What does the instrument manual actually say?
NI's NI-DMM manual, updated 11 May 2026, describes AC Volts and AC Volts DC Coupled as separate modes. It states that the DMM's RMS algorithm is insensitive to the DC component even when the input coupling capacitor is bypassed. The mode name therefore cannot be read as a promise to report AC plus DC RMS.
That is a statement about the documented instrument family and function, not every meter or oscilloscope. Commissioning Docs is independent and is not affiliated with NI. Check the selected model, firmware and approved method before interpreting its output.
Which fields prevent a misleading handover?
A result labeled only volts RMS can hide a different measurement boundary. Preserve the original displayed result and attach the settings rather than relabeling it from memory.
| Field | Keep with result | Question |
|---|---|---|
| Function | Exact mode name | AC component or total? |
| Coupling | Actual input arrangement | What reaches digitization? |
| Algorithm | Applicable manual reference | What quantity is reported? |
| Signal | Approved test description | Is an offset expected? |
| Limits | Range and overload evidence | Was this a valid reading? |
| Approval | Procedure and reviewer | Is the result fit for purpose? |
How can the same signal produce a documentation error?
Illustrative example. A fictional power supply test has a ripple requirement and a separate DC output requirement. The folder contains an AC Volts DC Coupled reading, which a handover spreadsheet copies into a total-voltage field because it sees DC in the mode name.
The reviewer leaves the original record intact and marks the total-voltage evidence unresolved. The actual function documentation and approved procedure determine which result belongs in each field. No arithmetic conversion from that isolated reading can recover a missing DC observation.
What closes the evidence gap?
Record the responsible technical review and any approved repeat measurement. Coupling, algorithm, bandwidth and settling conditions may all matter, but this checklist does not authorize changes to leads, settings or live equipment.
A valid ripple record and a valid DC record answer separate questions. Engineering sign-off is performed only by the registered engineer on the job.
Common questions
What else should the bid team know?
Does DC coupled always mean AC plus DC RMS?
No. The measurement function and algorithm determine the reported quantity.
Can the missing DC component be inferred from the mode name?
No. Retain the approved observation that actually measures it.
Is this a test instruction?
No. The approved procedure and competent technical personnel govern measurement.