Diode Tests - Fluke 28IIEX User Manual

28 II Ex
Users Manual

Diode Tests

WCaution
To prevent damage to the Product or to the
equipment under test, disconnect circuit
power and discharge all high-voltage
capacitors before you do a diode test.
Use the diode test to examine diodes, transistors, silicon
controlled rectifiers (SCRs), and other semiconductor
devices. This test sends current through a semiconductor
junction, while it measures the junction's voltage drop. A
good silicon junction drops between 0.5 V and 0.8 V.
To do an out of circuit diode test, set up the Product as
shown in Figure 7. For forward-bias measurements on a
semiconductor component, put the red test lead on the
component's positive terminal and put the black lead on
the component's negative terminal.
In a circuit, a good diode will cause a forward-bias
measurement of 0.5 V to 0.8 V. A reverse-bias
measurement can be different because of 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 measurement is 0.100 V.
This measurement shows a short circuit. The display
shows "OL" if the diode is open.
26