NIST currently provides its most accurate capacitance calibrations for value "islands". The existing measurement system is optimized to provide precise calibration on decade capacitance values (1 pF, 10 pF, 100 pF, etc.). The nominal values of capacitors to be calibrated must be within ±500 ppm of these decade values. This system cannot be readily used to determine an "odd value" capacitor (say, 10.35 pF) at metrological accuracy. However, a recent development by Yicheng Wang and Lai Lee of the Electricity Division holds promise for being able to address these "gaps" in our calibration service. They have developed a prototype programmable capacitor consisting of 23 binary-weighted capacitor elements on a single fused-silica disk which has capacitance programmable over six orders of magnitude from 0.0001 pF to 110 pF, with a resolution of 0.0001 pF. Methods have been outlined to allow precise calibration of each element and, thus, calibration of arbitrary combinations.
The potential applications of a well-characterized programmable capacitance standard are numerous. The current work on a capacitance standard based on single electron tunneling (SET) involves an "odd value" cryogenic capacitor. The programmable capacitor will provide a crucial link to compare an SET-based capacitance standard with the SI farad represented by the Farad Bank. This comparison is not only important to confirm the accuracy of the new standard but also necessary for closing the metrology triangle via the SET-based capacitance standard. Another example that requires precise measurement of an "odd value" capacitor is a new pressure standard based on measurements of the dielectric constant of helium. CSTL has proposed to use cross capacitors for accurate measurements of the dielectric constant; however, it is difficult to construct a cross capacitor with a precise value. A programmable reference capacitor can also be used to test the linearity of commercial precision capacitance bridges.
Contact: Jerry Stenbakken, x2440
May 2003
EEEL-Developed Wideband Sampling Voltmeter Provides Increased Accuracy to Calibration Laboratory Customers
A wideband (10 Hz to 1 GHz) sampling voltmeter (WSV) has been developed that greatly improves NIST's ability to perform accurate measurements of various electrical waveform parameters. Three replicas of this instrument have been delivered to the sponsors of this work for use in their calibrations laboratories. One WSV unit is being used by Sandia National Laboratories to characterize pulse response of oscilloscopes at peak amplitudes up to 100 V. The accuracy requirements precluded the use of commercial equipment of these measurements. At the Army and Air Force primary metrology laboratories two other units are being used to measure the ac gain flatness of state-of-the-art commercial ac voltmeters and calibrators at frequencies up to 30 MHz. The combination of wide bandwidth, large dynamic range and high accuracy requirements make these measurements extremely difficult to perform. The two laboratories turned to NIST and the WSV after failures in meeting their goals with traditional thermal transfer technology. A fourth WSV is being used at NIST in the pulse calibration service and a fifth will be used soon in a distorted power calibration service.
The instrument consists of a mainframe unit and a set of two sampling comparator probes. Two types of probes have been developed. One probe type is designed for the sampling of high-speed signals in a 50 ohm environment and the other for the sampling of lower bandwidth signals in a high impedance environment. A key feature of both these probes types is that their gain flatness response may be conveniently characterized using step response techniques. Several instrumentation manufacturers have expressed interest in the commercialization of the WSV.
Contact: Jerry Stenbakken, x2440
April 2003
Testbed Developed by EEEL for SCADA Encryption Modules
With the increased emphasis on protecting the U.S. critical infrastructure from terrorist attacks, the need for improving security on IT systems used to control the nations electric power grid has become more evident. This need for improved security is further emphasized by the increased use of IT controllers by the electric power industry as it continues to proceed with deregulation efforts.
In support of this goal, the Electricity Division has developed a testbed to measure the timing parameters of encryption modules intended to secure Supervisory Control and Data Acquisition (SCADA) System control loops. These systems are used to control large area energy distribution networks and other large commercial operations. Because of the vulnerability of these distributed systems to attack by terrorists, the industries considered part of the U.S. Critical Infrastructure are being encouraged to harden these control loops with encryption techniques. However, these control loops often have strict timing requirements. The newly developed NIST testbed provides techniques to measure the latency and jitter of commercial encryption modules designed for both TCP/IP and RS 232 communications channels. The testbed has been designed to provide the information required by the proposed American Gas Association test method AGA-12-1. The testbed was developed in cooperation with representatives from the gas and electric power industries.
