RPM reading using a Hall sensor

Professorwiz

I was looking at the article here.
http://www.parallax.com/html_pages/robotics/machining/RPM_display.asp
I was wanting to do the same thing and update my CNC spindle, but it looks like he has the magnet on center of the spindle.· I don't understand how the unit would give pulses if the magnet is just spinning, on the current spindle I have they put a magnet mounted onto the pully on the side and it passes by the sensor.
I read the sheets and it looks like it shows it picking up differences in material and not a magnet.· I'm pretty confused.
Russ

Dave-W

Russ,
On a round magnet the outside edge will give you the necessary pluse. Half of the outside is North and the other half is south. So, the sensor must be placed off center to get the required input.

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D. A. Wreski

Professorwiz

Right, but in the article, he has a picture of him machining the part, and he's holding it in a 3 jaw chuck.· It doesn't look like it's off center.· He has the pickup what looks like directly above it.· Perhaps he has it off center.

Russ

Capt. Quirk

It doesn't matter where you put the Hall Sensor, so long as the numbered side of the sensor·has a clearence of·1mm or less. If your using the Melexis Hall sensor, the south pole must be facing up. Use a compass to determine the pole.

The magnet can be mounted to the surface of the spindle, resesed or covered by a non ferrous material.

Count works real well if that's the only thing your doing, besides displaying it on an LCD. If not Bean wrote some good code for the SX, that's based off only a single revolution, it's in the best sx threads.

Bill


btw, the hall goes low·as it passes·the magnet.