Design and development of frontal temperature gun

2021-11-24 09:59:23 fandoukeji

The forehead temperature gun (infrared thermometer) is designed for measuring the forehead temperature of the human body. It is very simple and convenient to use. It can measure temperature accurately in 1 second without laser point, avoiding potential damage to eyes, no need to contact human skin, avoid cross infection, one key temperature measurement and check influenza. It is suitable for family users, hotels, libraries and large enterprises and institutions. It can also be used in hospitals, schools, customs, airports and other comprehensive places. It can also be provided for medical personnel to use in clinics.

1、 Purpose of forehead temperature gun

(1) Human body temperature measurement: accurate measurement of human body temperature, replacing the traditional mercury thermometer. Women who want to have children can use infrared thermometer (frontal temperature gun) to monitor basic body temperature at any time, record the body temperature during ovulation, choose the right time to conceive, and measure temperature to judge pregnancy, etc. Of course, the most important thing is to observe whether your body temperature is abnormal at any time, so as to avoid infection with influenza and prevent swine flu.

(2) Skin temperature measurement: measure the surface temperature of human skin. For example, it can be used for limb replantation surgery.

(3) Object temperature measurement: measure the surface temperature of an object, such as the temperature of the surface of a tea cup.

(4) Liquid temperature measurement: measure the temperature of the liquid, such as the temperature of the baby's bath water. Measure the water temperature when the baby takes a bath, and don't worry about being cold or hot anymore; It can also measure the water temperature of the milk bottle to facilitate the preparation of baby's milk powder.

(5) Room temperature can be measured.

Design and development of frontal temperature gun

2、 Working principle of frontal temperature gun

When any object is above absolute zero (- 273 ℃), it will send out infrared rays. The forehead temperature gun receives infrared rays through the sensor to obtain the induced temperature data. The principle of frontal temperature gun is to accurately convert the voltage signal output by pyroelectric sensor into temperature value for display. The key device is pyroelectric sensor, which is also known as human infrared sensor. Although the measurement principle is not complicated, there are still five technical difficulties in the finished frontal temperature gun.

(1) The output signal amplitude of the sensor is small, and the measured voltage is as low as 2 μ V。  (2) The output signal amplitude of the sensor will be affected by the ambient temperature, which needs to be compensated. (3) The traditional frontal temperature gun scheme is not open to the outside world, and there are few engineers with relevant experience. (4) A good frontal temperature gun requires a comprehensive knowledge of electronics, optics and heat. (5) Design and production require precise experimental test environment (constant temperature environment) and instruments and equipment (constant temperature bath).

2.1 principle of infrared temperature measurement

When the object is above absolute zero, because of the movement of charged particles in it, it radiates energy outward in the form of electromagnetic waves with different wavelengths. The wavelengths involve ultraviolet, visible and infrared light regions, but they are mainly 0.76 ~ 3 μ M near infrared, 3 ~ 6 μ M mid infrared, 6 ~ 15 μ M far infrared region. The infrared radiation energy of an object and its distribution by wavelength are closely related to its surface temperature. Therefore, by measuring the infrared energy radiated by the object itself, its surface temperature can be measured accurately, which is the objective basis for infrared radiation temperature measurement.

2.2 working process of infrared thermometer

The infrared thermometer consists of optical system, photodetector, signal amplifier, signal processing, display output and so on. The optical system collects the target infrared radiation energy in its field of view, and the size of the field of view is determined by the optical parts and position of the thermometer. The infrared ray radiated by the measured object first enters the optical system of the thermometer, and then the optical system gathers the incoming infrared ray to make the energy more concentrated; The gathered infrared is input into the photodetector. The key component of the detector is the infrared sensor, whose task is to convert the optical signal into electrical signal; The electrical signal output from the photodetector is transformed into the temperature value of the measured target after being corrected by the amplifier and signal processing circuit according to the internal algorithm of the instrument and the target emissivity.

3、 Usage of forehead temperature gun

Place the temperature measuring probe on the bridge of the nose. The middle part of the two eyes is the radiation source closest to the normal body temperature relative to the measured body surface temperature. Put the forehead temperature gun at a distance of 5-6cm to measure the temperature. The accuracy is ± 0.3. It is not recommended to be used for medical treatment, but it can be used for rapid and non-contact safety screening of influenza. The alarm can be diagnosed in time by the hospital for prevention and treatment.

The average normal body temperature is between 36 ℃ and 37 ℃. If it exceeds 37.1 ℃, it is fever, 37.3-38 ℃ is low fever, and 38.1-40 ℃ is high fever. Life is in danger at any time above 40 ℃.

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4、 What is the normal temperature of the forehead temperature gun?

