| 摘要 |
<p>The system uses ultrasonic transducers (9, 10, 11, 12) to provide an indication of level whilst avoiding the equipment sensitivity and unreliability inherent in ultrasonic echo tecnhiques. The equipment is robust and readings are positive. A high frequency generator (30) excites ceramic piezo-electric plates at or near their resonant frequency. The current drawn by the transducers is a function of the damping experienced by the outermost plate. A control unit (29) monitors the currents and illuminates indicator lights (32, 33, 34, 35) when the current falls below the threshold, indicating that the transducer is covered. Residual powder on the plates is shaken free by the vibration of the plate and inclination of the front plate also facilitates this. The transducer units are housed separately and fit into circular recesses in the vessel wall.</p> |
