Norwegian Metrology Service

ABSTRACT The study describes significant outcomes of the ‘Metrology for Meteorology’ project, MeteoMet , which is an attempt to bridge the meteorological and metrological communities. The concept of traceability, an idea used in both fields but with a subtle difference in meaning, is at the heart of the project. For meteorology, a traceable measurement is the one that can be traced back to a particular instrument, time and location. From a metrological perspective, traceability further implies that the measurement can be traced back to a primary realization of the quantity being measured in terms of the base units of the International System of Units, the SI . These two perspectives reflect long‐standing differences in culture and practice and this project – and this study – represents only the first step towards better communication between the two communities. The 3 year MeteoMet project was funded by the European Metrology Research Program ( EMRP ) and involved 18 European National Metrological Institutes, 3 universities and 35 collaborating stakeholders including national meteorology organizations, research institutes, universities, associations and instrument companies. The project brought a metrological perspective to several long‐standing measurement problems in meteorology and climatology, varying from conventional ground‐based measurements to those made in the upper atmosphere. It included development and testing of novel instrumentation as well as improved calibration procedures and facilities, instrument intercomparison under realistic conditions and best practice dissemination. Additionally, the validation of historical temperature data series with respect to measurement uncertainties and a methodology for recalculation of the values were included.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new type of ac current shunt for ac–dc current transfer is presented for which the ac–dc current differences at frequencies from 10 to 100 kHz are calculated with uncertainties smaller than <formula formulatype="inline"><tex>$\pm 9\ \mu\hbox{A/A}$</tex></formula> in the current range of 30 mA–10 A. This is an independent realization of the ac–dc current-transfer standards in addition to the step-up method used at most National Metrology Institutes. The construction, modeling, and experimental verification of the shunts are described. </para>

The design and construction of a predictable quantum efficient detector (PQED), suggested to be capable of measuring optical power with a relative uncertainty of 1 ppm (ppm = parts per million), is presented. The structure and working principle of induced junction silicon photodiodes are described combined with the design of the PQED. The detector uses two custom-made large area photodiodes assembled into a light-trapping configuration, reducing the reflectance down to a few tens of ppm. A liquid nitrogen cryostat is used to cool the induced junction photodiodes to 78 K to improve the mobility of charge carriers and to reduce the dark current. To determine the predicted spectral responsivity, reflectance losses of the PQED were measured at room temperature and at 78 K and also modelled throughout the visible wavelength range from 400 nm to 800 nm. The measured values of reflectance at room temperature were 29.8 ppm, 22.8 ppm and 6.6 ppm at the wavelengths of 476 nm, 488 nm and 532 nm, respectively, whereas the calculated reflectances were about 4 ppm higher. The reflectance at 78 K was measured at the wavelengths of 488 nm and 532 nm over a period of 60 h during which the reflectance changed by about 20 ppm. The main uncertainty components in the predicted internal quantum deficiency (IQD) of the induced junction photodiodes are due to the reliability of the charge-carrier recombination model and the extinction coefficient of silicon at wavelengths longer than 700 nm. The expanded uncertainty of the predicted IQD is 2 ppm at 78 K over a limited spectral range and below 140 ppm at room temperature over the visible wavelength range. All the above factors are combined as the external quantum deficiency (EQD), which is needed for the calculation of the predicted spectral responsivity of the PQED. The values of the predicted EQD are below 70 ppm between the wavelengths of 476 nm and 760 nm, and their expanded uncertainties mostly vary between 10 ppm and 140 ppm, where the lowest uncertainties are obtained at low temperatures.

