about that. There's a world of difference between an
application that needs to know little more than "which way is up", and an
instrument which is capable of sensing the vertical to a minute, or a very
few minutes, of arc. In respect of the stability of the output, in terms of
sensed angle of a piezo accelerometer, particularly against changes in
temperature, these devices are at present woefully lacking. They are, of
course, getting better all the time, but I suggest they have a long way to
go yet before doing the same job as a precise bubble.

The same fundamental problem, in distinguishing gravitational acceleration
from the unwanted accelerations caused by wave disturbance, faces such
electronic devices, just as it challenges mechanical contrivances such as
that of Bush. The combination of accelerometer with a vibrating "gyro" can
indeed help to filter out the wheat from the chaff. In that respect
electronics does have a distinct advantage over mechanics, in that precise
filtering is easier to implement in circuitry than it is by weights,
springs, and viscous damping.

Such combinations could do a useful job, aboard, in applications where less
precision is required. I'm thinking particularly of providing compensiation
for ship's motion for a magnetic sensor, in making a strap-down magnetic
steering compass that avoids gimballing. We've discussed such matters
before, on this list.

If more sophisticated technology (the ring-laser "gyro"), ever comes down
from present stratospheric prices to those that the rest of us can
contemplate, then indeed a precise electronic artificial horizon could
become very practicable.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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