Gerald J. FitzPatrick
Denise D. Prather
Please contact the administration and logistics staff before shipping instruments or standards to the address listed below.
Wattmeter calibrations at other than power frequencies are considered Special Tests and must be arranged on an individual basis. The following limitations apply:
A. Instruments must have separate voltage and current input terminals.
B. The instrument must have a self-contained power indicator, or provide a direct current or voltage signal which is proportional to power, or provide an output frequency which is proportional to the power.
C. Measurements are generally limited to sinusoidal signals at frequencies between dc and 100 kHz. Input signal levels should not exceed 240 V and 5 A.
D. Instruments will be tested in the as-received condition, and test uncertainties will be based in part on the performance of the
Only standard electronic-type watt, watthour, var and varhour meters are accepted for test. Rotating types are no longer accepted except by special arrangement. If necessary, the meters should be cleaned or adjusted by the customer before they are shipped to NIST. NIST does not adjust meters and does not knowingly begin tests of faulty meters.
The test conditions must be specified by the customer. These include the current and voltage ranges to be tested, the frequency, the applied voltages, the applied currents, and the power factors. Values of these parameters which are available for routine testing are summarized in Table 9.12.
If necessary, measurements can sometimes be made at other values of these parameters. These would, however, be considered special tests. Separate, specific arrangements and a higher fee will be charged than for a routine calibration.
Prior to the calibration, the meters are energized for between 1 h and 4 h at rated voltage and current on one range. A calibration consists of at least two sets of measurements taken over a minimum period of 2 d.
For wattmeters, the values of the reported corrections (in watts) generally have relative expanded uncertainties of 0.05% of the full scale range in volt-amperes. For watthour meters, the reported values of the percentage registration generally have relative expanded uncertainties of 0.05% of the indicated value. Special, higher accuracy tests can be arranged for an additional fee. The relative expanded uncertainties for power or energy measurements in these special tests may be as low as 0.005% if the short-term standard deviation of the device under test is appropriately small. For the highest accuracy, voltages are limited to 120 V and currents to 5 A.
The Measurement Assurance Program for electric energy is designed to evaluate the performance of energy-measuring systems at the customer's laboratory. A NIST-owned, transport standard watthour meter of known stability is measured by NIST. It is then shipped to and measured by the customer, and shipped back to NIST. NIST analyzes the data and provides a report to the customer indicating the total uncertainty of the customer's measurement. This procedure enables the customer's standards to be measured relative to NIST standards without the downtime encountered when the customer's standards are shipped to and calibrated by NIST. In addition, and more important to those who calibrate standard watthour meters, the NIST MAP standard can be used by customers to evaluate their measurement process in a convenient and cost-effective way.
The uncertainty of a MAP includes the effects of the long-term and short-term instabilities of the NIST calibration system, the customer's calibration system, and the transport standard. Typically, the relative expanded uncertainty in a well-controlled comparison ranges between 0.03% and 0.05%. The Electricity Division maintains an active program of research and development in the area of electric power and energy measurements. This program often enables NIST to provide measurement support for watt and watthour meters beyond that listed in this section. Special tests will generally be conducted when the following conditions prevail:
A. The requested tests are fully developed and documented.
B. There is a significant technical or economic justification for traceability of the test on the item to national standards.
C. There has not been a routine or recurrent need for the test.
This calibration service is offered for customers interested in a fast turn-around time, and reduced service cost for a limited number of specific test points. The three test points measured for this service are at 120 V and 5 A with power factors of unity, 0.5 lag, and 0.5 lead. These are the only test points offered for this service. If the customer requests additional test points, the price and turn-around time will be those for the routine calibration service (see Service ID Number 56200C). The relative expanded uncertainty assigned to a watthour meter for this service is 0.02%. This service will only accept standard watthour meters that have a pulse output. The turn-around time will be two weeks. Due to the short turn-around time of this service, the customer will need to schedule this calibration with the appropriate contact, and a purchase order must be submitted either with the instrument, or be received before the instrument arrives at NIST.
The PMU test conditions are selected from the following:
Information to be provided with PMUs for test
References-Power and Energy Measurements, Low Frequency
Digitally Synthesized Power Calibration Source, N. M. Oldham, O. B. Laug, and B. C. Waltrip, IEEE Trans. Instrum. Meas. IM-36 (2), 341 (June 1987).
NBS Wideband Sampling Wattmeter, G. N. Stenbakken, O. B. Laug, A. G. Perry, B. A. Bell, and T. H. Kibalo, Natl. Bur. Stand. (U.S.), Tech. Note 1221 (May 1987).
A Wideband Sampling Wattmeter, G. N. Stenbakken, IEEE Trans. Power Appar. Syst. PAS-103 (10), 2919 (Oct. 1984).
A Calibration Service for Wattmeters and Watthour Meters, J. D. Ramboz and R. C. McAuliff, Natl. Bur. Stand. (U.S.), Tech. Note 1179 (July 1983).
A Measurement Assurance Program for Electric Energy , N. M. Oldham, Natl. Bur. Stand. (U.S.), Tech. Note 930 (Sept. 1976).
Transfer of the Kilowatthour, S. R. Houghton, IEEE Trans. Power Appar. Syst. PAS-94 (4), 1232 (July-Aug. 1975).
Sampling Techniques for Electric Power Measurement, R. S. Turgel, Natl. Bur. Stand. (U.S.), Tech. Note 870 (June 1975).
A Current Comparator System to Establish the Unit of Electrical Energy at 60 Hz, K. J. Lentner, IEEE Trans. Instrum. Meas. IM-23 (4), 334 (Dec. 1974).