User manual

individual impedances, you need to remove at least one connection of the
resistors switched in parallel from the circuit. Only this permits testing every
single one of the individual resistors, which may also be more than two.
You may also measure total impedances, such as the total impedance of all
resistors or the joint circuit. The total impedance of our circuit, for example,
is 1,139 Ω. The 2,000 Ω measuring range is sufficient for this. These 1.1 kΩ
correspond approximately to the dropping resistor of 1 kΩ that an LED needs to
light up.
Including the LED, the overall impedance of the circuit is 31.3 kΩ. To be able
to measure it, switch to the 200 kΩ range.
Impedance measurements in circuits are to be performed without voltage supply
only, so that no battery must be connected to the circuit.
Figure 57: Only the overall impedance of, in this case, 493 Ω, can be measured
at the two 1 kΩ resistors installed in parallel in the circuit.
Figure 58: To determine the individual resistors in a parallel circuit,
disconnect the resistor on one side. Only this permits measurement of the
impedance values of each individual resistor.
Figure 59: Measurement of individual resistors in a circuit works correctly only
if no other components are switched din parallel with them.
Figure 60: Determination of the overall impedance of the circuit; if an infinite
resistor was measured, this may suggest a defective circuit.
14
Measuring in a Circuit: Determining Individual Currents in the Circuit
In a pure serial circuit, the same current will flow through all consumers (e.g.
resistors). Therefore, the current is the same everywhere. Where several
consumers are switched in parallel, the overall current splits up into
individual currents. They become larger the lower the impedance of the consumer
and vice versa. The total of the individual currents of a parallel circuit is
the same as the total current. This results to the following relationship for
parallel circuits:
I
ges
= I1 + I2 + … In
For series circuits with several consumers, the following applies:
I
ges
= I1 = I2 = … In
For this measuring exercise, set up a circuit of three resistors in parallel,
two of which with 330 Ω each and the third with 2.2 MΩ. To be able to switch the
multimeter in the different paths, provide wire bridges that you can pull out
easily of required. Provide another 1 kΩ resistor in series with the three
parallel resistors. Last, install the LED supplied via the resistors. Provide a
possibility for current measurement in this string as well.
The total current I
ges
determined for this circuit is at 4.87 V. It is the total
current that flows through the three parallel and then through the series
resistor and the LED.