Choosing the Sense Point for Electronic Load Tests

An electronic load connected through cables and connectors does not necessarily see the same voltage that exists at the board output. The difference becomes significant when testing a low-voltage rail at substantial current. Choose the voltage observation point deliberately before comparing load regulation or dropout behavior.

Draw the complete current path

Include the board connector, harness, adapters, current-measurement elements, and load terminals. Mark where the force current flows and where voltage is sensed. A four-wire arrangement separates those functions, but its usefulness still depends on the selected points and the instrument’s operating mode.

The Keysight EL30000 user guide describes remote sensing at the device under test and distinguishes its role from constant-current operation. Consult the manual for the actual load: sensing can affect voltage-based control or readback without making every operating mode regulate voltage at the board.

Quantify an ordinary harness error

As an illustrative calculation, a total force-path resistance of 40 milliohms carrying 5 A drops 0.20 V and dissipates 1 W. A board output of 3.3 V would therefore present about 3.1 V at the load terminals under those assumptions. A local load reading could incorrectly be reported as the board’s output voltage.

Measure at the intended interface and identify whether the connector drop belongs inside or outside the product requirement. If the specification is at the far end of a supplied cable, sensing at the PCB pads answers a different question.

Review instrument limits and dynamics

• Check minimum operating voltage and power limits for the required current.
• Follow the load manufacturer’s sense wiring and connection sequence.
• Confirm the selected sensing mode in the saved configuration.
• Keep force and sense routing consistent with the instrument guidance.
• Observe board voltage during dynamic tests with a suitable independent measurement.

A programmed current step is not proof that the same step reached the board instantaneously. Harness inductance and the load’s control behavior affect the actual waveform. Record measured current and voltage when interpreting transient response.

Save a connection diagram, sense locations, harness description, load mode, and operating settings with the results. If changing a cable appears to improve the regulator, repeat the comparison with the original arrangement before changing the circuit. A well-defined load test separates the board’s performance from the limitations and voltage losses introduced by the bench setup.

Label adapters that belong to the qualified setup. Replacing one with a visually similar connector can alter both contact resistance and the transient current path.