Electrical Parameter Testing

Why this measurement is difficult to get right

Electrical parameter testing establishes what a device actually draws and delivers. It underpins incoming inspection, design verification, type testing and end-of-line pass-fail decisions, and in every one of those contexts the required accuracy depends on the tolerance being judged rather than on the instrument catalogue.

The measurement is usually straightforward; the ambiguity comes from deciding which quantity to record and under which load condition. Fixing that before choosing an instrument prevents the common outcome of a meter that measures everything except the one figure the test report requires.

What has to be measured

• Input voltage and current at the specified operating point, including the low end of the range.
• Active power in watts, plus apparent and reactive power where the load is not purely resistive.
• Power factor, which indicates how far the load departs from unity.
• Frequency, and energy accumulation where consumption over time is the subject of the test.

Which instrument measures what

Practical considerations

• Confirm whether the instrument is true-RMS. On switched-mode and phase-controlled waveforms, a mean-sensing meter will report a figure that does not correspond to the real heating effect.
• Check the resolution at the low end of the current range, not just the maximum range. Most low-power tests are decided by a reading taken near the bottom of the span.
• Establish the accuracy class and the standard it is referenced to before quoting a tolerance in a test report.
• Decide early whether readings must be logged or exported, which determines whether a communication interface is mandatory.