Leslie Pendrill

Time Transfer by Passive Listening Over a 10-Gb/s Optical Fiber

A technique for time and frequency transfer over an asynchronous fiber optical transmission control protocol (TCP)/IP network is being developed in Sweden by SP Measurement Technology together with STUPI. The technique is based on passive listening to existing data traffic at 10 Gb/s in the network. Since the network is asynchronous, intermediate supporting clocks will be located and compared at each router. We detect, with a specially designed high-speed optoelectronic device, a header recognizer, the frame alignment bytes of the synchronous optical network (SONET)/synchronous digital hierarchy (SDH) protocol, as a reference for the supporting clock comparison. The goal of the project is to establish a time transfer system with an accuracy on the nanosecond level. In this paper, we present the results of a time transfer over a distance of 5 km. We have compared two clocks: a cesium clock at the Swedish National Laboratory for time and frequency and a remote rubidium clock. The results of the time transfer with the fiber link have been simultaneously compared to measurements with a Global Positioning System (GPS) carrier phase link in terms of precision and stability. The root-mean-square (rms) difference between the time difference measured with the fiber link and the GPS link is approximately 300 ps. A large part of the difference is due to the heating of the GPS antenna cable, which introduces daily delay variations on the order of 1 ns from peak to peak. For one of the days with small day-to-day variations in temperature, the corresponding rms difference is 72 ps, and the Allan deviation is below 30 ps for averaging times longer than 5 min.

Requirements of weighing in legal metrology

A review is given of recent developments in the formulation of requirements of weighing where such measurements are performed in society and industry with legal implications such as safety, fair trade and environmental considerations. Traditional legal metrology in the area of weights and measures has been developed and given an expanded scope in recent years. This reflects, on the one hand, technical and scientific development (computerization of weighing devices, improved weight manufacturing and new methods of magnetism determination, for example), and on the other hand, administrative evolution (global requirements of the market and the Measurement Instrument Directive). Particularly fruitful has been the joint effort by the scientific mass metrology and legal metrology communities in the development in the last decade of international recommendations—especially OIML R111—on weighing. Consensus has been reached in the international weighing forum concerning important areas such as maximum permissible errors for weights, how to calculate measurement uncertainty and how measurement uncertainty should be accounted for in relation to conformity assessment. These international recommendations for weights as mass standards include both tolerances and extensive instructions about various influence quantities that affect the weight result, such as magnetization, surface roughness and volume of weights. Much remains to be done, however: corresponding requirements of weighing devices in particular need to meet the challenges of a rapidly changing technology. The promising collaboration between scientific and legal metrology initiated in the area of weights may act as a model and stimulate similar developments in other areas of metrology, particularly where requirements are generic (for instance uncertainty and conformity) or analogous.

Refractometry and gas density

A review is given of how measurements of intensive thermodynamic properties of a gas, such as of refractivity and permittivity, can enable single-parameter monitoring of gas density. The last decade has seen the introduction of a number of new and improved optical and dielectric measurement techniques as well as significant advances in atomic structure calculations. Such advances may find application, for example, in the determination of primary gas mixtures and fundamental constants, buoyancy compensation in precision mass metrology and in dynamic pressure metrology.

Time and frequency transfer in an asynchronous TCP/IP over SDH-network utilizing passive listening

A technique for time and frequency transfer over an asynchronous TCP/IP network is being developed by SP, Swedish National Testing and Research Institute together with STUPI. When implemented, users will be able to compare their clocks by connecting to the system. The technique is based on passive listening to existing data traffic in the network. Since the network is asynchronous, intermediate clocks are located and compared at each router. We use the frame alignment bytes of the SONET/SDH protocol as references in order to compare these clocks. As a test bed for the experiment, we will use the Swedish University Computer Network (SUNET). A preliminary assessment of the technique in a lab environment will be performed late 2005

Density of Moist Air Monitored by Laser Refractometry

Air-buoyancy corrections are often a dominant source of error in the transfer of the unit of mass through weighing of nominally equal weights of different densities. The possibilities of monitoring air density through measurement of the refractive index of air are considered. A critical discussion is given of the present knowledge of the refractivities of air and its constituent gases. A simple laser refractometer capable of resolving air-density variations of 0.15 × 10-3 kg m-3, corresponding to a change in air buoyancy of 9 μg, is demonstrated in weighings of the Swedish prototype kilogram with stainless-steel standards.

