GB746045A - Dimension-indicating device - Google Patents

Abstract

746,045. Electric measuring systems. POWER JETS (RESEARCH & DEVELOPMENT), Ltd. May 11, 1954 [May 20, 1953], No. 14149/53. Class 40(1) [Also in Group XXVI] Apparatus for measuring the distance of an object from a datum level comprises a probe which is driven towards the object until the distance separating them is sufficiently small to discharge a condenser connected in parallel, whereupon the driving mechanism is reversed during recharge of the condenser, and the forward motion is then repeated, so that the probe finally takes up a position, about which it dithers, which is indicative of the distance of the object from a datum level. As shown (Fig. 4), the probe 1 is moved towards the blades 55 of a rotating turbine propeller 56 by a motor M through a synchronous transmitter T and receiver motor M1, also driving a counter 53 through a clutch 54 by a second receiver motor M2. Initially the probe 1 is at a datum position and the counter 53 is set at zero. The condenser 59 is charged from a power supply P feeding into a control circuit C comprising a double triode valve 66, the potential relations being such that anode 66c is non-conducting and anode 66d conducting to energize a relay winding 51a operating switch 51 to cause motor M to drive the probe in the forward direction towards the blades 55 until condenser 59 is discharged by a spark from the probe 1 to the tip of the longest blade 55, when the change in conditions in circuit C due to the charging current of condenser 59 causes anode 66c to conduct instead of anode 66d, relay 51a falls, contact 51 changes over, and the motor M is driven in the reverse direction to retract the probe. When condenser 59 is again fully charged relay 51a is again energized, and probe 1 again proceeds forward to repeat the cycle. The charging rate of condenser 59, and the forward and reverse speeds of motor M are such that the probe is finally brought to a position of small steady oscillation with its point just clear of the longest blade 55, and the counter 53 indicates this distance from the datum position. Probe construction. The probe consists of a metal wire 1 (Fig. 1) electrically insulated by a sleeve 2, and slidably mounted in a holder 6 fixed to a casing 4 assembled as required, e.g., to the top of an axial flow turbine. Part of the holder 6 is screwed at 6a to carry a nut 8 acting as a worm wheel 8a meshing with a worm 10 driven through a shaft 18 by the motor M1, mounted on the casing 4. The datum position of the probe is established by an adjustable back contact 33 which lights a lamp 75 (Fig. 4) when the probe is retracted !to this position, overrun being prevented by stop pegs 8b, 6c. Air passages 5c are provided round the probe and the motor to allow for the circulation of cooling air under pressure.