SMUs are DC measurement sources operating in four quadrants, i.e. as both source and load (Source Measure Unit). They were first marketed by Keithley. The combination of an accurate voltage or current source, or accurate power simulation, and parallel measurement at the level of a 6 ½ digit multimeter offers unique versatility. Recently, models with pulse mode have been added for component testing where prolonged operation changes the parameters of the item being measured.
