Precise Temperature Measurements with Invisible Light | NIST

Operation of the NIST Ambient Radiation Thermometer, which is approximately 60 cm (24 in.) long: (1) Infrared (IR) light from a fixed-temperature calibrated source (at right, not shown) enters the thermometer enclosure through this lens, which focuses the radiation onto a “field stop,” analogous to the f-stop aperture in photography. (2) A circular metal chopper slices the IR beam into a sequence of pulses. (3) The first lens inside the central cylinder converts the light from the field stop to a parallel beam. (4) The light passes through this insulated cylinder about 30 cm (12 in.) long, which is temperature-controlled by a feedback system. Stray radiation is blocked by another stop. (5) A second lens focuses the light onto a pyroelectric detector. (6) The detector output is routed to an amplifier that boosts the signal to readily readable levels. Credit: NIST

NIST News, May 6, 2019

Ordinarily, you won’t encounter a radiation thermometer until somebody puts one in your ear at the doctor’s office or you point one at your forehead when you’re feeling feverish. But more sophisticated and highly calibrated research-grade “non-contact” thermometers—which measure the infrared (heat) radiation given off by objects without touching them—are critically important to many endeavors besides health care.

However, even high-end conventional radiation thermometers have produced readings with worryingly large uncertainties. But now researchers at the National Institute of Standards and Technology (NIST) have invented a portable, remarkably stable standards-quality radiation thermometer about 60 centimeters (24 inches) long that is capable of measuring temperatures to a precision of within a few thousandths of a degree Celsius.

Source: Precise Temperature Measurements with Invisible Light | NIST