Electromagnetic MeasurementsImpedance Measurements (Except Resistors)Low-Frequency Capacitance and Inductance Measurements and StandardsTechnical Contact: Denise D. Prather Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements Special Four Terminal-Pair (4TP) Capacitance and Dissipation Factor Characterization (52100S)This service covers the characterization of capacitance and dissipation factor for standard 4TP air-dielectric capacitors with nominal values of 1 pF, 10 pF, 100 pF and 1000 pF, in the frequency range from 1 kHz to 10 MHz. first, three-terminal capacitance measurements are taken at 1 kHz for each capacitor under test, thus linking these values to the NIST Calculable Capacitor. Single-port complex impedance measurements are then taken at frequencies in the 100 MHz range, linking these values to the NIST Air Line Standard. Next, a mathematical extrapolation algorithm is used to predict the 4TP resistance and inductance at the test frequencies, and finally the 4TP capacitance and dissipation factor of the capacitor under test are then computed at the test frequencies. The estimated uncertainties for the 10 pF, 100 pF and 100 pF 4TP capacitance are in the range of 20 ppm to 300 ppm at 1 MHz and in the range of 1100 ppm at 10 MHz. The 1 pF capacitance uncertainties are in the range of 700 ppm for 1 MHz and 14000 ppm (1.4 percent) for 10 MHz. Estimated dissipation factor uncertainties for the 10 pF, 100 pF and 1000 pF standard capacitors lie between 20 microradians (µrad) and 300 µrad at 1 MHz and between 600 and 1400 µrad at 10 MHz. The estimated 1 pF dissipation factor uncertainties are in the range of 300 µrad at 1 MHz and 5700 µrad at 10 MHz. It is recommended that potential customers contact A. Koffman 301/975-4518 to schedule requests for this service. The service will provide capacitance and dissipation factor characterization, with uncertainties for each, at the following frequencies: 1 kHz, 10 kHz, 100 kHz, 500 kHz, 1 MHz, 2 MHz, 3 MHz, 4 MHz, 5 MHz, 6 MHz, 7 MHz, 8 MHz, 9 MHz and 10 MHz. Additional frequencies will increase the cost. back to top of page | back to index of electromagnetic measurements Low-Frequency Capacitance and Inductance Measurements and Standards (52110S-52181C)These services cover the calibration of standard capacitors and inductors in the audio-frequency range. Three-terminal standard capacitors having fused-silica (1, 10, and 100) pF, nitrogen (10, 100, and 1000) pF, and air, from 0.001 pF to 10 000 pF, dielectrics can be measured at (100, 400, and 1000) Hz. Two- or three-terminal capacitors with mica dielectrics in the range from 0.001 µF to 1 µF can be measured at (66, 100, 400, 1000, and 10 000) Hz. Two-terminal air and mica dielectric capacitors with high frequency (HF) coaxial connectors, from 1 pF to 10 000 pF, including GR900 terminations, are calibrated only at 1 kHz. Air-core standard inductors having nominal values between 0.05 mH and 10 H can be measured at (100, 400, and 1000) Hz. Standard inductors of 100 mH or less also can be measured at 10 kHz. Calibration of impedance standards other than those mentioned above will be considered for Special Test Under Service ID Number 52110S (see below). The calibration of some types of high frequency capacitance standards at frequencies as low as 1 kHz can be provided by the NIST Radio-Frequency Technology Division in Boulder, CO, provided the uncertainty required exceeds 0.01%. In some circumstances this can eliminate the necessity of sending a standard to both Gaithersburg and Boulder Laboratories for a complete calibration. See also Service ID Numbers 52210C-52310C for calibration of capacitors at higher frequencies. For additional details please inquire at NIST/Boulder: Telephone 303-497-3609. back to top of page | back to index of electromagnetic measurements Special LF Impedance Measurements, by Prearrangement (52110S)This service provides for the testing or evaluation of prototype impedance standards or measurement instrumentation at the state-of-the-art, and other impedance measurements (such as the calibration of decade or variable capacitance standards), at the discretion of NIST technical experts. Component capacitors, inductors, and resistors are not considered for testing by NIST unless their performance approximates that of the best available