A method of using a pump set on a pump to deliver a supply of liquid to a patient. The pumping apparatus has a control system for controlling operation of the pump. An electromagnetic radiation source is controlled by the control system to emit an electromagnetic radiation signal in a direction for striking a safety interlock device associated with the pump set. The safety interlock device affects the direction of the electromagnetic radiation. An electromagnetic radiation detector is operatively connected to the control system for receiving the electromagnetic radiation signal when the direction is affected by the safety interlock device, and provides an indication to the control system that the pump set conduit is properly positioned in the pump. The pump is controlled to pump liquid in the pump set only when electromagnetic radiation emitted from the first source is detected by the first detector.