A diode is like an electronic switch. If the voltage is above a certain value, the diode will conduct. Typically a silicon diode turn-on voltage is 0.6V. And diodes only allow current to flow in one direction.
When checking diodes or junctions, the multimeter will not only give a wide reading range but also drive currents greater than 50mA. (see Table 1)
When measuring the resistance of circuits containing diodes, the test voltage of the DMM will be lower than 0.6V, preventing the crystal junction from conducting.
When selecting a diode test, the test voltage is raised in order to check the functionality of the diode or semiconductor crystal.
Some DMMs have a diode test function. This function measures and displays the actual voltage drop across the diode. The voltage drop of the silicon junction should be less than 0.7V during forward testing, and the circuit will be open during reverse testing.
How to Test Resistance
1. Turn off the circuit power
2. Select electric blocking
3. Insert the black test lead into the COM jack. Insert the red test lead into the resistance test jack
4. Connect the test lead probe to both ends of the component or circuit under test
5. Check the reading and note the unit of ohm (Ω), kilo-ohm (kΩ), or megohm (MΩ).
Note: 1,000Ω=1KΩ; 1,000,000Ω=1MΩ
It is important to note: Turn off the power when testing resistance.