The normal value of frontal temperature is 35.8 to 37.8 degrees Celsius. The forehead temperature gun can accurately measure the forehead surface temperature after measuring the infrared energy radiated by the forehead through the built-in sensor. Because of the advantages of simplicity, simplicity, rapidity and no cross infection, the forehead temperature gun is more suitable for places with large traffic such as airports, stations and shopping malls.

When measuring body temperature, in order to ensure the accuracy of the results, avoid hair and use alcohol to remove oil and dirt from the skin. Select the middle part of the forehead and operate at a distance of 3 to 5 cm. It is recommended to measure multiple times and select the highest one as the result. However, because the forehead is exposed skin, it is greatly affected by the external temperature. You can choose wrist, neck and other parts, and the results will be more realistic and accurate.

5、 Scheme design of frontal temperature gun

Body temperature is the most basic physiological parameter of human body, which is very important for daily nursing and disease detection. Many diseases can be predicted by the change of body temperature. Infrared temperature measurement provides a fast and non-contact measurement means for measuring human body temperature, and solves the problem of contact in traditional temperature measurement. It has the characteristics of fast response speed, high measurement accuracy, wide measurement range and simultaneous measurement of target temperature and ambient temperature. The non-contact infrared thermometer has a good effect on specific groups, such as children or the elderly. Therefore, the design of frontal temperature gun has important practical significance.

5.1 overall scheme of frontal temperature gun

As the control center of the whole system, SPCE061A simplified development board is responsible for controlling the startup temperature measurement, receiving the measured data, calculating the temperature value, controlling the playback and display process according to the obtained key value, and playing the temperature value through the audio output channel; The infrared temperature measurement module is responsible for temperature measurement and acquisition, and transmits the collected data to SPCE061A single chip microcomputer through the data port; The keyboard in the LED keyboard module controls the temperature display and playback, and the nixie tube displays the temperature value. SPCE061A determines whether to conduct temperature measurement according to the key value input by the LED keyboard module. If temperature measurement is required, start the infrared temperature measurement module through ioa13 for temperature measurement, read the clock of the infrared temperature measurement module through ioa14, judge the negative jump edge of the clock, and read the measurement data through ioa15. The block diagram of frontal temperature gun system is shown in Figure 1.

Design and development of frontal temperature gun

5.2 software design of frontal temperature gun system

The main program flow chart is shown in Figure 2. Initialize the infrared temperature measurement module and initialize the keyboard; Enter the main program loop, call the keyboard scanner to scan the keyboard, and judge which program branch to execute according to the key value. If the first key (K1) is pressed, call the measurement temperature program to determine whether the target temperature is correctly measured, otherwise continue the measurement until the correct data is measured; If yes, play and display the target temperature value. Then call the temperature measurement program to determine whether the ambient temperature is correctly measured, otherwise continue to measure until the correct data is measured; If yes, play and display the ambient temperature value. If the second key (K2) is pressed, call the measurement temperature program to determine whether the target temperature is correctly measured, otherwise continue the measurement until the correct data is measured; If yes, play and display the temperature value. If the third key (K3) is pressed, call the measurement temperature program to determine whether the ambient temperature is correctly measured, otherwise continue the measurement until the correct data is measured; If yes, play and display the temperature value; If no keyboard is pressed, return to rescan the keyboard.

图 2 额温枪主程序流程图

5.3 overall test of frontal temperature gun system

First, confirm that the short-circuit sleeve on S5 has been pulled out, check whether the connection of each part of the circuit is correct, and turn on the power supply of the battery box after confirmation. Aim the probe of the infrared temperature measurement module at the measurement target, and the measurement is controlled by K1 ~ K3 of the LED keyboard module, where K1 is the measured and broadcast target temperature and ambient temperature, K2 is the measured and broadcast target temperature, and K3 is the measured and broadcast ambient temperature. After testing, the measurement accuracy of the frontal temperature gun system can reach two digits after the decimal point, which meets the design requirements, and the voice broadcasting function can also work normally. In terms of measuring distance, there will be a certain deviation in manual alignment of the measuring target during measurement, so the accuracy of long-distance measurement will be reduced, but the degree of reduction is within the allowable range.

summary

The operation of this system is very simple. Although it is called "forehead temperature gun", in fact, it does not mean that the temperature can only be measured from the forehead, but also the surface temperature of any object with infrared emission. It is just to measure the temperature at the forehead, which is mainly to measure the body temperature of the human body. Taking SPCE061A simplified development board as the control center of the whole system, combined with infrared temperature measurement module, keyboard and LED display module, the system realizes non-contact infrared measurement and voice broadcasting of temperature. The measurement accuracy can reach two digits after the decimal point, which meets the design requirements and has certain practical value.