Patent GB-712412-A (GB)
Title: Improvements in or relating to tachometer devices and control systems including such devices
IPC: G01P3/58
Filed: 1951-06-28
Abstract: 712,412. Electric indicating and control systems for lifts and colliery winders. GENERAL ELECTRIC CO., Ltd., EMMS, S. A. G., and PELTON, B. S. June 13, 1952 [June 28, 1951], No. 15409/51. Class 40 (1). A tachometer device e.g., for lifts and colliery winders comprise a first shaft rotatable at a speed dependent on the speed to be measured, a second shaft driven at a predetermined speed, and an electric generator coupled to the two shafts through a differential gear so that the generator speed is dependent on the sum or difference of the speeds of the shafts, and is continuously variable throughout the speed range of the first shaft, the generator also being arranged to rotate when the first shaft is rotated at any speed within its working range. In Fig. 1 the input shafts of a differential 12 of ratio e.g., 1:1 are respectively coupled to a winder motor 15 and a constant speed motor 16 running at e.g., twice the maximum speed of the winder, and the output shaft drives a separately excited D.C. tachometer generator 10 at a speed varying unidirectionally over a range corresponding to winder speeds from maximum through zero to maximum in the opposite direction. The tachometer output energises windings 22, 23 of polarized differential relays 20, 21 having other windings 24, 25 energised through pre-set variable resistances 26, 27 so that when the tachometer voltage exceeds or falls below a predetermined value (corresponding to the winder exceeding a pre-set speed in either direction), the appropriate relay operates to close contacts 28 or 29 to operate an alarm or emergency brake circuit on the winder motor. In Fig. 2 greater sensitivity is obtained by exciting the tachometer field winding proportionately to the winder speed through a ballast resistance 42 compensating for temperature changes, from a generator 40 whose field is separately excited through a pre-set variable resistance 44, a resistance 45 shortcircuitable by switch 46, and a resistance 47 variable by a cam 66 rotatable in dependence on the position of the winder cage in the shaft (in the appropriate direction). The output of tachometer 10 thus varies in accordance with the winder speed, the cage position and whether men are carried instead of material (in which case the resistance 45 is shortcircuited), and is applied through oppositely poled restifiers 54, 55 to windings 50, 51 of two polarized relays 52, 53 whose differential windings 56, 57 are energised through pre-set resistances 58, 59. When the speed of the winder motor 15 in either direction exceeds a predetermined value dependent on the cage position and the nature of the load carried, the appropriate relay operates to close contacts 60 or 61 of alarm circuit 62 and apply the emergency brakes at a progressively decreasing winder speed, as the cage approaches bank at either end of the travel. The tachometer output voltage may be compared with a fixed reference voltage corresponding to the second shaft speed so that the voltages are equal at a predetermined first shaft speed.