Design and establishment of a new calibration system traceable to the national standards

−47− Synthesiology English edition Vol.1 No.1 (2008) In the 1990s, a U.S. company developed a new infrared clinical thermometer in which measurement was taken by inserting the sensor probe into the ear canal (hereinafter will be called “ear thermometer”), and was marketed in the United States and Europe. Figure 1 shows the external appearance of ear thermometers and the schematic diagram of the measurement principle. Ear thermometer consists of optical probe, infrared sensor, compensating internal temperature sensor, signal processing circuit, and display unit. The tip of the optical probe is inserted into the ear canal, the intensity (radiance ) of infrared radiation at around 10 μm wavelength emitted from eardrum and skin surface of inner ear canal is measured, and the temperature of measured part is determined from the relation of Planck’s law of thermal radiation . The calibration of temperature reading is conducted by using the ear thermometer to measure the radiation from ideal blackbody cavity for which accurate temperature is known.