Mass and Density Measurements

The National Institute of Standards and Technology (NIST) timescale produces a real-time realization of UTC(NIST) in the form of a pulse-per-second (PPS) time signal and a 5 MHz frequency reference. UTC(NIST) contributes to UTC (Coordinate Universal Time) using TWSTFT (Two-Way Satellite Time and Frequency Transfer) and common-view GPS (Global Positioning System) techniques. The NIST timing signal is also disseminated to the international and domestic communities using various other techniques: NIST Automated Computer Time Service (ACTS), Internet Time Service (ITS) and NIST Time Measurement and Analysis Service (TMAS). The accuracy of NIST contribution to UTC and of the dissemination of the NIST PPS time signal depends upon the quality of the calibration of the time delay between each user and the UTC(NIST) reference point. Hardware constraints, spatial constraints, and in some cases simple convenience, require that the physical input to the transfer and dissemination equipment be distributed throughout the NIST campus. A robust on-campus timing distribution and calibration system is required to ensure the accuracy and stability of these signals: for example, the current error budget for a typical time transfer calibration requires local delays to be known to an uncertainty of less than 200 ps. We utilize a clock trip calibration protocol to measure the delays introduced by the local time distribution system at NIST: a clock trip involves measuring the time difference between the UTC(NIST) reference point and a travelling clock, then transporting the travelling clock to a secondary reference point where another measurement of the time difference is performed. Clock trips are advantageous as they are a nonintrusive measurement of the full system delay. To achieve calibrations with an accuracy on the order 100 ps, we have developed a means to transport a cesium clock between remote locations on site with minimal vibration and an analysis protocol to maximize the information acquired by each clock trip. We will introduce the system used to distribute time signals at NIST, the hardware and protocol we have developed to calibrate secondary timing reference points, and data we have collected based on their implementation.

The National Institute of Standards and Technology (NIST) maintains a real-time estimate of Coordinated Universal Time (UTC), which is called UTC(NIST). UTC(NIST) is realized by steering the output of a hydrogen maser to minimize the difference between UTC(NIST) and UTC, a time scale computed by the International Bureau of Weights and Measures (BIPM). The difference between UTC(NIST) and UTC is published in the BIPM monthly Circular T. The reference for UTC(NIST) is AT1, a free-running time scale computed at NIST in real-time from an ensemble of cesium clocks and hydrogen masers maintained at the NIST laboratory in Boulder. The steering that implements UTC(NIST) is realized using a commercial phase stepper that produces an output that can be offset either in time or in frequency from the input signal from the maser. The current algorithm, which has been used for many years, maximizes the frequency smoothness of UTC(NIST) at the expense of its time accuracy. Since both AT1 and UTC have improved significantly in the last few years as a result of better clock hardware, this algorithm may no longer be optimum. We are investigating other choices which may be able to preserve the desirable goal of frequency smoothness while at the same time improving the RMS time accuracy.

The Clean Air Mercury Rule (CAMR) which was published in the Federal Register on May 18, 2005, requires that calibration of mercury continuous emissions monitors (CEMs) be performed with NIST-traceable standards. Western Research Institute (WRI) is working closely with the Electric Power Research Institute (EPRI), the National Institute of Standards and Technology (NIST), and the Environmental Protection Agency (EPA) to facilitate the development of the experimental criteria for a NIST traceability protocol for dynamic elemental mercury vapor generators. The traceability protocol will be written by EPA. Traceability will be based on the actual analysis of the output of each calibration unit at several concentration levels ranging from about 2-40 ug/m{sup 3}, and this analysis will be directly traceable to analyses by NIST using isotope dilution inductively coupled plasma/mass spectrometry (ID ICP/MS) through a chain of analyses linking the calibration unit in the power plant to the NIST ID ICP/MS. Prior to this project, NIST did not provide a recommended mercury vapor pressure equation or list mercury vapor pressure in its vapor pressure database. The NIST Physical and Chemical Properties Division in Boulder, Colorado was subcontracted under this project to study the issue in detail and to recommend a mercury vapormore » pressure equation that the vendors of mercury vapor pressure calibration units can use to calculate the elemental mercury vapor concentration in an equilibrium chamber at a particular temperature. As part of this study, a preliminary evaluation of calibration units from five vendors was made. The work was performed by NIST in Gaithersburg, MD and Joe Rovani from WRI who traveled to NIST as a Visiting Scientist.« less

