phototube current meter

phototube current meter

[′fōd·ō‚tüb ′kə·rənt ‚mēd·ər]
(engineering)
A device for measuring the speed of water currents in which a perforated disk, which rotates with the current by means of a propeller, is placed in the path of a beam of light that is then reflected from a mirror onto a phototube.