Contact: Jerry Stenbakken, x2440
March 2003
EEEL Display Metrology Project Supports Development of Digital Cinema Testbed
The Digital Cinema Initiatives (DCI), a consortium of several major film studios, has contracted with the Entertainment Technology Center (ETC) of the University of Southern California (USC) to provide a testbed for developing open standards for digital movie releases. This testbed would include robust, reproducible methodologies for characterizing digital cinema projectors. The DCI hopes to correlate results of human evaluation (using different display technologies) to the projector characterization. The results would lead to a standard for setting up and maintaining the quality of the projection systems in theaters, and for determining acceptable means of digital distribution. The Display Metrology Project (DMP) in EEEL's Electricity Division has provided technical expertise for this effort via test patterns and measurement procedures developed for characterizing projector performance. The DMP also demonstrated methods for improving measurement capabilities through diagnostics and stray-light compensation. This work is being done in conjunction with the Convergent Information Systems Division of ITL.
Contact: Kevin Brady, x3644
February 2003
EEEL Researchers Develop Improved High-Resistance Standards
Researchers in the Electricity Division have developed a new generation of high-resistance standards and delivered the standards to the Primary Standards Laboratories of the Army and Air Force. These new standards, with nominal resistances of 1 Gohm and 10 Gohm, have performance characteristics that are substantially better than have been demonstrated by any prior standards at these resistance levels. As a result of this superior performance, NIST was able to deliver these standards with calibration uncertainties reduced by factors of 3 and 5, respectively, below those that can be provided for other high-resistance standards.
The improved performance characteristics will allow the Department of Defense (DoD) standards laboratories to deliver improved high-resistance measurements. Demand for improved high-resistance measurement capability has in recent years driven substantial improvement in the measurement instrumentation and techniques. However, performance characteristics of existing high-resistance standards did not allow electrical metrology laboratories to achieve the full potential of the improved instrumentation. A recent NIST-led international comparison of high-resistance measurement capability (CCEM-K2) clearly demonstrated the potential for improved metrology with improved standards. NIST undertook development of these improved standards as a critical step required for the DoD laboratories to maintain their high-resistance measurement capabilities at the necessary state-of-the-art.
The NIST standards are based on commercially available film-type resistance elements. These elements underwent heat treatment, which leads to a very large improvement in the long-term stability of their resistance. Sets of the treated elements were carefully selected to form composite standards with net resistance very close to the nominal value, and with minimal residual net drift rate. These composite elements were hermetically sealed in brass cylinders to improve their long-term stability and to mitigate the effects of environmental humidity, and then shock-mounted in aluminum enclosures using highly damped visco-elastic material. Calibrated thermistor probes were permanently mounted inside each enclosure to permit monitoring of the temperature. Mounting of the coaxial terminals on circular polytetrafluoroethylene (PTFE) plates allows these standards to be fully guarded, which suppresses the leakage of current to ground. The resulting stable and robust standards have excellent traveling characteristics and are suitable for use as primary resistance standards.
These standards were characterized for their drift with time and for their dependence on temperature and voltage. The 1 Gohm resistance standards were found to typically exhibit temperature coefficients of 5 × 10 -6 / ƒC, voltage coefficients of 0.003 × 10 -6 / V, and drift rates of less than 10 × 10 -6 / year. The 10 Gohm resistance standards were found to typically exhibit temperature coefficients of -3 × 10 -6 / ƒC, voltage coefficients of 0.003 × 10 -6 / V, and drift rates of less than 20 × 10 -6/ year. For comparison, high-resistance standards that are presently available commercially have typical thermal coefficients that are 1 to 10 times larger and voltage coefficients that are larger by a factor of 100 to 300. The observed drift is improved by a factor of 3 to 5.
Contact: Michael H. Kelley x3722
February 2003
EEEL Completes First Phase of Electronic Dictionary Mapping
Electronic component dictionaries are one of the most essential and fundamental architectural components required to make product data exchanges possible. Presently, there are three widely accepted and used international dictionaries throughout the global industry to support electronic commerce: RosettaNet's Technical Dictionary (RNTD) , the IEC's Data Dictionary (IEC 61360), and the Electronic Industries Association of Japan (EIAJ) ECALS Dictionary. In order to promote international electronic commerce, an effort has begun under the IEC TC93 WG6, co-convened by NIST's Infrastructure for Integrated Electronic Design and Manufacturing Project (IIEDM), that will try to harmonize the three dictionaries. The goal is to identify steps that can be taken to bring the three dictionaries into closer harmonization and to establish some of the mappings necessary to allow electronic component queries to cross systems backed by these dictionaries.
