Jack Russell

So what is up with the Garmin Electronic compass in the new G76cs. In an
open field it registers one way and in a car it is WAY off. I understand
this with a magnetic compass but are electro-compass's going to fail as
well??

sniper-joe

Yes - same thing with the electronic compass ... the magnetic sensor
inside the GPS will detect stray magnetic fields inside the car just
like with any plain jane compass.



Jack Russell wrote:

> So what is up with the Garmin Electronic compass in the new G76cs. In an
> open field it registers one way and in a car it is WAY off. I understand
> this with a magnetic compass but are electro-compass's going to fail as
> well??
>
>
>

Bob

It's called magnetism. Doesn't care if it is displayed by a needle
or electronics, it's affected by magnetic fields which abound in
the electric circuits (Alternator, wiper motors etc)
Use of the satellite compass will cause that to dissapear, but
when you stop, your out of luck.

Jack Russell wrote:
> So what is up with the Garmin Electronic compass in the new G76cs. In an
> open field it registers one way and in a car it is WAY off. I understand
> this with a magnetic compass but are electro-compass's going to fail as
> well??
>
>

David Lee

Easily calibrated out - after all magnetic compasses are used in steel
ships!

A worse problem in an electronic compass with only a two axis sensor (as in
Garmin GPS) is the vertical component of the earth's magnetic field. The
Earth's field dips towards the poles, the angle increasing with distance
from the equator - at latitudes in England (or New York) the angle is about
70 degrees, so the field is predominantly vertical! This is not a problem
for a magnetic compas since it's mode of suspension means that it will
always balance horizontally and so will indicate the horizontal direction
towards north. However a two-axis electronic instrument will indicate the
direction of the component of the field in the plane of the instrument and
will only give accurate results if it is held absolutely horizontal (or
possibly at exactly the same angle to the horizontal that it was at when
calibrated). Tilting the instrument towards magnetic north or south won't
have much effect on the result but even small tilts in an east or westerly
direction can cause very large errors in the measured bearing. So unless
you can mount it on Gimbals it's only much use on the flat or when going up
or down north-south oriented hills!

David

Bob wrote...
> It's called magnetism. Doesn't care if it is displayed by a needle
> or electronics, it's affected by magnetic fields which abound in
> the electric circuits (Alternator, wiper motors etc)
> Use of the satellite compass will cause that to dissapear, but
> when you stop, your out of luck.
>
> Jack Russell wrote:
> > So what is up with the Garmin Electronic compass in the new G76cs. In an
> > open field it registers one way and in a car it is WAY off. I understand
> > this with a magnetic compass but are electro-compass's going to fail as
> > well??
> >
> >
>

Bjorn Gabrielsson

Easily calibrated out - after all magnetic compasses are used onboard
airplanes.

You need to add some accelerometers to sense attitude. In case you
have severe dynamics some gyros might be added too.

You can read more on

http://www.ssec.honeywell.com/magnetic/landnav.html

All Garmin would have to add is dual axis accelerometer, something
like a ADXL203 from Analog Devices. A 8 lead 5x5x2 mm chip, very low
power.

That could give the 76 sensor models good GPS reception at the same
time as a funcioning compass. The present compass should be held
horizontal, while the GPS antenna should be kept vertical for best
signal reception.

To use the present 76CS/S in a car you need to mount them horizontal,
which is hard to do if you want to have a good viewing angle of the
screen.

My 2 (euro)cents

/Björn


"David Lee" <davidlee_malvern@dont.use.this.bit.hotmail.com> writes:

> Easily calibrated out - after all magnetic compasses are used in steel
> ships!
>
> direction can cause very large errors in the measured bearing. So unless
> you can mount it on Gimbals it's only much use on the flat or when going up
> or down north-south oriented hills!
>
> David
>
> Bob wrote...
> > It's called magnetism. Doesn't care if it is displayed by a needle
> > or electronics, it's affected by magnetic fields which abound in
> > the electric circuits (Alternator, wiper motors etc)
> > Use of the satellite compass will cause that to dissapear, but
> > when you stop, your out of luck.
> >
> > Jack Russell wrote:
> > > So what is up with the Garmin Electronic compass in the new G76cs. In an
> > > open field it registers one way and in a car it is WAY off. I understand
> > > this with a magnetic compass but are electro-compass's going to fail as
> > > well??
> > >
> > >
> >