Patent GB-690034-A (GB)
Title: Improvements in or relating to electric control mechanism
IPC: G05B11/01
Filed: 1949-07-25
Abstract: 690,034. Automatic level control systems. RHEOLAVEUR GENERAL CONSTRUCTION, Ltd., PAROLLE ELECTRICAL PLANT CO., Ltd., HALMSHAW, H., FAWCETT, R. H., and ARCHBOLD, E. F. Oct. 25, 1950 [July 25, 1949], No. 19532/49. Class 38 (iv). [Also in Group XXXVIII] The thickness of the shale bed in a coal washing trough is automatically maintained constant by controlling the rate of shale extraction in accordance with the thickness of the shale bed, variations in the thickness being transmitted to the control point by a step-by-step transmission system comprising a transmitter rotary switch d<SP>1</SP> having a single contact arm c<SP>2</SP> and a receiver rotary switch f<SP>1</SP> having three ganged contact arms g<SP>1</SP>, g<SP>2</SP> and g<SP>3</SP> actuated by a motor m which operates the sliding gate of the extraction box. As shown, the arms g<SP>1</SP> and g3 have arcuate extensions g<SP>6</SP> and g<SP>7</SP>. When the thickness of the shale bed varies, the water level b<SP>1</SP> in the trough b varies in a corresponding manner and the angular position of contact arm c<SP>2</SP> is set in accordance with the water level by means of a counterbalanced float a in a chamber a<SP>1</SP> mounted on the outside of the trough. The rate of extraction of the shale is determined by the angular position of a pivoted lever h which operates the sliding gate of the extraction box and lever h is connected by a pin h<SP>3</SP> to an endless chain j passing over sprocket wheels kl, k<SP>2</SP> and k<SP>3</SP>, wheel k3 being driven by motor m through reduction gearing and a slipping clutch and wheel k<SP>1</SP> being locked to a wheel k<SP>4</SP> coupled to the spindle g4 of the receiver switch by a chain j<SP>1</SP> so that lever h is positioned in accordance with the setting of contact arm g2 which is positioned in accordance with the setting of contact arm c<SP>2</SP> of the transmitter switch as described below. Transmission system. The transmitter switch d<SP>1</SP> comprises a rotatable contact arm c<SP>2</SP> and a plurality of equi-spaced contacts d connected by individual lines to corresponding contacts f of the receiver switch f<SP>1</SP> whose three ganged contacts may engage any three adjacent contacts f. The transmitter contact arm c<SP>2</SP> is connected to the bottom line of a power supply p, the receiver contact arm g<SP>2</SP> is connected to the top line of the power supply through relay coil s and receiver contact arms g<SP>1</SP> and g<SP>2</SP> are connected to the top power line through relay coils u and t respectively and one set of contacts of relay s; the other contacts of relay s control the power supply to motor m and the contacts of relays t and u control its energization and direction of rotation. When the system is in a steady state, contact arms c<SP>2</SP> and g<SP>2</SP> are on corresponding contacts, relay s is energized and its associated contacts are open, thereby deenergizing motor m and disconnecting relay coils t and u from the top power line but when contact arm c<SP>2</SP> is moved to an adjacent contact, relay s is de-energized, thereby energizing motor m and connecting relay coils t and u to the top power line, and either relay coil t or u is energized via contact arm c<SP>2</SP> (depending upon the direction of movement of c<SP>2</SP>) so that the motor rotates contact arms g<SP>1</SP>-g<SP>3</SP> until the position of arm g<SP>2</SP> corresponds with the new position of arm c<SP>2</SP> when relay s is again energized to stop the motor. According to the Provisional Specification the two switches d<SP>1</SP> and f<SP>1</SP> may be interchanged.