Rotation of a rotatable assembly of a medical pumping apparatus (100) such as a pump rotor of a rotary peristaltic pump is monitored via electromagnetic radiation (e.g., infrared radiation). The rotatable assembly is formed such that it has portions that are reflective (212) and non-reflective (214) with respect to the electromagnetic radiation. A electromagnetic radiation emitter-detector pair (208) is positioned such that as the rotatable assembly rotates, the reflective and non-reflective portions alternately pass through the electromagnetic radiation emitted by the emitter. The detector receives electromagnetic radiation reflected by the reflective portions, but the non-reflective portions absorb or disperse the radiation such that it is not received by the detector.An output circuit (218) provides a signal indicating the position of the rotatable assembly as a function of the electromagnetic radiation received by the detector.
