Control system for controlling a plant including a mobile suction device for sucking suspendible material

Method of controlling a device for sucking a material suspendible in air or liquid having a suction nozzle connected to a pump through a conduit by means of a sensor connected to said conduit, the suction nozzle being supported via a flexible supporting means by a hoisting device which is carried by said device for moving the hoisting device and the nozzle along at least one horizontal axis at adjustable velocity, while the nozzle is vertically adjustably carried by the hoisting device, wherein the hoisting device for vertically adjusting the nozzle is controlled by means of a control device by signals from the sensor in such a way that said sensor is preset to supply a control signal to the hoisting device for raising or lowering the nozzle to thereby restore the quantity per unit time in the conduit when the quantity per unit time exceeds or falls below a predetermined value which lies below a maximum value, and wherein the control device to which the sensor is connected, is adapted, when the quantity per unit time exceeds or falls below a certain upper and lower threshold level therefor as a function of time and working depth of the nozzle, to send the control signal from the sensor to control the quantity per unit time within definite limits the steps comprising:

• determining a maximum quantity by running the pump and nozzle in air or liquid which is free of the suspended material, assigning a limit range for the sensor that is less than the maximum quantity, selecting a time interval for a time relay within which deviations from the limit range of the sensor will not alter control of the device but in excess thereof will alter control, switching the control circuit from control of the working depth of the nozzle by regulating the hoisting device to control the pump rate of the control valve depending on signal strength, time and certain nozzle depth sensed, moving the hoisting device and the nozzle with regard to the quantity sensed, which is pumped through the conduit, moving the hoisting device in dependence on the inclination of the flexible supporting means at definite limits of inclination angle and in combination with time, controlling the quantity in dependence on signals supplied by a device for sensing the weight load carried by the movable supporting means or the tension of said means.