Faulty reed switch?

Hi all. Hope you are all keeping safe.

I have a reed switch on a PCB that normally sits next to a magnet on a wheel which obvs activates it. I believe it is a NO switch and is some years old.

I know it is not working as it should as the item has stopped working and is pointing towards this sensor/switch.

  • When I measure across the switch when its operational (wheel and magnet spinning past) it doesn't do anything, stays CLOSED. Ie. doesn't flick on, off, on, off as it should.

  • When I removed the PCB and SW away from the magnet it reads OPEN.

  • When I put it near the magnet/wheel (both spinning or not) it goes to CLOSED.

Is it possible that this switch has gone bad and lost the ability to switch between open and closed quickly or has some issue with the magnetism over time that means it won't work properly?

Also, from experience, is the magnet ever at fault or is that not likely to breakdown over time?

Many thanks,

Sounds like its gradually been magnetized and needs degaussing.

My experience: I have commercially made anemometer head with a reed switch that is opened/closed twice per revolution of the cup assembly. It became erratic and I finally took it down to see what the problem was. All the reed switches I have ever seen consist or TWO flexible arms which make contact together when magnetized. I have never seen a failure.

The reed switch in my anemometer was a SINGLE piece reed which made contact with a fixed contact point. The fixed contact point seems to have become slightly magnetized and would not immediately release the contact. I had one standard reed switch small enough to replace the original one and the failures went away.

See what you have for a reed switch and replace it if it's like the one I found.