Members from ECALS, MERCI (Europe), RosettaNet, WG6, and the IEC have been participating in an experiment in which electronic component queries are generated based on one dictionary and responses are received from systems based on the other two dictionaries. Phase 1 of the experiment focused on generating RosettaNet based queries that were then submitted to ECALS and MERCI systems. The responses to those initial electronic component queries were generated by MERCI and ECALS based systems and then returned to RosettaNet based system. The resulting queries, responses, and dictionary mappings were then analyzed by the group to identify harmonization issues. The results of the first phase of the experiment have been released as an IEC draft document, giving participants a chance to add additional comments and analysis of the results. The next two phases of the experiment (Phase 2 and 3) are currently underway. Harmonization recommendations to all three groups ECALS, RosetttaNet, and IEC will be submitted as each phase of the experiment is completed.
February 2003
New Pulse Measurement System for Oscilloscope Characterization Developed
A new Sampling Waveform Analyzer (SWA) system has been developed for measuring voltage pulses of microsecond duration with amplitudes up to 100 V. At their request, the turnkey system has been delivered to the Sandia National Labs sponsor for accurately characterizing the pulse measurement performance of commercial digitizing oscilloscopes used in the SNL laboratory.
The system consists of a NIST Wideband Sampling Voltmeter mainframe, a commercial off-the-shelf pulse generator, and newly developed hardware and software. The new hardware consists of an accurate sampling probe and frequency-compensated voltage attenuator. The software, written as a user-friendly graphical user interface, provides all the necessary features for hardware control and data collection, signal processing, and coded procedures for calibrating the system. The pulse generator provides a pulse stimulus for the oscilloscope under test. Although pulse aberrations may reach 5 percent, the effects of pulse distortion are minimized by normalizing the response of the oscilloscope to the response of the SWA. With traceability to NIST dc and time-domain measurement standards, the SWA is able to measure accurately a variety of performance parameters. As delivered, the system measures oscilloscope sensitivity, tilt, transition duration, settling error, and input impedance. The measurement uncertainty of sensitivity is less than 0.2 percent at 100 V.
Feedback from the sponsor about the new system is favorable and encouraging: "The new digitizer calibration system developed by NIST's Electricity Division enables Sandia to calibrate digitizers using well-characterized pulse inputs for the first time. The digitizers support critical pulse voltage and pulse current measurements... One significant feature of the new system is that the NIST staff developed specific calibration procedures for Sandia digitizers, as well as an uncertainty analysis for the calibration process." - Richard B. Pettit, Manager, Primary Electrical Standards, Primary Standards Laboratory, Sandia National Laboratories.
January 2003
EEEL Performs First Comparison of the Gamut Assessment Standard with other NMIs
John Libert of the Electricity Division in the Electronics and Electrical Engineering Laboratory (EEEL) conducted inter-laboratory color measurement comparisons with the National Measurement Laboratory (NPL) of the United Kingdom and the National Research Council (NRC), Canada. These measurement inter-comparisons among national metrology institutes (NMI's) and EEEL's Display Metrology Project, kick-off the first phase of interactions aimed at reducing the variability of color gamut and other measurements used to characterize and specify performance of electronic displays. A key feature of the project is the development by EEEL of a standard illumination source fitted with color filter artifacts selected to test the instruments and methods used in display measurement. The device, the Gamut Assessment Standard (GAS), will be circulated among additional NMI's, instrument manufacturers, and industry laboratories initially to evaluate the measurement variability of the display industry. Later the device will form the basis of a NIST-calibrated transfer standard -- DMATS (Display Measurement Assessment Transfer Standard), allowing industry laboratories to evaluate their measurement procedures and instruments. This work is a cooperative effort with Drs. Yoshi Ohno and Steve Brown of the Optical Technology Division of the Physics Laboratory.
