Patent GB-326309-A (GB)
Title: Improvements in or relating to means for the control of temperature
IPC: G05B1/04
Filed: 1929-02-13
Abstract: 326,309. Electroflo Meters Co., Ltd., (Republic Flow Meters Co.). Feb. 13, 1929. Thermostats.-In a device for controlling temperature, a temperature-responsive member determines the action of a clutch which couples a driving to a driven shaft. The driven shaft controls the' heating through a switch or valve. The temperature responsive device comprises a thermocouple operating a moving coil 3 carrying a pointer 2 moving over a scale 1. The pointer can be held in any position by means of a bar 12 carried by a rod 11 pivoted at 10. The rod 11 carries a pin 13 overlying another pivoted rod 8. the upward movement of which lifts the rod 11. The rod 8 has a terminal portion 15, 16, Fig. 9, engaging the pointer only within small limits. and has a backward extension 17 in the path of one arm 18 of a bell crank 19 pivoted at 20. The other arm 21 of the bell crank engages a cam 23 rotated by an electric motor 25. †. shaft 27 in line with the shaft 24 is adapted to be intermittently connected with it through a clutch device 28. This consists of a plate 29 secured to the shaft 24 and having a hook 30 pivoted to it at 31. A tripping lever 33 is pivoted to the plate at 34 and to a link 36 at 35, the link 36 being pivoted to the hook 30 at 37. The hook 30 engages an arm 38 to drive the shaft 27. A selector 40 pivoted at 41 is biassed towards the shaft 24, and has pins 43, 44 adapted to engage the lever 33 to move the hook 30 out of engagement with the. arm 38.. A pin 45. on the plate 40 engages with the arm 21 of the bell crank 19, and a latch member 46 is adapted to engage a trip pin 50 on the cam 23 and the pin 45 on the plate 40. In operation, continuous rotation of the cam 23 actuates the bell crank 19 intermittently thus causing intermittent depression' of the rod 8 into the path of the pointer 2. Assuming that the furnace is to be heated up from the cold, the depressor 8 is set so that except at and above the predetermined temperature it is not intercepted by the index 2. When the cam 23 is rotated and the bell crank 18 and depressor 8 actuated, ihe latter passes the index 2 as shown in Fig. 2. The pin 50 raises the latch 46 so that the detent 49 on the latch does not engage the pin 45 on the plate 40. Further rotation of the cam permits the arm 21 to engage the pin 45 and raise the plate 40 to the position shown in Fig. 2, where it is retained by the detent 49 when the latch 46 is allowed to fall. As long as the depressor 8 continues to pass the index 2, the plate 40 is held in the upper position either by the pin 45 or by the arm 21. Further rotation of the cam causes the hook 30 to engage the crank arm 38, and the shaft 27 is driven so that heating medium is delivered to the furnace. One half a revolution is sufficient for this purpose, and the driving and driven shafts are then disconnected by the outstanding part of lever 33 engaging with pin 44 and breaking the toggle, thus disengaging the hook 30 from the crank arm 38. In succeeding cycles, the plate 40 remains in its upper position, the pin 44 remains in the path of the lever 33, and the toggle is broken when otherwise the arm 38 would be engaged by the hook 30. When the temperature is sufficiently raised, the index 2 interrupts the movement of the depressor, and the arm 21 allows the plate 40 to fall when the cam 23 raises the latch 46. The pin 43 is then in the path of the lever 33, and the pin 44 is out of its path, so that the hook 30 engages the crank arm 38 and the shaft 27 is rotated to diminish the heating until the lever 33 contacts the pin 43 and the clutch is released. There is no further engagement between the hook 30 and crank arm 38 until the temperature falls sufficiently to move the index 2 out of the path of the depressor 8. If thermal lag causes the furnace temperature to rise after the heating is. reduced or cut off, the index 2 is prevented from moving out of the path of the depressor by the part 15. In the application to an electric switch, Fig. 7, the driven shaft 27 operates through an arm 55 and link 56, a bellcrank lever 57 which is connected by a spring 60 to an arm 61 operating the contacts 62 of a snap switch 58. In the application to a gas or oil heated furnace, Fig, 8, the driven. shaft 27 operates valves 65, 66, through linkwork 55, 56, 68, 69, 70. Specification 318,308 is referred to.