ABSTRACT
Level meters are classified into two types: continuous and discrete. This chapter describes the methods for the measurement of powder level by classifying them into several groups: mechanical, electrical, ultrasonic wave, radiometric, pneumatic, and other methods. Mechanical level meters are long established and most reliable. Several electrical properties of powder are also utilized in the measurement of powder level: electric capacitance and electric resistance between electrodes. If the ultrasonic wave is emitted from the level meter to a powder bed, a part of the wave is reflected at the surface of the powder bed and detected by a sensor of the level meter. When several adjacent storage vessels are equipped with radiometric level meters, the orientation of the source beams must depend on the arrangement of these vessels. The principle of pneumatic level switches is similar to that of the gas-purge flowmeter or the nozzle flapper utilized in pneumatic controllers.