A Look at its Past Decade and a Gaze towards its Future. As the National Metrology Institute (NMI) for the United States, the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards, has provided measurement services, both calibrations and reference materials, for more than 100 years. Through these services, our customers have benefitted from our measurement capabilities and expertise in many areas, including amount of substance; dimensional metrology; electricity and magnetism; ionizing radiation; mass and related quantities; photometry and radiometry; thermodynamics; and time and frequency. NIST’s customers have also had access to some of the lowest measurement uncertainties available and a dependable way to establish traceability to the International System of Units (SI) [http://www.nist.gov/pml/wmd/metric/si-units.cfm].In response to the signing of the International Committee for Weights and Measures (CIPM) Mutual Recognition Arrangement (MRA), NIST first established an institution-wide quality system for the measurement services 10 years ago [http://www.bipm.org/en/cipm-mra/objectives.html]. NIST’s Quality System for Measurement Services has advanced the quality of service and measurements we provide our customers by fostering an environment in which NIST management and staff work towards continual improvement in the development and delivery of NIST measurement services. This paper describes NIST’s Quality System for the Measurement Services and its relevance to international standards of quality, such as the International Organization for Standardization and the International Electrotechnical Commission (ISO/IEC) 17025 standard and ISO Guide 34 [http://www.nist.gov/nistqs/]. It also provides a history of this quality system and a glimpse of future goals for improving its implementation.

Material standards and reference materials for disease biomarkers: Needs assessment and development

In 2009, the United States Congress charged the National Institute of Standards and Technology (NIST) with supporting climate change research. As part of this effort, the Gas Sensing Metrology Group at NIST began developing new gas standard mixtures for greenhouse gas mixtures relevant to atmospheric measurements. Suites of gravimetrically prepared primary standard mixtures (PSMs) were prepared at ambient concentration levels for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-air balance. In parallel, 30 gas cylinders were filled, by the National Institute of Water and Atmospheric Research (NIWA) in Wellington, New Zealand, to high pressure from pristine southern oceanic air at Baring Head, New Zealand, and shipped to NIST. Using spectroscopic instrumentation, NIST analyzed the 30 cylinder samples for mole fractions of CO2, CH4, and N2O. Certified values were assigned to these mixtures by calibrating the instrumentation with the PSM suites that were recently developed at NIST. These mixtures became NIST Standard Reference Material (SRM) 1721 Southern Oceanic Air and are certified for ambient mole fraction, the first of their kind for NIST. The relative expanded uncertainties corresponding to coverage intervals with 95% probability are no larger than 0.06% of the certified values, representing the smallest uncertainties to date ever assigned to an NIST gas SRM.

In the fall of 2019, the National Institute of Standards and Technology (NIST) funded threes studies to better understand equity and inclusivity. This report documents phase two of a three phased sequential, exploratory mixed methods study designed to provide an in-depth look at the population of NIST federal employees to identify factors, attitudes, and processes that might result in gender- specific barriers at NIST. Phase 1 analyzed human resources demographic data, compensation data, and performance data of NIST federal employees from 2011 to 2019 to determine any relevant trends. Phase 1 informed the development of an in-depth interview protocol designed to identify the differences, if any, in the ways in which men and women experience work at NIST. A total of 40 (36 female and 4 male) participants were interviewed. Three interconnected themes emerged in the data: 1) a culture at NIST that creates a Chilly Climate for women; 2) gendered experiences that contribute to and are outcomes of that chilly climate; and 3) gendered outcomes that influence women s experiences in the organization. The culture has evolved from NIST s scientific roots, scientific excellence, a strong belief in meritocracy, and as a Federal agency. Each of these characteristics contribute to a gendered social structure and the perception that change is not needed. This backdrop sets the stage for the characterizations of NIST from the interviews as a Boys Club and an Elitist environment. The radically different perspectives of men and women based in the culture result in experiences and outcomes that provide advantages and opportunities for men while erecting barriers to survival for women, including isolation and possibly exclusion. These barriers result in consequences of discrimination as well as lack of trust and resignation. Participant quotes are used as exemplars to provide details related to each of these themes. Overall, the interviews demonstrate that women and men experience a very different NIST.

