On 29 Aug 2005 04:17:01 -0700, "Dave" wrote:

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?

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.