User manual

Our LED circuit actually comprises of two consumers: The resistor and the LED. A
voltage drop occurs at either. Its total corresponds to the total voltage.
Mow determine the voltage drop at the resistor by connecting both strings to its
two connections. Observe correct polarity. The red string corresponds to the
plus pole, the black one to the minus pole. If you connect the strings to the
circuit in the wrong direction, you will read a negative prefix before the
measured value. Also set the correct measuring range for the most precise
measurements possible. Also measured the voltage drop at the LED and the overall
voltage drop at resistor and light emitter diode.
When consumers are switched in series, the voltages are at the following ratio:
U
ges
= U1 + U2 + … Un
Figure 42: Setup of the simple LED circuit. A voltage drop occurs at both
consumers, i.e. the resistor and the LED (U1 and U2).
U
ges
indicts to total voltage drop at all consumers.
Figure 43: Setup of the simple LED circuit
Figure 44: The overall voltage of 8.2 V was determined.
Figure 45: A voltage of 5.59 V drops at the 1 kΩ resistor. For precise voltage
measurement, always set the best measuring range.
How to Measure Alternating Voltages?
Alternating voltages are generally measured like direct voltages. Observe that
the multimeter is set for an alternating voltage range. Otherwise, you your not
measured any voltage even though it is there.
Switch the multimeter to the alternating voltage range of 200 V and take the LED
circuit set up before in operation again. Now measure the individual voltages at
the resistor and the LED, as well as the overall voltage.
Although the LED is still lit, the display will always show twice the voltage
value.
If you want to determine the alternating low voltage of a mains adapter while
the multimeter is set to direct voltage, you would instead measure 0.0 V –
although there is,in fact, voltage applied!
Do not perform any measurements with 230 V voltage at a mains adapter. For one
thing, this would mean working with high voltages where you may contact blank,
current-conducting parts directly at the measuring prods. This may cause fatal
accidents! Multimeters also often are designed for a maximum voltage of 250 V
only. In direct proximity of a substation, this may be exceeded and overload the
meter.
Figure 46: If you try to measure voltage drops at the circuit with an
alternating voltage range set, you will determine twice the voltage as when the
instrument is set correctly to direct voltage. In fact, the circuit did not
change as compared to before.