November 2002
SUN Distributes NIST Test Patterns for Flat Panel Displays
Purchase any new Flat Panel display from SUN Microsystems, and you will receive with it a CD containing the product documentation. Included on that CD are 135 test patterns developed in EEEL by the Flat Panel Display Laboratory. Also included is the Document by Edward F. Kelley of NIST and J. V. Miseli of Sun titled "Setup Patterns for Display Measurements - Version 1.0," NISTIR 6758, 14 pp., June 2001. The Test Patterns have been incorporated into the VESA Flat Panel Display Measurements document (FPDM). The patterns are a number of setup targets for setting up a display and are also useful in demonstrations and measurement of display characteristics. The test pattern files included are in .png (Portable Network Graphics) format, to assure lossless compression. The document and patterns can be viewed at: http://www.fpdl.nist.gov/patterns.html
November 2002
EEEL Develops Straddling Bridge for Improved NIST Calibration Services
Electronic bridge circuits have many measurement applications, but are particularly important for NIST calibration services. A new bridge, known as the straddling bridge, has been developed to improve calibrations of the high precision inductive voltage dividers (IVDs) that are pervasive in NIST equipment used for calibration of electronic components. IVDs that scale voltages down with very high precision are characterized by the ratio of their input to output voltages. They are used as reference standards for ac voltage ratio in a variety of applications, including NIST calibration instrumentation for precision electrical components such as inductors and capacitors. The straddling bridge compares an IVD under test with a reference IVD, but the advantage of the straddling bridge technique is that it allows the IVD to be self-calibrated, i.e., to have its errors evaluated independently of the errors of the reference IVD. Errors associated with the new straddling bridge are below 50 parts per billion, which is insignificant relative to the errors of IVDs that are tested. The straddling bridge will lead to improvements in NIST calibration services, and will be used in the CCEM K-7 comparison of ac voltage ratio measurement capabilities among national measurement laboratories.
September 2002
EEEL Researchers Complete Uncertainty Analysis for Linking ECCS to SI Farad
Researchers Yicheng Wang and Neil M. Zimmerman of the Electronic and Electrical Engineering Laboratory's (EEEL) Electricity Division have completed an uncertainty analysis for the comparison of a cryogenic vacuum-gap capacitor against the NIST calculable capacitor. This work is a critical step in the development of the Electron-Counting Capacitance Standard (ECCS), which is being pursued in collaboration with workers in the Electromagnetic Technology Division.
The essential idea of the ECCS is to place an accurately known electric charge, by counting individually each of about 108 electrons, onto the plate of a cryogenic vacuum-gap capacitor and then to measure the charging voltage with high accuracy. The capacitance of the device is determined directly from the charge-to-voltage ratio. Three valuable uses have been identified for the ECCS. It will serve as a "turnkey" primary representation for capacitance, it will provide an additional route for the measurement of the fine-structure constant, and it will provide a means to close the "quantum metrology triangle" formed by the Josephson voltage, the quantum Hall resistance, and the fundamental electron charge.
A recently reported advance for the capacitor was to increase its capacitance to a value of approximately 10 pF (within a few percent), thus allowing a direct comparison of the vacuum-gap capacitor to the NIST calculable capacitor using existing high-precision instrumentation. The calculable capacitor is a large mechanical capacitor which, through a fundamental theorem of electrostatics, provides the SI realization of the Farad. The comparison of the two capacitors is crucial for the ECCS, both for demonstrating its usefulness as a representation of capacitance, and for determination of the fine-structure constant or closure of the quantum metrology triangle.
The advance noted here is the completion of the detailed uncertainty analysis of this comparison, including statistical and systematic uncertainties. This analysis shows that the total relative uncertainty of the comparison is about 4 × 10-8. This compares favorably with the total relative uncertainty of 2 × 10-8, which is achieved for the highly optimized comparisons against the calculable capacitor that are performed as part of the regular maintenance of NIST's primary bank of capacitance standards. Indeed, this measurement of the cryogenic capacitor was designed to utilize, as closely as feasible, the same instrumentation and measurement procedures as those routinely used for measurements of the room-temperature transfer standard. The close similarity both simplified this uncertainty analysis and contributed to the ultimate quality of the result. Future improvements in the measurement system could reduce the uncertainty to a value even closer to that for the highly optimized measurements.
With the completion of the uncertainty analysis, the new 10 pF cryogenic capacitor is now fully ready to be used in the ECCS, with a route to tie the ECCS to the SI unit of capacitance with an uncertainty of a few parts in 108.
A paper describing this work has been submitted for publication in the IEEE Transactions on Instrumentation and Measurement.
