Magnetic Reed Switch limitations

[belwar]

Hi all,

Does anyone know off the top of thier head what the RPM limit is with Magnetic Reed switches? I did a quick search and could come up with nothing.

I'm adding multiple counters to my winder; one to measure turns of the bobbin and one to measure the rotation on the traverse cam mechanism.(overkill I know, but I want precision, and im a tinkerer). Optical is likely not an option.

belwar

[Joe Gwinn]

Does anyone know off the top of their head what the RPM limit is with Magnetic Reed switches? I did a quick search and could come up with nothing.

Reed switches are not rated in rpm because there is more to it than that. Reed switches close and open in a few milliseconds each way.

Electronic counters such as the Red Lion CUB3 require a minimum pulse width of 5 milliseconds; shorter pulses are ignored. If we assume that switch closure and switch opening both take 2.5 mS, that's another 5 mS, for a total of 10 mS. At least 5 mS is required between counts, so the entire cycle is 15 mS. 60(1/0.015)= 4000 rpm.

It's your problem to arrange the mechanics and magnetics to ensure that the switch is opened and closed for the required periods even at high speed.

I'm adding multiple counters to my winder; one to measure turns of the bobbin and one to measure the rotation on the traverse cam mechanism.(overkill I know, but I want precision, and i'm a tinkerer). Optical is likely not an option.

What's wrong with optical?

[chevalij]

Optical is dirt cheap and extemely reliable. No bounce to worry about, good up to about 10k rpm.

[John_H]

I've tried reed switches, hall sensors, and optical for triggering counters. I wish I would have tried optical first instead of last. It's simpler then you think. What are you using for a counter?

[belwar]

I dont have an objection to using optical, but I was under the impression that an optical censor had to be inclosed in darkness. It's not possible on my minder. To be honest, I'm having a hard time grasping the optical sensor concept.

My current counter is a direct rotating shaft counter similar to mcmaster carrs 1697T32 part number. It's driven by pulley with a 1:1 ratio. I want to eliminate that counter and add several other counters to various pulleys and uliminately my cam disk.

[chevalij]

No it doesnt' have to be enclosed. If I put a flashlight in your eye in the middle of the afternoon, it would still be bright Besides, the distance between the LED and the sensor is normally only about 0.200 apart. Not a lot of light gets into the small gap.