Ultrasonic liquid-in-line detector for tubes

Abstract

An apparatus and method for detecting the presence of liquid in pipes or tubes using ultrasonic techniques A first piezoelectric crystal is coupled to the outside of the pipe or tube at the location where liquid in the tube is to be detected. A second piezoelectric crystal is coupled to the outside of the pipe or tube at the same location along the tube but circumferentially displaced from the first crystal by an angle around the pipe or tube of less than 180°. Liquid in the pipe or tube is detected by measuring the attenuation of an ultrasonic signal sent by the first piezoelectric crystal and received by the second piezoelectric crystal.

The embodiment of the invention in which an exclusive property or privilege is claimed is defined as follows: 
     
       1. An apparatus for detecting the presence of liquid in a tube comprising: a sending transducer in direct contact with said tube, a receiving transducer in direct contact with said tube at the same location along said tube as said sending transducer but circumferentially displaced from said sending transducer by an angle less than 180°,   means for sending an ultrasonic pulse from said sending transducer,   means for selectively measuring the amplitude of an ultrasonic pulse received by said receiving transducer, said selective measuring means operably capable of selectively measuring the amplitude of an ultrasonic pulse during a time period that includes the time period after which an ultrasonic pulse arrives at said selective measuring means by a path through the tube less than 180° and ends before an ultrasonic pulse arrives at said selective measuring means through the tube by a path through the tube greater than 180°,   whereby the presence of liquid in the tube can be detected by the attenuation of a pulse sent by said sending transducer and received by said receiving transducer.   
     
     
       2. The apparatus of claim 1 in which said means for sending a pulse comprises: means for sending an approximately 0.5 microsecond pulse at a 1,000 pulse per second repetition rate.   
     
     
       3. The apparatus of claim 2 in which the tube has an outer diameter between approximately 0.5 and 0.75 inches. 
     
     
       4. The apparatus of claim 3 in which the sending transducer is a piezoelectric crystal. 
     
     
       5. The apparatus of claim 4 in which the receiving transducer is a piezoelectric crystal. 
     
     
       6. The apparatus of claim 5 in which the tube has a wall thickness in the range of approximately 0.049 to 0.056 inches. 
     
     
       7. The apparatus of claim 1 in which said receiving transducer is displaced approximately 150° around the tube from said sending trasnsducer.