August 2002
EEEL Display Metrology Project Hosts International Standards Meeting
The Display Metrology Project of EEEL Electricity Division hosted the semiannual meeting of the International Organization for Standardization (ISO) TC159/SC4/WG2 (Visual display requirements) at NIST, May 15-17, 2002. This working group, consisting of ergonomists and engineers from Asia, Europe, and the U.S., is responsible for the development of standards that set requirements for the design factors of electronic visual displays that affect user comfort and fatigue in an office environment. A series of standards have been published concerning cathode ray tubes (CRTs): ISO 9241 (Ergonomic requirements for office work with visual display terminals [VDTs]) Part 3: Visual display requirements, Part 7: Display requirements with reflections, and Part 8: Requirements for displayed colors. A new standard series for flat panel displays is now in publication: ISO 13406 (Ergonomic requirements for work with visual displays based on flat panels) Part 1: Introduction, and Part 2: Ergonomic requirements for flat panel displays.
WG2 is presently working on a grand revision of their display standards, incorporating not only their existing standards but also expanding the scope to include additional technologies and applications. The Display Metrology Project provides technical support and evaluation of display measurement procedures that the working group will adopt for inclusion in this new standard.
July 2002
EEEL Flat Panel Display Project Impacts Display Industry
Dr. Edward F. Kelley of EEEL presented a four-hour short course, Fundamentals of Display Metrology, at the 2002 Society for Information Display International Symposium held in Boston, May 19-24, 2002. The course was held on Sunday from 6:00 pm to about 10:30 pm (May 19)--a terrible time for travelers and locals alike!--yet there were over 200 attendees. The course addressed a wide spectrum of concepts and problems encountered in making display measurements including general photometry, management of stray light and veiling glare, reflection characterization, near-eye displays, and associated diagnostics. The attendance underscores the heightened interest in display metrology. The uninitiated consider display metrology to be a simple matter, however experience quickly teaches otherwise. This course will serve as the basis for a course on display metrology that will be offered here at NIST along with laboratory experiments in the near future.
Dr. Kelley also presented a paper entitled "Sensitivity of Display Reflection Measurements to Apparatus Geometry" in the Display Metrology Session. There was standing room only for Dr. Kelley's talk, with again over 200 people in attendance. This paper attempted to distinguish the difference between reproducibility and robustness. It showed that some of the preferred reflection measurement methods currently being used in display measurement standards or proposed to be used are not robust methods. That is, to make them reproducible will require more effort than most technicians will tolerate. Eight different measurement apparatus were analyzed according to methods of experimental design (full or fractional factorial orthogonal designs with randomized blocks). The results of this paper are already influencing the selection of reflection measurement methods being considered by two display standards organizations.
July 2002
EEEL Researchers Improve High-Resistance Measurement Capability
Randolph E. Elmquist in the Electricity Division of the Electronics and Electrical Engineering Laboratory (EEEL) has developed a new technique that enables more accurate scaling from the primary NIST quantum Hall resistance standard to high resistance levels of 1 MW and above. The technique exploits a unique property of the quantum Hall effect, which allows a quantized Hall resistance standard to serve as a near-ideal two-terminal resistor whose resistance, 12906.4035 W, is essentially independent of the resistance of the room-temperature connecting leads. This will allow calibration of NIST 1 MW working standards with a relative uncertainty of better than 1 ¥ 10-7, an improvement of about an order of magnitude. The new measurement system was recently used to calibrate a set of four 1 MW resistance standards for an NCSLI inter-laboratory comparison. The relative uncertainty for these calibrations is about 1 ¥ 10-6, a factor of three improvement over the present NIST calibration service.
The property exploited by the new measurement system is unique to the quantum Hall effect and determines exactly how current flows in device leads when more than two connections are made to a single QHE device. The new NIST bridge incorporates a cryogenic current comparator, relies on superconducting leads for many connections, and is compatible with conventional guarding techniques. The ultimate result is a bridge that is significantly less susceptible to leakage errors than the series-parallel resistance networks (Hamon devices) previously used for high resistance scaling. It may be possible to extend the range of this direct scaling measurement up to 10 MW or even 100 MW by using larger turns-ratio current comparators.
