Development of a New InGaAs Radiation Thermometer at NMIJ

Abstract

The first InGaAs radiation thermometer at NMIJ was developed more than ten years ago as a standard radiation thermometer operating from 150 to 1, 100 • C. Its size-of-source effect (SSE) was as large as 1% from 6 mm in diameter to 50 mm in diameter. The new thermometer has an SSE of 0.3%. The reason for the error in measuring the SSE of InGaAs thermometers was also found. The new thermometer at first suffered from nonlinearity and the distance effect (DE). These deficiencies arose from the misalignment of optics inside the thermometer and were solved by increasing the detector size from 1 mm in diameter to 2 mm in diameter. Unfortunately, the detector of 2 mm diameter had a smaller S/N ratio than that of the 1 mm one at the indium (In) point. The final design uses a detector of 1 mm diameter, but the radiation is focussed on a smaller area of the detector. The new thermometer is smaller and lighter than preceding designs and other standard InGaAs radiation thermometers. The temperature of the main part of the instrument, including the filter, the detector, and the preamplifier board, is controlled at 30 • C. In addition to the calibration with the six fixed points of copper (Cu), silver (Ag), aluminum (Al), zinc (Zn), tin (Sn), and indium (In), the linearity from the In point to the Cu point, the SSE, the DE, and the spectral responsivity were measured.

Calibration of Radiation Thermometers and Blackbodies in the Temperature Range from 160 °C to 420 °C

“…The uncertainty of the SSE measurement is estimated to be 0.005 % [20]. The SSE of the present thermometer at d = 50 mm is improved to be 0.17 %, which is compared with 0.20 % of the previous thermometer [6]. The improvement (0.03 %) in the SSE corresponds to the SSE correction in temperature of about 30 mK at 400 • C. An example of the SSE correction in temperature in the calibration of a DUT can be calculated from this SSE function and a radiance distribution over an opening of a DUT blackbody (see Sect.…”

“…The 1.6 µm radiation thermometer consists of an InGaAs semiconductor detector, a narrowband wavelength filter, and an objective lens [6]. A full-width at halfmaximum (FWHM) is 0.14 µm at the center wavelength of 1.61 µm ( λ/λ = 0.087) and out-of-band suppression is as good as 10 −4 .…”

“…This article describes the establishment of a new standard thermometer with a 1.6 µm InGaAs radiation detector calibrated against the In, Sn, and Zn fixed points in the temperature range from 160 • C to 420 • C. Previously, the NMIJ developed the 1.6 µm InGaAs radiation thermometer to be used in remote sensing [5,6]. The design of the present 1.6 µm InGaAs radiation thermometer (described in Sect.…”

“…The design of the present 1.6 µm InGaAs radiation thermometer (described in Sect. 2.3) is modified from the design in [5,6] to make it suitable as a part of the standard facility. The maintenance of the 1.6 µm radiation thermometer is much easier than that of the 4.7 µm facility, because liquid nitrogen cooling is not applied for the former.…”

Middle Temperature Scale for Infrared Radiation Thermometer Calibrated Against Multiple Fixed Points

“…In the range below 200 • C, the InGaAs thermometer has relatively low sensitivity [9,10]. The present article describes the establishment of a temperature scale with a 4.7 µm InSb infrared thermometer calibrated at the In (157 • C), Sn (232 • C), and Zn (420 • C) fixed points in the middle temperature range.…”