Abstract: A system for sensing flow faults in a membrane system for intravenous fluid introduction is provided. A scanner is pulsed to generate reflected energy signals representative of the position of a membrane within a chamber. The scanner is pulsed both before and after the membrane is commanded to move within the chamber. The signals are then compared by an electronic circuit to determine the difference between them. If there exists a sufficiently large difference between the signals, this indicates that the membrane is moving in response to the command signals and the system is functioning properly. If there exists little or no difference between the signals, this indicates that there is a flow fault in the system, and an alarm is sounded.