TEST ENGINEERING. KNOWLEDGE
How do you calibrate a DC charging station on site for legal metrology and AFIR?
To calibrate a DC charger on site, choose a traceable energy-measurement method and document the charging point, operating conditions and measurement uncertainty. Calibration evidence and national legal-metrology approval are distinct, while AFIR adds its own public-infrastructure and user-access requirements.
Test area and evidence
| Test area | What to define or record |
|---|---|
| Measurement | Traceable reference and defined method. |
| Operating point | Record real-load or applicable phantom-power setup. |
| Evidence | Report result, uncertainty and device identity. |
| Legal scope | Confirm national rules and the responsible authority. |
Keep the calibration result, national legal-metrology assessment and AFIR operating checks in separate report sections. AFIR Article 5 addresses public charging access and pricing; it is not a calibration procedure. [1] European Commission: AFIR Article 5 Q&A
A repeatable test workflow
- Define the measurement boundary. Identify station, meter, connector and the point where reference energy is measured. Agree the applicable national procedure, measurement uncertainty and decision rule with the responsible metrology party.
- Prepare a traceable reference. Check the reference certificate, applicable range and calibration status. Record cable/setup identifiers, polarity, ambient conditions and the reference connection according to the equipment instructions.
- Select the operating points. Cover the voltage/current combinations, duration and repetitions required by the approved method. Specify real-load or phantom-power operation and the conditions under which the selected method is accepted.
- Compare like-for-like energy. Use matching start/stop boundaries for station and reference readings. Calculate relative deviation as (station energy minus reference energy) divided by reference energy, and include uncertainty.
- Record operating checks separately. For an applicable publicly accessible point, capture ad hoc access and the displayed price information. Route legal-metrology findings and operational findings to the appropriate owner.
Define the acceptance evidence
| Check | Evidence for the verdict |
|---|---|
| Traceability | The reference certificate and range support the stated result and uncertainty. |
| Energy boundary | Both energy readings represent the same session interval and agreed measurement location. |
| Metrology decision | The report states the applicable limit, uncertainty and decision rule; calibration data are kept distinct from approval. |
| Public charging evidence | Access and pricing checks identify the applicable AFIR case and are documented independently of energy accuracy. |
Fault examples and diagnostic checks
Mismatch at low current
Check offsets, range selection, resolution and uncertainty at that operating point before adjusting the station meter.
Different session totals
Compare start/stop timestamps, meter increments and the agreed treatment of losses or auxiliary energy.
Accurate meter, incomplete customer access
A calibration pass does not test the payment path. Execute the relevant ad hoc access and price-information checks separately.
Practical tip. Save both raw energy readings, start/stop markers and the uncertainty calculation. A rounded percentage alone makes an on-site measurement difficult to review.
Design a reproducible test case
Define the measurement being compared
Identify the charging point and energy meter, the measurement boundary and the transaction or operating interval. Record the reference system and its traceability documentation, together with the selected method and relevant environmental conditions. Keep the meter indication and reference result distinguishable in the report. A difference between two readings is not yet a complete calibration result: the method, uncertainty and decision rule determine how that difference can be interpreted. If a transaction includes pauses or auxiliary behaviour, establish which energy belongs to the comparison before investigating the apparent deviation.
Plan operating points from the actual question
Choose operating points that address the agreed measurement task and are supported by the installed station and calibration setup. Record the executed voltage, current or power conditions and the interval used for the energy comparison. Keep non-executed points visible instead of presenting a limited field visit as coverage of the full operating range. Repeat a relevant point when conditions change and retain both observations. Where the instrument or installation imposes a limit, state it in the report. That makes a field comparison useful to a later reviewer without inventing a wider measurement capability.
Keep calibration and legal acceptance as separate evidence
Calibration describes a measurement relationship under a defined method. Formal legal-metrology acceptance depends on the applicable jurisdiction and authorised process. Identify the responsible decision-maker and the required documents for the installation rather than treating a calibration report as automatic legal approval. Likewise, a charging-infrastructure obligation does not set every instrument specification or metrology procedure. Keep product certification, installation inspection and energy-measurement reports in separate records with clear links. A customer can then see which question the field result answers and which approval or verification still belongs to another process.
Example: investigate an apparent energy difference
Consider an illustrative field comparison in which the station's transaction indication differs from the reference measurement. Confirm that both readings cover the same boundary and interval before changing the station configuration. Check the reference identity, operating conditions and the handling of any interrupted session. Repeat the agreed point where the method permits it and retain the readings and uncertainty information. Report the comparison and its limits separately from a formal legal decision. This example is a measurement-planning workflow, not an observed customer deviation, a universal tolerance or a statement that the charging point satisfies every AFIR or national metrology obligation.
Questions about this test scope
Does AFIR define the national calibration tolerance?
Use the applicable national metrology requirements and accepted procedure for the accuracy decision. AFIR access and pricing provisions address a different scope.
Is phantom-power testing always accepted?
Confirm acceptance for the equipment, method and jurisdiction before the campaign. The report must identify the selected method and its measurement boundary.
Can Plug & Charge replace ad hoc access checks?
The Commission distinguishes contract-based Plug & Charge from ad hoc charging. Check the applicable ad hoc access requirement separately.
What should accompany an on-site energy comparison?
Identify the meter and charging point, reference traceability, measurement boundary, operating interval, conditions and uncertainty information. State the method and decision rule used for any verdict. Keep the reference reading and the station indication separately visible so that another reviewer can understand the comparison.
Does a mobile calibration result approve the installation legally?
A calibration result supports the documented measurement comparison. Legal approval or verification follows the applicable jurisdiction and authorised process. Confirm the required evidence with the responsible authority or qualified body; do not relabel a technical comparison as an approval it did not grant.
Sources and further reading
Technical content: comemso. Updated .