Parasitic echo pulse rejector for ultrasonic liquid level meter

Abstract

An ultrasonic echo-ranging meter for measuring the changing level of liquid in a tank or open channel, the meter including a transducer at a raised position above the liquid surface. Pulses of ultrasonic energy transmitted by the transducer are directed toward the liquid surface and reflected thereby to produce main echo pulses that are picked up by the same transducer. The round trip transmit time of the pulse energy in the gaseous medium above the liquid depends on the distance between the transducer and the liquid surface, this time being measured to provide a reading of liquid level. Also intercepted by the transducer are parasitic echo pulses originating from reflecting wall surfaces and other obstacles in the vicinity of the tank or channel, which parasitic pulses may be confused with the main echo pulses and result in an erroneous reading. In order to reject these parasitic pulses without appreciably slowing down the response time of the meter to liquid level changes, means are provided that discriminate between parasitic and main echo pulses and act to render the meter insensitive to parasitic pulses.