Method and apparatus for acoustic level measurements

Abstract

An acoustic ranging system monitors the level of material inside one or more vessels. The system includes an ultrasound transducer mounted in each vessel that is connected to a transmitter and a receiver through a transmit/receive isolation switch and a multiplexer. The transmitter applies a transmit signal to the transducer responsive to a trigger signal generated by a processor thereby causing the transducer to generate an ultrasound signal. An electronic receiver coupled to the transducer generates a receive signal responsive to the reflections of the ultrasound signal from the material. The receive signal is coupled to the processor which determines the elapsed time interval between generating the trigger signal an receipt of each receive signal. The processor then converts one of the elapsed time intervals into a distance indication corresponding to the level of the surface of the material. The transmitter includes a variable frequency oscillator, and the receiver includes a programmable bandpass filter, both of which are set to the operating frequency of the transducer. The processor controls the duration and repetition rate of the trigger signals as a function of the elapsed time intervals to maximize the rate at which the material level is determined. The system also compensates for an exponentially decaying 'ringdown' signal that is generated in the transducer immediately following the generation of the ultrasound signal, and it performs a number of functions to make the system less sensitive to noise, interference, and spurious reflection problems.