The predictable quantum efficient detector (PQED) is intended to become a new primary standard for radiant power measurements in the wavelength range from 400 nm to 800 nm. Characterization results of custom-made single induced junction photodiodes as they are used in the PQED and of assembled PQEDs are presented. The single photodiodes were tested in terms of linearity and spatial uniformity of the spectral responsivity. The highly uniform photodiodes were proved to be linear over seven orders of magnitude, i.e. in the radiant power range from 100 pW to 400 µW. The assembled PQED has been compared with a cryogenic electrical substitution radiometer with a very low uncertainty of the order of 30 ppm. Experimental results show good agreement with the modelled response of the PQED to optical radiation and prove a near unity external quantum efficiency.

A comparison of the phase error of existing shunts for currents between 10 and 100 A and frequencies from 500 Hz to 100 kHz has been organized. Measurement processes were performed at Istituto Nationale di Ricerca Metrologica on some shunts using the first prototype of a new type of a phase comparator and a step-up method for data processing. Results of the relative measurement processes have shown good repeatability. The method for evaluation of reference values was based on similar shunts and suitable assumptions and derived by extrapolation. For the type of resistance elements employed in these shunts, the derivation of the reference is not very accurate and still needs to be improved.

The spectral responsivity of a predictable quantum efficient detector (PQED) is calculated based on the responsivity of an ideal quantum detector and taking into account reflection losses from the surface of the photodiode and internal charge-carrier gains/losses inside the diode. The internal quantum deficiency (IQD) is obtained from simulations with the PC1D software using the material data of the produced PQED photodiodes. The results indicate that at room temperature the predicted IQD of the PQED is close to zero with an uncertainty of about 100 ppm over the visible range. It is further concluded that a primary standard of visible optical power with an uncertainty of approximately 1 ppm is achievable using the PQED at low temperatures.

Surfaces with low ice adhesion represent a promising strategy to achieve passive anti-icing performance. However, as a successful and robust low ice adhesion surface must be tested under realistic conditions at low temperatures and for several types of ice, the initial screening of potential low ice adhesion surfaces requires large resources. A theoretical relation between ice adhesion and water wettability in the form of water contact angle exists, but there is disagreement on whether this relation holds for experiments. In this study, we utilised molecular dynamics simulations to examine the fundamental relations between ice adhesion and water contact angle on an ideal graphene surface. The results show a significant correlation according to the theoretic predictions, indicating that the theoretical relation holds for the ice and water when discarding surface material deformations and other experimental factors. The reproduction of the thermodynamic theory at the nanoscale is important due to the gap between experimental observations and theoretical models. The results in this study represent a step forward towards understanding the fundamental mechanisms of water–solid and ice–solid interactions, and the relationship between them.

A femtosecond laser comb was used in an optical clock configuration to measure simultaneously the optical frequency of an iodine-stabilized Nd:YAG laser at 532 nm and an iodine-stabilized He-Ne laser at 633 nm at the International Bureau of Weights and Measures (BIPM). The noise characteristics of the data corresponds well to those of the reference standards and the lasers under study. In a second series of measurements during which the comb was phase-locked to a hydrogen maser, laser standards at 532 nm and at 633 nm were measured. A standard deviation of 6/spl times/10/sup -15/ during 2 h of measurements for the Nd:YAG laser illustrates well the excellent stability of these standards and, at the same time, the capabilities of the comb techniques.

We developed an optical pulse-drive for the operation of the Josephson Arbitrary Waveform Synthesizer (JAWS) using a fast photodiode (PD) operated at 4 K, close to the JAWS chip. The optical pulses are transmitted to the PD by an easily removable optical fiber attached to it. A bare-lensed PD is mounted by flip-chip technique to a custom-made silicon-carrier chip. This carrier chip is equipped with coplanar waveguides to transmit the electrical pulses from the PD to the JAWS chip mounted on a separate printed circtuit board (PCB). The main components of this optical setup are a laser source, a high-speed Mach-Zehnder modulator, and the modulator driver. The waveform pattern is supplied by a commercial pulse pattern generator providing up to 15 GHz electrical return-to-zero (RTZ)-pulses. Unipolar sinusoidal waveforms were synthesized. Using a JAWS array with 3000 junctions, an effective output voltage of 6.6 mV root mean square (RMS) at the maximum available clock-frequency of 15 GHz was achieved. Higher harmonics were suppressed by more than 90 dBc at laser-bias operation margins of more than 1 mA.