Quantifying Human Response: Linking Metrological and Psychometric Characterisations of Man as a Measurement Instrument

A better understanding of how to characterise human response is essential to improved person-centred care and other situations where human factors are crucial. Challenges to introducing classical metrological concepts such as measurement uncertainty and traceability when characterising Man as a Measurement Instrument include the failure of many statistical tools when applied to ordinal measurement scales and a lack of metrological references in, for instance, healthcare. The present work attempts to link metrological and psychometric (Rasch) characterisation of Man as a Measurement Instrument in a study of elementary tasks, such as counting dots, where one knows independently the expected value because the measurement object (collection of dots) is prepared in advance. The analysis is compared and contrasted with recent approaches to this problem by others, for instance using signal error fidelity.

Measurement with Persons:A European Network

Abstract: The European ‘Measuring the Impossible’ Network MINET promotes new research activities in measurement dependent on human perception and/or interpretation. This includes the perceived attributes of products and services, such as quality or desirability, and societal parameters such as security and well-being. Work has aimed at consensus about four ‘generic’ metrological issues: (1) Measurement Concepts & Terminology; (2) Measurement Techniques: (3) Measurement Uncertainty; and (4) Decision-making & Impact Assessment, and how these can be applied specifically to the ‘Measurement of Persons’ in terms of ‘Man as a Measurement Instrument’ and ‘Measuring Man.’ Some of the main achievements of MINET include a research repository with glossary; training course; book; series of workshops; think tanks and study visits, which have brought together a unique constellation of researchers from physics, metrology, physiology, psychophysics, psychology and sociology. Metrology (quality-assured measurement) in this area is relatively underdeveloped, despite great potential for innovation, and extends beyond traditional physiological metrology in that it also deals with measurement with all human senses as well as mental and behavioral processes. This is particularly relevant in applications where humans are an important component of critical systems, where for instance health and safety are at stake.

Overall accessibility to traveling by rail for the elderly with and without functional limitations: the whole-trip perspective

Elderly persons’ perceived accessibility to railway traveling depends on their functional limitations/diseases, their functional abilities and their travel behaviors in interaction with the barriers encountered during whole trips. A survey was conducted on a random sample of 1000 city residents (65–85 years old; 57% response rate). The travels were perceived least accessible by respondents with severely reduced functional ability and by those with more than one functional limitation/disease (e.g., restricted mobility and chronic pain). Those who traveled “often”, perceived the accessibility to be better than those who traveled less frequently. For travelers with high functional ability, the main barriers to more frequent traveling were travel costs and low punctuality. For those with low functional ability, one’s own health was reported to be the main barrier. Our results clarify the links among existing functional limitations/functional abilities, the barriers encountered, the travel behavior, and the overall accessibility to traveling. By operationalizing the whole-trip concept as a chain of events, we deliver practical knowledge on vulnerable groups for decision-making to improve the transport environment for all.

Time transfer using an asynchronous computer network: Results from three weeks of measurements

We have performed a time transfer experiment between two atomic clocks, over a distance of approximately 75 km using an 10 Gbit/s asynchronous fiber-optic computer network. The time transfer was accomplished through passive listening on existing data traffic and a pilot sequence in the SDH bit stream. In order to assess the fiber-link clock comparison, we simultaneously compared the clocks using a GPS carrier phase link. The standard deviation of the difference between the two time transfer links over the three-week time period was 243 ps.

Metrology of human-based and other qualitative measurements

The metrology of human-based and other qualitative measurements is in its infancy - concepts such as traceability and uncertainty are as yet poorly developed. This paper reviews how a measurement system analysis approach, particularly invoking as performance metric the ability of a probe (such as a human being) acting as a measurement instrument to make a successful decision, can enable a more general metrological treatment of qualitative observations. Measures based on human observations are typically qualitative, not only in sectors, such as health care, services and safety, where the human factor is obvious, but also in customer perception of traditional products of all kinds. A principal challenge is that the usual tools of statistics normally employed for expressing measurement accuracy and uncertainty will probably not work reliably if relations between distances on different portions of scales are not fully known, as is typical of ordinal or other qualitative measurements. A key enabling insight is to connect the treatment of decision risks associated with measurement uncertainty to generalized linear modelling (GLM). Handling qualitative observations in this way unites information theory, the perceptive identification and choice paradigms of psychophysics. The Rasch invariant measure psychometric GLM approach in particular enables a proper treatment of ordinal data; a clear separation of probe and item attribute estimates; simple expressions for instrument sensitivity; etc. Examples include two aspects of the care of breast cancer patients, from diagnosis to rehabilitation. The Rasch approach leads in turn to opportunities of establishing metrological references for quality assurance of qualitative measurements. In psychometrics, one could imagine a certified reference for knowledge challenge, for example, a particular concept in understanding physics or for product quality of a certain health care service. Multivariate methods, such as Principal Component Regression, can also be improved by exploiting the increased resolution of the Rasch approach.