Resistance is the measure of difficulty electrons have in flowing through a particular object. It is similar to the friction an object experiences when moving or being moved across a surface. Resistance is measured in ohms; 1 ohm is equal to 1 joule per second or 1 volt of electrical difference per 1 ampere of current. Resistance can be measured with an analog or digital multimeter or ohmmeter. Use the following steps to measure resistance to electric current.
- If you are testing resistance with an analog multimeter, you must zero the meter before performing the actual test. Touch the probes to each other to create a short circuit, then adjust the controls to read 0 ohms. Digital multimeters do not need to be zeroed out.
- Some digital multimeters will adjust the range for you automatically.
You may need to adjust the multimeter’s range downward to get a suitable reading.
- If you change the range on an analog multimeter, you’ll have to zero it out again before touching the probes to the object to be measured under the new range setting.
This keeps the batteries from being drained when the multimeter is not in use.
Measuring resistance on a component in a circuit will cause inaccurate readings because the multimeter is also measuring resistance from the other components in a circuit as well as the one being tested. Sometimes, however, it is necessary to test resistance on components in circuit.
Current flowing through a circuit will cause inaccurate readings, as the increased current will create a higher resistance. Also, the additional voltage could damage the multimeter. (For this reason, testing the resistance of a battery is not advised.)
- Any capacitors in a circuit being tested for resistance should be discharged before testing. Discharged capacitors may absorb charge from the multimeter’s current, creating momentary fluctuations in the reading.