Hall Effect sensor design - opposite input

[zepto-]

I am terrible with electric. I just need some guidance on reconfiguring a hall sensor to read the opposite input.

I have an analog tachometer from the '80s that was used to sense a groove on a grounded, spinning disk.

I want to use the probe (which has 3 wires) to sense a raised piece of metal in the same conditions (grounded, spinning disk).

I have a three wire sensor for both arrangements. When using the sensor that is intended for the raised metal design, the tachometer does not read the signal.


I am familiar with the physics involved and could figure out the math, I am just unsure about where to start, or what key terms should be researched.

All suggestions otherwise are welcome.

[Bob S]

Is there a magnet somewhere? Hall Effect sensors are sensitive to magnetic field polarity. Reversing the polarity of a magnet will reverse the sign of the pulse.

A bare Hall Effect probe looks similar to a Wheatstone bridge connection with 4 wires. A linear analog output probe with a differential amplifier and temperature compensation has three wires. Do you want a linear or nonlinear (2-state) output? What are the part numbers on the sensors?

Bob S

[zepto-]

Yes, the magnet is in the sensor. There are coils around the magnet and the moving metal (or lack of metal) creates the flux.

Type 2 in the picture is the intended use of the gauge I have, but I want to use it to sense type 1.
http://physicsforums.com/attachment.php?attachmentid=29698&d=1289177311

I really wish I had the vocabulary/ experience to keep up with you, but I am pretty sure this is not a Hall probe.

The 'probes' in each type provide the magnetic field to sense the movement of a grounded conductor.

[Bob S]

Without analyzing it, I would say that the changing inductance in the coil produces a voltage pulse; I = V dL/dt, so you get either a voltage or current pulse when the gap passes by. The raised piece of metal should be at least as thick as the groove is wide, possibly wider because of the lack of iron in the vicinity. In any case, changing the polarity of applied voltage will change the polarity of the output. Going from a gap to a raised piece of metal will also change the polarity. A little laminated iron around the coil may help also.

Bob S