Bryan C. Waltrip

Precision Differential Sampling Measurements of Low-Frequency Synthesized Sine Waves With an AC Programmable Josephson Voltage Standard

We have developed a precision technique to measure sine-wave sources with the use of a quantum-accurate AC programmable Josephson voltage standard. This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high-purity and low-frequency (a few hundred hertz or less) sine-wave voltages. We have performed a variety of measurements to evaluate this differential technique. After averaging, the uncertainty obtained in the determination of the amplitude of a 1.2 V sine wave at 50 Hz is 0.3 muV/V (type A). Finally, we propose a dual-waveform approach for measuring two precision sine waves with the use of a single Josephson system. Currently, the National Institute of Standards and Technology (NIST) is developing a new calibration system for electrical power measurements based on this technique.

Error and Transient Analysis of Stepwise-Approximated Sine Waves Generated by Programmable Josephson Voltage Standards

We are developing a quantum-based 60 Hz power standard that exploits the precision sinusoidal reference voltages synthesized by a programmable Josephson voltage standard (PJVS). PJVS systems use series arrays of Josephson junctions as a multibit digital-to-analog converter to produce accurate quantum-based dc voltages. Using stepwise-approximation synthesis, the system can also generate arbitrary ac waveforms [i.e., an ac programmable Josephson voltage standard (ACPJVS)] and, in this application, produces sine waves with calculable root mean square (rms) voltage and spectral content. The primary drawback to this ACPJVS synthesis technique is the uncertainty that results from switching between the discrete voltages due to finite rise times and transient signals. In this paper, we present measurements and simulations that elucidate some of the error sources that are intrinsic to the ACPJVS when used for rms measurements. In particular, we consider sine waves synthesized at frequencies up to the audio range, where the effect of these errors is more easily measured because the fixed transition time becomes a greater fraction of the time in each quantized voltage state. Our goal for the power standard is to reduce all error sources and uncertainty contributions from the PJVS-synthesized waveforms at 60 Hz to a few parts in 107 so that the overall uncertainty in an ac power standard will be a few parts in 106.

Development of a 60 Hz Power Standard Using SNS Programmable Josephson Voltage Standards

We are implementing a new standard for 60 Hz power measurements based on precision sinusoidal reference voltages from two independent programmable Josephson voltage standards (PJVS): one for voltage and one for current. The National Institute of Standards and Technology PJVS systems use series arrays of Josephson junctions to produce accurate quantum-based DC voltages. Using stepwise-approximation synthesis, the PJVS systems produce sinewaves with precisely calculable RMS voltage and spectral content. We present measurements and calculations that elucidate the sources of error in the RMS voltage that are intrinsic to the digital-synthesis technique and that are due to the finite rise times and transients that occur when switching between the discrete voltages. Our goal is to reduce all error sources and uncertainty contributions from the PJVS synthesized waveforms to a few parts in 10 7 so that the overall uncertainty in the AC-power standard is a few parts in 106

A wideband sampling voltmeter

A high accuracy sampling voltmeter, designed to span the frequency range of 10 Hz to 200 MHz, is described. The instrument operates autonomously, at a measurement update rate of at least one per second. A novel quasi-equivalent time sampling process is used, with a custom strobed comparator as the sampling device and decision element. The architecture and control are presented, along with the time-base design principles. Major error sources associated with the time-base are also discussed.

Automatic inductive voltage divider bridge for operation from 10 Hz to 100 kHz

A bridge to calibrate programmable and manual inductive voltage dividers is described. The bridge is based on a programmable 30-b binary inductive voltage divider with terminal linearity of +or-0.1 ppm in phase and +or-2 ppm quadrature at 400 Hz. Measurements of programmable test dividers can be automated using software developed to align the bridge components and perform an automatic balance. >

Digitally synthesized power calibration source

A digitally synthesized source of “phantom” power for calibrating electrical power and energy meters is described. Independent sources of voltage, current, and phase angle are programmable between 0 and 240 V, 0 and 5 A, and 0 and 360 deg, respectively. The accuracy of the active and reactive power is estimated to be within ±100 ppm of the full-scale apparent power (volt-amperes).

Intercomparison of calibration systems for AC shunts up to audio frequencies

An intercomparison of calibration systems for ac shunt up to audio frequencies between the National Research Council of Canada, Japan Electric Meters Inspection Corporation, and the National Institute of Standards and Technology, U.S.A., is presented. The transfer standard used for the intercomparison is a 10 A, 0.1 shunt

The sensitivity of a method to predict a capacitor's frequency characteristic

Several groups have worked on the characterization of four terminal-pair (4TP) capacitance standards at high frequencies. This paper describes a variation of the technique to predict a capacitors frequency characteristic. The method is sensitive to regression parameter selection and the paper gives a detailed analysis of the techniques used to calculate reasonable values for these parameters. The results of the analysis of the capacitor frequency characteristic prediction methods sensitivity to exponent parameter variation have shown that this sensitivity is a major uncertainty component in the uncertainty analysis of NISTs capacitance standard measurement system.

Audio-frequency current comparator power bridge: development and design considerations

The development, design, construction, and partial evaluation of a system for performing active and reactive power measurement from 50 to 20 kHz is described. The technique is an extension of a power bridge based on a current comparator capacitance bridge that was originally restricted to power frequencies. The design features and component characteristics for wideband operation are emphasized. A digitally synthesized, dual-channel signal source provides the required voltage and current signals. >

Precision differential sampling measurements of low frequency voltages synthesized with an AC Programmable Josephson Voltage Standard

Sampling is a promising technique for comparing the stepwise-approximated sine waves synthesized by an AC Programmable Josephson Voltage Standard to the sinusoidal voltages of a secondary source at low frequencies (a few hundred hertz or less). This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high purity sine wave voltages by comparing them to quantum-accurate waveforms.