Improvements relating to the stroboscopic observation of shafts and like rotating members

600,980. Electric indicating systems. BRITISH THOMSON-HOUSTON CO., Ltd., and CASTELLAIN, A. P. Oct. 8, 1945, No. 26170. [Class 40 (i)] The speed or other characteristic of a rotating body is measured by inducing a voltage in a coil at each revolution of the body and applying this transient voltage to a cathode ray oscillograph arranged to indicate the speed or other characteristic. Two or more pick-up coils may be used, e.g. for indicating the torque transmitted by a shaft one of the pick ups being used to trigger the line scan of the C.R.O. As shown, the shaft 4, Fig. 4, whose speed is required, carries a disc 3 having a magnetic inset 2 which co-operates with fixed magnetic elements 1a, 1b (the inset 2 or the elements 1a, 1b being permanently magnetised) to induce transient voltages in pick-up coils 10a, 10b mounted on the elements. These voltages are fed to a C.R.O. 13, the voltage from pick-up 10a triggering the line scan and the voltage from 10b producing a blip in the line at a position corresponding to the shaft speed. Alternatively, the speed may be indicated by the adjustment of the line scan sweep speed control necessary to bring the blip to a standard position. The pick-up coil 10a may be dispensed with in which case the line scan control is derived from a separate source. In the Fig. 5 arrangement, a third pick-up coil 10c is provided co-operating with a magnetic inset 2a in a collar 15 secured to a sleeve 16 fixed to the shaft 4 at a remote point 17. As before the output from coil 10a is used to trigger off the line scan and the outputs from coils 10b, 10c used to produce blips on this line the displacement between which is a measure of the torque transmitted by the shaft. Alternatively the torque may be indicated by the adjustment of the line scan sweep speed control necessary to main the blips at a standard spacing corresponding to, e.g. zero torque. In a modification, Fig. 6 (not shown) the disc 3 has two circumferentially spaced magnetic insets for providing improved indications on the C.R.O. According to the Provisional Specification the apparatus may be used for determining the angular displacement between two shafts and hence the slip in a magnetic coupling or belt drive.