= Shunt resistor
A \b[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> gives
$$
V_s=IR_s,\qquad I=\frac{V_s}{R_s}.
$$
The 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> dissipates
$$
P=I^2R_s=0.25\,\mathrm W.
$$
Reducing 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.<LTC6115 data sheet by Analog Devices>[printedp11, Sense Resistor Connection and Figure3]{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.
Back to article page
