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PTB Seminar on "Current Advances of Electrical Calibrations at Low and High Frequencies 2017"

26.06.2017

With the 303rd PTB seminar, "Current Advances of Electrical Calibrations at Low and High Frequencies 2017", held on 17 May 2017 at the Physikalisch-Technische Bundesanstalt in Braunschweig, PTB continued the series of seminars that have treated current challenges in industrial electrical measurement techniques for many years.

 

 

 

The seminar traditionally takes place in connection with the spring meetings of the "Direct current and Low frequency" and also "High-frequencies and Optics" committees of the Deutscher Kalibrierdienst (DKD)/ Deutsche Akkrediterungsstelle GmbH (DAkkS). Overall, the seminar served the purpose of exchanging information and experience between specialists from PTB, from accredited calibration laboratories as well as users from research and industry. The goal of the seminar was to present new developments from industry and PTB in the areas of electrical calibration measurement techniques and metrology and to present impulses for new measurement procedures and measurement methods that help laboratories to meet the demands placed on them.


A significant event is in store for the scientific community with the introduction of the revised International System of Units (SI), which is presently planned to take place on World Metrology Day, 20 May 2019. In the revised SI, all seven base units will be defined by corresponding constants and, at the same time, the disseminated electrical units will be directly anchored in the SI. World-wide coordinated experiments are establishing the relation between the constants and units. For example, the unit of electric current (ampere) will be defined by the number of elementary charges which are transported through a conductor per time unit. Counting the individual charges that are transported by a self-referenced single-electron pump, one can realized the unit electric current in the revised SI. PTB has contributed significantly to the world-wide efforts in this field. The dissemination of the unit of electric current by PTB to the accredited calibration laboratories is carried out using transfer standards. Thanks to a new development it is now possible to disseminate the unit for small AC currents.


For the exact measurement of large DC and AC currents, such as in magnetic accelerators, current transformers are used, which compensate magnetic flux in the core. Influence of temperature and drift effects are minimized to large extent, especially for measurements of currents.


In addition, a new method for evaluating isolation current transformers in stationary meter test stations was presented. For that method, the customer’s own power meters and the "0 - Ohm burden", which is provided by PTB, were used. The measurements can now be conducted independently and more quickly by test centers.


For the calibration of bridge standards, an improved measuring set-up was presented, which allows calibrations in the frequency range from 225 Hz to 5 kHz, at considerably reduced effort. In comparison to the previously used calibration device, this measuring set-up provides small uncertainties for high-precision measurements at 225 Hz and more stable calibration conditions with decreased uncertainty for high measurement frequencies up to 5 kHz.


The coupling networks used in testing the immunity to conducted disturbances according to IEC EN 61000-4-6 must exhibit a characteristic asymmetric impedance connection of the test sample in the frequency range of 150 kHz to 80 MHz. How to determine them with the help of a vector network analyzer was presented. A comparison between numerical simulations and practical measurements showed good agreement.


PTB has been involved with the calibration of vector network analyzers (VNA) and their residual uncertainty. This year, a new calibration method for multiport analyzers, which can be used cost-effectively in industry and production, was presented.

VNA are used in various ways in high-frequency metrology for scattering parameter measurements (the reflection and transmission properties of components and networks), and for antenna calibrations. For the first time, near-field/far-field transformation was applied to the transmission data measured between two antennas in PTB’s spherical antenna scanner. Using this data, it is possible to determine the far-field antenna gain from a reference antenna in a compact laboratory set-up.

In addition to antenna scanner and open area test site measurements, PTB has realized an on-site measuring technique for permanently installed antenna systems. The WERAN project studies the potential interaction between wind energy plants and terrestrial navigation sites as well as radar systems with the help of new high-frequency instrumentation on an octocopter (unmanned aerial system). Initial measurements at radar stations near a wind farm were presented.

Calibration laboratories that have been accredited in Germany regularly participate in intercomparisons in the framework of the Deutscher Kalibrierdienst to validate their competence and work out processes for suitability tests. In this context, the intercomparison "rise time of oscilloscopes" was presented.

The large number of participants (120 specialists) as well as the lively discussions after the talks proved that the seminar well addressed the needs of the community.

Dr. J. Melcher, Dr. T. Schrader, Department 2.1 and 2.2 of Division 2