Ultrasonic air-in-line detector self-test technique

An ultrasonic air-in-line detection system including a self-test mode for testing the ultrasonic air-in-line detection system to ensure that it is operating properly, comprising:

• a first ultrasonic transducer located on one side of a fluid passageway, said first ultrasonic transducer being resonant at a first frequency;
• a second ultrasonic transducer located on the other side of said fluid passageway;
• means for selectively driving said first ultrasonic transducer either at said first frequency or at a second frequency at which said first and second ultrasonic transducers are not resonant, said first ultrasonic transducer when driven at said first frequency generating ultrasonic vibrations which are transmitted to said one side of said fluid passageway, said ultrasonic vibrations passing through said fluid passageway and being received by said second ultrasonic transducer when there is fluid in said fluid passageway, said ultrasonic vibrations substantially not passing through said fluid passageway and not being received by said second ultrasonic transducer when there is an air bubble in said fluid passageway;
• receiver means for detecting the ultrasonic vibrations received by said second transducer and providing either a first output signal indicative of there presently being fluid in said fluid passageway between said first and second transducers or a second output signal indicative of there presently being an air bubble in said fluid passageway between said first and second transducers;
• self-test means for causing said driving means to drive said first transducer at said second frequency and determining whether said first output signal or said second output signal is generated by said receiver means;
• and
• means for generating a fault signal when said self-test means determines that said first output signal is generated by said receiver means when said driving means is driving said first transducer at said second frequency.

In an ultrasonic air-in-line detection system having an ultrasonic transmitter driven by a frequency sweep signal encompassing a resonant frequency and an ultrasonic receiver for producing a first output signal when there is fluid in a fluid passageway and a second output signal when there is an air bubble in the fluid passageway, a self-test system comprising:

• means for driving said ultrasonic transmitter at a non-resonant frequency;
• means for monitoring the output signal from said ultrasonic receiver to determine whether said first output signal or said second output signal is produced;
• and
• means for providing a fault signal if said monitoring means determines that said first output signal is produced by said ultrasonic receiver when said ultrasonic transmitter is driven at said non-resonant frequency.

In an ultrasonic air-in-line detection system having an ultrasonic transmitter driven at a first resonant frequency and an ultrasonic receiver for producing a first output signal when there is fluid in a fluid passageway and a second output signal when there is an air bubble in the fluid passageway, a method of testing said ultrasonic air-in-line detection system to ensure that it is operating properly comprising:

• driving said ultrasonic transmitter at a second non-resonant frequency;
• monitoring the output signal from said ultrasonic receiver to determine whether said first output signal or said second output signal is produced;
• and
• means for providing a fault signal if in said monitoring step it is determined that said first output signal is produced by said ultrasonic receiver when said ultrasonic transmitter is driven at said second non-resonant frequency.