Patent GB-390904-A (GB)
Title: Improvements in or relating to power measuring apparatus
IPC: H02K49/08
Filed: 1932-01-19
Abstract: 390,904. Rotary-absorption dynamometers. HEENAN & FROUDE, Ltd., ROSS, E. G., and SMETHURST, T. G., Worcester Engineering Works, Worcester. Jan. 19, 1932, No. 1538. [Class 106 (ii).] Relates to prime mover running-in and testing apparatus of the type having a swinging frame or carcase, and consists in exciting one coil of a wattmeter from a source of electric current supply not derived from the dynamometer but the potential of which is controlled by the movement of the frame and consequently proportional to the torque while the other coil of the wattmeter is excited by a small direct current generator driven from the dynamometer shaft and having an E.M.F. characteristic proportional to the speed of the shaft. The shaft 3 of the dynamometer is connected at one end to the prime mover 5 and at the other end to a small generator 6. An arm 7 fixed to the swinging frame is constrained by springs 8 the compressions or extensions of which are proportional to the torque of the dynamometer. The arm 7 carries a pointer 9 running over a torque scale 10 and also carries insulated brushes 11, 12 moving over resistances 13, 14. The central point of resistance 14, and the brush 12 are connected to the coil. 17 of the wattmeter 16. The resistance 14, 13 and the brush 11 are connected in series with the supply A to the dynamometer 1 in the case of an electric dynamometer or to a direct current source where the dynamometer is not electric. The connections are such that movement of the brush 12 alters the total resistance of the parallel circuit 14, 12, 17 and therefore the effective total value of resistance 14, while the movement of brush 11 varies in the opposite manner the resistance 13 so maintaining constant the total value of the resistance connected across the circuit that is maintaining a constant voltage gradient across the resistance 14. The small generator 6 is connected across coil 18. The movement of the brush 12 is proportional to the torque and therefore the potential drop between the centre part 15 and brush 12 is proportional to torque and also that across the coil 17. The needle 19 therefore moves proportionally to brake horse power. The invention may be used for alternating current dynamometers by deriving the supply for resistances 13, 14 from a small rectifier the primary of which is connected to the dynamometer excitation circuit. Alternately any direct current source may be employed. A speedometer 53 is connected as shown. In a second form the arm 7 is connected to a spring balance and scale pan, and the indicating pointer of the balance is connected to an arm carrying insulated contacts 11, 12 moving over resistances 13, 14 as before. In a further form, Fig. 3, applied to a direct current electrical dynamometer, an arm 27 is driven by a motor 40 connected to its supply through the insulated contacts 34, 35 of a solenoid relay 36. The operating coil 37 is connected through contacts 25 to the same supply. An extension 38 of arm 27 carries brushes 41, 42 rubbing over resistances 43, 44. The resistance 43 is connected in series with the coil 23 of relay 24 and the resistance 44 in series with the coil 18 of the wattmeter and in parallel with resistances 23-43. As the resistance 43 is increased, the resistance 44 is diminished and the resistance of the whole parallel circuit 23-43-44 maintained constant whereby the voltage-speed characteristics of the generator 6 is also maintained constant. The coil 17 is supplied with current from the source A as before. The voltage relay 24 is first arranged to come into operation when the speed of the motor 6 has reached a predetermined value. Contacts 25 are then closed energizing the coil 37. This closes contacts 34, 35 and starts the motor 40. The system 27, 38, &c. is therefore driven and the speed of the motor 6 is increased depending on the torque at the dynamometer shaft. During this operation the resistance 44 is increased to such a value that coil 23 releases the switch at the contact 25 thus de-energizing the coil 37 and stopping the motor 40. When the friction of the prime mover falls further the relay 24 is again energized and the motor 40 again operates. This sequence is repeated intermittently until the part 29 operates the switch 30 to shut down the complete equipment. In the application to hydraulic dynamometers, the parts 26-29 are replaced by mechanical gearing which is driven from the motor 40 and operate sluices or other controls.