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    Re: New ways to create false horizons?
    From: Don Seltzer
    Date: 2017 Jul 21, 10:35 -0400

    On Thu, Jul 20, 2017 at 6:13 PM, Pete Solon Palmer <NoReply_Palmer@fer3.com> wrote:
    Maybe there is an electronic AH solution.  The sensors (mag, gyro, accel, gravity) in my smart phone seem to be less accurate than a ball bearing and a toy compass, so I don't see a solution involving phones soon. 

    Ever since I took Frank's course I have been toying around with this idea.  Some years ago I developed some automated test stations for measuring performance of multi-axis MEMS  sensors such as those used in phones and other devices today.

    A two axis MEMS accelerometer is very plausible for determining the gravitational vertical.  The three main error sources are bias offset, scale factor error, and temperature drift.

    Bias offset is easy to deal with, and is conceptually similar to sextant index error.
    Scale factor error is a problem for measuring a wide range of angles.  When simply trying to determine a very small range around 'zero' angle it is of minor concern.
    The most challenging problem is temperature sensitivity of these devices.  Changing temperatures will cause all the other parameters to shift.

    Analog Devices is a leading manufacturer of MEMS multi-axis accelerometers, some costing less than $20.  I once did a rough error analysis of some of their devices and it seemed that it might be possible to achieve a resolution of about 1 or 2 arc minutes around zero.

    Don Seltzer
       
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