standards. Even under those conditions, calibration will only be done on a limited basis to ascertain the possible use of the components in precision measurement applications. The cost for such tests are determined on a case-by-case basis, and may be considerably higher than the posted fee for Calibration Services because of needed additional preparation and extra measurements required to perform an uncertainty assessment. back to top of page | back to index of electromagnetic measurements Special Measurement Assurance Program for Standard Capacitors (52120S)The Capacitance MAP (C-MAP) transfers are carried out for standard capacitors at the 1000 pF and 100 pF levels, at a frequency of 1 kHz. A commercial 1 kHz capacitance meter is used as the transport standard. The client laboratory (Lab) is responsible for performing measurements (using the Lab calibration system and the transport standard) on its own reference and/or check standards, and on the two pairs of dummy capacitors from NIST of the same nominal values. Prior to the initiation of the C-MAP, the Lab is required to complete a CAPACITANCE MAP INFORMATION SHEET, and to provide a description of its calibration procedures. At the time the transport standard and the dummy capacitors are shipped to the Lab for a C-MAP transfer, the Lab will also receive detailed instructions for carrying out the C-MAP and the software for enabling the transport standard (commercial capacitance meter) to make measurements automatically. The Lab is also required to collect and reduce the data from its calibration system, and to enter the results on to the CAPACITANCE MAP DATA SHEET. The transport standard and the dummy capacitors are normally kept in the Lab for about 4 to 6 weeks, as eight to twelve sets of measurements are required. After the completion of post MAP measurements and a data analysis at NIST, a REPORT OF CALIBRATION from NIST is issued to the Lab. This report provides the difference between the unit of capacitance maintained by the Lab and the farad, and the assigned values for the Lab reference standards (and their uncertainties) to bring the difference to zero. back to top of page | back to index of electromagnetic measurements Fused-Silica Dielectric Standard Capacitors (52130C-52131C)Air-bath type, fused-silica dielectric standard capacitors are generally submitted in temperature-controlled ovens due to their (10 x 10-6)/°C temperature coefficient. Because of the magnitude of the temperature coefficient, it is recommended that a reliable temperature sensor having a resolution of 0.001 °C, or better, be permanently mounted in the oven and thus included as part of the calibration. For baths not so equipped, the temperature is measured in terms of the International Temperature Scale of 1990 (ITS-90), using a standard platinum resistance thermometer. Some capacitance standards consist of a fused-silica dielectric capacitor completely sealed within a temperature-controlled oven and the ancillary circuitry required for its operation, but with no means of measuring or monitoring the oven's internal temperature. Since the actual temperature of the capacitor cannot be measured, it is not reported. Some such standards measure and display the ambient temperature. For these, the mean value of the display readings taken at the times of measurement is reported, but the significance of this value is decided by the user. Oil-bath type, fused-silica dielectric capacitors are calibrated in an NIST oil bath maintained at (25 ± 0.01) °C, if the normal temperature of use for these capacitors is approximately 25 °C. If the capacitors are supplied with built-in sensors, the sensors and the oil temperature are both measured. Requests for the calibration of oil-bath type, fused-silica dielectric capacitors are accepted as Special Tests (52110S). Calibrations are carried out at (100, 400, or 1000) Hz, or any combination of these frequencies chosen by the client. A minimum of five measurements is made over a 2-week or longer period, comparing the test capacitor directly with an NIST fused-silica standard at 10 pF. The number of readings taken depends on the stability of the temperature of the test capacitors. The averages of the measured values of capacitance and temperature are reported. The uncertainty of the reported capacitance