Kenneth K. Clarke

Phase measurement, traceability, and verification theory and practice

Presently available technology allows the construction of phase calibration equipment with phase resolutions of at least one part in 2/sup 18/, that is, a phase resolution of 0.00137 degrees . The users and the manufacturers of such equipment are faced with the practical problem of verifying their phase accuracy-both relative and absolute-and their traceability to some more accurate source. The authors present measurement methods that allow both relative and absolute high-resolution phase determinations in the vicinity of 0 degrees , 60 degrees , 90 degrees , and 180 degrees angles. They also present practical methods of implementing all of these methods together with comparative experimental data for all of them. >

Circuit techniques for use in a digital phase-angle generator

A proven basic technique for the digital generation of two sine waves having a known and adjustable phase difference has been used to produce a commercial phase-angle standard. While the final performance for this instrument meets or exceeds those previously reported for a unit built by the National Bureau of Standards, a number of different circuit techniques have been used to achieve greater phase resolution, circuit simplifications, easier mechanisms for detecting possible circuit problems, and significant cost reductions.

Evaluation of 100 ampere, 100 kHz transconductance amplifiers

This paper presents experimental evaluation of the performance of more than 25 production units of a 100 A, DC to 100 kHz transconductance amplifier. In addition to the stability, uncertainty, distortion, and frequency response, experimental results seem to indicate that the output impedance may be closely modeled by a parallel combination of a resistor and a capacitor in series with a resistor. This model is then used to estimate, and to correct for, the effect of load inductance on high-frequency, high-current measurements.

Digital Wattmeters for Loss Measurements of Power Transformers

This paper gives particular attention to the theoretical and practical difficulties that arise in the measurement of power losses in very large transformers or inductors. The most serious of these problems is the measurement of very low power factor loads, values down to 0.01 or 1% may be encountered. Major difficulties in making these measurements include problems associated with non-ideal power sources, problems introduced by the necessity - in some cases - of making measurements on highly distorted waveforms, and problems associated with making measurements in a restricted amount of time. While a measurement involves a complete system, the emphasis in this paper is upon the power measurement circuitry itself. An attempt is made to point out the theoretical limitations of various approaches and to separate these from the practical limitations of certain types of circuits. The major emphasis is upon digital methods of measuring power. The final section of the paper provides a comparison between some of the available types of digital wattmeters. It is hoped that this paper will provide help in selecting and in understanding the use of instruments to be used in the measurement of transformer losses.

A 1000 A/20 kV/25 kHz-500 kHz Volt-Ampere-Wattmeter for loads with power factors from 0.001 to 1.00

Many industrial processes and scientific experiments utilize large amounts of ac power at frequencies from 3 kHz to 500 kHz. The phase angle and the impedances of these loads often vary over a wide range. This paper describes an instrument to provide an accurate measurement of currents (1 A to 1000 A), voltages (100 V to 20 kV), and powers (100 W to 20 MW) over the frequency range from 25 kHz to 500 kHz. It deals with loads having power factors down to nearly zero and with load impedances from 10 /spl Omega/ to 20 k/spl Omega/. The paper contains practical details of both the design and the calibration of the front-end voltage and current transducers. The characteristics of a nearly ideal broadband current transducer are presented. Overall instrument calibration, verification and traceability problems are considered in detail.

Phase verification of power test systems

One aspect of the problem of the measurement of the losses in low power factor devices such as power transformers or power reactors is the verification of the phase angle properties of both the complete system and its various component parts. The use of a digital phase standard as a solution to this and other phase measurement problems is proposed. When a phase standard is synchronized in both phase and frequency, then its precise digital phase shift properties, used in conjunction with passive phase bridges, allow the design of high-power, high-accuracy (better than 0.001), phase verification schemes. Methods using this approach are outlined that use commercially available, easily transportable equipment to provide rapid and accurate phase angle measurements for almost all possible combinations of current and voltage. >

External phase autozero loop to extend the voltage and/or current capabilities of a digital phase standard

After reviewing the phase autozero concept used in existing phase standards the authors demonstrate how to extend the technique so as to include an external voltage amplifier and/or an external current amplifier within an external phase autozero loop. A suitably configured phase verification bridge is used as the output phase measuring device in all external cases. The calibration of voltage and current sampling circuits is discussed, and the results for several practical systems are presented. In one case, the available voltage from the phase-controlled system is extended from 100 V RMS to 350 V RMS while the available output current is increased from 15 mA to 7.5 A. This system operates satisfactorily from 50 Hz to at least 5000 Hz. In another case, the system is used for phase measurements of a 50-ohm load at 50 kHz and 90 kHz with an output combination of 40 V and 800 mA (32 W). In all cases, the accuracy of the phase standard is maintained.<<ETX>>