 Shunt resistor

A shunt resistor is a resistor used to establish a known relation between current and a measured electric potential difference. For current sensing, it is placed in the measured current path, and Ohm's law givesThe voltage-sensing circuit should draw negligible extra current for this simple relation to describe the desired branch current. Its small series voltage drop is often called the burden voltage.

An original example uses $R_s=10\mathrm{m\Omega }$ and $I=5\mathrm{A}$. The sensed drop is50millivolts and Joule heating dissipatesReducing resistance lowers both the burden and dissipation, but also reduces signal relative to a fixed amplifier offset or readout noise. The nominal resistor value alone therefore does not determine measurement quality.

Lead and contact resistance can dominate a low-value shunt. If a10milliohm shunt is inadvertently measured together with2milliohms of current-carrying interconnect, interpreting the total voltage using only the nominal shunt value overestimates current by20percent. Four-terminal sensing separates the high-current connections from the voltage-sense connections. Analog Devices' LTC6115 data sheet illustrates these Kelvin sense paths and explains how interconnect resistance introduces error.^[ref]

A practical characterization drives known currents through the shunt while measuring the voltage at its sense terminals, then repeats after thermal settling. Temperature coefficient of resistance, self-heating and connection geometry affect the realized conversion. The amplifier's operating range and measurement calibration must be assessed alongside the resistor.

A shunt converts current into a local voltage signal; it does not inherently provide electrical isolation between the measured circuit and its readout. High-side current sensing and low-side current sensing describe alternative placements of that measurement relative to the load and reference conductor.