value depends on the stability of the temperature as well as on the performance of the capacitance standard itself. Because the temperature coefficients of individual standards are usually not known quantitatively, the results cannot be temperature corrected. Despite these factors, the Type A standard uncertainty can be as low as 2 x 10-8 of the capacitor's nominal value. back to top of page | back to index of electromagnetic measurements Standard Capacitors (52140C-52176C)The following guidelines apply to the calibration of standard capacitors having dielectrics other than fused-silica. Calibrations are ordinarily performed at a normal laboratory ambient temperature of (23 ± 1 °C) except for measurements of high-stability nitrogen dielectric capacitors. These are measured more than once in a period of several days to observe their stabilities and to ensure that the variation of the measurements is within the required limit of the standard errors for these measurements. Simultaneously, a digital thermometer with a resolution of 0.001 °C is placed near the capacitors to monitor the temperatures during calibrations. The calibration temperature, nominally 23 °C, is reported to within ± 0.01 °C. Relative humidity is maintained at 50% or less in all cases. Precision three-terminal nitrogen dielectric capacitors, such as ESI Model SC1000 and GENRAD Model 1404, have been found to be variously affected by mechanical shock and orientation. Accordingly, two types of calibrations, featuring different levels of uncertainty are offered. See Table 9.3 . A qualification test (52150C) is available to supplement the small uncertainty calibration (52140C) in order to determine the effects of various impacts (physical shocks) and orientation on the capacitors. Results of this test should be coupled with the Type-B uncertainty of the precision calibration that follows to provide an expanded uncertainty for the calibration of a particular standard. Requests for the small uncertainty calibration without the physical tests are also accepted. For the large uncertainty test (52160C), a similar calibration, but with reduced resolution, is performed. Three-terminal air dielectric capacitors are accepted for the large uncertainty calibration (52160C) only. In the case of direct or three-terminal capacitance standards, the connectors are assumed to be coaxial, such as the GENRAD Type 874. While the connectors available for this purpose are adequate, it should be noted that changes or instabilities in the impedance of the shield or guard connection of a three-terminal capacitor can change the capacitance significantly. Capacitors requiring terminal plugs (banana plugs) for parallel connection should be sent to NIST together with the plugs that will be used with the capacitor after calibration. If such a capacitor arrives without plugs, NIST must attach plugs temporarily in order to calibrate the capacitor. Those used by NIST are GENRAD Type 274-P plugs. If, after calibration with these plugs, the capacitor is used with plugs of even slightly different length and base, the capacitance can differ significantly from that reported, and such differences will not be reflected in the calibration uncertainties reported. Unless otherwise requested, the measured value reported by NIST is the added capacitance when the standard is plugged directly into the binding posts of the NIST bridge. For two-terminal GENRAD capacitors, Type 509 and Type 1409 (when used as a two-terminal capacitor), a capacitance increase ranging from 0.01 pF to 0.04 pF has been found for different plugs. No significant change in conductance has been found in either the two-terminal or three-terminal value. The importance of terminal connection methods becomes extremely critical when capacitance values of 0.01 µF or less are being measured. Improved accuracy in two-terminal measurements can be realized if standards are provided with precision coaxial connectors. The terminal connections, either as two-terminal or three-terminal capacitors, for capacitors with mica dielectric, should be specified in the customer's purchase order. Otherwise, they will be calibrated as two-terminal capacitors (with the case "Ground" connected to the "Low" terminal). The capacitance value given is the equivalent parallel capacitance. In general, an