mA Measuring Prosedure

The meter must go in *series* with the load whose current you want to measure. (If you put it across the load like you do for measuring voltage, it acts like a short circuit and pops an internal fuse.)

With a portable (battery operated) DMM you can typically just put it in series with the hot or ground power lead to the circuit under test. I usually use the positive lead, and connect the positive DMM lead to the positive power supply, and the negative DMM lead to the positive input on the load. But if you reverse the meter leads, you just get negative readings... no problem.

If you have an AC-operated meter you may want to insert it in the ground lead instead, so that the ground of the meter and the ground of the power supply are connected, and the positive meter lead goes to the ground of the circuit under test. This does mean that if you are also probing the circuit for voltage with a scope or another meter, that the ground reference may be "off" by the drop of the current measuring shunt in the meter. This may or may not be a problem.

Note that the above assumes you want to measure DC current. Cheap DMMs don't have AC current ranges, or low AC voltage ranges. If you are trying to measure low AC currents (why?), then you should probably be looking for someplace in the circuit where the current passes through a resistor, and just measure the AC voltage drop across the resistor with a scope and use Ohm's Law to get current.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis