Abstract: The trouble with the operation of the medium draining screen in coal preparation plant is that the falling-off of its screenplate is unable to be timely detected, and there exists severe time delay in locating the faulty plate through patrol inspection in a traditional manner. To address this issue, a screenplate dropping-off detection device is specifically designed based on analysis of the faulty plate detection technologies currently available, and the working principle of the vibrating-rod-type level monitor, providing a new technical scheme capable of giving early warning of blockage of medium system by material. Practice shows that the device can be adjusted flexibly according to working conditions; and it works remarkably well with anti-clogging, impact-resistant and material sticking or gripping prevention capacities. Its other attractions include easy installation and routine maintenance, low fabrication cost, high working sensitivity and reliability.