TESTING THE 720-12R WESTACH ROTOR SHAFT HALL EFFECT SENDER UNIT.
This sender can be simply yet accurately tested either in situ in the helicopter or as a “bench test”. If in situ then it can be tested whilst connected to the rotortach and I’ll do a separate post for that that also includes testing the rotortach itself.
However this thread is for testing the hall effect sender when it is NOT connected to the rotortach. It is a simple but important fundamental test of the sender itself, and I think this is a particularly useful test when there appears to be some problem with the rotor speed display and there is a difficulty identifying whether the problem is actually with the sender, the rotortach, or the wiring.
All you will need is a multimeter, a resistor, a magnet, and a voltage source - anything between 5V – 12V.
NOTE: the sender unit expects to see the South pole of a magnet. It won't work with a North pole.
A few comments relating to the alignment of the magnet ring :-
1/ The active part of the hall effect sender is dead centre in the middle of the threaded barrel. Ensure that your magnet ring is vertically aligned so that the centre of it passes over the centre of the sender. If it is too high or low then the sensor in the sender may not “see” the magnet. There have been a couple of different styles of magnet rings over the decades, but the same theory holds.
2/ Don’t adjust the sender so that it is almost touching the magnets. It’s not necessary. The actual hall effect sensor semiconductor used in the sender is extremely sensitive to shock or any impact. If a magnet hits or touches the epoxy face of the sender it is likely to damage it. Typically 1.5-2.0mm gap should work fine.
Instructions are in the drawing. Let me know your comments and if anyone has any questions.
![[Image: Hall-Effect-Sender-test-circuit-001.jpg]](https://i.ibb.co/tgNMj4T/Hall-Effect-Sender-test-circuit-001.jpg)
This sender can be simply yet accurately tested either in situ in the helicopter or as a “bench test”. If in situ then it can be tested whilst connected to the rotortach and I’ll do a separate post for that that also includes testing the rotortach itself.
However this thread is for testing the hall effect sender when it is NOT connected to the rotortach. It is a simple but important fundamental test of the sender itself, and I think this is a particularly useful test when there appears to be some problem with the rotor speed display and there is a difficulty identifying whether the problem is actually with the sender, the rotortach, or the wiring.
All you will need is a multimeter, a resistor, a magnet, and a voltage source - anything between 5V – 12V.
NOTE: the sender unit expects to see the South pole of a magnet. It won't work with a North pole.
A few comments relating to the alignment of the magnet ring :-
1/ The active part of the hall effect sender is dead centre in the middle of the threaded barrel. Ensure that your magnet ring is vertically aligned so that the centre of it passes over the centre of the sender. If it is too high or low then the sensor in the sender may not “see” the magnet. There have been a couple of different styles of magnet rings over the decades, but the same theory holds.
2/ Don’t adjust the sender so that it is almost touching the magnets. It’s not necessary. The actual hall effect sensor semiconductor used in the sender is extremely sensitive to shock or any impact. If a magnet hits or touches the epoxy face of the sender it is likely to damage it. Typically 1.5-2.0mm gap should work fine.
Instructions are in the drawing. Let me know your comments and if anyone has any questions.