Nile M. Oldham

Electronic limitations in phase meters for heterodyne interferometry

Abstract Limitations imposed by the phase meters used in heterodyne interferometers are evaluated. These instruments measure the phase relationship between electrical signals generated by the heterodyning process, allowing the interferometers to resolve fractions of an optical fringe. Measurements indicate that the phase meters used in currently available heterodyne interferometers probably limit achievable accuracy to a greater extent than barriers imposed by the optics. We show that a new class of time interval counters offers a means of greatly improving accuracy in these instruments.

Overview of bioelectrical impedance analyzers

Six commercial bioelectrical impedance analyzers were evaluated to determine their accuracy as impedance meters, their sensitivity to contact impedance, and other operating parameters such as maximum current amplitude and test wave-form. Over a range of impedances that simulate human body impedance, analyzer errors varied from < 1% to nearly 20%. Larger errors were observed when the contact impedance was at the limits of the operating range of the analyzer. Body models, sources of error, and several simple tests that the user can perform 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).

Exploring the low frequency performance of thermal converters using circuit models and a digitally synthesized source

Low-frequency errors of thermal voltage converters are described and estimated using a circuit model that includes easily measured parameters. A digitally synthesized source is used to confirm the estimated ac-dc differences in the 0.01 Hz to 40 Hz range.

Low voltage standards in the 10 Hz to 1 MHz range

A step down procedure is described for establishing voltage standards in the 1 mV to 100 mV range at frequencies between 10 Hz and 1 MHz. The step down employs low voltage thermal voltage converters and micropotentiometers. Techniques are given for measuring input impedance and calculating loading errors.

New low-voltage standaards in the DC to 1-MHz frequency range

Several techniques for measuring the RMS value of 1-600-mV signals are described and compared to existing thermal transfer standards. Differences between the techniques at 100 mV are typically within +or-20 p.p.m. in the audio-frequency range and within +or-100 p.p.m. out to 1 MHz. A new low-voltage thermal transfer standard has made it possible to compare thermal converters, micropotentiometers, and a digitally synthesized source to a precision of 1 p.p.m. The results indicate that micropotentiometers, are inherently more accurate transfer devices in the DC to 1-MHz frequency range than low-voltage TVCs (thermal voltage converters). >

A high-accuracy 10 Hz-1 MHz automatic AC voltage calibration system

An automatic system for calibrating high-accuracy ac voltmeters and calibrators is described. The system is based on traditional coaxial, thermal voltage converters to provide ac voltage measurement uncertainties of 5–20 ppm in the audiofrequency range and 5–250 ppm over the full range from 10 Hz to 1 MHz at voltages between 0.5–600 V. Lower levels (0.01–0.5 V) are realized using wideband inductive dividers. Specialized hardware and measurement techniques make it possible to achieve these uncertainties in test periods of approximately 1 min. Random errors introduced by the measurement system are typically less than 2 ppm (one standard deviation).

An international comparison of 50/60 Hz power (1996-1999)

An international comparison of 50/60 Hz power is described. The traveling standard was an electronic power transducer which was tested at 120 V, 5 A, 53 Hz, at five power factors (1.0, 0.5 lead, 0.5 lag, 0.0 lead, and 0.0 lag). Fifteen national metrology institutes from six metrology regions participated in the comparison.

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.