GB471669A - Improvements relating to temperature and other regulating means - Google Patents

Abstract

471,669. Fluid-pressure servomotorcontrol systems. REAVELL & CO., Ltd., and HUMBY, A. J. D. Feb. 4, 1936, No. 3332. [Class 135] In the regulation of physical values such as temperature, humidity or calorific value, which can be measured as electromotive force or as variations of electrical resistance, a potentiometer or allied instrument is combined with a fluid relay of the pivoted jet type described in Specification 224,655, [Class 135], through a cam on the instrument spindle and a leverage system controlling the position of the pivoted jet. The pivoted jet relay may operate the control means directly or through a second relay provided with a device to prevent hunting. Movement of the slide wire contact of the potentiometer to restore a balance, disturbed for instance by a temperature-change of the resistance in one of the legs, is effected automatically, according to the galvanometer deflection, by any suitable relay. A cam 2 on the potentiometer spindle 1 thus controls, through a pivoted arm 4, pusher 7, and cranked lever 8, the position of pivoted jet 11 according to the controlling temperature, a rise in temperature increasing the fluid pressure (lowpressure air) transmitted to (say) pipe 16, and lessening it in pipe 15. The differential pressure, by a diaphragm 19, moves the pivoted jet 21 of a second relay, increasing the oil pressure (supplied at 33) on one side, and lessening it on the other, of a piston 35 operating the steam or gas valve 36 to be controlled. A piston 27 with a byepass and centralizing springs 28 is provided in the line between the jet 21 and the servo-piston 35, and connected to the anchorage of spring 22 acting on jet 21, in order to prevent hunting. To set the apparatus for different temperatures, the arm 4 is adjusted relatively to the cam 2 by rotating the bush 6 which may be provided with a scale.