Diode Tests - Fluke 27-II User Manual

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Users Manual

Diode Tests

WCaution
To avoid possible damage to the Meter or to
the equipment under test, disconnect circuit
power and discharge all high-voltage
capacitors before testing diodes.
Use the diode test to check diodes, transistors, silicon
controlled rectifiers (SCRs), and other semiconductor
devices. This function tests a semiconductor junction by
sending a current through the junction, then measuring
the junction's voltage drop. A good silicon junction drops
between 0.5 V and 0.8 V.
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To test a diode out of a circuit, set up the Meter as shown
in Figure 7. For forward-bias readings on any
semiconductor component, place the red test lead on the
component's positive terminal and place the black lead on
the component's negative terminal.
In a circuit, a good diode should still produce a forward-
bias reading of 0.5 V to 0.8 V; however, the reverse-bias
reading can vary depending on the resistance of other
pathways between the probe tips.
A short beep sounds if the diode is good (<0.85 V). A
continuous beep sounds if the reading is 0.100 V. This
reading would indicate a short circuit. The display shows
"OL" if the diode is open.