April 2002
EEEL Offers Tutorial on Coulomb Blockade
Researchers from NIST's Electronics and Electrical Engineering Laboratory recently organized, in conjunction with the March Meeting of the American Physical Society (APS), a half-day tutorial entitled "Coulomb Blockade and Single Electron Tunneling". The annual March Meeting, attended by approximately 5000 physicists, is one of the principal scientific meetings concentrated on condensed matter physics. On the Sunday before the conference begins, the APS traditionally runs selected tutorials on a range of subjects, designed as in-depth introductions for newcomers to a field. The single-electron tunneling (SET) tutorial was organized and run by Neil Zimmerman of the Electricity Division and featured presentations by both Neil and Mark Keller of the Electromagnetic Technology.
Mark was one of the expert lecturers and presented two talks. The first highlighted NIST's world-leading work on developing a fundamental capacitance standard based on counting electrons one-by-one onto the plate of a standard capacitor. The other a collection of secrets for experimentalists, entitled "The three 'f's of SET experimentation: fuses, fabrication, filtering".
Rather than just present a lecture, Neil opted to provide a hands-on simulation demonstration for the students. This was apparently the first time such a demonstration was made part of an APS tutorial. The demonstration consisted of an exercise in which teams of two or three students were given a set of experimental data, challenged to figure out the correct parameters for theoretical fits to the data, and then asked to infer from the simulation something about the physical meaning of the derived parameters.
The demonstration was quite challenging, and the students' results varied substantially. About half of the teams completed the exercise fully; most of the rest completed much of it. The excitement in the room during the exercise was palpable; at the end of the exercise, significant effort was required to pull the students' attention away from the simulations.
A total of 46 students registered, with many more turned away both before and the day of the event. The simulations were made possible by the rental of sixteen laptop computers, funding for which was provided by Bill Anderson, Director of EEEL.
April 2002
EEEL Reduces Uncertainties in Fast Pulse Calibration Service
The application of new test instruments, a new test procedure, and an improved uncertainty analysis has resulted in a significant reduction in the reported uncertainty for transition duration (i.e., rise time and fall times) provided by Special Test 65200S "Fast Repetitive Pulse Transition Parameters." The uncertainties have been reduced from -2.2 ps / + 4.4 ps to ±1.5 ps. In addition, the parameters of overshoot and undershoot have been added to the list of parameters provided by the 65200S. The addition of these parameters was possible because of the new uncertainty analysis. The 65200S calibration service is used by manufacturers of high-speed samplers, military calibration laboratories, and aerospace and computer industries to calibrate the output of high-speed pulse generators and the step response of high-speed samplers. The reduction in transition duration uncertainty is significant because of the increase in speed of commercial samplers and in the circuits that they are intended to test. With these improvements there are no other national metrology laboratories that surpass the measurement capability of NIST in high-speed pulse parameters.
February 2002
Consumer Power Quality Guide for NRECA Written by EEEL Staff
Electric power quality problems are often monitored by electric utilities through customer reporting: if the lights flicker or go out, the utility learns of the problem when customers affected by the problems call in to report them. The National Rural Electric Cooperative Association (NRECA) has just published a guide written by FranÁois Martzloff of the Electricity Division aimed at helping the utility customer service representatives and customers communicate better and quickly identify the causes of their power problems. This 36-page manual, Consumer Power Quality Problems: Troubleshooting by Telephone, provides a summary of typical power quality disturbances and their effects on appliances, lights, and other electronics, with suggestions for possible remedies. A systematic classification of the types of appliances and the symptoms of the problems enables the customer service representatives of these sometimes small electricity cooperatives to lead the affected customers through a series of questions that narrows down the possible causes and allows a tentative diagnosis to be formulated. The service representatives can then suggest possible solutions, resulting in a highly cost-effective telephone session. NRECA is an organization of more than 900 rural electric power systems whose member cooperative utilities own about 45% of the nation's distribution systems but provide power to less than 10% of the nation's people, primarily in sparsely populated areas of 46 states. Solving problems over the telephone rather than traveling long distances for a site visit is an important factor in reducing the costs and time spent correcting power quality problems. The guide is now being disseminated with great success among the member utilities of NRECA.
