Proximity rpm sensor detection range

[martik777]

https://www.ebay.com/itm/1PC-4-Digi...var=521326555147&_trksid=p2057872.m2749.l2649

Specs state 1-10mm range but I can't get mine to work over .25mm gap between sensor and magnet. Anyone else have experience with these?

 

[MikeInOr]

I ordered mine about a week ago and it has not shown up yet. I will let you know when I give it a try. I was under the impression that we are supposed to use a magnet mounted to the shaft we are sensing?

 

[hman]

Martik - Are you testing the prox (actually a Hall effect sensor, not strictly a "proximity" sensor) "by hand" on the bench, or with the magnet mounted on the actual shaft and rotating at realistic speeds? This might make a difference, because rate-of-change may be what the sensor is most sensitive to. You might also want to try with a different magnet. A nice size rare earth magnet to use would be ¼" or 5/16' diameter and ⅛" thick. The magnet pictured in the listing looks like it's only about 1 mm thick. Range of the Hall effect sensor does depend on the strength of the magnetic field.

Of course, you do have the remedy of returning it. Amazon is pretty good about that, and if you can't get it to work, you definitely have justification.

I used to use lots of prox and other sensors in the equipment I designed and built while at HP. Bought one of those tachometers a couple years ago, but wired it to a reflective fiber optic photosensor. Didn't have a good way to mount the supplied sensor.

 

[MikeInOr]

I believe I read that if the sensor isn't picking up the magnet well you should try turning the magnet over so the opposite pole is facing the sensor.

 

[martik777]

I've tried magnets 2x the size. It seems hit and miss which may be explained by the random flipping of the poles. It's mounted on the lathe and I have some adjustment so it's working good now. I was just disappointed it needed to be so close to the sensor.

Edit: I just flipped the magnet and it stopped working, flipped again and it works. Good tip re: the poles!

I am using a 12VDC supply, maybe a higher voltage would increase sensitivity?

 

[mksj]

Increasing the voltage input will have no effect on sensitivity, there is a voltage regulator, the hall sensors supplied work down to 4.5V. The hall sensors used on these units is polarity specific as mentioned above, I always check the magnet polarity and mark the face toward the sensor. I usually use a neodymium magnet which are much stronger than those provided. There also may be some dampening effect if embedded in steel vs. aluminum, but I typically use a gap distance of 0.1-0.2" with no problem. They will sense further away but may get some error at high RPM.

 

[martik777]

I probably wasted a few hrs not knowing about specific polarity. The supplied magnet looks the same as my other neodymium magnets and works great now that I know about the polarity. Would be nice if the vendor supplied the polarity info!