A priming sensor for a medical fluid delivery device is disclosed. In an example, the priming sensor includes light emitters and a detector. The detector is configured to detect light emitted by the emitters that interacts with a patient tube connected to the priming sensor. A processor of a medical fluid delivery device causes the emitters to operate in a sweep pattern during a sweep period. The processor receives output data from the detector that is indicative of light detected during the sweep period. The processor creates an output waveform corresponding to the sweep period based on the output data and compares the output waveform to at least one reference waveform to determine one of (a) a no-tube state, (b) a dry tube state, or (c) a wet tube state. The processor provides an output indicative of the comparison for operation of the medical fluid delivery device.