Patent GB-430078-A (GB)
Title: Improvements in and relating to systems for stabilising variable conditions
IPC: G05D23/275
Filed: 1933-09-28
Abstract: 430,078. Thermostats. BECK, H. C., 5631, Wissahickon Avenue, Germantown, Philadelphia, U.S.A. Sept. 28, 1933, No. 26730. Convention date, Oct. 4, 1932. [Class 64 (ii)] In a system for automatically producing or maintaining a given condition a portion of the primary control action effected upon a departure of the condition from that desired in one direction remains effective until the condition departs in the opposite direction,' with the object of balancing the conditionmaintaining force against the " demand " or tendency to change whatever its cause. The extent of this secondary control action may be proportional to the number of successive departures in one direction and in certain embodiments of the invention the primary and secondary controls become more or less proportional to the magnitude of the departure. The primary control means in one form is shown in Fig. 1, wherein a shaft 8 carrying switch cams 9, 10, 11 is actuated in accordance with changes in the condition, for example by a thermostat element 6 responsive to furnace temperature, and the condition-maintaining force, for example a valve 3 controlling fuel supplied to the furnace, is adjusted by an electric motor 17 carrying switch cams 19.. 22. The reversed fields of the motor are controlled during small variations of the condition by the contacts 12, 23, 24, actuated by the cams 9, 19, 20 and during larger variations by the switches 13, 14, 25, 26 actuated by the remaining cams which effect the full opening or closing of the valve. The secondary control is effected as shown in Fig. 3 by mounting the cams 19, 20 on a sleeve 41 so that they may be rotated with respect to the cams 21, 22 and so effect a change in the balancing position of the valve to correspond with the change in the "demand." A gear 46 fixed on the shaft drives the sleeve 41 through a pinion 44 on a shaft journalled in a crank 42 on the sleeve 41 and braked by springs 49. A ratchet wheel 43 is fast with the pinion 44 and is caused to engage to an adjustable extent fixed pawls 48, 50 as the shaft 16 carrying the cams 21, 22 rotates. The sleeve 41 and cams 19, 20 are accordingly moved in relation to the cams 21, 22 to a predetermined extent on each departure of the condition in excess of a predetermined amount and the secondary control so effected remains until such departures occur in the opposite direction. Additional switches and cams and further sets of pawls may be associated with this mechanism, thus introducing a corresponding degree of proportionality between the extent of the departure and the condition and the primary control effected and also between the primary and secondary controls. The Specification describes the construction of a mechanism having an additional pair of cams and an additional pair of pawls. The Specification also describes diagrammatically an arrangement in which the sleeve has the pairs of cams and switches and five pairs of pawls. A motor may act in place of or in conjunction with the pawls and operate in impulses ; a balancing cut-out contact may open the motor circuit and replace the pawls. In an air-operated control a stop-valve might operate under large or prolonged condition variations to prevent the balancing action. The invention may be embodied in an electrical bridge circuit the secondary control introducing a bias in the bridge.