Calibration law-compliant charging points - thanks to SAM

The electromobility market is growing strongly - and there is an associated demand for charging stations. To ensure everything proceeds correctly during charging and that consumers can trust the accuracy of their bills, charging stations have had to comply with calibration law since 2019. 

But who - or what - is this calibration law? How can charging stations comply with calibration law? And what makes the local SAM solution so attractive? Compleo outlines the answers to these questions for you in brief articles. Gain a rapid and well-founded overview of this issue - and you will see how it is ultimately possible to effectively and intelligently implement the Verification Act in the marketplace, despite its high demands and complexity during the development phase.

How does SAM work?

Install SAM® – and your charging station is immediately compliant with calibration law. No maintenance, no complex cloud software, no monthly charges. This is all facilitated by the certified storage and display module (or SAM® for short). So let's take a look at the Compleo solution in detail.

Since 2019 charging stations must comply with calibration law on the basis of the revised law governing calibration. Compleo has decided to use a local solution that is stable, reliable and secure. It works without any additional limitations or ongoing costs whatsoever. However, the road to market readiness was long.

It took two and a half years to develop SAM®. Compleo considered that the sole solution available on the market - that was compliant with calibration law - was not an optimum one, so Compleo - under the direction of electrical engineering development team leader Ingo Stahl - developed its own local solution for charging stations that is guaranteed to deliver in practice. The objective here was to enable operators to deal with the issue of calibration law in a stress-free manner by commissioning the storage and display module. The need for the operator to provide an additional backend and the associated lock-in effect through the operator are thereby eliminated.

To ensure maximum flexibility it was important to the developers that end customers should not require any transparency software.

"The local concept dictates that I solve all of the issues within the charging station, thereby allowing non-reproducible measurements to be stored. This, in turn, is a requirement for implementation in compliance with calibration law",


explains Ingo Stahl. From his point of view this is the most appropriate solution, "so that it is not necessary to set up any servers or give any thought to where information is stored and which stakeholders are involved in the business transaction. Local implementation was therefore the most appropriate for us". And instead of tying operators in, SAM® enables them to comply with calibration law in a streamlined and sustainable fashion.

For the implementation of SAM®, Compleo initially looked at the solutions already available on the market and at what other concepts existed over and above these. In this manner, the engineers rapidly discovered how they could best implement the preferred concept.

The most notable challenges were the many visits to deal with the authorities. From a technical perspective electromagnetic compatibility (EMC) presented the greatest challenge. "A product standard does not exist for a meter's ancillary equipment, which is why we have certified SAM® in exactly the same manner as for an electricity meter, i.e. in accordance with the meter standard", explains Stahl. This standard contains EMC requirements that are three times higher than for normal charging points.

"Even medical devices do not have such high radiation requirements as the meter standard."

This gave rise to a relatively high degree of technical complexity during development, where repeated measurements, corrections and optimisations had to be performed.

Two and a half years later our own in-house solution was ready and - in the same manner as for the production site itself - was successfully certified by the German Institute of Physics and Metrology (PTB). "Looking back, my team and I are proud to have stayed on track given the tight timeline", Stahl is pleased to note about this performance. The engineers' next task will be to develop a certified DC electricity meter.

How charging points comply with calibration law

Since 31.03.2019 charging stations must comply with calibration law. What does this mean exactly, what different solutions are available - and can these solutions be implemented retrospectively? We will answer these questions in this article.

Electric cars are the future. They are charged with electricity at charging stations. But how can consumers be sure they only pay for the electricity that has actually been used for charging? Calibration law exists to ensure a reliable answer to this question.

It defines the requirements pertaining to measuring instruments to ensure that reliable measurement results are achieved. The results must be verifiable, presented in a suitable form and must also be protected against falsification during processing. (For further information read "Calibration law explained in simple terms".)

