Tobias Möhring

Bio: Tobias Möhring is an academic researcher from German National Metrology Institute. The author has contributed to research in topics: Signal & Power (physics). The author has an hindex of 4, co-authored 7 publications receiving 26 citations.

A current transformer test set for the audio frequency range

Abstract: This paper describes the setup of a test set for current transformer (CTTS) calibrations using a two-channel voltage ratio measurement method. A wideband two-channel digitizer and a differential analogue front-end are used as the heart of the ratio measurement system. The front-end suppresses some static errors of the digitizer and is tested for the frequency range up to 200 kHz. Various active or passive shunts adapt the secondary output current to the ± 2 V or ± 10 V input range of the ratio measurement system. Furthermore, the system is used to set up future measurement systems for efficiency measurements in the frame of current European Metrology Programmes (EMRP).

Characterization of a 2-channel digitizer with differential inputs

Abstract: The input characteristics of a two-channel high speed digitizer have been improved utilizing high accurate and matched instrumentation amplifiers and the complete system has been characterized. DC linearity and stability have been investigated and a correction function for the digital filter of the digitizer has been formed for up to 35% of its sampling frequency.

Real power measurement using a thermal converter

Abstract: In this paper, a new application of thermal converters is presented which allows energy, power and rms measurement without the need to substitute the measurement signal with a dc signal as performed in ac–dc transfer. Using a mathematical model of standard planar multijunction thermal converters (PMJTCs), the effective power acting inside the heater of the PMJTC is calculated from the output signal of its thermocouples. Due to the underlying physical principles, this method not only allows the calculation of the rms value of sinusoidal signals but also the average power and absolute energy contained in non-sinusoidal, non-periodic and even non-stationary signals, as appearing in the characterization of energy harvesters.

Electrical waveforms from vibrational energy harvesters: A trilateral measurement comparison

Abstract: The traceable measurement of the output signals of vibrational energy harvesters is needed in any determination of their electromechanical energy conversion properties. These signals have highly distorted waveforms, for which conventional meters show poor measurement performance. In the framework of the EMRP 2009 Metrology for energy harvesting project we realized three different meters, based on two strongly different measurement principles (ac-dc thermal transfer, and sampling) and performed a comparison of the methods; a summary of the experimental implementations and the results of the comparison are here reported.

Current Leads for Wendelstein 7-X and JT-60SA

Abstract: Forschungszentrum Karlsruhe has taken over the responsibility for the design, construction and testing of the High Temperature Superconductor (HTS) current leads for two fusion experiments, i.e. the stellarator WENDELSTEIN 7-X (W7-X) and the satellite tokamak JT-60SA. W7-X is presently under construction at the Greifswald branch of the Max-Planck-Institute for Plasma Physics and consists of 50 non-planar and 20 planar coils with a maximum conductor current of 17.6 kA. In total 14 current leads are required with a nominal current of 14 kA that are mounted upside down with the warm end at the bottom. In the frame of the Broader Approach Agreement between Japan and the EU and concomitantly to the ITER project, the satellite tokamak project JT-60SA has been agreed in 2006. The magnet system of JT-60SA consists of 18 toroidal field coils, 4 central solenoid modules and 7 poloidal field coils. In total 26 leads mounted in vertical, normal position are required. For W7-X and JT-60SA a common basic design will be used which will be adapted to the special needs of the machines. All current leads will be of the Cu-HTS binary type. The HTS part covers the range between 4.5 K and 60 K and is cooled by heat conduction from the 4.5 K end, only. The Cu heat exchanger is cooled with 50 K He and covers the range between 60 K and room temperature. The paper describes the status of the HTS current lead development for W7-X and JT-60SA.

An AC Current Transformer Standard Measuring System for Power Frequencies

Abstract: This paper describes the design and setup of the new ac current transformer (CT) calibration system at Physikalisch-Technische Bundesanstalt, which uses enhanced, actively compensated current comparators (CCs) for rated primary currents from 5 A up to 60 kA, and a new CT bridge based on the differential method. The bridge makes use of modern, high-resolution analog-to-digital converters, and makes it possible to connect traditional CTs as well as two-stage CTs with rated secondary currents from 100 mA to 5 A. The lower current ranges are integrated to enable a calibration of CTs of the highest available precision for national power standards. The current transducers and the two-channel sampling system of the bridge allow a resolution of approximately $10^{\mathrm {-9}}$ , while the estimated Type B uncertainty of the bridge is around $10^{\mathrm {-8}}$ .

A Wideband Current Transformer Bridge

Abstract: The development and testing results of a new current transformer (CT) test set at Physikalisch-Technische Bundesanstalt are described The operation range for the ratio based bridge is intended for frequencies from 167 Hz up to 20 kHz Equal setups of magnetically shielded current comparators with primary windings for rated currents from 100 mA up to 5 A convert the secondary currents of the standard CT and of the transformer under test (TUT) into proportional voltages The errors of the TUT are calculated from the subsequent measurement of the complex voltage ratio This current bridge and the voltage-ratio-based method allow comparing CTs with nonequal ratios At 50 Hz, the measuring system offers an extended measurement uncertainty of less than 2 ppm or μrad, respectively The bridge is verified for use with uncertainties of below 200 ppm or 400 μrad at a frequency of 20 kHz

A wideband current transformer bridge

Abstract: The work progress on a new current transformer test set at PTB is described. The operation range for the ratio based bridge is intended for frequencies from 16.7 Hz up to 20 kHz. Equal setups of magnetically shielded current comparators with primary windings for currents from 100 mA up to 5 A convert the secondary currents of the standard current transformer and of the transformer under test (DUT) into proportional voltages. The errors of the DUT are calculated from the subsequent measurement of the complex voltage ratio. At 50 Hz, the measuring system offers a basic accuracy in the order of less than ± 2 ppm or μrad respectively.

OOK power model based dynamic error testing for smart electricity meter

Abstract: This paper formulates the dynamic error testing problem for a smart meter, with consideration and investigation of both the testing signal and the dynamic error testing method. To solve the dynamic error testing problems, the paper establishes an on-off-keying (OOK) testing dynamic current model and an OOK testing dynamic load energy (TDLE) model. Then two types of TDLE sequences and three modes of OOK testing dynamic power are proposed. In addition, a novel algorithm, which helps to solve the problem of dynamic electric energy measurement's traceability, is derived for dynamic errors. Based on the above researches, OOK TDLE sequence generation equipment is developed and a dynamic error testing system is constructed. Using the testing system, five kinds of meters were tested in the three dynamic power modes. The test results show that the dynamic error is closely related to dynamic power mode and the measurement uncertainty is 0.38%.