Patent GB-690948-A (GB)
Title: Improvements relating to industrial process control units
IPC: G05B11/00
Filed: 1950-09-05
Abstract: 690,948. Indicating-apparatus. YOXALL, L. S. (Foxboro Co.). Sept. 5, 1950, No. 21867/SQ. Class 106 (iv). [Also in Groups XXIV and XXIX] An industrial process control unit comprises two separate systems whereby first and second variables are automatically controlled to set points, each system including a datum-setting member, and there is an adjustable ratio linkage interposed between the two datumsetting members so that, in adjusting the datum of one system, the data of both systems are adjusted in the set ratio, and said linkage is disconnectible from the datum-setting members by adjustment of the linkage to an extreme position. The variables are applied to shafts 16, 16a, Fig. II, the movements of which actuate, through the apparatus shown, flaps controlling nozzles 38, 62, and the resultant pressures set up by the nozzles and flaps actuate valves controlling the two variables in question. 26 denotes the main axis of the mechanism. Through the medium of a link 30 and a lever 28, shaft 16 rotates a sector-shaped frame 29 about the axis 26, the frame 29 being connected to a pen 41 which is also pivoted on axis 26 and records the value of one variable. Frame 29 is connected by a link 34 to one end of a bell-crank 33 pivoted on an arm 27, and the other end of the bell-crank is connected by a linkage 39 to the controlling flap of nozzle 38. Arm 27 is pivoted on axis 26, but the pivoting point of bell-crank 33 on arm 27 is off-set from that axis although the connecting-point between linkage 39 and the bell-crank coincides with axis 26 for zero values of the variable, i.e. when the value of the variable as indicated by the position of the bell-crank coincides with the value set by the position of arm 27. The latter carries an arm 43 to indicate the datum point to which this first-mentioned system has been set, and adjustments of the datum point are effected by actuating a knob 47 which rotates an arc-shaped arm 44 pivoted at 45, offset by parallel to the axis 26, and connected to arm 27 by a link 49. A similar connecting and datumsetting apparatus is provided between the shaft 16a and the control nozzle 62 of the other control system, except that the direct connection between the arc-shaped datum-adjusting arm and the arm carrying the bell-crank is replaced by a lever 74 connected by a link 76 to the arm 52 and spring-pressed against a pin 73 on arm 68. The connection between the two datumadjusting devices whereby the setting of the datum of one system also sets the datum of the other system in a pre-determined and adjustable ratio is provided by a lever and linkage mechanism shown in Fig. III. Arms 44, 68 constitute levers which are connected to shafts 51, 75, respectively, coinciding with the respective pivoting axes of the arms. The upper ends of the shafts carry arms 99, 97 connected by links 98, 96 to levers 82, 95 pivoted at 79, 78 on axes off-set from axis 26 on which a sector-shaped arm 91 is pivoted. The last-mentioned arm is adjusted by a knob 93 and an extension 90 of the arm is joined by a link 88 to the common pivoting point of two further links 84, 83 connected to levers 82, 95 so that, adjustment of the position of arm 91 varies the ratio of the movement imparted to shaft 51 when shaft 75 is adjusted to set the datum of the system to which it is connected. When adjustment of the data of the two systems is to be made in the ratio determined by the knob 93, arm 68 is swung back until pin 73 loses contact with arm 74, and if the data of the two systems are to be adjusted separately, arm 99 is swung round until it loses contact with an abutment 100 carried by shaft 51.