Every airplane needs a compass like this one, it's
mandatory by FAA/JAR or
the more modern version we bought
In flight this is your main heading information.
Some airplanes are equipped with a directional gyro.
It just looks like the compass and is giving you the same information.
However the working is not magnetic as your compass, but a gyro
is doing the work.
Both principles have disadvantages
Gyro's are running a way over time and the compass inertia is screwing
up the heading.
So by using both people hope to
have a better heading approximation.
Gyro systems need an update at certain elapsed flight
By using a digital compass module, we can give feedback
to the gyro system.
The HMR3000 Digital Compass Module is an electronic
compass that outputs heading along with roll and pitch readings.
This electronically gimbaled compass gives accurate heading even
when the compass is tilted up to 40 degrees. The highly reliable
HMR3000 is a completely solid state device with no moving components.
It is a low power, small device, housed in a non-magnetic metallic
enclosure. It is easy to install on any platform
The HMR3000 consists of three magneto
sensors and a liquid filled two-axis tilt sensor to produce tilt
compensated heading data. A microprocessor controls the measurement
of the sensors, and all the parameters
that control the operation are stored in an EEPROM. The output sentences of the
HMR3000 conform to the NMEA 0813
standard for Marine communication.
We bought the stuff at Digi-key, ( CAS-rating )
They are cheaper than Honeywell and
you can order more items.
HMR3000 have a large field range of ± 1G
(± 100 mT), compared to
0.65 G (65 mT); the maximum of earth’s total magnetic field,
Baud rate is user configurable to 1200, 2400, 4800, 9600, 19,200
We use 19200 which gives good graphics responds.
The only important thing we need is the Heading, Pitch and Roll
$PTNTHPR, Heading,Heading Status,Pitch,Pitch Status,Roll,Roll Status*hh $PTNTHPR,85.9,N,-0.9,N,0.8,N*2C
This is updated 825 times per minute. 13.75Hz
The HMR300 was only intended for compass info, however the roll
and pitch info is present.
It's limited to 45 deg.
So that's why we still need gyro's in the system!
But it looks pretty fancy.