Multimeter Resistance Test
- Set the multimeter to read "resistance." Check that the two probes are inserted in the right holes.
- What does the readout say when the probes are not touching anything? When the two probes are separated, there is an infinite resistance separating them, since air does not conduct electricity. Make a mental note of your multimeter's readout for infinite resistance, because it varies with the manufacturer.
- Touch the two probes together. Now what does the readout say? When you touch the two probes together, the resistance is close to zero, since the metal tips are excellent conductors.
- Measure the resistance of some resistors that are not attached to a circuit. For example, test resistors of 100 Ω (ohms), 10,000 Ω, and 1 MΩ (megaohm, or 1 million ohms). You can buy these online at www.radioshack.com. Touch the probes to the wires on either side of the central cylinder. Watch the units: a "k" means kilo-ohms (thousands of ohms), and an "M" means megaohms. Look online for a chart that tells you how to read the value of the resistance based on the colored bands.
- Never measure resistance in a circuit when power is applied. You must also discharge capacitors in a circuit before measuring resistance, because if there is any source of current other than the multimeter itself, you will get erroneous readings. If the circuit you are working with has large capacitors, you should test them to see if they are carrying a charge. Test the capacitor for charge using a voltmeter, set to high DC voltage. If there is a charge on the capacitor, use a high-wattage resistor to discharge it. Carefully touch the two leads of the resistor to the leads of the capacitor. It may take several seconds for the capacitor to discharge. For more details about how to safely discharge capacitors, visit the following website: Capacitor Testing, Safe Discharging, and Other Related Information
