Avionics News - October 2023 - 50

THEORY & PRACTICE
Continued from page 49
them is by the technology used.
Using this method, one can divide
them into two groups. One group
uses a gyroscope, and the other uses
electronic means of determination.
Another way of characterizing these
systems is by their location. The
direction sensing instrument can
be mounted in the instrument panel
as part of the instrument used for
display, or the sensing instrument
can be remotely mounted - separate
from the display instrument.
Gyroscopic instruments use a
spinning mass. As you learned in
grade school science, a spinning
mass tends to stay rigid in space.
Engineers design heading indicating
instruments around this principle.
The instrument can use air pressure
or electricity to spin a wheel-shaped
moving mass called a rotor. The
rotor will be mounted in a gimbal
assembly to allow it to remain rigid
while the aircraft moves around
it. The gyro can be mounted in the
instrument panel, or remotely, with
an indicating instrument.
Friction, even a small amount,
will cause a gyro to slowly change
      
      
with a simple directional gyro is
taught to check the gyro indication
against the wet compass every 20
minutes or so, and then correct the
directional gyro indication. Typically,
these adjustments are a few degrees.
An electronic compass system with a
gyro will be corrected automatically. To
correct the compass system, engineers
      
sense the direction of the Earth's
     
       
depending on the manufacturer, but
they all have a few things in common.
      
     
often by 400 hertz. A coupler will
        
magnetic azimuth information obtained
     
detectors must be mounted as far away
from magnetic interference as possible,
typically in the tail or wingtip of a
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50 AVIONICS NEWS * OCTOBER 2023
PIC 1 3 PG Ad 2023.indd 2
8/16/2023 3:07:13 PM
Most heading systems designed this
century are part of an attitude heading
reference system or an air data heading
reference system. We will discuss air
data and attitude in future articles, but
this month we will cover the heading
part of the reference system.
Although an AHRS or ADHRS can use
      
A magnetometer is a sensitive device that
can sense the strength and direction of a
      
Anyone entering a secure area such as
an airport terminal or courtroom will be
familiar with the magnetometers used by
security personnel to check for weapons.
The magnetometers used for heading
determination is much more sensitive
     
     
mounted as far as possible from magnetic
interference.
Thanks to powerful microprocessors,
accelerometers combined with
magnetometers can be used to
    
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Avionics News - October 2023

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