The National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards, was established by the U.S. Congress in 1901 and charged with establishing a measurement foundation to facilitate U.S. and international commerce. NIST provides reference materials and reference instruments that are used to ensure the accuracy, metrological traceability, and comparability of measurement results in many diverse fields of science, industry, and technology. This document provides and explains the vocabulary used at NIST to describe the reference materials and reference instruments available to NIST s customers. This document also describes the methods used in developing NIST reference materials. The definitions and descriptions provided supersede those used in the original versions of this publication, NIST SP260-136 and SP260-136-2020.

This paper presents a summary of the strategies and activities underway at the National Institute of Standards and Technology (NIST) in electronics packaging, interconnection and assembly (P/I/A). In addition, a sampling of collaborations involving these works is included. The overall NIST effort in P/I/A is composed of targeted programs conducted by the NIST laboratories and by the NIST Advanced Technology Program (ATP). A dominant aspect of the laboratory-based P/I/A program focuses on the metrology and data needed to support the product technologies envisioned within industry roadmaps. A significant aspect of the work includes efforts in metrology, materials, complex material assemblies, and microelectronic components and circuits. In parallel, the NIST ATP is supporting on a cost-share basis a variety of industry-based development projects of high-risk enabling technologies for new or improved products, manufacturing, and processes in P/I/A.

Standards provide critical benefits across a wide variety of contexts, including safety and health, environmental protection, and quality of products and services. However, while these benefits are generally acknowledged, estimating the social and economic value of standards and determining how specific entities and activities influence their development require careful analysis. In October of 2018, the National Institute of Standards and Technology (NIST) asked the RAND Corporation to estimate the benefit of NIST’s research contributing to particular fire safety standards. The original objectives of the project were to (1) document the role of the NIST in the standards development process, (2) estimate the value these standards provide to society, and (3) thereby inform the economic value of NIST’s contribution to these standards. This report presents results for the first two objectives. Given that NIST’s contribution is one of several inputs combining to create these standards, NIST’s share of the credit for their value could not be quantified. Our analysis focused on case studies in standards for home smoke alarms and for protecting structures at the wildland-urban interface (WUI). Our analysis draws on a wide variety of qualitative and quantitative methods to holistically describe the impacts of these standards and NIST’s role in their development. The intended audience of this report includes those who work on fire safety research, fire safety standards, building codes, and technology transfer. The conclusions presented here may also be of interest for broader resource allocation and federal budget justification purposes. Finally, this report was written to be accessible to any interested members of the general public.

The National Institute of Standards and Technology (NIST) employ the 1000 watt FEL-type quartz-tungsten-halogen (QTH) lamp as its transfer device for the spectral irradiance scale. The cost of the calibrated lamps from the NIST makes it prohibitive to use them for routine calibrations. To dilute the costs and extend the working lifetime of the lamps it is customary to transfer the NIST scale to secondary lamps and then using these to transfer to tertiary (working standards) lamps. NOAA's Central UV Calibration Facility (CUCF) currently owns six of the NIST primary standards of spectral irradiance. The CUCF transfers the spectral irradiance scale from the NIST primaries to secondary standards, which in this case are also used as working standards. Careful seasoning and screening of the secondary lamps is essential to achieve the maximum benefit out of this transfer and the operation of the expensive primary standards. The process of lamp seasoning and screening techniques used by the CUCF is described here. They include visual inspection of the lamp envelope, filament and lead wires during each step of the screening process. Also, the temporal stability of the lamp irradiance, lamp current and voltage and anomalous emission and absorption lines is discussed. Some of the problems that the CUCF has found with lamps are also shown.

