Yokogawa power meter underpins VDE system

When the driver of a conventional internal combustion engine vehicle pulls away from a fuel station, they are unlikely to think twice about whether the amount of petrol or diesel they’ve been charged for is what has actually ended up in their tank. Over the course of decades, public confidence has been established by robust laws that govern how the flow measurement system in every pump has to be accurately calibrated.

Now that electric vehicles (EVs) are accounting for a rapidly increasing proportion of traffic on European roads, public charging points have to earn the same level of trust. That means creating new calibration systems which ensure a driver can be confident that when they have paid for 50 kWh of electricity, their battery has been topped up with that amount of energy.

In Germany, it was natural that manufacturers developing metering products for the EV charging market turned to the non-profit VDE Institute to provide a measurement set-up for calibration that complies with the EU Measuring Instruments Directive. The Institute, which employs more than 500 people at its headquarters in Offenbach am Main, is behind the VDE mark that for more than 100 years has been synonymous with the safety and quality of electrical and electronic devices, components and systems. Every year, VDE’s independent test engineers subject more than 100,000 devices to product, quality and safety tests that are recognised in more than 50 countries around the world.

Creating a measurement system that complies with the EU Measuring Instruments Directive and Germany’s Measurement and Calibration Act was challenging. The law specifies that meter readings must be accurate to at least 3% and no higher than the actual amount of energy supplied. This means the room for error in calibration is minuscule: the accuracy of the power meter used in the test system had to be better than the specification by at least a factor of ten, or ±0.3%.

At the heart of VDE’s solution is the WT3000E power meter from Yokogawa Test & Measurement, whose accuracy of ±0.04% is almost an order of magnitude better than the minimum specification. Combined with a programmable power supply controlled by Yokogawa’s FG420 function generator, the system provides extremely accurate measurement of voltage, current and total energy.

Other features of the WT3000E include a short interval between stored samples of just 50ms, and easy interfacing to precision current sensors supplied by LEM/SIGNALTEC.

For new designs, Yokogawa offers the WT3000E’s successor product, the WT5000 Precision Power Analyzer, a versatile platform that provides a high level of precision and exceptional performance in the most demanding applications. As well as increased accuracy of ±0.03% it boasts high-speed operation up to 10 MS/s (18 bit) and power measurement bandwidth of 5 MHz.

During this project, Yokogawa also supported development of the Raspberry Pi-based control program and measurement data acquisition system which provide an interface to the device under test. This was particularly useful when VDE engineers were faced by an absence of relevant libraries or drivers.

Following accreditation by Germany’s national Physikalisch Technische Bundesanstalt (Federal Physical Technical Institute), the test system is now being used by companies manufacturing energy meters for the country’s rapidly expanding network of public EV charging stations. With 1 million charging points set to be installed across the country by 2030, the VDE seal of approval will play an important part in establishing consumer confidence.

VDE engineer Sven Grünberg, who was part of the team that developed the system, has more than 35 years of experience with different types of test equipment. In this case, a need for ultra-high accuracy that made the choice of power meter crucial to the success of the entire project meant that he automatically turned to Yokogawa.

“To be honest, there is hardly anything else worth considering,” says Grünberg. “The Yokogawa WT3000E has been used in our calibration departments for years, and measures so precisely that it is also perfectly suited for the charging station test bench.”