>I'm trying to build an underwater tachometer for an AUV (autonomous
>underwater vehicle) being built at the University of Victoria by a group
>of engineering students.  What we hope to do is the standard shaft
>encoder scheme where one determines speed by counter the number of strips
>that pass by a photoreflector for a given time period.  As such, we are
>looking for an IR photoreflector that is contained in a waterproof casing
>(maximum depth we will be going is 30 feet).  Can anyone recommend such a
>photoreflector or an alternative way to match the speed of two motors?

Search for fiber optic coupled industrial optocouplers. Then you can put
them in a dry place and glue the fiber head into a suitable flange or
gland as you need.

Peter

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