Dynapar has a series of encoders: the HDN and DHP shaftless encoders.. As the video below shows, the encoders are completely contactless. You put a magnet onto the end of the shaft being monitored, and the encoder monitors the changes in the magnetic field as the shaft rotates. Because you don’t need any contact with the encoder, it’s very easy to use in applications where you would normally need a shaft and a seal. They even show the encoder working in a fish tank!

You can find more information in Dynapar’s press release and in a sample datasheet data sheet for the encoder.