As the medical needs of development, in many cases, the average temperature has failed to meet the rapid and accurate temperature measurement requirements, such as stations and airports, and so the population density of the larger places the human body temperature measurement. Although the temperature of this foreign technology are relatively mature, but the domestic technology in this area is still in development stage. Therefore, in order to meet the medical needs of development, to effectively carry out special environment of temperature measurement, thereby effectively control and prevention of atypical pneumonia, such as the special category of the spread of the disease, an urgent need to design a temperature measuring speed, high accuracy rate of temperature measurement LAU. For general industrial use of the infrared thermometer accuracy is not high enough, according to the principle of infrared temperature measurement, through the choice of key components, aimed at the design and temperature compensation to improve the automatic adjustment of the infra-red thermometer Accuracy, a design used infrared temperature measurement circuit for the staff-intensive and large flow of occasions to conduct rapid body temperature measurement. Original location
One of the principle of infrared temperature measurement
All natural temperature is higher than absolute zero (-273.15 ℃) objects, as elements of the campaign, are kept to the surrounding space, including infrared radiation, electromagnetic waves, the radiation energy density of objects and their relations with the temperature Radiation law.
Group principle of radiation - radiation law:
Where: E for the radiation of a radio, W/m3; σ for Stephen - Boltzmann constant, 5.67 × 10-8W / (m2 K4); ε objects to the radiation rate; T is the temperature of the object, unit K ; T0 to objects around the ambient temperature, unit K.
Measured by the launch of the E, the temperature can be drawn.
Take this principle into the infrared temperature measuring instruments called temperature instrumentation. This measure does not require contact with the measured object, it is non-contact measurement. Infrared temperature meter wide temperature range from -50 ℃ until more than 3 000 ℃. In different temperature ranges, targets of the electromagnetic energy sent the distribution of different wavelengths, at room temperature (0 ~ 100 ℃) range, mainly concentrated in the energy in the infrared and far infrared wavelengths. For different temperature range and targets for measuring the different instruments, their specific design are also different.
Under-(1) the principle, the instrument measured the infrared radiation as follows:
Where: A for the optical constants, and the specific instrument design structure; ε1 object to the measured rate of radiation; ε2 infrared thermometer for the radiation rate; T1 to the temperature measured object (K); T2 for infrared thermometers The temperature (K); him from a built-in temperature detection devices measured.
Ε is a radiation rate for the launching of objects of the electromagnetic capacity factor scale from 0 to 1.0. Radiation is the ideal radiation rate of 1.0 objects of objects, called blackbody physical. This is a theoretical concept, a fact not object to the radiation rate reached 1.0. But you can create very close to the actual ε = 1.0 blackbody for the thermometer calibration. All the real objects, including all parts of the body surface, ε values are lower than a 1.0 value. As ε extremely difficult to measure the value and uncertainty, measured in meters E, according to type (2) calculated the T1 there will be errors. In practice, the instrument is ε = 1.0 on the blackbody calibration good factory, only measurement of the object ε = 1, the only indication of the actual temperature representative object, if the object does not mean that ε 1, the instrument readings does not object The actual temperature, should be amended.
In the main body radiation wavelength 9 ~ 10 μ m infrared, the human body through its own infrared radiation measurement of energy, will be able to accurately determine the surface temperature of the human body. As the wavelength of light is not absorbed by air, thus the use of the infrared radiation of human energy accurately measure the body temperature of the surface.
The infrared radiation of the human body and the surface temperature has a very close relationship, therefore, the human body through its own infrared radiation of energy measurement, will be able to accurately determine the surface temperature of the human body. Infrared temperature measurement technology is the biggest advantages of speed testing, 1 s test can be completed within. As he fired only to receive the body of the external infrared radiation, no other physical and chemical factors in the human body, so no harm to the human body.
2 structure diagram and circuit design
2.1 The design of the structure diagram
As shown in Figure 1 for the design of the overall structure diagram.
2.2 Temperature Sensor
The temperature measurement devices use infrared sensors, he can receive objects emit infrared and converted into a voltage signal. I choose the PM611 unit pyroelectric sensor, although this is the single-sensitive sensor yuan, because he used a receiver yuan and 2 yuan parallel series connection of the compensation structure, it also can effectively compensate the ambient temperature fluctuations, vibration equivalent to Nuisance effects. His temperature is -20 ~ +70 ℃, particularly suitable for measuring the body temperature. PM611 and the index relatively well, so he has chosen to do for the temperature probe.
As shown in Figure 3: The sensor D, S, E and the circuit respectively, in marked D, S, E can be connected.
2.3 measuring circuit
Measuring circuit shown in Figure 4.
2.4 integral circuit
在将模拟信号转变成数字信号中，选择了ICL7106积分式A/D转换器。 In the analog signal into a digital signal, select the ICL7106 integral A / D converter. 他主要有以下的优点： He mainly have the following advantages:
Integral A / D converter, the conversion of high accuracy and low cost; his precision and integral resistors, capacitors integral unrelated to the accuracy, it can reduce the quality of the components of the requirements in the anti-disturbance capacity; his simple external circuit.
However, ICL7106 there are also some shortcomings: the power base of the changes directly affect the accuracy of conversion, when the chip's internal voltage reference generally more affected by temperature, when high accuracy, should use an external reference voltage source; lower the pace of work, in general 1 to 20 / s.
Therefore, the main characteristics of integrated ICL7106, in particular to improve the accuracy and the use of the design of the external reference voltage source. In addition, because the temperature measurement used is one of the fastest / s, ICL7106 lower the pace of work on the shortcomings of the design did not affect us, he is very suitable for design of the merits of the needs, thus ICL7106 is A / D converter of choice .
2.5 LCD display circuit
Showing part by the number of LCD drive ICL7106 and standards-Purpose LCD screen and some other components EDS801 composition.
3 debugging
In the experiment by adjusting the A1 output 10 k Ω rheostat so that the size of A3 output signal change, when the A3 output is less than 2.0 V, the range can adapt to ICL7106 to 2.0 V of the work, so the two potential A3 Used-A3 output is used to adjust the size, to ensure that the high temperature does not exceed 2.0 V.
Commissioning, with a known temperature (20 ~ 70 ℃) objects placed in the probe before the regulation ICL7106 part in the R12, so that LCD display to the right temperature,a known temperature, continue to adjust this potential, so that Show accurate value equivalent to the known temperature and repeated several times to adjust. Be careful not to over PM611 sensors and ICL7106 A / D integration with the temperature limit.