Thermostatic control

摘要

637,582. Automatic temperature control systems. LORD & BURNHAM CO. Nov. 19, 1946, No. 34277. [Class 38 (iv)] [Also in Group XXXVII] A thermostatic control for greenhouse ventilators comprises a temperatureresponsive element 30, Fig. 7, controlling a switch arm 61, Fig. 5, adapted to close either of two switches 68, 69, a knob 36, Fig. 8, for setting the temperature to be maintained constant, and a handle 75 preset to impose an overriding limit to the degree of opening of the ventilators, and also manually fixing the maintained degree of opening of the ventilators when the knob is turned to a position rendering the thermostatic control inoperative. A follow-up arm 43 connected between the ventilators and a nut 39 fixedly mounted on a threaded shaft 38 of the device serves to restore the switches to neutral after the set temperature is reached. The shaft 38 carries and rotates the entire thermal unit about a lower pivot 45 and by its axial movement relative to the knob 36 counteracts the effect upon a spring 34 connected between the nut 39 and thermal element of the action' of the bellows 30. The spring 34 is initially set under compression, the control temperature being reached when the compression due to the spring and bellows is balanced by the spring 71. The switch arm 61 is mounted on leaf spring supports 64 so that its control movement is multiplied by the bellows linkage 57 and carries magnets 66, 67 operating the switches 68, 69, which respectively operate through a relay a reversing motor to open and close the ventilators. The knob 36 is mounted between an internally-threaded socket 76 and the externally-threaded shaft 38 on which the nut 39 is secured, the threads being of differential pitch. The socket 76 is releasable and independently adjustable to calibrate the device. A cam 41 on the handle 75 sets an over-riding limit to the extent of opening of the ventilators. The cam 41 operates by engaging a pin 40 on the nut 39 of the follow-up arm 43, which pin engages a spring-biassed yoke 42, Fig. 5, which by abutting a set-screw 72 on the switch arm 61 actuates the latter into a neutral position and cuts out the ventilator opening switch 68. In manual position M, Fig. 2 (not shown), of the knob, the spring 34 is extended under such tension that the switch arm 61 is biassed toward the ventilator opening switch 68 and the cam 41 then exercises control in such a way that'the pin 40 is always on the inclined surface of the cam 41. The position of the ventilators is then determined manually by the handle 75. A mercury switch interrupts the ventilator closing circuit to prevent jamming if the driving motor is not cut off when the ventilators are fully closed.