Patent GB-624309-A (GB)
Title: Improvements in or relating to electrically operated apparatus for controlling temperature
IPC: G05D23/22
Filed: 1945-10-18
Abstract: 624,309. Fluid-pressure servomotor-control systems. TINSLEY (INDUSTRIAL INSTRUMENTS), Ltd., and STEGHART, F. L. F. Oct. 18, 1945, No. 27364. [Class 135] [Also in Group XXXV] A temperature-controlling system comprises means, e.g. a thermocouple 5, responsive to temperature changes such as that of liquid issuing from a heat exchanger 1, to produce an electric current which is amplified and applied to the coil 70 of a solenoid controlling the vertical movement of a soft iron core 71 serving as a sleeve valve to control the fluid pressure within a cylinder and thereby control the operation of a piston valve 85 controlling the admission of pressure fluid through ports 96, 97, leading to an oil motor 98 of the rotating vanetype connected to regulate a valve 4 controlling the admission of heating fluid to the heat exchanger. The oil motor 98 also rotates a cam 101 bearing against a fixed collar on a rod 102 which is normally pressed downwardly by a spring 103, the upper end of the rod providing a mounting for a cylinder 104 containing a plunger 79 which can be moved upwardly against the pressure of a spring 105 at its upper end. A bleed hole 106 regulated. by a screw 107 controls the effect of the movement of rod 102. A switch contact arm 75 mounted on a fixed pivot 77 has one end connected to the upper end of plunger 79 and the other end in movable contact with a rheostat 76 in parallel with the solenoid coil 70, the arrangement being such that a follow-up control proportional to the time integral of the change in the physical magnitude is provided by the reduction in the current through the solenoid coil, allowing the core 71 to drop. The core 71 moves over a lateral hole 92 in the upper end of the valve rod 85, which has a central passage connecting with the upper port 87 of the servomotor through a hole 91, so that in the raised position of the core 71, due to temperature unbalance, oil can escape through the hole 92, whereas the core covers the hole when the medium discharged from the heat exchanger is at the required temperature. Oil is fed into the passage 83 of the system by a gear pump 81 driven by a motor 82 which is also arranged to drive gear wheels to rotate the piston 85 and rod 102 to reduce friction during the vertical movement. The lateral ports 87 and 88 receive oil from the lower end of passage 83. through a valve 86. The electrical amplifying circuit comprises a mirror galvanometer 8 in series with the thermocouple 5 and resistor 9, and a light-sensitive cell 19 connected .to the grid of a gas-filled triode 16, whereby the phase and magnitude of the grid potential is varied in accordance with voltage variations in the circuit of the light sensitive cell. In a modification, Fig. 4 (not shown), the feed-back or counter-balancing force applied to the solenoid core 71 is applied mechanically instead of electrically by replacing the rheostat 76 associated contact arm by a leaf-spring which is secured at one end to the plunger 79 and at the other end bears against a collar on the solenoid core to urge the latter downwardly. The cam operated by the oil motor is arranged so that it allows the cylinder 104 housing the plunger 79 to be lowered when the solenoid core 71 is raised, thereby increasing the downward pressure on the core and ultimately causing it to descend and reduce the openings of the ports 96, 97 controlling the operation of the oil motor to rebalance the system. Specification 542,962, [Group XXXV], is referred to in the Provisional Specification.