Photo/proximity sensor?

I'm looking for some sort of sensor to use on a center pivot irrigation
system. These are outdoor conditions with water, dust and a range of
temperatures.
The sensor needs to close a circuit to activate a 110VAC relay. It needs
to detect something like a flat metal plate or maybe some sort of reflector.
The sensor would have to work even if the sensor to activator alignment
varies. The alignment might vary as the depth of the pivot wheel track
changes through the season. Operating range of maybe 2 feet. It should not
activate because a corn plant or weed happens to get in front of it.
I did a search and found retro reflective and diffuse sensors. The
proximity sensors I found didn't seem to have enough range.
Thanks for any guidance or comments.
Dean

Dean, for an operating range of 2 feet, you will be needing some kind of optical sensor for sure. There are other types around (eg. ultrasonic) but over that sort of distance you need a tightly focused spot to switch with any sort of accuracy.

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manufacture a range of all kind of optical sensors. I have used a stack of sensors from various manufacturers (Turck, Banner, Vega, Siemens, AB, P+F, etc. etc.) and have found the Sick stuff to be a bit more expensive than the others, but heaps more reliable.
You could either use a focussed retro-reflective sensor (eg WL24) or an optical proximity with background suppression (eg. WT24) but there are heaps of others you could use too. The Sick retro-reflective sensors come with a polarising reflector so that the sensor will only trigger if it sees the reflector - even shiny metal won't do it. If you contact your local rep. he will put you onto the right one for your application.
HTH, Cameron:-)

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