Measuring a resistor's value accurately while it is still connected within an electronic circuit can be tricky and is often not recommended. Based on standard practice and the provided reference, it's important not to take the reading while the resistor is in the circuit, especially if the circuit is powered.
Why is measuring a resistor in a powered circuit problematic?
- Other components in the circuit can interfere with the resistance reading.
- Applying the multimeter's test voltage (which is how it measures resistance) to a powered circuit can damage the multimeter or other components.
For the most reliable measurement, a resistor should be measured when it is out of the circuit.
Measuring a Resistor Out of the Circuit
The recommended method, as indicated by the reference, involves using a multimeter.
Here's how to do it:
- Ensure the Circuit is Off and the Resistor is Isolated: First, make sure the circuit containing the resistor is completely powered off. To get an accurate reading and follow the guideline "It's important not to take the reading while the resistor is in the circuit," you should ideally desolder at least one end of the resistor to isolate it, or remove it entirely from the circuit board.
- Select the Resistance Setting on Your Multimeter: Turn your multimeter's dial to the resistance measurement setting, usually denoted by the Greek letter Omega (Ω), representing Ohms (the unit of resistance).
- Connect the Probes: Plug the red probe into the terminal labeled 'VΩmA' or similar, and the black probe into the common 'COM' terminal.
- Take the Measurement: Take your two probes and firmly press them against each end of the resistor. The multimeter will then display the resistance value in Ohms (Ω), Kilo-Ohms (kΩ), or Mega-Ohms (MΩ).
| Step | Action |
|---|---|
| 1. Isolation | Power off circuit; ideally, remove resistor or desolder one leg. |
| 2. Multimeter Setup | Select Ohms (Ω) setting. |
| 3. Probe Connection | Red probe to VΩmA, Black probe to COM. |
| 4. Measurement | Press probes firmly against resistor ends; read the display. |
Following these steps will give you the correct resistance value of the component itself, free from interference from other circuit elements or power sources.
