Ultrasonic sensor

Abstract

An improved ultrasonic system for detecting the level of a material that has a surface, for example a liquid level inside of a tank, which improves the ability to detect levels particularly when the tank is nearly full. A transmitted ultrasonic signal from a transducer is reflected against the material in the tank, and when received back at the transducer, an output pulse is provided from the transducer. The distance or level is determined by determining the time between the transmission and the reflected signal. A comparator compares the signal from the transducer with a reference and provides an output when a pulse of greater magnitude than the reference is received. In order to avoid problems of high output signals caused by vibration of the transducer after a control signal is removed until the transducer reaches rest (called 'ring down' time), the reference signal is adjusted on a time basis so that it initially will be above the expected level of any unwanted 'ring down' signal, but it will recognize a valid reflected signal when the tank level is close to full because the reflected signal also will have a high magnitude, and the reference signal will decrease with time to a desired level where lower magnitude reflected signals associated with lower tank levels will be properly identified.