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- Posted on
July 13, 2003, 2:54 pm
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One method to reduce error is to strap on a GPS unit and combine
measurements. I think Analog Devices has an application note for this. They
went in to quite a bit of detail and discussed several approaches. GPS +
accelerometers seem to be the best of both worlds.
Here's what Analog says:
In this application, position is determined by dead reckoning (double
integration of acceleration over time to determine actual position). Real or
fantasy? See answer G.
G. Personal navigation: Dream Land. Long term integration results in the
accumulation of error due to small dc errors in the accelerometer,
integrator input circuitry, wiring thermocouples, etc. Double integration
compounds the errors (t2). Without some way of "resetting" the actual
position from time to time, huge errors result. This is analogous to
building an op-amp integrator by simply putting a capacitor across it. Even
if the accelerometer's accuracy is improved by ten or one hundred times
better than currently available, huge errors would still eventually result.
It would just take longer to happen.
Accelerometers can be used in conjunction with a GPS system when the GPS
signals are briefly unavailable. Integration over a short time (a minute or
so) can give satisfactory results. Click here for more information about
navigation. Go to next question.
My personal favorite is:
The accelerometer senses low-frequency vibration in the passenger
compartment, and the noise-cancellation system nulls it out, using the
speakers in the car stereo system. Real or fantasy? See answer J.
Car-noise cancellation: Dream Land. While the accelerometer has no trouble
picking up the vibration in the passenger compartment, noise cancellation is
highly phase-dependent. So while we may cancel the noise in one location
(say around the head of the driver), it will probably be increased at other
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