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Kirchhoff's Law » Physics » Electricity » Measuring Current-Voltage » Let's go... » Experiment 3 - Real Ammeter

Experiment 3 - The Real Ammeter


Real Ammeter

The model of a real ammeter consists of an ideal ammeter  and an resistor Ri in series.


Equivalent circuit diagram real ammeter.


Circuit diagram with a real ammeter.

This has a direct influence on the measurement. The total resistance Rtotal of the circuit is...

Rtotal  =  RL + Ri

and is always greater than the load resistance RL alone. Thereby is...

  • A real ammeter shows a smaller current than would flow in the circuit without ammeter!

The value of the internal resistance is dependent on the measuring device (digital, analog multimeters, etc.) and the selected measuring range. Typical values ??range from a few Ω to several kΩ.

You can examine this by connecting the analog and digital ammeter and measuring the current at different measuring ranges. Thereby you see that the measured values differ due to the internal resistance.

In the next experiment, you look at the voltage measurement...

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