GB621181A - - Google Patents

Abstract

621,181. Automatic control systems; moisture content. PNEULEC, Ltd., and COWLAM, K. W. Dec. 20, 1946, No. 37594. [Class 38 (iv)] For controlling the moisture content of a mixture of water and sand or other finely divided material carried on a conveyer, the supply of water to the material is controlled by an electromagnetically-operated valve which is opened intermittently for periods of time governed by the resistance between spaced electrodes dipping into the material, the arrangement being such that the duration of each period of opening is inversely proportional to the moisture content of the material so that the moisture content is maintained substantially constant. In one arrangement, the valve is controlled by a relay in circuit with the electrodes and a resistance periodically varied by a constant speed motor, the time incidence of the opening and closing of the relay in the cycle being dependent on the resistance of material between the electrodes. A manually variable resistance may be provided to adjust the mean moisture content and a second relay included in the circuit to cut off the water supply when there is no material on the conveyer. In a modification, the time cycle is produced by a relaxation oscillator controlling the valves through a thermionic valve, the resistance between the electrodes being employed to vary the biassing conditions within the time cycle. In a further modification, the water valve is actuated by a relay switch, the opening and closing of which is controlled by the charging and discharging of a condenser in circuit with the electrodes dipping into the material. The valve is maintained open during charge for a time dependent on the moisture content, after which the condenser is discharged through an auxiliary resistance, the value of which is preset manually. A relay in circuit with the auxiliary resistance is released at the end of discharge to close the charging circuit through the electrodes and thus restart the cycle. Ina further arrangement, the valve may be operated in such a way that the amount of opening is proportional to the duration of the operating current in the time cycle.