Compass

 

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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. img69.gif (2321 bytes)

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.

 

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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.

 

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