WET VIBRATING SCREEN AND METHOD FOR REMOVING FOREIGN MATTER IN LIQUID TO BE TREATED

PURPOSE:To eliminate troubles of liq. overflowing, overflow of a liq. to be treated, breaking of a screen net, etc., by arranging a non-contact sensor above the screen net and calculating the liq. depth on the screen net based on the signal of the sensor. CONSTITUTION:An ultrasonic distance sensor 1 as the non-contact sensor for transmitting an optical or electronic signal is set above a top rim 4 at a height of about 1m from the screen net 8. When the distance between the sensor 1 and the net 8 is expressed by Lo, the liq. surface position is obtained by Lo-L (m)=(331+0.6t)(To/2-T/2), where t is the ambient temp. ( deg.C), T is the time required to transmit and receive an electric wave between the sensor and liq. surface, To is the time required to transmit and receive an electric wave between the sensor and net, and Lo-L the liq. depth. The depth of a liq. to be treated is calculated in an arithmetic part 2 from the equation and compared with the preset value, and the liq. depth is controlled to the set depth by adjusting the turning rate of a pump 17 or flow control valve 16. The liq. supply is stopped, when the liq. surface lowers from the reference value at the rate of 10mm/sec.