In areas with high incidence of new crown pneumonia virus, epidemic prevention points have been set up at the gates of many communities, and one of the important tasks is temperature measurement. Most of the instruments used for temperature measurement are infrared non-contact thermometers to measure temperature. Many businesses claim that the infrared portable temperature meter can be measured in 1 second. Compared with the mercury thermometer needs to be placed under the armpit for a few minutes, the infrared portable temperature meter can be said to greatly improve the work efficiency, so how does the infrared portable temperature meter accurately measure the human body What about body temperature?

Infrared temperature measurement technology has played an important role in product quality control and monitoring, equipment online fault diagnosis and safety protection, and energy saving during the production process. In the past 20 years, non-contact infrared human body thermometers have developed rapidly in technology, with continuous improvement in performance, continuous enhancement of functions, continuous increase in varieties, and continuous expansion of the scope of application. Compared with contact temperature measurement methods, infrared temperature measurement has the advantages of fast response time, non-contact, safe use and long service life. Infrared portable temperature meter are widely used, ranging from various industries to our daily life. Maybe many people don’t know much about this infrared portable temperature meter. Let me tell you about this infrared portable temperature meter.

Infrared portable temperature meter, as the name suggests, use infrared portable temperature meterto measure temperature. Infrared rays were discovered by British scientist Herschel. He split the sunlight with a prism and placed thermometers on the ribbons of different colors. He found that the thermometer outside the red light heats up the fastest, so Herschel believed : In the solar spectrum, there must be invisible light outside the red light, which is called infrared light. So what is the relationship between temperature and infrared light?

Here we should understand a piece of knowledge: Infrared is an electromagnetic wave with a wavelength between microwave and visible light, which is invisible to our naked eyes. Any object above the absolute temperature (-273°C) will continuously emit infrared radiation energy into the surrounding space, which is called heat rays in physics. The size of the infrared radiation energy and its wavelength distribution are closely related to the surface temperature, so the surface temperature of the object can be accurately measured by measuring the infrared energy radiated by the object. This is the theoretical basis of infrared thermometers.

Although the appearance of the infrared portable temperature meter is different, its internal structure is generally similar. Infrared portable temperature meter are generally composed of optical systems, photodetectors, signal amplifiers, signal processors, and display parts. When a thermometer wants to measure the temperature of an object, it needs to first measure the infrared radiation of the target object, and then calculate the temperature of the measured object through a signal processor. The infrared energy radiated by the measured object is collected by the optical system, and the size of the field of view collected is related to the optical parts and positions. The collected energy will be gathered on the photodetector and converted into the corresponding electrical signal. The electrical signal is amplified by the signal amplifier and processed by the processor, converted into the temperature value of the measured object according to the algorithm inside the instrument, and finally displayed on the display.

In nature, when the temperature of an object is higher than absolute zero, due to the existence of thermal motion inside it, electromagnetic waves will be continuously radiated to the surroundings, including infrared rays with a band of 0.75μm-100μm. His biggest feature is that at a given temperature and wavelength, the radiant energy emitted by the object has a maximum value. This material is called a black body, and its reflection coefficient is set to 1, and the reflection coefficient of other materials is less than 1. It is a gray body, because the spectral radiant power P(λT) of the black body and the absolute temperature T satisfy Planck’s law. Explain that at absolute temperature T, the radiation power of a black body per unit area at wavelength λ is P(λT). According to this relationship, the corresponding relationship curve can be obtained, which can be obtained:

(1) As the portable temperature meter increases, the radiant energy of the object becomes stronger. This is the starting point of infrared radiation theory and the design basis for single-band infrared thermometers.

(2) As the temperature rises, the radiation peak shifts to the shortwave direction (to the left), and the Wien displacement theorem is satisfied. The wavelength at the peak is inversely proportional to the absolute temperature T. The dotted line is the peak connection. This formula tells us why high-temperature thermometers mostly work at short wave, and low-temperature thermometers mostly work at long wave.

(3) The rate of change of radiant energy with temperature, the shortwave is greater than the longwave, that is, the thermometer working at the shortwave has a relatively high signal-to-noise ratio (high sensitivity) and strong anti-interference. The thermometer should try to work at the peak This is particularly important at the wavelength, especially in the case of low temperature small targets.

The principle of infrared portable temperature meter

Infrared portable temperature meter is composed of optical system, photodetector, signal amplifier, signal processing, display output and other parts. The radiation of the measured object and the feedback source is modulated by the modulator and then input to the infrared detector. The difference between the two signals is amplified by the anti-amplifier and the temperature of the feedback source is controlled so that the spectral radiance of the feedback source is the same as that of the object. The display indicates the brightness temperature of the measured object.