Automatic DC voltage precision resistive divider with ratios between 10:1 and 107:1

At INRIM a DC Voltage precision resistive divider performing decade ratios from 10:1 to 107:1 was built. It can be automatically calibrated with a top-class calibrator and a precision multimeter calibrated in terms of deviation from linearity. It is made up of 90 kΩ, 9 kΩ, 900 Ω, 90 Ω, 9 Ω, 0.9 Ω, 90 mΩ and 10 mΩ bulk metal foil resistors connected in series, in four-terminal configuration. Peculiarities of the calibration method of the divider are: the evaluation of the DMM input impedance to correct its readings minimizing the load error and a solution to reduce the emfs effect of the relays. These operations are made during the calibration of the divider. The calibration and use uncertainties of the divider span respectively from 6.1 × 10 7 to 5.9 × 10 4 and from 6.7 × 10 7 to 6.5 × 10 4. The project is transferable to secondary laboratories in the framework of the INRIM knowledge transfer task

Distortion-free sensing of neural activity using graphene transistors

Graphene solution-gated field-effect transistors (g-SGFETs) are promising sensing devices to transduce electrochemical potential signals in an electrolyte bath. However, distortion mechanisms in g-SGFET, which can affect signals of large amplitude or high frequency, have not been evaluated. Here, a detailed characterization and modeling of the harmonic distortion and non-ideal frequency response in g-SGFETs is presented. This accurate description of the input-output relation of the g-SGFETs allows to define the voltage- and frequency-dependent transfer functions, which can be used to correct distortions in the transduced signals. The effect of signal distortion and its subsequent calibration are shown for different types of electrophysiological signals, spanning from large amplitude and low frequency cortical spreading depression events to low amplitude and high frequency action potentials. The thorough description of the distortion mechanisms presented in this article demonstrates that g-SGFETs can be used as distortion-free signal transducers not only for neural sensing, but also for a broader range of applications in which g-SGFET sensors are used

Energy-Scale Systematics at the KATRIN Main Spectrometer

This thesis deals with the systematic uncertainties related to the high-precision energy filtering of electrons at the Karlsruhe Tritium Neutrino (KATRIN) experiment. A high degree of understanding of corresponding effects is essential to reach the targeted ?-mass sensitivity of 200 meV (90% C.L.)

DIRECT VOLTAGE MEASUREMENTS USING BULK ACOUSTIC WAVES IN LiNbO3

Accurate (\u3c 1%) direct measurement of high voltage pulse amplitudes above 10 kilovolts becomes challenging due to voltage breakdown limitations in materials, parasitic impedance effects that can distort the pulse shape, and pickup of extraneous signals resulting from electromagnetic interference effects. A piezoelectric crystal-based bulk acoustic wave sensor using lithium niobate (LiNbO3) that has applications to metrology, research, and power metering was developed to overcome these measurement issues with the factors of scalability, ease of use, and compactness in mind. A Y+36° cut LiNbO3crystal was coupled to two acoustic transducers, where direct current (DC) voltages ranging from 128—1100\u2009V were applied transversely to the crystal. An acoustic wave was used to interrogate the crystal before, during, and after voltage application. Both single and multiple pass measurements were performed and compared to linear piezoelectric theory. A comparison study between Y+36° and 0° X-cut LiNbO3 was performed to evaluate the influence of crystal cut on acoustic propagation. The study was extended to applying alternating current (AC), and pulsed voltages. The measured DC data was compared to a 1-D impedance matrix model that was based on a three port circuit with voltage-induced strain effects inputted as a model parameter. An uncertainty budget was carried out for both crystal cuts and compared. Environmental effects such as pressure and temperature were also measured to determine their influence on the sensor under ambient conditions. Published literature regarding material constants, such as elastic constants and piezoelectric constants, for LiNbO3 do not account for the influence of an electric field. In light of this, measurements of the acoustic velocities and material constants under the presence of a DC electric field were performed up to 896 V. This information was used to develop an uncertainty analysis for the determination of stress-charge form piezoelectric constants e15 and e22. All measured and calculated values were input into a Monte Carlo simulation to determine the error of the strain-charge form piezoelectric constants, dij, and how these new values can be used to predict the voltage sensor response

Calibration of voltage and current transducers for dc railway systems

To establish a single European railway area, the European Commission requires, by 2019, that energy billings shall be computed on the actual energy consumed. So, in the near future, all the trains shall be equipped with an energy measurement system, whose measurement accuracy should be assessed and periodically reverified, as required by EN 50463-2. As for every energy and power measuring system, the voltage and current transducers play a crucial role as their accuracy could determine the performance level of the entire measurement chain. To answer to this emerging need, this paper presents a calibration system allowing the accurate testing of dc voltage and current transducers, up to 6 kV and 300 A and up to 10 kHz. It is able to reproduce all the tests prescribed by EN 50463-2, but in order to characterize the transducers in actual operating conditions, a series of additional tests can also be performed using synthetic complex waveforms or even signals acquired on-board trains. The expanded uncertainty (level of confidence 95%) of the calibration system is 43 mu extV /V and 24 mu extA /A at dc and 520 mu extV /V and 820 mu extA /A at 10 kHz. Moreover, the calibration of two commercial voltage and current transducers, currently installed in the trains of an Italian operator, is presented

Current Step Generation and Measurement with Rise-time in the Range of Nanoseconds

A current step generator based on a charged coaxial cable is designed and tested for characterizing impulse current shunts. This thesis has developed a traceable calibration infrastructure for fast shunts and other current sensors, defined measurement techniques for a current step and improved the test procedure and measurement capabilities. For calibration of shunts, current coil sensors are used in the measurement circuits. Since no calibration services are currently available for impulse current measuring systems, a best circuit combination is proposed for current step generation with a rise time of less than 5 ns, along with a proposed reference shunt that aims to provide the best and most stable measurement results with negligible noise, oscillations, and droop in the measured current step. Based on techniques found in the literature, current steps are generated, and different sensors were used to measure the generated steep front current steps. The generation system consists of a 110-m long, 50-Ω coaxial cable and a spark gap. Various spark gap switches, including the SF6 spark gap, are used for generating current steps. With the coaxial cable charged from one end, a current step is generated after reflecting back from the open end with a step length of twice the cable transmission delay. The cable is than discharged to the shunt (or coil) through the spark gap. The measurement system consists of shunts and coil current sensors, 5:1 and 6.6:1 attenuators based on the requirement of the sensors. The recording instrument is a 1-GHz, 8-bit, 1-GS/s digitizer. The proposed step generator can produce current steps with a stable current of up to 100 A. The rise time of the step varies from 1.6 ns to 15 ns, depending on the spark gap used for switching. The produced current is constant within 0.5% for a step length of 960 ns generated with a coaxial cable 110 m in length. To improve the test procedure and measurement capabilities, the thesis also analyzed factors affecting current step measurement, such as the type of coaxial cable, type of connection, extra shielding, clearances, interference sources, media of the spark gap, and the spark gap electrode distance (arc length). It is found that the measurement system and the rise time of current step is affected by many factors, including the coaxiality of the connection, impedance mismatch, interference, clearances, stray capacitances, and stray inductances. These results will enable future standardization of impulse current sensors