Field testing a diode with an ohmmeter: What readings should a good PN diode show when measured with a multimeter in resistance mode for forward-bias and reverse-bias orientations?

Introduction / Context:
A quick bench check of a diode uses a multimeter in resistance or diode-test mode. A healthy silicon diode should conduct in one direction (forward bias) and block in the other (reverse bias). Understanding expected readings avoids confusion during troubleshooting of rectifiers and protection networks.

Given Data / Assumptions:

• Standard PN junction diode.
• Analog or digital multimeter with sufficient internal test voltage.
• Ohmmeter polarity defines forward vs reverse orientation.

Concept / Approach:
In forward bias, the diode conducts, giving a relatively low resistance reading (or a forward-voltage readout in diode mode). In reverse bias, the diode blocks, so the meter indicates very high resistance or open circuit. Large deviations (short both ways or open both ways) imply a faulty device.

Step-by-Step Solution:
Connect meter so anode is positive relative to cathode → forward bias.Observe low resistance (or ~0.6–0.7 V in diode mode).Reverse leads → reverse bias: observe very high resistance (or OL).Compare to known-good behavior to confirm health.

Verification / Alternative check:
Use diode-test mode: a good silicon diode reads ~0.6–0.7 V forward and OL reverse. Schottky or germanium diodes show lower forward readings.

Why Other Options Are Wrong:
High both ways: suggests an open diode or meter issue.Low both ways: indicates a shorted diode.High forward and low reverse: opposite of correct behavior.

Common Pitfalls:
Confusing meter lead polarity; some meters source current from the red lead, others from the black (older analog meters). Always consult the meter manual.

Final Answer:
high resistance when reverse biased and low resistance when forward biased