In article ,
says...

"Ned Simmons" wrote in message
...
In article 1125314221.369142.83390
@f14g2000cwb.googlegroups.com, says...
Are optical interrupters used in industrial machines or are they too
vulnerable to dirt? I'm guessing magnetic sensors might be more immune
except that the magnets might attract ferrous grit. What is the
preferred proximity/shaft sensor?


Optical sensors are widely used. Some are more susceptible
to dirt than others, particularly those that sense
reflected rather than transmittd light. Some good info from
Banner here...

As Ned sed. But be cautious about one thing.

I design automation for pyrotechnic manufacturing.

Yikes, hope your liability insurance is paid up g. My
agent got jumpy just beacause I mentioned that I
occasionally build automation for a medical products
manufacturer, I wouldn't dare mention explosives to him.

One design used dozens
of IR reflective sensors to pick up end-points on various parts. I had
debugged the firmware and tweaked the hardware in my shop before delivering
the unit. It worked nicely.

Imagine my consternation when the very first time we fired it up on site, it
crashed several actions.
Huh?

Well, it turned out the "IR" sensors were just as sensitive to visible light
as to IR. Ambient light (not direct sunlight) from a nearby window was
fooling all the sensors whose targets were illuminated by the window.

Several wasted hours of building guards and shuttering the windows solved
the problem -- but what a ****er!

If it was only several hours you got off easy g. I
remember running into this once or twice, but can't recall
the exact circumstances. Maybe on a machine with a UV lamp
for curing a potting compound? Most photosensors modulate
the light source and tune the detector to be sensitive to
its own source. This is done primarily to eliminate
crosstalk between sensors, but has the side benefit of
reducing sensitivity to ambient light.

Ned Simmons