January 2002
EEEL Reviews Impact of Conservation Voltage Reduction for Electric Power Industry
The old debate about the possibility of reduce the peak power demand that electric utilities have to meet by lowering the system voltage level by a few percent (known as a "brownout") has been rekindled by the incidence of rolling blackouts in response to overloaded transmission and distribution systems. The State of California is considering this approach, now called "Conservation Voltage Reduction" (CVR), which rests on the undisputed fact that constant-resistance loads - such as incandescent lighting - draw power proportional to the square of the supply voltage. It would appear that a systematic reduction of a few percent could significantly reduce or "shave off " the peak demand, reducing the possibility of overloads. Such overloads might otherwise make it necessary to arbitrarily cut-off the supply to some sections of the distribution system to avoid a collapse of the complete system. Prompted by these CVR proposals, an objective review of their implications has been made by Francois Martzloff of the Electricity Division for publication by EPRI, the major electric power industry R&D organization, as a "PQ Commentary." The conclusion of this review entitled The Power Quality Implications of Conservation Voltage Reduction (see www.epri.peac.com) is that while some peak demand shaving might be beneficial, sophisticated loads that are already sensitive to brief voltage reductions known as "sags" caused by incidents on the power grid would be even more vulnerable if these sags would occur during a CVR period. The report urges cooperation among equipment manufacturers and users, together with electric utilities and regulatory agencies, supported by an objective test program on the possible side effects of CVR. It will serve to illuminate the old debate and help to raise awareness of the possible negative consequences to before CVR is implemented.
January 2002
EEEL Researchers Two Steps Closer to Electron-Counting Capacitance Standard
A team of scientists including Yicheng Wang and Neil M. Zimmerman of the Electronic and Electrical Engineering Laboratory's (EEEL) Electricity Division, in collaboration with Mahmoud El Sabbagh, an intern from the University of Maryland, have made two advances in the development of cryogenic capacitors for use with the Electron-Counting Capacitance Standard (ECCS). The ECCS is being developed, in collaboration with the NIST Electromagnetic Technology Division in Boulder, as a quantum-based representation of capacitance. It relies on pumping a precisely counted number of electrons (about 100 million) onto the plates of a cryogenic capacitor and measuring the resultant charging voltage. Besides providing a "turnkey" primary capacitance representation, the ECCS will also provide an alternate route for experimental determination of the fine-structure constant.
Two recent advances have been implemented for the cryogenic capacitor. First, physical design changes have improved its stability and allowed an increase of its nominal value by an order of magnitude, to 10 pF. This larger value makes the ECCS more attractive as a turnkey representation because it should support lower uncertainties for typical commercial capacitance calibrations. This increase in value was made possible by improved machining tolerances, which allowed fabrication of the device with a gap between the two capacitor plates of about 0.05 mm over a distance of about 10 mm. An additional benefit of the improved machining tolerances is that the capacitance value is within 1 % of nominal, which is important for use with much of our precision measurement instrumentation. The new device exhibits excellent stability; after equilibration at low temperatures, its capacitance drift is less than about 10-9 per hour.
The second advance was the performance of a preliminary measurement of the cryogenic capacitor directly against the NIST calculable capacitor. The calculable capacitor is a large mechanical capacitor that, through a fundamental theorem of electrostatics, provides the SI realization of the Farad through a measurement of displacement. Measurement against the calculable capacitor is crucial for the ECCS, both in terms of demonstrating its usefulness as a capacitance representation, and for the measurement of the fine-structure constant. The stability of the cryogenic capacitor was an essential requirement for this measurement. The measurement noise in the comparison of the capacitor at low temperature against the calculable capacitor was roughly the same as observed in the routine measurements involving the calculable capacitor.
Some further refinements are needed. In addition to a full characterization of its performance and error budget, a more accurate means is needed for the course determination of the capacitance value; routine measurement against the calculable capacitor only yields capacitance values modulo 1.5¥10-6.
January 2002
EEEL's Collaboration with Industry Results in the Release of Several New Supply Chain Standards for Electronics Manufacturing
The nearly complete outsourcing of board fabrication and assembly in the domestic electronics industry has created a critical need for an efficient means to transfer design intent and production results among manufacturing partners. Electronics Manufacturing Services (EMS) providers, who perform board assembly and other services for major manufacturers, are forced to maintain small companies within their operations that do nothing more than interpret the data that their customers send them in hundreds of differing formats. As a result of a project co-led by EEEL researcher Barbara Goldstein and Intel manager John Cartwright, the electronics industry now has three new IPC standards and ten new RosettaNet consortium production specifications to enable standard supply chain transactions, thereby reducing the translation burden faced by EMS companies.
