Multimeters

Learning Intentions

• To learn how to use multimeters to measure resistance (Ω, ohms) and voltage (V, volts)
• To learn how to use multimeters to test for continuity

Notes

Multimeters allow you to measure a variety of properties of electric circuits, including continuity, resistance, voltage, and current.

•  Continuity
  • Continuity between two points means that there is almost no resistance between the two points (the circuit is continuous)
  • Begin by preparing the multimeter
    • Turn the multimeter to the position labelled “Continuity”, “Buzz”, or )))
    • Plug the red banana plug into the jack labelled “Ohms” or Ω
    • Plug the black banana plug into the jack labelled “COM” (common) or “GND” (ground)
    • When you touch together the two probes, the multimeter should emit a buzz
      • If there is no buzz, use a working multimeter to test the continuity of each of the probes
  • To test a material or component (such as alligator clips) for continuity, touch one probe to one end of the material, and the other probe to the other end of the material. If the multimeter buzzes, there is continuity through the material
    • To make it easier to test for continuity, you can attach an alligator clip (that you know works) to the end of the probe
    • In general, continuity works in either direction, so it does not matter which probe you touch to which end of the material or component you are testing
  • Test various objects around you for continuity. What patterns do you notice?
• Resistance
  • A multimeter can measure the electrical resistance between two ends of a material or component
  • Begin by preparing the multimeter
    • Turn the multimeter to the position labelled “Ohms” or Ω
    • Plug the red banana plug into the jack labelled “Ohms” or Ω
    • Plug the black banana plug into the jack labelled “COM” (common) or “GND” (ground)
    • When you touch together the two probes, the multimeter should measure a resistance of 0.0 Ω
      • If the resistance read OL (overload, or over limit, or out of range), it means that there is infinite resistance between the probes
  • To accurately measure the resistance of a component, it must be removed from the circuit
    • Do not measure the resistance of anything that contains a battery!
  • Start at the lowest resistance range. If the meter reads “0L” , go to the next largest resistance range. If it reads 0L at the highest resistance range, the resistance is so large that in most practical applications it can be assumed to be infinite.
    • Find the resistance of your skin. Do NOT jab the metal probe leads into your skin (unconfirmed Darwin Award).
    • Find the resistance of various objects around you.
    • Find the resistance of a pencil line on a paper.
      • What happens as you make the pencil line thicker?
      • What happens as you make the pencil line longer?
• Voltage
  • A multimeter can measure the voltage between two ends of a material or component
  • Begin by preparing the multimeter
    • Turn the multimeter to the position labelled “DC Volts” or V|
    • Plug the red banana plug into the jack labelled “Ohms” or Ω
    • Plug the black banana plug into the jack labelled “COM” (common) or “GND” (ground)
  • Always measure the voltage of something that does have a battery. Otherwise, you will always read a voltage of 0V.
  • Touch the black test lead to the area that you will use as your baseline (datum). Touch the read test lead to the other end of the component whose voltage you want to measure.
  • You may need to hold the test leads in place for several seconds for the measurement to stabilize.
    • Create a circuit with a USB battery pack, LED, and resistor. Measure the voltage across:
      • The USB battery pack
      • An LED (light emitting diode)
      • A resistor
    • What happens as you change the resistance of the resistor?
• Current
  • This mode is used to measure the current (in Amperes, or Amps) through an electric circuit. It is rarely used in building and designing electronics, and we will not use this mode at all.