Multimeter Tutorial

A multimeter is a tool that is used to measure electric voltage, current, and resistance.

Parts of a Multimeter:

Display – shows the measured value and units

Dial – used to switch between different settings

Ports – this is where the probes are plugged in

How to Measure Voltage:

  1. Plug your black and red probes into the ground (labelled “COM”) and voltage (labelled “V”) ports.
  2. Choose the appropriate voltage setting on your multimeter’s dial. Remember that most battery-powered circuits will have direct current, but the setting you select will depend on the project you are working on. For example, if your circuit is powered by a single 9V battery, it probably doesn’t make sense to select the setting for 200V, and 2V would be too low. If available, you would want to select 20V.
  1. Touch the probe tips to your circuit in parallel with the element you want to measure voltage across. Be sure to use the red probe on the side connected to the positive battery terminal, and the black probe on the side connected to the negative battery terminal (nothing will be harmed if you get this backwards, but your voltage reading will be negative).
  2. You might need to adjust the range. If your multimeter’s screen just reads “0,” then the range you have selected is probably too high. If the screen reads “OVER,” “OL,” or “1” (these are different ways of saying “overload”), then the range you have selected is too low. If this happens, adjust your range up or down as necessary.

How to Measure Resistance:

  1. Plug your red and black probes into the ground (labelled “COM”) and resistance (labelled “Ω”) ports.
  2. Choose the appropriate resistance measurement setting on your multimeter’s dial. If you have an estimate for the resistance you will be measuring (for example, if you are measuring a resistor with a known value), that will help you pick the range.
  3. Important: Turn off the power supply to your circuit before measuring resistance. If you do not do this, your reading might be incorrect. If your circuit has multiple components, you might need to remove the component you want to measure in order to accurately determine its resistance.
  4. Connect one of your multimeter’s probes to each side of the object whose resistance you want to measure. Resistance is always positive and the same in both directions, so it does not matter if you switch the black and red probes in this case (unless you are dealing with a diode, which acts like a one-way valve for electricity, so it has a high resistance in one direction and a low resistance in the other direction).
  5. If your multimeter is not auto-ranging, you might need to adjust the range. If your multimeter’s screen just reads “0,” then the range you have selected is probably too high. If the screen reads “OVER,” “OL,” or “1” (these are different ways of saying “overload”), then the range you have selected is too low. If this happens, adjust your range up or down as necessary.

How to Measure Current:

  1. Plug your red and black probes into the ground (labelled “COM”) and voltage (labelled “A”) ports. Note: It is always safer to start out with the port that can measure a larger current. WARNING Failure to do so may blow the fuse. Plug the red probe into the high-current port.
  2. Start from the highest current setting (largest number). You will probably see a 0. If this is the case, keep turning the dial to get to your target range. (If you start from low to high, you may blow a fuse). Remember to check if your circuit is direct current or alternating current, and that almost all battery-powered circuits will be direct current.
  3. Connect the multimeter probes in series to the current you want to measure. Be sure to use the red probe toward the battery’s positive side, otherwise your current reading will be negative.
  4. You might need to adjust the range. If your multimeter’s screen just reads “0,” then the range you have selected is probably too high. If the screen reads “OVER,” “OL,” or “1” (these are different ways of saying “overload”), then the range you have selected is too low. If this happens, adjust your range up or down as necessary.

Continuity Check (which ensures that there is a conductive path between two points in your circuit):

  1. Set your multimeter to the continuity check symbol.
  1. Plug your red and black probes into the ground (labelled “COM”) and voltage/current/resistance (labelled “V,” “A” or “Ω”) ports.
  2. Important: Turn off the power supply to your circuit before doing a continuity check.
  3. Touch two parts of your circuit with the probes. If the two parts of the circuit are electrically connected with very little resistance between them, your multimeter should beep. If they are not connected, it will not make a noise and might display something on the screen such as “OL,” “OVER,” or “1,” which all stand for “overload.”

Troubleshooting:

Don’t panic! There are several common mistakes that can be easily fixed.

  • Make sure your multimeter has fresh batteries.
  • Some multimeters have an auto power-saving feature, and will turn off after a certain period of inactivity. If this happens, turn your multimeter’s dial to “off” and then turn it on again.
  • Make sure you have your probes plugged into the correct ports for what you want to measure.
  • Make sure you are connecting your probes to your circuit in the correct manner (series or parallel) for what you want to measure
  • Make sure you have the correct setting chosen on your multimeter dial for what you want to measure; for example, if you need to measure DC voltage, make sure you don’t have current, resistance, or AC voltage selected on the dial.
  • If your multimeter is not auto-ranging, you might need to manually adjust your range. If your multimeter screen always reads “0,” this might mean the range you have selected is too high. If it reads “OL,” “OVER,” or “1,” the range you have selected could be too low.

Sources: https://www.sciencebuddies.org/science-fair-projects/references/how-to-use-a-multimeter#usingamultimeter

https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/all