The electrical characteristics of two different 1-V binary programmable Josephson arrays, an superconductor/insulator/normal conductor/insulator/superconductor-type Josephson array, and an externally shunted superconductor/insulator/superconductor-type Josephson array, were investigated at ten metrology institutes. Various operational parameters were evaluated and compared using different Josephson array voltage standard setups at microwave frequencies around 70 GHz. The results of the measurements show that both arrays have been working very well and the main differences were not imposed by the arrays themselves, but by the different measurement setups of the laboratories.

Establishment of appropriate vibration criteria is essential when designing vibration-sensitive metrology laboratories. Boundary values that are too severe may lead to unnecessarily high construction costs, whereas limits that are too broad may result in degradation of the performance of measurement equipment. The Norwegian Metrology and Accreditation Service (Justervesenet) inaugurated a new facility early in 1997. The facility will allow measurements of mass, density, dimensional, force, volume, optical, pressure, temperature and electrical quantities. Vibration control is of concern in most of the laboratories. Vibration criteria have been defined in terms of frequency-dependent peak values. In this paper, these criteria are described and the most conservative criterion is compared with other known vibration criteria for standard laboratories and high-technology facilities. The vibration criteria considered have different formulations and cannot be compared directly. They are therefore compared with regard to three different kinds of idealized vibration excitation, that is, transient, harmonic-motion and broad-band noise. The comparison shows that the most conservative Justervesenet vibration criterion is stricter with respect to high-frequency vibrations than are the others, but it is less strict for low-frequency vibrations.

An optoelectronic module for operation at 4 K is developed, intended for use in pulse-driven Josephson arbitrary waveform synthesizer. Multiple InP/InGaAs photodiodes with customized optical fiber assembly were assembled on a single silicon carrier. Photodiodes were flip-chip bonded on the carrier using Au stud bumps, and laser-cut silicon fixtures were aligned and adhesively bonded to the carrier in order to attach pigtailed borosilicate ferrules. Optical simulations were performed to estimate the tolerance for fiber-chip misalignment. The photodiodes were bonded with an average misalignment of 8 μm, while the misalignment between the silicon fixture and the photodiodes after bonding was 13 μm. The electrical response to continuous-wave laser inputs was measured at room temperature and at 4 K by direct immersion in liquid helium. The results show that the assembly technique could facilitate a stable and efficient optical coupling. The individual photodiodes were able to deliver currents up to 12 mA at room temperature and 7 mA at 4 K.

The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. &#13;\nFor both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.

This paper discusses different network topologies used in Internet-enabled metrology and calibration and explores and compares two different remote calibration systems used by the National Metrology Institutes in England and Norway: the National Physical Laboratory (NPL) and the Justervesenet (JV). The two systems are iGen (NPL) and iMet (JV). The systems both deal with remote calibration of electrical equipment but have substantial architecture differences. In iGen, calibration procedures are downloaded from a server and then locally run at the instrument client, where the operator sits. The client is generic in such a way that it is not dependent on the structure of the measurement procedures. In iMet, two clients can communicate via a public server, and the calibration process may be remotely controlled and monitored. That is, the instruments and the operator may be separated by the Internet.

From 2002 to 2004 the Consultative Committee for Thermometry (CCT) carried out a Key Comparison (KC) of water triple point cells (CCT-K7). In 2005 the Regional Metrology Organization (RMO) EURAMET decided to initiate an additional KC of water triple point cells, EUROMET.T-K7, to extend the metrological equivalence to a larger number of national metrology institutes (NMIs) from the EURAMET region.

