PSS Series Precision Power Shunt Resistors

What are the PSS Series Precision Power Shunt Resistors?

The PSS is RARA Electronics’ precision power shunt resistor, designed for applications that require accurate high-current measurement combined with sustained power handling in a compact, thermally efficient package. Rated at 100W on a suitable heatsink and 40W in free air, and capable of sustaining currents up to 1400A at the lowest resistance value of 50μΩ, the PSS series addresses demanding current sensing requirements in power conversion, energy storage, and industrial metering systems where both precision and robustness are non-negotiable.

A current sensing resistor — commonly called a shunt resistor — is a precision low-resistance component connected in series with a load circuit to measure electrical current without interrupting the load path. By accurately measuring the small voltage drop that develops across the known resistance using Ohm’s Law (V = I × R), the current flowing through the circuit can be precisely determined. The three fundamental requirements for an effective shunt resistor are very low resistance to minimise power dissipation and circuit loading, tight tolerance to ensure the measured value accurately represents the actual current, and a low temperature coefficient of resistance (TCR) so that the resistance remains stable as the component heats up under continuous load.

The PSS achieves this through its 4-terminal (Kelvin) connection architecture. In a standard 2-terminal resistor, the current-carrying and sense-voltage terminals are shared, meaning any resistance in the connecting leads or contact points adds directly to the measured value — an error that becomes significant at sub-milliohm values. The 4-terminal design uses dedicated current input and output terminals together with independent sense voltage terminals, completely isolating the voltage measurement from the current conduction path. This approach eliminates lead-resistance error and is the accepted standard for precision current measurement at low resistance values.

The resistance range spans 50μΩ to 1mΩ, covering five discrete values: 50μΩ, 0.1mΩ, 0.2mΩ, 0.5mΩ and 1mΩ. Tolerance options of ±0.1%, ±0.5% and ±1% are available, with TCR options of ±5 ppm/°C and ±10 ppm/°C. The PSS is specified for short-time overload stability of ΔR ±0.05% at twice rated power for five seconds, and for long-term load life stability of ΔR ±0.2% after 2000 hours of cyclic loading. Thermal EMF is specified at a maximum of 2μΩ/°C between 0°C and 100°C, a parameter that matters in low-voltage measurement circuits where thermoelectric voltages at dissimilar metal junctions could otherwise corrupt the sense signal. Dielectric strength exceeds 1000V AC for one minute with insulation resistance of 1GΩ at DC 500V, confirming suitability for industrial line-voltage environments.

Model: PSS
Resistor type: Current sensing
Description: High power precision
Power Rating: 100W
Rated Current: 1400A max.
Resistance (Ω): 50u~1m
Tolerance (%): ±0.1, ±0.5, ±1
TCR (ppm/C): 3, 5, 10

More Information

Model: LPS
Resistor type: Current sensing
Description: Low cost precision
Rated Current: 200A~300A
Resistance (Ω): 0.1666m~0.25m
Tolerance (%): ±0.5, ±1
TCR (ppm/C): 15, 30

Model: IRHF
Resistor type: Current sensing
Description: High power precision
Rated Current: 30A~500A
Resistance (Ω): 0.2m~3.333m
Tolerance (%): ±0.1, ±0.5, ±1
TCR (ppm/C): 15, 30

Model: LT
Resistor type: Current sensing
Description: High power precision
Rated Current: 50A~500A
Resistance (Ω): 0.2m~2m
Tolerance (%): ±0.1, ±0.5, ±1
TCR (ppm/C): 30

Model: UHPS
Resistor type: Current sensing
Description: Ultra high power precision
Power Rating: 100W
Rated Current: 707A max.
Resistance (Ω): 0.2m~1m
Tolerance (%): ±0.05, ±0.1, ±0.5, ±1
TCR (ppm/C): 3, 5, 10