Patent GB-664756-A (GB)
Abstract: 664,756. Interrupters. BLACK-CLAWSON CO. Jan. 31, 1949. [Feb. 13, 1948 ; Feb. 12, 1948] Nos. 2589/49 and 2590/49. Class 38 (v). [Also in Groups VIII, XXXV and XXXVIII] A pressure sensitive, especially liquid pressure, switch for use in a variable-on/off-time type of automatic control system (see Group XXXV) comprises a contact-carrying beam 70 adapted to be rocked by a bellows element 60 about its left-hand end, Fig. 3, and move upper or lower contacts 140, 141 into or out of engagement with motor-cam-vibrated contacts 150, 151 to control for example a reversible servomotor, Fig. 2 (not shown). .The Specification states that the device may be used to measure e.g. pressure, temperature or humidity by causing the servo-motor to drive the lead screw 110 to move the weight 120 until the beam is in a balanced condition ; the pressure being indicated by a pointer 127 attached to the weight registering on a scale on the cover. Pressure element. Fig. 3. The bellows 60 is housed in a cup 59 which is filled with the pressure-liquid through pipe 86, a vent-cock 87 being provided to remove air-locks. The inside of the bellows is vented to atmosphere through a hole 99 in the top plate of the cup through which passes a rod 100 transmitting movement of the bellows to the beam. When the pressureliquid contains suspended matter it may be arranged to transmit pressure through a diaphragm in the bottom of the cup, Fig. 8 (not shown), to a suitable filling liquid. For differential pressure response a pair of similar bellows is arranged to act upon the beam, Fig. 10 (not shown). Beam construction. The beam is pivoted at its left-hand end to a block 80 on the housing by a Z-shaped blade-spring 74 and a pair of flat blade-springs 82 (see Fig. 6 (not shown), for detailed construction), to permit motion of the other end between stops 105 on the housing. A biasing coil spring 146 connected between the stop lug 105 and the contact carrier may be used to reduce extreme sensitivity of the beam to rapid pressure change. At this other end is fastened a strip of insulating material 135 carrying the moving contact assembly comprising upper and lower contact springs 140, 141 and adjustable screw back-stops 145, which are set so that in the balanced position of the beam the contacts 140, 141-do not engage their associated contacts 150, 151 at the outward limit of their vibratory movement. A weight 120 is movable along the beam by a screwed rod 110 with adjusting knob 115 outside the housing to vary the controlled pressure setting, which is indicated by a pointer attached to the weight registering on a scale on the transparent front cover of the housing, Figs. 4 and 5 (not shown). Vibrating contacts. The "fixed" contact spring assembly is carried by an insulating block 153 attached to the base of the housing, and the contacts are vibrated by an irregular octagonal cam mounted between them and driven by an electric clock motor at e.g. 4 r.p.m., the screw stops 155 being adjusted to maintain the contacts in engagement with the cam face throughout the whole revolution. The cam is shaped as shown in Fig. 9 so that following the start of a cycle, each high point is at about five thousand less than the preceding, whereby displacement of the beam causes one. of the contacts to make a proportional number of engagements with its cooperating contact throughout each revolution of the cam until balance is restored.