User manual

10 How to Measure Currents?
You have already learned that a voltage drop occurs at every component if
several consumers (like the simple LED circuit) are switched in sequence. The
total of these individual voltages is the overall voltage. Let us have a closer
look at this circuit again. You will see that all consumers are in a single line
strand. The same current flows through all of them. The overall current
therefore is the same as the current strength flowing through every single
consumer.
To measured currents, the multimeter must be switched in series with the
consumer or consumers. Therefore, remove the wire bridge between the LED and the
minus pole of the battery. Connect the multimeter instead. The red string must
be connected to the LED, the black one to the battery's minus pole.
Before connecting the battery, switch the multimeter to the largest current
measuring range of 200 milliampere (mA). Then reduce the measuring range until
you can read the precise measurement.
In this measurement, this is the 20 mA range with which you will determine about
5.5 mA flowing through the circuit.
Do not switch to too small a current measuring range. The meter would be
overloaded.
Usually, current measuring meters are protected by fuses. They must only be
replaced when the multimeter is not performing any measurements.
The same current as for the other consumers of this circuit flows through the
meter. Since the multimeter has a very low internal resistor in the area of
current measurement, it does not falsify the circuit and therefore the measured
result.
Attention! Never measure the current right at a consumer. If you touch both
strings to the connections of a battery, this would be about the same as short-
circuiting it. Extremely high currents would flow, which are very dangerous and
would also destroy the meter!
Figure 47: To measure currents, the multimeter must be installed in the circuit.
Figure 48: The multimeter is installed in the circuit to replace the wire bridge.
It is switched in series to the other consumers.
Figure 49: The same current as for the other consumers of this circuit flows
through the multimeter.
How to Measure a Line Passage?
Measurement of line passages can be interesting for several reasons. For example,
if you want to find a specific core in a multi-core wire or if you check a cable
for function or cable break.
Many multimeters have their own measuring range for this, which no only displays
the measuring results but also have a beeper installed that will emit an
acoustic signal at line passage.
Line passages can also be determined easily with the ohm meter function
(impedance function). A few basics on this: Switch the multimeter to the Ω range