Detection of malfunction of flow monitoring sensors in a section of tube of an administration set. A sensor is positioned adjacent to the tube to transmit a signal through the tube and any fluid therein. This sensor could e.g. be an infrared sensor, which senses the infrared light transmitted through the tube and generates an output signal. A frequency of the output signal is a function of an intensity of the light transmitted through the tube. A processor receives and determines the frequency of the output signal, and compares the determined frequency to threshold frequency values to determine whether fluid is in the tube. The processor can also send a second drive signal, different from a first drive signal, to detect a malfunction of the sensor.
