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3. Now connect the test probes to the test points, an unpowered
semiconductor circuit, with the red probe to the anode and the
black probe to the cathode (these usually being indicated by a
coloured ring, spot or similar).
To check a diode path in the conducting direction, a voltage of
approx. 0.25 V (germanium) or 0.7 V (silicon) will be measured,
provided that the diode path is not defective.
When the test probes are reversed, i.e. red to the cathode and
black to the anode, then the high resistance direction of the
diode path will be checked.
If "OL" is displayed, the diode is serviceable. If on the contrary
a value between 0 V and "OL" is displayed, either the test points
have been incorrectly chosen or the diode is faulty.
The test voltage under diode test is sufficient to cause most (low
current) LEDs to emit light. With LED operating voltages of
more than 2.0 V, however, the DMM can incorrectly indicate
that the LED is faulty.
Attention!
During the diode test, ensure that the diode and circuit in which
it is installed are completely voltage-free. Any capacitors must be
discharged.
6.6 Frequency measurement
Attention!
It is essential to observe the max. input levels!! Do not connect
any voltages greater than 250 VDC or VAC rms max. With volta-
ges greater than 25 VAC or 35 VDC, there is danger to the user in
the event of contact.
32
1. Connect the red instrument lead with the V/
Ω
socket and the
black instrument lead with the COM socket.
2. Position the measurement function switch to resistance measu-
rement (Ohm).
3. Then connect the test probes with the absolutely voltage-free
test points. Auto Range sets the appropriate measurement
range, to produce the smallest possible measurement error.
The resistance of the test leads can normally be ignored (approx.
0.1 to 0.2 Ohm). However, even this low value can lead to inaccu-
racies in the 400 Ohm measurement area. To compensate for these
"measurement errors", the REL function (described under 4.4.3.C)
can be used.
When resistance measurements are performed, take care that the
test points which are to be touched with the test probes are free
from dirt, oil, solder flux or similar. Such conditions can falsify the
measured value.
With resistances greater than approx. 4 MOhm the display can
take some time to become stabilised. As soon as "OL" appears in
the display and the bar graph flashes, the measurement range has
been exceeded, or the circuit being measured is open circuit/high
resistance (> 40 MOhm).
6.5 Diode test
For measurement of unpowered semiconductor circuits (diodes,
transistors, rectifiers, etc.), proceed as follows:
1. Connect the red test lead to the V/
Ω
socket and the black test
lead to the COM socket.
2. Set the rotary switch to "
/
" and press the blue button
once. The following symbols are shown in the display: The diode
symbol "->l-", "mV" and "OL" (for overload or here: "infinite-
ly-high resistance"). Manual range selection is not possible.
