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?
Thanks
People I worked with at one time were more concerned with the grease, oil, and dirt than with ferrous chips, so they tended to use magnetic sensors more. The optical can be more precise, but indeed are subject to obscuration. The applications we were dealing with was on engines (autos, trucks), but I got the feeling the same was true for general machinery. One had to be careful to enclose optical sensors if dirt and grease were a concern.
Gear tooth sensors are usually hall effect (magnetic). Sealed optical encoders are used on rotating shafts too. Some lower-speed machines use proximity switches, aka proxis or ECKO's (Eddy Current Killed Oscillator) which are highly immune to both chips and dirt, but are not as fast as Hall or optical.
"Industrial Machine" includes a huge variety of requirements and environments. Which is the "right" sensor depends greatly on the specific application.
"Dave" wrote in news:1125314221.369142.83390 @f14g2000cwb.googlegroups.com:
Depends on the application Dave. If you are sensing metal in close proximity to the sensor, you will most likely be using a normal capacitive / hall effect proximity sensor. These have a limited range, depending on the barrel size. (See Balluff BES series - Balluff.com) If you need to sense items farther than say 3-4 mm, there are several options. There are retro-reflective, many with adjustable ranges, these contain both the infared emitter and receiver in one body. There are two types, one requires a reflector mounted some distance away, the other type does not require a reflector. (See Balluff BOS series) Then you have the fiber-optic beam sensors, in which you have separate emitter/receiver, placed some distance apart. There is a light beam that travels between them. (See Banner OSFX series ) Then you have the various laser sensors, these are programmable for sensing distance (See Keyance corp) You also have untrasonic type distance sensors (See Banner/Turck website)
Hall Effect sensors
Gunner
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...
Banner uses the term "excess gain" to indicate how sensitive a given sensor is to dirt or other attenuation of the light beam.
Photosensors of the sort Banner makes are relatively expensive compared to inductive proximity sensors, which have become a commodity item in the common configurations. They're available for around $20.
Air cylinders can be ordered with magnetic pistons that will trigger Hall effect or reed switches that clamp to the cylinder.
And sometimes an old fashioned mechanical limit switch is the best solution.
Ned Simmons
As Ned sed. But be cautious about one thing.
I design automation for pyrotechnic manufacturing. 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 pisser!
LLoyd
Yikes, hope your liability insurance is paid up . 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.
If it was only several hours you got off easy . 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
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