timing pulley becoming magnetized (PROXIMITY) issue.

For what ever reason, we have a piece of equipment that employs

2 hollow shafts both with timing pulleys on the end of each and the inside pulley gets magnetized.

The inside unit happens to be connected to the outer hollow shaft. these 2 shafts turn at different speeds and such that we have prox's mounted on a nonferrous plate aligned vertical into the timing teeth of these pulleys.

just picture 2 hollow shafts, one fits inside of the other, both having a pulley connected to them on the same end.

Both Prox are of the same type etc, I discovered a problem where the inside pulley had critical issues allowing the prox to properly sense the passing timing teeth. At slow RPM's it seems to work fine how ever, as RPM's increase the sensor goes into a latched output effect and simply stays in a constant on state, this is obvious via the monitoring equipment connected to it and scope I used. Pulling the prox away from the pulley allows for higher RPM's to develop before the output turns to a constant one state.

These units are basic N.O. NPN output..

Trying to assess as to why the pulley becomes magnetized which is causing the problem here.

I guess a mechanical engineer may have an answer to that. I did observe a mechanical thumping noise that could be a bearing issue on that shaft that has the magnetized pulley.

Apparently hitting it a few times with a hammer fixes it for a short period. I'm not a mechanical engineer but I do have some ideas in the back of my head on how to neutralize the mag in the pulley..

Any idea's?

Reply to
Jamie
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What sort of proximity sensor? There are quite a few ways of measuring proximity, and iit would help if we knew which one was being used - manufacturer and part number would be even more helpful.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

Maybe have the pulley pass through an AC magnetic field to prevent it from building up magnetic flux? Like a degaussing coil or tape eraser.

- Tim -

Reply to
Tim

Ye's. You don't pluralize with an apostrophe.

Reply to
a7yvm109gf5d1

And how does that help me with my question?

Oh wait, you're useless. How could I have made such a mistake!.

My apologies.

Reply to
Jamie

we found the problem.

I had to dig out some old reference material I have here and a little on line probing kind of jog the old memory.

This particular timing pulley has a disc brake attached to it that is bolted on the back side of it. After a while from use of the brake, the timing pulley which has it's teeth perpendicular to the surface of the disc brake with a unsymmetrical pattern causes the pulley to become magnetized over time, with use of the brake system.

This effect can be seen in the use of drill bits where friction causes the bit to become magnetized because of the unsymmetrical shape of the bit at the end.

Getting back to the pulley, when the RPM's start to pick up the small magnetic field in the pulley effects the prox and causes it to lock on.

We tried inductive and Hall. Both have the same problem. The hall is worse.

I'll do have an idea that I once did years ago to remove the effects of a magnetized slide bar and that was a shorted coil being placed near the moving magnetized metal so that it wouldn't disturb the sensors ahead.

Reply to
Jamie

it helps you ask it correctly!

Reply to
Jasen Betts

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