On September 5–8, 2023, the National Institute of Standards and Technology (NIST) held the second Standards and Performance Metrics for On‐Road Automated Vehicles Workshop. This four‐day virtual event provided updates on NIST’s recent work in automated vehicles (AVs) and gave stakeholders an opportunity to provide feedback and input on current and future NIST research. The workshop included high‐level keynote presentations, a series of industry keynote presentations, and NIST presentations on its current AV activities. The industry keynotes and NIST presentations were paired with breakout sessions that discussed NIST’s progress, community challenges, and stakeholder research needs in six key areas: systems interaction, perception, cybersecurity, communications, artificial intelligence, and digital infrastructure. There was general agreement that developing standards allows for better comparisons and evaluations of emerging technologies. Other key themes included: 1) Digital technologies for automation and related security/privacy concerns, including artificial intelligence, machine learning, and smart communication technologies (i.e., vehicle‐to‐vehicle (V2V), vehicle‐to‐infrastructure (V2I), and vehicle‐to‐everything (V2X)), 2) Need for standardized or common language to improve information sharing, 3) Open data sets to support and validate technical advances and standardization across system components and areas (i.e., standards evolving in parallel with technology), and 4) Pivotal role for NIST as a convener to bring diverse stakeholders together for knowledge exchange and cross‐industry dialogue.

The calibration and related measurement services of the National Institute of Standards and Technology (NIST) are intended to assist the makers and users of precision measuring instruments in achieving the highest possible levels of accuracy, quality, and productivity. NIST offers over 300 different calibrations, special tests, and measurement assurance services. These services allow customers to directly link their measurement systems to measurement systems and standards maintained by NIST. These services are offered to the public and private organizations alike. They are described in NIST Special Publication (SP) 250, NIST Calibration Services Users Guide.

In consultation with ASTM and other stakeholders in Tissue-Engineered Medical Products (TEMPs) industry, the National Institute of Standards and Technology (NIST) initiated a project designed to produce Reference Material scaffolds for tissue engineering. The rationale for Reference Material scaffolds was developed through several NIST/Industry workshops. In brief, Reference Material scaffolds have multiple uses: facilitating the development and the validation of new test methods that measure interactions among various components of a TEMP; comparison with other scaffolds and scaffold materials in terms of cellular responses, biodegradation, and releases of growth factors; and comparisons of responses among various cell lines. The primary customers for Reference Material scaffolds are expected to be the TEMPs industry, academic researchers, regulators, and standards developing organizations. There are many properties of a TEMP that warrant development of multiple Reference Material scaffolds. Currently, NIST is defining a set of Reference Material scaffolds based on geometric descriptors such as permeability, pore volume, pore size distribution, interconnectivity, and tortuosity. In consultation with ASTM, NIST is testing three candidate scaffolds produced by: three dimensional (3-D) printing, stereolithography, and fused deposition modeling (FDM). Scaffolds made by these methods have been obtained from Mayo Clinic (Rochester, MN), Case Western Reserve University (CWRU) (Cleveland, OH), and Osteopore International (Singapore), respectively, for structural characterization. These prototype scaffolds, with well-defined architectures, have been selected to address the following items of interest: 1) establishment of useful functional definitions of porosity content, interconnectivity, and pores; 2) evaluation of testing methods listed in the Standard Guide for the Porosity of Polymeric Scaffolds for Use in Tissue-Engineered Medical Products, which is being drafted by ASTM. Currently, NIST and the Center for Devices and Radiological Health of the Food and Drug Administration, as well as other groups from US and foreign laboratories, are actively carrying out cross-validation test of these prototype scaffolds.

Recent experiments in neutron interferometry and optics at NIST