Knowledge / EVSE metrology
EVSE Calibration with Controlled Real Load
Compare the energy recorded by a charging station with a calibrated reference while the station supplies a controlled real load. Set repeatable voltage, current and duration. Record the metrological result separately from additional observations during charging.
Which calibration method fits the measurement task?
Basis and scope
The national guidance discussed below concerns Germany. A calibration result does not by itself complete legal verification.
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Energy measurement for the charging bill
Measure energy while the charging station supplies real power.
Compare station and reference readings
Illustrative values: the reference measures 10.00 kWh and the station records 10.05 kWh. The relative deviation is (10.05 − 10.00) / 10.00 × 100 = +0.5%. The result must be assessed with the measurement uncertainty and the limits of the applicable procedure.
Voltage is measured in volts (V), current in amperes (A), power in kilowatts (kW), and energy in kilowatt-hours (kWh). For DC, power is voltage × current. Energy accumulates as power flows over time.
Observe charging under controlled real load
Observe charging operation and assess measurement accuracy.
| Test benefit | What the setup lets you investigate |
|---|---|
| The station supplies the test power | The station’s power conversion operates under load. Use appropriate measurements to examine its electrical response during the energy comparison. |
| Defined current and duration | Hold the operating point for the required interval. Observe how the measured behaviour changes during operation and as the system warms up. |
| Repeatable conditions | Repeat the selected operating point after an adjustment, repair or update. Keep the test conditions with both results so they can be compared. |
| A shared charging record | Keep the energy result with the charging session, requests and measured voltage or current when these channels are included in the setup. |
Real-load tests let you observe actual operation during the energy comparison. Define additional measurements and evaluation to assess electrical safety, EMC compliance and the required dynamic responses fully.
Plan repeatable operating points
Specify voltage, current and duration alongside kW.
State the required measurement uncertainty with the voltage, current and duration.
| Voltage | Current | Power | Planning question |
|---|---|---|---|
| 150 V | 500 A | 75 kW | Can the setup hold high current at this low voltage for the required duration? |
| 1,000 V | 10 A | 10 kW | Can the reference and load work at this high-voltage, low-current point with the required uncertainty? |
Include stabilisation time, the energy interval and the repeat sequence. Peak or boost operation must be distinguished from a continuously sustainable operating point.
Easy Chester Calimera
Compare energy readings at the installed charging station.
Calimera combines charging communication, reference measurement and controlled real load in a mobile setup. Use comframe to keep the selected conditions, recorded measurements and report together.
- Define the point
Record the charging station, procedure, voltage, current and duration.
- Compare the readings
Measure the station and reference over the same interval after the required stabilisation.
- Keep a repeatable record
Save the deviation, measurement uncertainty and test conditions. Repeat the required operating points.
A vehicle is also a real load, but its requested current changes with battery condition, temperature and charging control. A controlled load gives the operator more direct control over repeatable points within the supported range.
Explore Calimera operating modesReal load and phantom power in test planning
Choose the load method for the measurement task.
Why choose real load when phantom equipment can be smaller?
Phantom equipment applies the voltage and current needed for the metrological comparison without transferring the equivalent full charging power. This can reduce the load-equipment and energy requirement. Choose real load when the test also needs the station’s actual power-conversion operation at controlled points. Compare compatibility, installation work, duration and the required observations as well as equipment size.
Does a phantom test reproduce every operating effect?
No. In the published PTB setup, the station’s internal DC supply was disconnected. The arrangement could include cable losses, so phantom testing should not be described as always excluding them. Its metrological result does not establish identical behaviour of the complete powered station. The real/phantom comparison covered 20, 40 and 70 A at 200 and 420 V; additional phantom measurements at higher current were not equivalent high-current real-load comparisons. PTB study, pages 1–2.
Can phantom power be acceptable for legal metrology?
Yes, for a suitable charging installation and the applicable verification procedure. German guidance published in June 2026 with AGME and PTB explicitly describes field testing with phantom power, provided the installation supports the technique. This is not a blanket approval of every test device and station combination. German guidance, pages 4 and 11.
OIML G 22:2022, section 6, note 2, allows real or phantom load within its test programme; national requirements still apply. DKE lists E DIN VDE V 0122-2-100:2025-06 as a draft interface specification. Neither document alone proves that a particular station has passed its required legal verification. OIML G 22 · DKE document status.
Does calibration mean that the station is legally verified?
Calibration establishes the relationship between the station reading and a reference under stated conditions. Adjustment changes the instrument to reduce a deviation. Legal verification (Eichung) follows the requirements and procedure for the specific installation. A calibration result is useful evidence, but it does not automatically complete the legal process.
Sources and reading scope
Practical operating-point examples and Calimera workflow: comemso calibration webinar. Metrological-method boundaries: the linked PTB conference paper (CPEM 2022; repository publication 2025), OIML G 22:2022, the June 2026 German guidance and the DKE catalogue entry. The regulatory discussion concerns Germany; another country may prescribe a different procedure.
Metrological-method sources checked: 4 October 2026. The examples explain test planning and do not constitute an approval of a particular charging station.
Plan an EVSE calibration application