Goldstein and Cartwright co-led the National Electronics Manufacturing Initiative (NEMI) Virtual Factory Information Interchange Project, whose mission was to "define standards which when implemented will shorten the time and reduce the cost to establish and maintain information exchange partnerships across the manufacturing supply web." To encourage the broadest possible industry adoption, the NEMI VFIIP project teamed up with both IPC, an ANSI-accredited standards development organization, and RosettaNet, an industry consortium creating supply chain standards, to develop a robust mechanism for information exchange. This effort resulted in the release of the following IPC standards on November 12: IPC-2571 Generic Requirements for Supply Chain Communication; IPC-2576 Requirements for Supply Chain Communication of As-Built Product Data; and IPC-2578 Requirements for Product Design Configuration. A fourth standard, IPC-2577 for the communication of quality data across the supply chain, has been released by IPC as a "standard proposal" for industry comment. All four documents are publicly available at http://webstds.ipc.org/ . The team's collaboration with RosettaNet has led to the release of ten RosettaNet Partner Interface Process (PIP) specifications, 2C1 through 2C10, which enable distribution and update of product design and change notices. RosettaNet's is also developing a suite of manufacturing PIPs which will allow integrate the exchange of the IPC 2576 as-built product information. Released PIPs are publicly available at www.rosettanet.org .
November 2001
FPDM2 specification developed by EEEL could affect ARMY display acquisition for foreseeable future
The Video Electronics Standards Association's (VESA) Flat Panel Display Measurements, Version 2.0 (FPDM2) document is being used by the US Army for procurement of flay panel display technology. FPDM2 was released in June 2001, and the EEEL Flat Panel Display Laboratory (www.fpdl.nist.gov) was responsible for 70% of the document.
Over the last two years Bradley Engineering has been working on a specification and accompanying technical rationale for a common flat panel display. This material is being developed for the US Army Tank-automotive and Armaments Command (TACOM), Warren, Michigan. Drafts of both documents were delivered to the government in late spring of this year. It is expected that these documents will be the basis for a military performance specification that could affect Army displays acquisition for the foreseeable future (and perhaps Air Force and Navy acquisitions as well). FPDM2 is extensively referenced throughout the specification and is the basis for the test procedures.
Steve Kutner of Bradley Engineering specifically thanked the efforts of NIST's FPDL project leader Edward Kelley. "I express my appreciation for the contribution of Dr. Edward F. Kelley throughout the development and review process. Ed's energy and enthusiasm for proper metrology was the foundation for the requirements and test methods. Without his guidance and counsel, the specification would have had major errors and would have been delayed significantly. I cannot overstate his contribution. It was exceptional by any standard. We looked at other standards (ISO, TCO, NIDL, etc.) but nothing came close to FPDM2's depth, coverage, and practicality."
October 2001
EEEL Results Lead to Improvement in Zener Voltage Reference
Careful measurements made in the Electricity Division for the characterization of Zener voltage standards have enabled the manufacturer to redesign the instruments for improved behavior. As part of Electricity Division efforts to develop a 10 Volt Measurement Assurance Program (MAP), undertook an extensive study of the characteristics of eight Fluke 7001 Zener Voltage Standards under a wide range of differing environmental conditions. One striking feature of the measurements was that all units showed a strong correlation between the Zener voltage output and relative humidity. The time constant for response to humidity change was relatively short, on the order of about 2-3 weeks. This behavior would have seriously limited the use of these instruments as transport standards for the MAP.
The NIST measurement results were shared with the manufacturer in hope that the detailed characterization might point to the source of sensitivity to environmental humidity. A preliminary analysis by John Pickering, of Metron Designs Ltd. and a designer of the original product line, identified certain epoxy-encapsulated resistors as likely candidates for the problem. When relative humidity changed, the plastic molding would either absorb or evolve water. The resulting swelling or shrinking would change stress patterns across the resistor array chip. Numerical simulation predicted resulting voltage changes in reasonable agreement with thee NIST measurements. A retrofit to the product line was designed and implemented on four of the NIST units as a test. Subsequent measurements at NIST confirmed a large reduction in the sensitivity to humidity changes, greatly improving the potential for use of these devices as transfer standards for the NIST 10V MAP. The availability from NIST of the crucial data and the active response from the manufacturer resulted in a significant improvement in the performance of these high precision voltage standards.
October 2001