Need High Voltage Proximity Switch

[Bernie Hunt]

I'm looking for a 120VAC proximity switch, SPST NO, something like alarms use on doors and windows. Has anyone seen anything like this?

The application is to determine if an x-ray shield is in place. Unfortunately there is no AC in the area to be able to use a relay and low voltage sensors. There are just the two wire that need to be shorted when the shield/door is in the correct position. The previous solution was a reed switch, but the geometry of the shield/door makes this a very difficult solution and the sensor get's destroyed if the user doesn't manipulate the shield correctly. I'm hoping to change to a proximity senor to keep this from happening again.

Thanks, Bernie

[Smarty]

Bernie,

Perhaps an optical sensor using a reflective tape target, an ultrasound sensor which measures a nearby shield's reflection / echo, a ferric / magnetic sensor if the shield has any iron / ferric content, or some other form of non-contact approach or, instead, a weight sensor which relies on the mass of the shield / door using a solid state or other strain gauge?

Smarty

[Paul Franklin]

Do you know how much current you need to control? If it's not too much, say 200-400 ma, you can use an AC prox switch.

search for AC proximity Switch. They are available in NC and NO and change state when close to a metal object.

More $$ than a reed or mechanical limit switch, but very reliable.

If you need more current, just use a mechanical limit switch.

HTH,

Paul F.

[The Daring Dufas]

There are industrial limit switches that will handle the voltage. You might look at a limit switch that has a nylon rod or flexible spring actuator. I've used the nylon rod type and the rod can bend all sorts of ways without damage. Google "nylon rod limit switch".

TDD

[George]

Not knowing your profession, I'll point out that there's a whole world of 'industrial controls' from people like Omron, Square-D, Allen-Bradley. (It's been a long time since I was involved, so the names may have changed.)

But, it sounds like you want a non-contact, line-voltage, proximity switch that operates without power. (ie, the absent neutral.) It's not my area of expertise, but I think the pickings will be slim - maybe just reed magnets.

Finally, I don't know if this is a cross-post, so I'll also suggest sci.electronics.design. Not their primary focus, but there's a lot of knowledge there.

G

[Bernie Hunt]

Thanks everyone for thier input!

The general problem with a regular type switch is that it has to be triggered when the shield is swung into it's correct place, but has to let the shield over swing it's correct place and not trigger.

TDD get the cookie prize for this one. Both Grainer and MSC have a number of whisker tipped limit switchs that I think will do the job. I have to call MSC on monday to make sure their less expensive model has a normally open condition. (It seems normally closed is normal for limit switches, at least that's what Double D's catalog implies) If they do, then that's the chose. If not, then its the more expensive Telemecanique model from Grainger, but I figure it's worth waiting till monday to maybe save $50.

Thanks again everyone, it's great to have a resourse of thinking minds to access.

Bernie