Thomas E. Lipe

Thermoelectric transfer difference of thermal converters measured with a Josephson source

We have measured the thermoelectric transfer difference of two thermal voltage converters using a Josephson source and compared the results to similar measurements made with a conventional semiconductor source. Both sources use the fast reversed DC method. The Josephson source is an array of 16 384 superconductor-normal-superconductor Josephson junctions that is rapidly switched between voltage states of +0.5 V, 0 V, and -0.5 V. A marginally significant difference is detected between measurements with the two different sources.

Thermal voltage converter calibrations using a quantum ac standard

We report on the first-ever use of a quantum ac source to calibrate a thermal transfer standard as part of the NIST calibration service for such devices, with reductions in calibration uncertainty of as much as an order of magnitude over traditional ac–dc transfer methods. We briefly describe the basic quantum ac calibration system, its operation and measurement results. An analysis of the uncertainties for the measurements is presented and plans for further development are described.

AC-DC difference relationships for current shunt and thermal converter combinations

The relationship between the overall AC-DC difference of a thermal converter and current shunt combination and the characteristics of the separate thermal converter and current shunt is described. Predicted and measured results are given for shunts used with different thermal converters. The disagreement is generally small compared to the uncertainty of AC current measurements at the individual frequencies. >

A new fabrication process for planar thin-film multijunction thermal converters

Advanced thin film processing and packaging technologies are employed in the fabrication of new planar thin-film multijunction thermal converters. The processing, packaging, and design features build on experience gained from prior NIST demonstrations of thin-film converters with optimizations for improved sensitivity, bandwidth, manufacturability, and reliability.

Extension of the NIST AC-DC Difference Calibration Service for Current to 100 kHz

The NIST calibration service for ac-dc difference of thermal current converters relies on multijunction thermal converters as the primary standards, and various thermal converters and thermoelements (TEs) as the reference and working standards. Calibrations are performed by comparing the ac-dc difference of a customer’s thermal current converter to the ac-dc difference of a NIST standard current converter. Typical artifacts accepted for calibration include single-junction thermoelements, multijunction thermal converters, and transfer shunts for use with TEs. This paper describes the standards on which the calibration service is based and the results of the study to characterize the NIST standards over the extended frequency range from 50 kHz to 100 kHz at currents from 1 mA to 20 A. The general method for the frequency extension at high frequency involves the use of thermoelements in the 5 mA range, with small frequency dependence, as the starting point for build-up and build-down chains to cover the whole range from 1 mA to 20 A.

Development of thin-film multijunction thermal converters at NIST

This paper gives an overview of the development of thin-film multijunction thermal converters (FMJTCs) at the National Institute of Standards and Technology (NIST). A historical perspective of film thermal converters is presented, followed by descriptions of the motivation, fabrication processes, physical characteristics, and the electrical properties of the FMJTCs produced at NIST. Integrated micropotentiometers that incorporate FMJTCs and thermal converters, produced by an alternative fabrication technology using a CMOS foundry, are also described. The paper concludes with a report on the present status of the FMJTC project and future directions.

AC-DC difference characteristics of high-voltage thermal converters

This paper describes a study of high-voltage thermal converters (HVTCs) at voltages above 100 V at frequencies up to 100 kHz. Techniques for the construction of HVTCs are described, and the effects of aging and dielectric loss on the resistor, changes in the timing sequence of ac-dc difference tests, relay dead-times, warmup times, and voltage level dependence are given. >

Correction of Systematic Errors Due to the Voltage Leads in an AC Josephson Voltage Standard

NIST recently reported the first application of a quantum AC Josephson voltage standard (ACJVS) for calibration of thermal transfer standards in the 1 kHz to 10 kHz frequency range. This paper describes preliminary work on extending its frequency calibration range up to 100 kHz by correcting systematic errors due to voltage leads.

A reevaluation of the NIST low-frequency standards for AC-DC difference in the voltage range 0.6-100 V

A reevaluation of the NIST standards of ac-dc difference was undertaken in an effort to reduce the calibration uncertainty offered by NIST for thermal voltage converters (TVCs) at frequencies below 100 Hz. This paper describes the measurements taken in support of this effort, as well as the devices used for the reevaluation process and the analysis of the uncertainty of the measurements. This reevaluation of the NIST low-frequency standards will permit a significant reduction in uncertainty for ac-dc difference calibrations at 10 Hz in the voltage range from 0.6-100 V.

Thermal transfer measurements at microwatt power levels

This paper presents the design, fabrication and preliminary results for a thermal transfer standard operating at a power level of 20 /spl mu/W, or less, and at temperatures below 10 K. The new converter employs a superconducting-resistive-transition edge thermometer.