Patent ID: 8836519

Claim:
A dialysis system comprising: a dialysis machine; a control unit; a medical fluid tube connected to the dialysis machine; an ultrasonic transmitter positioned adjacent to the medical fluid tube; an ultrasonic receiver positioned adjacent to the medical fluid tube configured to receive one or more signals in response to the activation of the ultrasonic transmitter; and a computer storage medium encoded with computer program instructions that when executed by the dialysis system, causes the dialysis system to perform operations comprising: controlling repetitive activation of the ultrasonic transmitter, wherein controlling repetitive activation of the ultrasonic transmitter comprises, for each repetition: activating the ultrasonic transmitter for a first period of 2 to 15 milliseconds; and deactivating the ultrasonic transmitter for a second period of 998 to 985 milliseconds; receiving a signal from the ultrasonic receiver during an activation of the ultrasonic transmitter; and determining that fluid is absent or present in a portion of the medical fluid tube based on a comparison between the signal and a threshold value.