User manual

instrument should not display about the same measured values. If the instrument
indicates voltages in this measured range, you need to measure about 0.7 V to
0.8 V each. The VC-11 shows only relative values. They are, however, about equal
on either side with about "1080". This provides information on whether a
transistor is generally OK or not.
If you want to test a PNP transistor in this manner, you only need to swap the
measuring strings.
Figure 73: Simple multimeters can only be used for a general statement on
whether a transistors is OK or not. To test an NPN transistor, apply the rated
measuring string to the base connection, the black one alternatingly to the
collector and emitter.
Figure 74: In both cases, the display should not display about the same measured
values.
19 Inspecting Light Emitter Diodes
A very simple method to test light diodes can be performed with any multimeter.
Build a simple LED circuit on the experimenting board. Then precede the LED with
a 1 kΩ resistor and connect a 9 V battery so that the LED is lit.
Now measure the voltage drop at the LED. Connect the two measuring strings to
the two LED connections for this. Now the multimeter is switched in parallel to
the consumer, as generally required for voltage measurements. The voltage drop
determined in this manner is about 2 V. In addition to this, you can check if
the LED is lit or not.
Figure 75: With this simple LED circuit, the function of a LED can be tested
with the voltmeter function.
Figure 76: The voltage drop at the LED is about 2 V.
20 Measuring Temperatures
Various multimeters can also measure temperatures. This requires a separate
temperature sensor. In the Voltcraft VC840 multimeter, for example, a so-called
NiCrNi sensor(Nickel-Chrome-Nickel type K) is used. The temperature measuring
range of the instrument is from -40 °C to +1,000 °C. The wire temperature sensor
included with the multimeter is meant for temperatures up to +400 °C.
First set the multimeter to the measuring range "°C". It symbolises temperature
measurement. Switch on the device now. You will see that you can measure the
ambience temperature even without the temperature sensor connected. This permits
quick determination of the room temperature.
Now connect the two measuring lines of the temperature sensor to the multimeter.
Connect the black string to the COM socket as usual. The red string is connected
to the ΩAmA°C socket. Since you will hardly need this socket for measurements at
electrical components or circuits, this is unusual. This is also one of the most
common error sources when a temperature measurement is not working.
Attention! Do not connect any voltages to the ΩAmA°C socket. This may destroy
the multimeter.