Patent GB-368273-A (GB)
Title: Improvements in automatic apparatus for controlling a physical condition such as the temperature of a circulating fluid
IPC: G05D23/19
Filed: 1930-08-29
Abstract: 368,273. Electrically-actuated valves. HODGSON, J. L., IVANOFF, A., and HOWARD, G. P. E., Biscot Road Works, Luton. Aug. 29, 1930, No. 25794. [Class 135.] A valve for regulating the flow of a circulating heating fluid is controlled conjointly by a device actuated by means responsive to the extent of deviation of the temperature of the area heated by the fluid from a predetermined value, and a device actuated by means responsive to the deviation of the temperature from that of a preceding interval (these secondmentioned deviations furnishing a measure of the rate of change of the first-mentioned). The potentiometer wire 1<1> which in combination with a thermocouple serves to measure the temperature is mounted on a drum 7 with a vertical axis. Above this and on the same axis a galvanometer needle 5 rotates which indicates the state of balance of the potentiometer. A shaft 14 rotating at constant speed bears a cam 13 which at every revolution engages a lever 12 and so raises the potentiometer drum 7 so that the needle 5 is lifted off its suspension hooks and clamped between the drum and a ring 8. The potentiometer slider is carried by a parallelogram of jointed links so that it will not rub over the slide wire as the latter is raised or lowered. The shaft 14, through cams and levers, then causes two arms 16, 17 to approach each other and return the needle 5 to its zero position at the same time returning the drum 7 clamped to it to a position of balance. According to which side the needle is deflected either arm 16 or arm 17 will touch the needle and contacts 19, 20 will be made while the needle is being returned to zero for a time proportional to its deflection. As the potentiometer is balanced at each interval of measurement the galvanometer always starts from zero at the beginning of each interval and therefore its deflections form the secondmentioned deviations in the opening sentence. A cam plate 33, attached to the drum 7, operates a lever 34'according to the deviations of the potentiometer reading from the desired value and thus affords the first-mentioned deviations. To set the apparatus the cam 33 is locked in its mid-position and the drum 7 is rotated by a bevel 7<1> to the desired position. The lever 34 operates a rocker 35 carrying contacts 36, 37 which are engaged by contacts 38, 39 carried on a plate 40 rocked by a cam 41. Thus contacts are made for time intervals depending on the deviations of lever 34. A mercury switch 21 actuated by a cam on shaft 14 breaks all circuits at the end of the measuring operations. To combine the signals from the galvanometer and the potentiometer drum, differential devices such as are shown in Figs. 4 and 15 may be used. In Fig. 4, a shaft 42 bearing worms 44, 45 is driven at. a continuousspeed. Worm wheels 46, 47 may be pulled into mesh with these worms by solenoids 54, 55 connected to the galvanometer and potentiometer contacts as shown in Fig. 10. These worm wheels drive opposite sides of a differential gear 58 through further worm gearing and the resultant motion of gear 58 is transmitted through gearing 59 to shaft 60 which operates the valve in the circulating fluid conduit. A shaft 72, connected by links to shaft 60, locks the wheels 46, 49 in inoperative positions if the control valve reaches the limits of its travel. In Fig. 15, shafts 123, 124, driving the two sides of the differential through worm gearing, are driven by two identically similar motors which take the places of the solenoids 54, 55 in the previous construction. Bevel gearing 130 on the shaft 64 controlling the valve operates limit switches through shaft 132 which stop the driving motors when the limits of motion of the controlling valve are reached. Hand-operated controls may be provided for over-riding the control exerted by the apparatus. In both constructions the worms and wheels used are self-locking. Instead of using a differential, the contacts may be arranged one pair in each of the two ratio arms of a Wheatstone bridge with a relay controlling electric means for controlling the valve in place of the usual galvanometer. Specification 185,162, [Class 97 (iii), Thermometers &c.], is referred to.