Patent GB-511280-A (GB)
Title: Improvements in or relating to photo-electric systems for automatically controlling variable magnitudes
IPC: G05F1/00
Filed: 1938-01-11
Abstract: 511,280. Automatic control systems. TAGLIABUE MFG. CO., C. J. Jan. 11, 1938, No. 911. Convention date, Feb. 10, 1937. [Class 38 (iv)] [Also in Groups XXXVI and XL] Temperature &c. Changes in position of a light beam relative, to a photo-electric cell operate a relay to cause correction when a variable departs from a predetermined value and the relay operating effect of the light beam is altered by the relay to reduce the difference' between the value of the variable at which the relay is energised and de-energised respectively. The relay may move a shield for the photoelectric cell or connect a resistance in shunt with the operating coil of a mirror galvanometer 10, Fig. 1, connected in a temperatureresponsive Wheatstone bridge including a thermocouple. Mounted in a casing 48 is a lamp 25, a photo-electric cell 26 and an inclined transparent reflector 57 which reflects a part of the beam on to a scale in an aperture in the casing; this scale has a clear central portion separating differently coloured end zones and exhibits two images of the lamp filament spaced by a fine dark line. The cell is shielded by an aperture 54 in a fixed screen with a controlling edge dividing the beam equally under normal conditions. The photo-cell is in circuit with an amplified tube 27 and a relay or relays also mounted in the casing. To prevent the galvanometer sticking an electromagnet 33 supplied with A.C. actuates an armature 60 attached to the galvanometer bracket 58 and thus vibrating adjustable stops 89 which make a small area of'contact with the front of the mirror in its limiting positions. The face plate 92 of the galvanometer with stops and window 94 is shown in section in Fig. 13. The relay circuit shown in Fig. 7 comprises a single relay 34 with contacts 38 adapted for systems having one or two circuits for controlling the variable and also contacts 36 which shunt the relay through a resistance 35 so that its current is reduced to a value only slightly larger than the minimum required to keep it closed; the relay may be adjusted to oscillate with a variation in the percentage of time its contacts are closed as the light beam moves in respect to the photo-cell. A condenser 30 may prevent fluttering of the relay. To adjust the sensitivity of the control, a resistance 30a may be used. The resistance in the galvanometer circuit may be varied, the size of the light beam may be altered, the controlling edge or the like may be modified, voltage on the screen grid or an amplifier 27a, Fig. 9, may be changed or resistances in circuit with the photocell or lamp may be altered. A voltage regulator 28a is included in the supply circuit. Any type of electromagnetic or electronic relay device, including a gaseous triode supplying control output directly, may be used. A modified circuit is described having two electromagnetic relays, each arranged as above and responsive to different photo-cell outputs so that in normal conditions one relay is open and the other closed. The neutral zone of the controller may be adjusted by a screen 85, Fig. 11, having slot 86, or by an angularly adjustable sector 87, Fig. 12, replacing the controlling edge of the aperture 54. Fig. 9 shows a shield 34d adapted to vary the size of the aperture 54 when the relay 34 is operated. Specification 397,861, [Group XXXVI], is referred to.