accurate determination of the equivalent parallel conductance with high accuracy is not available. However, for mica dielectric capacitors in an approximate conductance value for each capacitor is also given. The frequencies available for capacitance calibrations depend upon the type of capacitor and its connectors. In general, capacitors with binding posts or GR 274-P plugs can be calibrated at (66, 100, 400, 1000, and 10 000) Hz. Capacitors with high frequency coaxial connectors (GENRAD Type 900) are calibrated only at 1000 Hz. The expanded uncertainty stated in the Report of Calibration is determined by the random behavior of each type of capacitor (determined from the analysis of measurement data taken from a large population of individual calibrations), as well as an estimate of the systematic errors of the NIST measurement process. These are calculated using the approach of NIST Technical Note 1297, per NIST policy. The expanded uncertainties are given in Table 9.3 and Table 9.4. The stated uncertainties are sufficiently broad to allow for variations in the stray capacitance at the connectors, in temperature of a few degrees Celsius, in relative humidity and atmospheric pressure, and in frequency deviations of a few percent from the stated test conditions. Depending on the frequency and the capacitance value, the relative expanded uncertainty usually lies between 0.0004% and 0.05% (see Tables 9.3 and 9.4 ). The uncertainties do not include allowances for effects of transportation; these must be determined by the owner using pre- and post-calibration data from the owner's facility. back to top of page | back to index of electromagnetic measurements Standard Inductors, Self or Mutual (52180C-52181C)Air-core standard inductors for use in ac bridges are tested at a room temperature of (23 ± 1) °C and a relative humidity of 50% or less. Measurements at 10 000 Hz are limited to standard inductors of 0.1 H or less. Most inductors used at 60 Hz can be tested at 100 Hz since the variation of inductance with frequency in this range is usually negligible. A metal-encased standard is calibrated with the case "Ground" connected to the "Low" terminal of the inductor unless other conditions are specified. The reported values are the self inductance values of the inductors.
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back to top of page | back to index of electromagnetic measurements References-Low-Frequency Capacitance and Inductance StandardsError Analysis and Calibration Uncertainty of Capacitance Standards at NIST, Y. May Chang, NIST Spec. Publ. 250-52 (Jan. 2000). NIST Calibration Service for Capacitance Standards at Low Frequency, Y. May Chang and S. B. Tillett, NIST Spec. Publ. 250-47 (Apr. 1998). NIST Measurement Assurance Program for Capacitance Standards at 1 kHz, Y. May Chang, NIST Technical Note 1417 (March 1996). NIST Capacitance Measurement Assurance Program (MAP), Y. May Chang, Measurement Science Conference, Anaheim, CA, (January 1993). New Realization of the Ohm and Farad Using the NBS Calculable Capacitor, J. Q. Shields, R. F. Dziuba, and H. P. Layer, Conf. Precision Electromagnetic Meas. (CPEM '88), June 7-10, 1988, Tsukuba Science City, Japan, Special Issue CPEM '88 IEEE Trans. Instrum. Meas. 38 (2), 249-251 (April 1989). Testing to Quantify the Effects of Handling of Gas Dielectric Standard Capacitors, C. R. Levy, Natl. Bur. Stand. (U.S.), Tech. Note 1161 (1982). New NBS Measurements of the Absolute Farad and Ohm, R. D. Cutkosky, IEEE Trans. Instrum. Meas., IM-23 (4), 305 (Dec. 1974). Applications of Coaxial Chokes to AC Bridge Circuits, D. N. Homan, J. Res. Natl. Bur. Stand. (U.S.), 72C (2) (June 1968). Improved Ten-Picofarad Fused Silica Dielectric Capacitor, R. D. Cutkosky and H. L. Lee, J. Res. Natl. Bur. Stand. (U.S.), 69C (3), 173 (Sept. 1965). Calibration of Inductance Standards in the Maxwell-Wein Bridge Circuit, T. L. Zapf, J. Res. Natl. Bur. Stand. (U.S.), 65C (3) (Sept. 1961). Capacitance Bridge NBS Type 2, R. D. Cutkosky, Natl. Bur. Stand. (U.S.), Report 7103 (Mar. 1961). back to top of page | back to index of electromagnetic measurements High-Frequency Standard Capacitors and InductorsTechnical Contact: Puanani L. DeLara Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
