Conrad M-4660M Bedienungsanleitung Seite 16

• Sometypes of transistors contain internal base-to-emitter resistance
which could cause undependable measuring results.
• The hFE-measuring value is no absolute measurement. It only indicates
if the transistor is operating or not. The true amplification of a transi-
stor depends on its operating current. This multimeter supplies a base
current up to 10 uA at a Uce of 2.8, the collector current is measured
to calculate the respective hFE-value.
• It is not possible to measure transistors which are connected in a circuit.
• It is not possible to measure the hFE-value of FETs or other unipolar
transistors.
• If a transistor (e.g. BD 242 etc.) has too large terminals for the test
socket, do not force it into the test socket, as it could be damaged.
• The hFE-measurement is affected by temperature differences As soon
as you touch the transistor when you plug it in the socket and warm it
with you fingers the measuring result could be influenced. If the hFE
reading is not stable, take the transistor out and let it come to room
temperature.
During hfe-paramenter measurement of small power transistors the
three sub-displays below the main-display are active. In the left sub-dis-
play the present reading is taken 1 second later, the middle display the
reading is taken 2 seconds later and in the right display the reading
appears 3 seconds later.
5.9 Logic Test
This measuring function lets you easily check logic levels in digital circuits
(5 V or 12 V or 18 V logic etc.).
The multimeter will display one of the three modes:
• if the high level at the test point exceeds 70 % of Vcc (or V++ or Vc or
V+ etc.) "Hi" is displayed (to max. 18 VDC, above "OL" for "Overload"
is displayed).
• if the test point shows a low-level falls below 30 % of Vcc, "Lo" is dis-
played.
26
• if the level at the test-point is between 30 % and 70 % of Vcc, "----" is
displayed.
To check the logic level and to set the level rans proceed as follows:
1. Switch on your measuring unit.
2. Set the rotary switch to "LOGIC". This function displays "rdY"
(= ready for measurement).
3. Connect the test-leads with the COM-input socket (black lead) and
the V-Ω socket (red lead).
4. Now connect the other end of the black test-lead to the "ground"
point of the digital circuit = " − " (normally).
5. While keeping the black test-lead connected to the ground touch
with the red test-probe to the supplying voltage point Vcc (or V++ or
V+ or Vc etc.) If the supply voltage is below 20 VDC and you confirm
once the button "SET/R", a buzzer sound is emitted and "Hi" is dis-
played.
Attention!
If this supply voltage is more than 20 VDC, a buzzer sound is emitted,
too and "OL" for Overload is displayed.
6. Now the multimeter is "ready" to check the logic level test points of the
circuit in question. Separate the red test-probe from the supplying
voltage point. Now move the red test-pobes to the points in question.
Hint
During logic-level measurement, the right sub-display will show the pre-
sent DC current value and the middle sub-display displays the frequency.
27