"A $60 tool makes measuring low levels of current consumption easy," Ganssle wrote in The well-engineered µCurrent.
The µCurrent attached to multimeter.
(Source: Embedded.com/Jack Ganssle)
One nifty tool is the µCurrent from EEVblog's Dave Jones. It's a very simple circuit adapter consisting of not much more than a selectable set of shunt resistors and an op amp. You could cobble up your own design in no time, but the µCurrent is inexpensive and well-engineered.
However, the unit is unfused, and, as Ganssle points out, "the shunt resistors are teeny little SMT things that will fry easily so one has to be careful not zap it with too much current."
Engineer Bob Paddock wrote in with a solution:
Place a silicon diode across the uCurrent terminals. High current (relative to the uCurrent range) will cause the diode to conduct, bypassing the uCurrent, preventing fried fuse. Diode will not conduct during the low uCurrent usage. Need to do tricks like this if you are testing a sleeping transmitter that could wake up and go from 20 nA sleep to +1A transmit with no notice.
Now comes µCurrent Gold.
µCurrent Gold is a precision current adapter for multimeters.