Fees are subject to change without notice. back to top of page | back to index of electromagnetic measurements High-Frequency Standard Capacitors and Inductors (52210S-52310S)Services provided in this category (and also Service ID Numbers 51310S and 52710C) are for passive devices over the frequency range from 10 kHz to 250 MHz. Highest accuracy is obtained only for standards equipped with precision coaxial connectors. Standards submitted for calibration should be in good repair and, except for very minor cleaning of connector surfaces, should require no pre-calibration maintenance. NIST does not provide repair services; items received that require maintenance will be returned to the sender and a handling fee charged.> Calibration services for some types of capacitance standards at frequencies as low as 1 kHz can be provided by the NIST Boulder Laboratory if the accuracy requirement does not exceed 0.01%. In some circumstances this can eliminate the necessity of sending a standard to both the Gaithersburg and Boulder Laboratories for a complete calibration. For additional details, please consult with the technical contact listed at the beginning of this section. Calibration services are not provided for measuring instruments such as bridges or meters. The uncertainty of these instruments should be verified by the owner through the use of stable standards especially selected for particular values and frequencies appropriate to the instrument in question. All calibrations are performed under typical ambient laboratory conditions of 23 °C, and an atmospheric pressure of approximately ((8.4 ± 0.2) x 104) Pa at Boulder, Colorado. Services at ambient conditions outside these limits are not provided. Also, the power applied to any device being calibrated does not exceed 1 W. Additional information about immittance (impedance and admittance) measurement and standards are contained in the references. back to top of page | back to index of electromagnetic measurements Two-Terminal, Low-Loss Standard Capacitors (52210S-52211S)In the frequency range from 10 kHz to 250 MHz, capacitance calibrations are available from 1 pF to 1000 pF depending upon frequency. The upper capacitance limit for calibration decreases as the frequency increases and is 50 pF above 30 MHz. From 100 kHz to 30 MHz, a special high-accuracy service is available for capacitors with nominal values of (50, 100, 200, 500, and 1000) pF if equipped with 14 mm coaxial connectors. The minimum relative expanded uncertainty* is 0.01% for the high accuracy device and 0.1% for the other calibrations. Reports of Calibration for capacitors normally do not give conductance values because the conductance values of capacitors of standard quality, especially those with air-dielectric, are too small to be measured accurately at the present state of the art. A technique for extrapolating the 1 kHz values of capacitance standards to high frequencies is described by R. N. Jones (see 1963 reference). That reference describes a technique for obtaining a high-frequency value of a capacitor equipped with an unshielded (banana plug) connector. The measurement technique yields effective capacitance values at high frequencies using the capacitance value at 1 kHz and the residual series inductance. The same technique, with some modifications, is usable for three-terminal and four-terminal pair capacitors. It is emphasized that these extrapolation procedures are only usable for air dielectric capacitors or capacitors with insulating materials whose dielectric constant does not change with frequency. back to top of page | back to index of electromagnetic measurements Three-Terminal, Low-Loss Standard Capacitors (52221C)Fixed-value reference standards are maintained by NIST for values of 10 pF, 100 pF, and 1000 pF. High-quality three-terminal air dielectric capacitance standards should have low residual series inductance (< 0.1 µH). This being the case, it may be assumed that, to within an expanded uncertainty of 0.10%, the capacitances of standards of 1 pF or less with air-dielectric is the same at 1 MHz as it is at 1 kHz. Thus, it is unnecessary to have capacitors smaller than 10 pF calibrated at 1 MHz. back to top of page | back to index of electromagnetic measurements Two-Terminal, High-Q Standard Inductors (52310S)In the frequency range from 10 kHz to 250 MHz, inductance calibrations