Someone asked why not use the nose? The reason is that the nose humidity is high and the nasal mucosa affects the measurement. The temperature of the tympanic membrane can be measured through the ear, because the blood vessels of the tympanic membrane are connected with the hypothalamus, which is the center to control the body temperature, so the temperature of the tympanic membrane can be said to directly reflect the body temperature. Ear holes are too small to reflect most of the light, and they can be regarded as complete absorbers, so they are similar to a perfect blackbody, so we choose to measure the temperature of the human body by measuring the ear temperature.
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Principle of temperature measurement by ear thermometer The molecules and atoms of any object will make random thermal motion by themselves, and continuously radiate heat energy in the form of infrared rays, which is also called electromagnetic wave radiation. Different substances absorb different solar energy, and their molecules and atoms move differently. The more intense the exercise, the greater the radiation energy, and vice versa. All objects whose temperature is higher than absolute zero (-273.6438+05℃) are constantly emitting infrared energy into the surrounding space. Its radiation characteristics, radiation energy and radiation wavelength distribution are closely related to the surface temperature of the object. By measuring the infrared energy radiated by the object itself, the surface problems can be accurately measured, which is the principle of infrared radiation temperature measurement.
Generally, the wavelength of infrared energy emitted by human body to the surroundings is 9~ 13μm, which is in the near infrared band of 0.76 ~ 100 μ m. The light within this wavelength range will not be absorbed by air. Therefore, by measuring the infrared energy radiated by the human body itself, the temperature of the human body surface can be accurately measured. The design principle of ear thermometer is to use infrared rays emitted by hypothalamus in the ear, and then use Wien's displacement law (one of the basic laws of thermal radiation)
λ(m)T=b(b=0.002897
M k, commonly known as Wien constant), the infrared energy radiated by hypothalamus is converted into voltage signal by infrared detector. After the voltage signal is sent to the receiving system, after data processing, the curve is automatically fitted, and finally the measured human body temperature is accurately calculated and displayed digitally.
Wien's displacement law shows that when the absolute blackbody temperature rises, the maximum radiation power moves to the short wave direction. Wien's displacement law is not only consistent with the short-wave part of the experimental curve of blackbody radiation, but also with the whole energy spectrum of blackbody radiation. It is the greatest exploration that classical physics can make on blackbody radiation. What is bold? "Black body" is a perfect absorber in theory, which can absorb all wavelengths of radiation without reflecting any light. ?
The structural infrared detection probe of the ear thermometer is responsible for collecting the infrared radiation energy of the target within its line of sight and converting it into a voltage signal. After the voltage signal is sent to the receiving system, it is processed by single chip microcomputer, and the curve is automatically fitted, and finally the measured human body temperature is accurately calculated, and the output is displayed digitally. The chip control circuit can realize key control, LCD display, electric quantity detection, early warning, pressure generator sounding and other functions.
After the probe of the ear thermometer is disassembled, it can be seen that it is a thermopile temperature sensor, which collects infrared radiation energy and converts it into voltage signal. The function of the metal heat sink outside the thermopile temperature sensor is to dissipate the heat transferred from the outside to the sensor as much as possible, so as to reduce the thermal shock to the sensor shell. The external plastic casing not only protects the chip, but also thermally isolates the radiator from the ear cavity. The design of these two components must meet the FOV principle of the sensor, that is, these components are not allowed to appear in the field of view of the sensor, so as not to bring additional interference to the test.
The amplifier amplifies the electric signal generated by the thermopile temperature sensor, converts it into a digital signal through digital-to-analog conversion (A/D conversion) or a frequency signal through modulation and demodulation, and then converts it into a medical-grade high-precision temperature value through compensation correction, parameter calibration and algorithm model. The accuracy can reach 0.65438 0℃. Together with the display drive circuit, LCD screen, shell and battery, it can be a complete ear thermometer. Adding memory circuit and microprocessor can become an intelligent temperature detector.
At present, mercury thermometers have been eliminated in the world (reading error, mercury is toxic and difficult to recycle), and electronic thermometers are advocated, but electronic thermometers also need contact measurement (armpit, mouth, anus, etc.). ), it is difficult and inconvenient for children and critically ill patients to measure their body temperature. Ear temperature gun (forehead temperature gun) does not need to touch the measured object, so as to avoid dangerous or untouchable objects such as infection and scald, especially sanitary facilities and medical supplies, and will not be polluted or damaged. Measuring the surface temperature of an object quickly and accurately has the advantages of fast response, high precision, low cost, long service life and safe use, and plays an important role in product quality control and monitoring, equipment online fault diagnosis and safety protection. The above personal views are welcome to criticize and correct. You can follow me if you like, thank you! Those who agree with me, please like to go again, thank you again!