User manual

Some example calculations:
How high if the current flowing through a 330 Ω resistor when the voltage at it
drops by 9 V?
I = U / R 9 V / 330 Ω = 0.027 A = 27 mA
The total resistance of a circuit is 1,500 Ω, the total current flowing through
the circuit
is I
ges
= 40 mA. What voltage is the circuit connected to?
U = I * R 0,04 A * 1,500 Ω = 60 V
16 The Multimeter as a Battery Tester
Multimeters meet the function of a battery tester as well. Since multimeters
measure voltages precisely, they permit a precise statement on how charged a
battery or rechargeable battery still is. The OK/NOK indication of many battery
testers only permit very vague statements.
To inspect battery voltage, the multimeter must be switched into the direct
voltage area. Since you already know how high the expected maximum voltage is,
you can set the correct measuring range at once: e.g. 2 V for 1.5 V batteries.
Now put the red string to the plus pole, the black one to the minus pole.
You can already read the precise voltage of the energy storage on the display.
Several multimeters, including the Voltcraft VC-11, have separate measuring
ranges for battery tests. They are at about 1.5 V and 9 V. You may use these
areas to measure batteries particularly precisely.
Even if the multimeter displayed voltages with an accuracy of two decimal digits
- the significance is not very high. The idle voltage measured here is always
higher than the voltage a battery supplies under load.
An indicative measuring result is only possible if the voltage drop is
determined at the battery or rechargeable battery under load.
Figure 66: The idle voltage of this battery is 9.6 V.
Figure 67: Under load,. the voltage drops to 9.43 V. Only under the load at
which the battery is usually operated can a reliable statement be made about
whether its charge is still sufficient.
Measuring Diodes
A diode only permits current to flow in one direction. To determine flow
direction, multimeters often have a dedicated diode test function integrated. It
usually also works as a passage tester and has a beeper that emits an acoustic
signal at current passage.