to a minimum expanded uncertainty of 0.1% are available from 0.01 µH to 1 mH. The upper inductance limit for calibration decreases as the frequency increases and is 1 µH at 250 MHz. In the Report of Calibration, the resistance of the inductor is also given. Service is available only for air-core inductors or inductors whose value is independent of current. back to top of page | back to index of electromagnetic measurements References-High-Frequency Standard Capacitors and InductorsCalibration Service for Low-Loss, Three-Terminal Capacitance Standards at 100 kHz and 1 MHz, G. M. Free and R. N. Jones, Natl. Inst. Stand. Technol. (U.S.), Tech. Note 1348 (Feb. 1992). Evaluation of Three-Terminal and Four-Terminal Pair Capacitors at High Frequencies, R. N. Jones, Natl. Bur. Stand. (U.S.), Tech. Note 1024 (Sept. 1980). The Measurements of Lumped Parameter Impedance: A Metrology Guide, R. N. Jones, Natl. Bur. Stand. (U.S.), Monogr. 141 (June 1974). A Precision High-Frequency Calibration Facility for Coaxial Capacitance Standards, R. N. Jones and L. E. Huntley, Natl. Bur. Stand. (U.S.), Tech. Note 386 (Mar. 1970). Lumped Parameter Impedance Measurements, L. E. Huntley and R. N. Jones, Proc. IEEE 55(6), 900 (June 1967). A Technique for Extrapolating the 1 kc Values of Secondary Capacitance Standards to Higher Frequencies, R. N. Jones, Natl. Bur. Stand. (U.S.), Tech. Note 201 (Nov. 1963). back to top of page | back to index of electromagnetic measurements Power-Frequency CapacitorsTechnical Contacts: Denise D. Prather Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements Power-Frequency Capacitors (52400C)A calibration service is maintained for capacitors designed for 60-Hz operation, especially at voltages above 100 V. Typical expanded uncertainties for a calibration are 100 x 10-6 of the capacitance, and 1% of the dissipation factor plus 1 x 10-5. Routine calibrations are limited to devices with a dissipation factor of 0.011 or smaller and which are operated at sufficient voltages that at least 40 µA passes through the device under test. The high-power limit for routine tests is 10 kVA. Some capability to perform tests outside of these limits exists, and NIST should be contacted to discuss special arrangements for such tests. back to top of page | back to index of electromagnetic measurements References-Power-Frequency CapacitorsA Calibration Service for Voltage Transformers and High-Voltage Capacitors, W. E. Anderson, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-33 (June 1988). An International Comparison of High-Voltage Capacitor Calibrations, W. E. Anderson, R. S. Davis, O. Petersons, and W. J. M. Moore, IEEE Trans. Power Appar. Syst. 97 (4), 1217 (July 1978). A Wide Range High-Voltage Capacitance Bridge with One PPM Accuracy, O. Petersons and W. E. Anderson, IEEE Trans. Instrum. Meas. IM-24 (4), 336 (Dec. 1975). back to top of page | back to index of electromagnetic measurements Q-StandardsTechnical Contact: Puanani L. DeLara Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements Q-Standards (52710C-52711C)Standards for Q-measurements are maintained at NIST. These are high-Q inductors equipped with banana plug connectors at a spacing of 1 inch on centers. These standards have inductance values of (0.25, 2.5, 25, 250, 2500, and 25 000) mH, and effective Q-values from 100 to approximately 600. These serve as working standards for calibration of Q-standards of a similar type. Calibration frequencies range from 50 kHz to 45 MHz. The calibration report includes effective resonating capacitance and effective Q. Relative expanded uncertainties are of the order of 0.2% for capacitance and 2% for Q. Provisions are made for calibrating each Q-standard at three frequencies; however, adequate assurance of stability is usually provided by re-calibrating only at the center frequency. back to top of page | back to index of electromagnetic measurements References-Q-StandardsStandards for the Calibration of Q-Meters, 50 kHz to 45 MHz, R. N. Jones, J. Res. Natl. Bur. Stand.(U.S.), 68C (4), 243 (Oct.-Dec. 1964). back to top of page | back to index of electromagnetic measurements Program questions: Calibrations Phone: 301-975-2200, Fax: 301-869-3548 NIST, 100 Bureau Drive, Stop 2300, Gaithersburg, MD 20899-2300 |
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