Absolute calibration of silicon photodiodes by purely relative measurements

In 2015, the energy measurement of some static electricity meters was found to be sensitive to specific conducted electromagnetic disturbances with very fast current changes caused by highly nonlinear loads, leading to meter errors up to several hundred percent. This article describes new results on the electromagnetic compatibility (EMC) of 16 different meters from all over Europe when exposed to real-world disturbance signals. Those test signals were obtained from household appliances and onsite measurements at metered supply points all over Europe. The results show that also the interference signals recorded onsite can cause measurement errors as large as several hundred percent, even for meters that pass the present EMC standards. This unambiguously demonstrates that the present immunity testing standards do not cover the most disturbing conducted interference occurring in present daily-life situations due to the increased use of nonlinear electronics. Furthermore, to enable the adoption of potential new test waveforms in future standards for electricity meter testing, artificial test waveforms were constructed based on real-world waveforms using a piece-wise linear model. These artificial test waveforms were demonstrated to cause meter errors similar to those caused by the original real-life waveforms they are representing, showing that they are suitable candidates for use in improved standardization of electricity meter testing.

Recent studies involving large errors in static electricity meters when exposed to step changes in the current waveform are reviewed. Triggered by these findings, a joint European research project has recently started to further evaluate these effects. A description is given of this pre-normative research programme which aims to provide evidence and techniques to resolve this unsatisfactory meter error situation. The need or otherwise for a regulatory and standardisation resnonse to these large meter errors is discussed.

Fiber Bragg gratings inscribed in single crystalline multimode sapphire fibers (S-FBG) are suitable for monitoring applications in harsh environments up to 1900 °C. Despite many approaches to optimize the S-FBG sensor, a metrological investigation of the achievable temperature uncertainties is still missing. In this paper, we developed a hybrid optical temperature sensor using S-FBG and thermal radiation signals. In addition, the sensor also includes a thermocouple for reference and process control during a field test. We analyzed the influence of the thermal gradient and hotspot position along the sensor for all three detection methods using an industrial draw tower and fixed point cells. Moreover, the signal processing of the reflected S-FBG spectrum was investigated and enhanced to determine the reachable measurement repeatability and uncertainty. For that purpose, we developed an analytical expression for the long-wavelength edge of the peak. Our findings show a higher stability against mechanical-caused mode variations for this method to measure the wavelength shift compared to established methods. Additionally, our approach offers a high robustness against aging effects caused by high-temperature processes (above 1700 °C) or harsh environments. Using temperature-fixed points, directly traceable to the International System of Units, we calibrated the S-FBG and thermocouple of the hybrid sensor, including the corresponding uncertainty budgets. Within the scope of an over 3-weeks-long field trial, 25 production cycles of an industrial silicon manufacturing process with temperatures up to 1600 °C were monitored with over 100,000 single measurements. The absolute calibrated thermocouple (Uk=2≈1K…4K) and S-FBG (Uk=2≈10K…14K) measurements agreed within their combined uncertainty. We also discuss possible strategies to significantly reduce the uncertainty of the S-FBG calibration. A follow-up measurement of the sensor after the long-term operation at high temperatures and the transport of the measuring system together with the sensor resulted in a change of less than 0.5 K. Thus, both the presented hybrid sensor and the measuring principle are very robust for applications in harsh environments.

Neurovascular compression has been postulated as a probable mechanism for a large number of cranial nerve syndromes, with trigeminal neuralgia (TGN) as the prime example. Microvascular decompression (MVD) is often cited as the procedure of choice for treatment of medically refractory TGN. Arguments against these assumptions are: MRA studies indicate that vascular contact with the trigeminal nerve is present in most healthy individuals. Treatment results of MVD in multiple sclerosis patients with TGN are almost as good (at least in the short term) as in idiopathic cases. MVD is reported to provide pain relief even in TGN patients without visible neurovascular contact . In other syndromes of cranial nerve'hyperactive dysfunction'--vertigo, tinnitus and neurogenic hypertension--the documentation is even weaker.