Infrared body thermometer circuits design

Because medical needs, in many cases, normal thermometers have satisfied a fast and accurate temperature measurement requirements, such as the station and airport, population density and a great place for the measurement of body temperature. Although now abroad this temperature measurement technology is more mature, but internally the technology is still in development stage. Therefore, in order to adapt to the needs of medical development, effective special environment temperature measurement, thereby effectively control and prevention, such as SARS, special spread that there is an urgent need to design a temperature measurement speed and accuracy of the thermometer. For general industrial use of infrared thermometer accuracy is not high enough, according to this principle of infrared temperature measuring, through key device choice, aiming system design, and temperature compensation automatically adjusted to improve the accuracy of the infrared thermometer, designed an infrared temperature measurement circuit for the personnel-intensive and the flow is large fora rapid body temperature measurement. 1 infrared temperature measurement principle of nature all temperature is higher than absolute zero (-273.15 ℃) objects, as molecular thermal motion of all keep the surrounding space radiation including infrared band, electromagnetic waves, its radiation energy density and the temperature of the object itself between radiation law. Group-radiation-radiation law principles: type: E-radiation emitting ° W/m3; σ to Stephen-Boltzmann constant, 5.67 × 10-8W/(m2 · K4); ε is an object's radiance; t is the temperature of a body, K; T0 to objects surrounding environment temperature, K units. Measurement of the emission of E, can reach the temperature. Use of this principle of temperature measuring instruments called infrared temperature meter. This measurement does not need to contact the measured object, therefore belongs to the non-contact measurement. Infrared temperature meter measuring range is very wide, ranging from-50 ° c up to more than 3 000 ° c. In different temperature ranges, object of the wavelength of electromagnetic energy distribution, at room temperature (0 ~ 100 ° c) range, the energy is concentrated mainly in the mid infrared and far infrared wavelengths. For different temperature ranges and for different measuring object, its specific design. According to the type (1) principle, instrument measured by infrared radiation:-: A for optical constants, and the specific design of structural instruments; ε 1 to be logging object of radiation rate; ε 2 for infrared thermometers of the radiation rate; T1 to the measured object's temperature (K); T2 for infrared thermometers for temperature (K); he is represented by a built-in temperature detection components measured. Emissivity ε is the one used to express the capacity of the emitted wave coefficient, a scale from 0 to 1.0. The best radiation is the radiation rate 1.0 objects, physically called blackbody. This is a theoretical concept, in fact, there is no object of the radiation rate can reach 1.0. But can produce extremely close to the actual ε = 1.0 blackbody calibration for thermometer. All real objects, including all parts of the body surface, its value is a ε below 1.0 values. As ε value extremely difficult to measure but not sure, the meter measured E, press-(2) calculated T1 there will be errors. In practice, the instrument is in ε = 1.0 blackbody calibration on a good factory, measurement of ε = 1, its indication that the object represents the object's actual temperature, if the object does not equal 1 ε, meter readings do not represent the actual temperature, the object should be amended. Radiation wavelength in the human body primarily 9 ~ 10 μm infrared, through the body's own radiation measurement of infrared energy, will be able to accurately measure the surface temperature of the human body. Because the wavelength range of the light is not absorbed by the air, thus the use of human radiation infrared energy to precisely measure the surface temperature of the human body. The body of the infrared radiation and he's surface temperature has a very close relationship, therefore, through the body's own radiation measurement of infrared energy, will be able to accurately measure the surface temperature of the human body. Infrared temperature measurement technique by the biggest advantage is the test speed, 1 s within the test is complete. Since he only receive human foreign emission of infrared radiation, no other physical and chemical factors on the human body, the human body without any harm. 2 structure diagrams and circuit design 2.1 structure diagram design as shown in Figure 1 as a design system architecture diagram. 2.2 temperature sensor for temperature measurement device using the infrared sensor, he is able to receive objects emitting infrared and converted into a voltage signal. I use a unit of Pyroelectric sensor PM611, this sensor is single-sensitive element, because he uses a receiver element and two parallel compensation element threaded structure, it can also be effective compensation environment temperature fluctuations, the effect of vibration is disturbing. He's working temperature is-20 ~ + 70 ° c, especially suitable for measuring body temperature. And the index are PM611, so use his temperature meter probe. As shown in Figure 3: the sensor D, S, E, respectively, and the markup in the circuit diagram D, S, E connection. 2.3 measurement circuit for measuring circuit shown in Figure 4. 2.4 integral circuits in the analog signal into a digital signal, select the ICL7106 integral-type A/D converter. He mainly has the following advantages: the integral-type A/D Converter Convert high precision, low cost; his precision and integral resistance, capacitance of precision-independent integral, it can reduce the quality of the components; requested against the interference ability; his peripheral circuit is simple. However, there are also some disadvantages ICL7106: baseline power changes directly affect conversion accuracy, when chip voltage reference within the General temperature influence is relatively large, when accuracy is high, you should use an external reference voltage source; the working speed is low, generally 1 ~ 20/s. So the main features of the integrated ICL7106, especially in order to improve the precision, the design uses an external reference voltage source. In addition, because for fastest measurement speed is 1/s, ICL7106 work speed lower disadvantage on our design has no effect, but his advantage is well suited to the needs of design, A/D ICL7106 is converted. 2.5 LCD display shows part of the circuit by many liquidCrystal display drive ICL7106 and standard-LCD EDS801 and other components. 3 debugging in the experiment by regulating A1 output 10 k Ω rheostat for A3 size of the output signal is changed, when A3 output less than 2.0 V, you can adapt ICL7106 quantum 2.0 V work characteristics, therefore two A3 potentiometer to adjust the size of the A3 output, make sure that when the temperature does not exceed 2.0 V. Debugging, using a known temperature (20 to 70 ° c) before the object is placed in the probes, regulating ICL7106 section of R12, LCD display the correct temperature, and a known temperature, continue to adjust the potentiometer, the displayed value is equal to a known temperature value accurately and repeatedly adjusted several times. Note do not exceed PM611 sensor and ICL7106 D A/Integrator temperature limit.