NIST has a long history of studying radiation thermometers. The new prototype instrument, which builds on that work, can measure temperatures between -50 C (-58 F) to 150 C (302 F). The corresponding infrared wavelengths are from 8 to 14 micrometers (millionths of a meter), which is a sort of thermodynamic sweet spot.
"All temperatures are equal, but some are more equal than others," said NIST physicist Howard Yoon, who created the thermometer design and directed the project, described in the journal Optics Express. "That 200-degree span covers nearly all naturally occurring temperatures on Earth. If you make a big impact in measuring objects in that range, it really matters."
In addition to clinical medicine, temperatures in that region are of urgent importance in applications where contact is not appropriate or feasible. For example, surgeons need to measure the temperature of organs prior to transplant.
Conventional radiation thermometers often contain little more than a lens for focusing the infrared radiation and a pyroelectric sensor, a device that converts heat energy into an electrical signal. Their measurements can be affected by temperature differences along the thermometer and by temperature outside the instrument.
The NIST design, called the Ambient-Radiation Thermometer (ART), is fitted with a suite of interior thermometers that constantly gauge temperatures at different points in the instrument. Those readings are sent to a feedback loop system which keeps the 30-cm (12-inch) cylinder containing the detector assembly at a constant temperature of 23 C (72 F).
It also features other design improvements, including a method for reducing errors from what is called the size-of-source effect, which results when radiation enters the instrument from areas outside its specified field of view.
The ART's major advantage is its unprecedented stability. After it has been calibrated against standards-grade contact thermometers, the instrument can remain stable to within a few thousandths of a degree for months under continuous operation. That makes the system very promising for applications that involve remote sensing over long periods.
MEDICA-tradefair.com; Source: National Institute of Standards and Technology
