Ultrasonic-filling position limit switch operating according to the echo principle

摘要

An ultrasonic filling position limit switch having disposed in the container at the full level thereof, at least one ultrasonic transducer for sending out ultrasonic pulses and for receiving echo pulses reflected off the opposite container wall. An amplifier of the electric output signals of the transducer is connected to a threshold limit switch which provides an output signal when the amplifier output signal exceeds a predetermined threshold value. The amplifier output is fed back to an amplifier control input by means of an amplifier control circuit which seeks to maintain the amplifier output signal at an adjustable constant nominal value. A control device blocks the control circuit for the duration of time in each sending period required for the sending out of the ultrasonic sending pulses and for receiving the echo pulses.