Burden voltage is the electric potential difference introduced between the terminals of an ammeter when an electric current flows through it. A shunt resistor makes a measurable signal by deliberately developing this drop, but the drop can also change the electric current being measured. In a real ammeter, leads, connections and a protection fuse can contribute as well as the shunt resistor.[ref]
Consider an ideal1volt source driving a100ohm resistor. Before inserting an ammeter, Ohm's law gives10milliamperes. If the inserted ammeter has10ohms of total series electrical resistance,The ammeter could report its own current perfectly and still measure a current9.09percent below the undisturbed value. This is a change in the measured electrical circuit, rather than a display-rounding error.
Reducing the shunt resistor's electrical resistance reduces burden voltage but also reduces the signal presented to an amplifier. A feedback ammeter instead uses a transimpedance amplifier to keep its input near a reference potential. National Instruments illustrates the distinction with a low-voltage leakage-current measurement, where the burden voltage consumes a substantial fraction of the applied test electric potential difference.[ref]
Minimizing Errors for Low-Current Measurements Using NI Hardware by National Instruments. Figures2–3 and associated leakage-current comparison
An experimental check uses several sensing resistors and records both the inferred electric current and the load's terminal electric potential difference. Dependence on the inserted electrical resistance reveals loading. Four-terminal sensing reduces errors from connection drops in the sensed signal; it does not remove the physical burden voltage across the shunt resistor.
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