| 摘要 |
PURPOSE: To easily and stably detect the presence or absence of a liquid by excluding the received waves of ultrasonic waves propagated at the outer periphery of a bath wall from a measurement target according to the quality and shape of the liquid bath. CONSTITUTION: Sensor heads 2a and 2b for transmitting and receiving ultrasonic waves are fitted to the outer surface of the bath wall of a liquid bath 1. The output of the received signal of the sensor heads 2a and 2b is binary-coded in reference to a specific threshold by a comparison circuit 7. A counting circuit 8 measures the signal reception start time and the life time of both binary-coded signals when there is and is not a liquid (a) in advance. An operation processing circuit 6 sets a measurement period so that unneeded reception waves (those received after being propagated at the outer periphery of the bath wall of the liquid bath 1) which appear when there is not liquid (a) in the liquid bath 1 based on both binary-coded signals. |
