1307897 Photo-electric indication of flow-rate BENDIX CORP 16 March 1970 [17 March 1969] 12601/70 Heading G1A [Also in Divisions F1 and G4] In a rotary mass-flowmeter a "drag" turbine rotor 36 is driven by a "drive" turbine rotor 22 to which it is coupled by a spiral spring 38, the mass rate of flow being proportional to the product of the speed of rotation and the angle by which the rotor 36 lags the rotor 22. To facilitate determination of said product light reflecting and non- reflecting strips 54, 56, 58, 60 are attached to the outer surfaces of the rotor 36 and a tubular shroud 34, which is coupled directly to the rotor 22 to rotate therewith. A slot 52 is formed in the shroud to expose a proportion of the strips on the rotor 36. Light from a lamp 62 reflected by the strips is received by photo-cells 64 through a window 48. The light reflected or absorbed by the strips on the rotor through the slot varies in accordance with the lag angle. The photo-cells thus produce pulses the duration of each of which is proportional to said product.