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| Recent developments in sensor technology have opened up the door the electronic
compasses. Just like regular compasses they work on the magnetic principle. They sense
where the North (or south ) pole is and show the information on a display. Now then . What
is the advantage of an electronic compass over a mechanical compass .At first sight
nothing. But .. An electronic compass can track your course and calculate the heading back
to your starting point. Suppose you started
out on 270 degrees , then you did the following +30 - 10 +40 -20. What heading should you
take back ? An electronic compass will be able to tell you .Furthermore , a good
electronic compass is capable of compensating for the presence of metal objects. As you
might know , the accuracy of a mechanical compass is influenced if in the presence of
metal objects.Electronic compasses can compensate for this. |
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Principles of Electronic compasses
In general there are 3 principles in use. Two of these are pseudo
mechanical , and the 3rd is a full electronic compass.
| Encoding disk  |
The principle behind these compasses is similar to that of
a Card-style mechanical compass.Inside a container is a rotating disk. Instead of numbers
on the disk there are markings that are readable for electronics.
A small lightsource ( typical a visible , or infrared LED ) is placed behind this disk.In
front of the disk a number of sensors pick up the code.This
information is then decoded and shown on a display. The disadvantages of these compasses
are the same as mechanical compasses : You need to keep it level , and it is influenced by
the presence of metal objects , or other magnetic fields. |
| 2nd Generation : Hall Sensors
This compass is still an adaptation of the old mechanical
compass. A rotating compass needle inside a body. However the position of the needle is
beeing sensed by a Hall-Sensor. This is a device which can sense magnetic fields .
The device sense the field emitted by the compass needle.A hall sensor has a directional
behavour. It is 'blind' along its own axis. Therefore 2 senors are used which are 90
rotated in respect to each other. A simple piece of electronics can then detect where the needle is. Again this information is
then processed and displayed. The drawback here is that you still need to keep it level
for the needle to rotate. The presence of metal objects can be cancelled to a certain
point. The presence of other magnets can be cancelled completely. A permanent field will
induce a certain signal in both of the sensors. This 'echo' can then be substracted from
the real signal. |
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3rd Generation : Direct Sensing
This compass uses a newly developed sening technique. There are no more
rotating or magnetic parts beeing used. The sensors pick up the Earth's magnetic field
directly.In this compass 3 senors are beeing used. This gives a 3 d vector to the north ,
independent how you keep the compass. You can turn it upside down or tilt it as you want.
It will show you where north is.The compass measures the magnetic field in a 3D
environment. The resulting 3 signals are then digitized and fed to a small microprocessor.
This calculates the vector towards the north
and displays it.This compass has no disadvantages as found in the other types.You do not
need to keep it level ,and it is not influenced by the presence of metal objects.
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For more information about these compasses and or the sensors used you
can follow these links :
| True North Technologies (compass) ITT intermetall ( Hall sensors)
HoneyWell Sensors (3D sensor
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