A low cost dynamic level measurement instrument using ultrasonics (with emphasis on electronic signal processing)

摘要

A practical low cost dynamic and non-contact level measurement instrument is presented which provides high speed and high accuracy solution for level measurement It uses the Time of flight (TOF) principle, which is today's state of art technology and most widely used. TOF technique is used for measurement because it is simple to implement and resistant to disturbance from unwanted ultra sound echoes. The transduction element emits bursts of 0.6ms, with pulse frequency of 40KHz. A burst of pulses is transmitted and an echo is produced when the transmitted burst encounters a fluid (surface). TOF is the time elapsed between the transmission of a pulse and its reception, from which the level can be calculated. Accuracy of level measurement depends on how accurately TOF can be measured with proper electronic signal processing and how well the speed of sound in the medium (normally air) is known. Levels up to 3m can be measured with an accuracy of 2%. Experimental results show that measurement accuracy depends on the precision obtained by digital processing with which time is measured and on the ambient conditions. Results are in close agreement with the calculation. Although this paper concentrates on liquid and limited measurement in laboratory, it can also be applicable in industries.