NDLI: A Cryostat for Automated mK-Level Thermometer Calibrations from −202 °C to 250 °C

Content Provider	Springer Nature Link
Author	Ballico, Mark Freund, Chris
Copyright Year	2011
Abstract	The National Measurement Institute of Australia (NMIA) has developed a vacuum cryostat capable of calibrating precision electronic thermometers with a transfer error less than 2 mK over the range from −202 °C to 250 °C. The calibration of precision temperature measurement probes such as platinum resistance thermometers is usually performed in circulated fluid baths to achieve mK-level calibration uncertainties, and requires the use of several baths to cover the commonly used range of −80 °C to 250°C. Below −80 °C, dry-well systems cooled by liquid nitrogen are available down to −196 °C, but achieve poor uniformity and stability. The increased use of cryogenic preservation in the biomedical area has seen an increase in demand for precision calibration of electronic thermometer systems, in particular, down to a few degrees below the boiling point of nitrogen (−196 °C). This has prompted NMIA to develop a new design of a dry-well calibrator, based around a 380 mm long, 50 mm diameter, oxygen-free copper block insulated by gold-plated radiation and guard shields. Temperatures down to −202 °C are achieved by controlling the flow of liquid nitrogen through a restricting orifice into an evacuated heat exchanger. Computer control of the nitrogen flow and of several immersion heaters achieve a temperature stability of a few mK at all temperatures over the operational range, requiring typically 60 min to equilibrate at each new setpoint. Radiative transfer limits operation to 250 °C where the uniformity is 0.5 mK · cm$^{−1}$ (and becoming negligible at lower temperatures). A significant design innovation is the thermometer entry region, which has a purge system to keep the wells free of condensed moisture or atmospheric gases without the need for a seal. As the block is only 50 mm from the face of the cryostat, thermometers as short as 250 mm can be calibrated. The system is now in regular use at NMIA providing fully automated calibrations of precison temperature measurement systems without the need to use multiple temperature enclosures.
Starting Page	2360
Ending Page	2369
Page Count	10
File Format	PDF
ISSN	0195928X
Journal	International Journal of Thermophysics
Volume Number	32
Issue Number	11-12
e-ISSN	15729567
Language	English
Publisher	Springer US
Publisher Date	2011-12-02
Publisher Place	Boston
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Comparison calibration Comparison enclosure Cryogenic calibration Cryostat Thermometer calibration Industrial Chemistry/Chemical Engineering Condensed Matter Physics Physical Chemistry Mechanics
Content Type	Text
Resource Type	Article
Subject	Condensed Matter Physics

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1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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