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e) Diode test
Make sure that all the circuit parts, switches and components and other objects of measurement are
disconnected from the voltage and discharged.
• Turn the digital multimeter on and select the measuring setting position
“
” with the rotary switch (5). “M” and the “ ” unit symbol are
displayed in the LC display (4).
• Resistance measuring in auto-mode is selected by default and cannot
be switched off. The symbol and M for mega indicate resistance
measuring mode appear in the LC display (4). To select the diode
testing mode, press the SELECT button (1) three time until the diode
symbol “ ” appears in the LC display (4).
• Insert the red measuring lead into the V socket (8) and the black
measuring lead into the COM socket (9).
• Now connect the two measuring prods to the object to be measured
(diode, transistor, etc.). The red measuring tip indicates the positive
pole, the black measuring tip the negative pole.
• Connect the test leads with the prods to each end of the diode. Record
the measurement displayed. Reverse the test leads and record the
measurement displayed as well.
• Press the HOLD button (12) in order to lock a measured value if
needed. The hold symbol appears in the LC-display (4). Press the
HOLD button (12) in order to release the locked value. The hold symbol
disappears from the LC-display (4).
D
• If the LC display (4) shows a voltage in volt (V), the diode shows a forward bias. A voltage drop of 0.5 - 0.8 may
be observed on the pn-junction of a good silicone diode. If “OL” (in the centre of the LC display (4)) is shown, the
diode measured is reverse biased, or the diode is faulty (interruption).
•
Perform a counter-pole measuring for verification. The red measuring lead corresponds to the positive pole
(anode), the black measuring lead to the negative pole (cathode).
• A silicone diode has an on-state voltage drop of approx. 0.5 – 0.8 V, germanium diodes typically have about
0.2 - 0.3 V.
• A diode is shortened if readings show the same voltage drop in both directions (approximately 0.4 V).
•
A diode is bad (opened) when not allowing current to flow in either direction. The digital multimeter shows “OL” in
both directions in such case.
• After measuring, remove the measuring leads from the measuring object and turn the digital multimeter off. Turn
the rotary switch (5) to the position “OFF”.