As a solution, two different approaches have emerged: a software solution and a hardware one. A software solution requires a user interface for end customers which gives rise to additional expenditure for (license) costs and maintenance. In brief: With software the cost rises. Furthermore, with software solutions, charging station operators usually remain tied to the provider's IT solution. This usually makes a flexible switch to a different provider impossible.

On the other hand, a hardware solution is stable, reliable and secure. It works without any additional software limitations or monthly costs whatsoever. Further licence fees, for instance, are eliminated and the operator does not have to supply cloud software. Instead, he is able to rely on a range of standardized backend connections as usual.

Compleo is also committed to such a solution with its certified storage and display module (or SAM® for short). SAM® is a local solution within the charging station. The replacement has already been certified by Compleo, which means that existing charging stations can be upgraded in Compliance with calibration law. In the same manner as for the production site itself, it is also module B and module D-certified to ensure consistent quality and, therefore, meet the requirements of calibration law. Furthermore, SAM® already contains an integrated memory. This makes the provision of additional software for storing the values unnecessary.

All AC charging stations are now factory-fitted with SAM® and therefore comply with calibration law. Compleo is already working on a solution for DC charging stations. Existing charging stations can be retrofitted with SAM® so they also meet the legal requirements for reliable metering and billing.

Calibration law explained in simple terms

Since 2019 charging points must be calibrated. But what actually is this calibration law, where does it still matter to us and why is it necessary for charging points? We will explain this, together with other fundamentals, in this article.

Calibration law comprises the "Measures and Verification Act" (MessEG) and the "Measures and Verification Ordinance" (MessEV). It defines the requirements pertaining to measuring instruments to ensure that reliable measurement results are achieved. The results must be verifiable, presented in a suitable form and must also be protected against falsification during processing.

In simplified terms, calibration law governs all of the fundamental areas where billing is based on the quantities consumed - for instance when filling a central heating tank with oil or reading a domestic electricity meter. For consumers, the reference to calibration law is often unobtrusive, yet omnipresent at the same time. For example, all petrol pumps at filling stations and all weighing scales in supermarkets must be calibrated. This ensures, for example, that 100 grams weighed out on a scale actually is 100 grams.

And, as with refuelling a conventional car, consumers want to be sure that only the amount of electricity actually used when charging an electric vehicle appears on their final bill. With charging points calibration law is even more important, because neither a payment kiosk nor a sales receipt are normally available there - cash payments, for instance, are not possible. This is why only charging points that comply with calibration law may be installed.

Being compliant with calibration law effectively means meeting the requirements of the Verification Ordinance. This is the purpose of state-accredited testing laboratories, which perform calibration of the charging points. The German Institute of Physics and Metrology (PTB) provides metrology supervision. As such, it falls under the authority of the German Federal Ministry of Economics and Technology. Calibration laboratories, on the other hand, perform or monitor the actual calibrations.

In general, it can be said that calibration law becomes necessary where a measurement is not repeatable and both parties to the business transaction are not present at the same time. In such cases the transaction must be secured using a different method, for instance by using the storage and display module (SAM) to store the transaction in the charging point itself, thereby rendering it verifiable at a later time.

In short: Calibration law ensures that consumers only pay for what they have actually received.

Local SAM solution: Why on-the-spot inspection is not a problem

  • The requirements of calibration law can be fulfilled with a "local concept" such as SAM®.
  • In practice, this trust-building measure renders re-examination of the measured values redundant.
  • The transfer of all measured and billing-relevant values to the CPO backend via the Open Charge Point Protocol‎ (OCPP) is assured. 
  • The CPO is capable of reading out the SAM® memory via remote maintenance.
  • Even with alternative solutions which offer a remote readout in the form of transparency software, the public key, which is affixed to the charging point meter, is binding in the event of a dispute. This would also require an on-the-spot inspection in order to determine the correctness of the public key.
  • All requirements of calibration law are fulfilled.
  • If desired, users are able to photograph the measurement results once the charging process is complete.
  • Even using alternative solutions derived from fundamental research on-the-spot verification of the public key is necessary in the event of a dispute.