Multimeter
For voltage and resistance measurements, the test leads of digital multimeters are connected to input jacks that are typically marked with a plus sign for the positive probe and a minus sign or the word "common" for the negative one. For current measurements, the test circuit must be interrupted so the meter can be connected in the current path. A special positive input jack is used to route the current into a low resistance shunt in the meter. The current then returns to the circuit through the meter's common terminal.
Instructions
1. Turn the meter on and set it for measuring AC or DC current. If there are multiple ranges, start with the highest setting to prevent exceeding the meter's range.
2. Insert the test leads into the correct meter jacks. The black lead connects to the common jack and the red lead connects to a jack that is specially made for current measurements and marked accordingly. There may be multiple positive current jacks for different ranges. Choose the one that you know is above the expected range for your measurement.
3. Remove power from the circuit you will be measuring.
4. Interrupt the current path in the circuit at a convenient place. Ideally this should be at a connection point that will be easy to restore.
5. Connect the red (+) lead from the meter to the current source side of the break in the circuit. Connect the black common lead to the point where the current should return to the circuit. The meter will now be in series with the current path that was interrupted. Make sure the clips on the test leads are secure so they don't fall off during the measurement.
6. Reapply power to the circuit.
7. If there are leading zeros on the digital display consider repeating the previous steps using a lower current range or a lower current connection point on the meter if one is available. This will increase the accuracy of the reading.
8. Turn off the circuit power and remove the meter leads from it. Restore the original circuit connections.
9. When all current measurements are complete, reconnect the meter leads to the standard jacks that are used for voltage and current measurements. This may prevent an incorrect connection of the meter in the future. Inadvertently connecting the meter to a voltage source when it is configured for current measurements could damage the meter or the external circuit.
Tags: current measurements, current path, test leads, connection point, jacks that, lead connects