The design of the human body infrared thermometer

Transcription

1 The design of the human body infrared thermometer Chenjie Zhang Changchun University of Science and Technology, Changchun , China Abstract In order to overcome the main shortcoming of the traditional thermometer measuring temperature, it is not convenient to measure the close distance between the measuring object and the measured object. Taking into account the high accuracy of the measurement of the premise, in order to pursue the principle of the lowest cost, the non-contact pyroelectric infrared temperature measuring instrument is developed, which can achieve the rapid and accurate measurement of the surface temperature of the human body. This paper mainly introduces pyroelectric principle of pyroelectric infrared sensor and is most suitable for the infrared detection of human body pyroelectric merit and equivalent circuit of piezoelectric sensor and expounds the working principle of the sensor of the infrared thermometer based on pyroelectric, discusses the method of design and implementation of the system, and briefly introduces the applicable conditions of temperature measurement system. Keywords Temperature measurement, Heat release, At89c51 1. Introduction Body temperature is the basic feature of human life activity, and it is also one of the important signs to observe whether the human body function is normal. At present, people use the most extensive thermometer gauge is according to properties of mercury with elevating temperature of the thermal expansion and contraction, by reading the scale value to judge the temperature value. Infrared thermometer provides a rapid and non contact measurement method for measuring human body temperature, so it can be widely used in the temperature measurement of dense population. And can display the measurement results in a digital way, so that the measurement process is intuitive, and time is short, often in a few seconds will be able to test results, and long life, is a more ideal temperature measuring instrument. Infrared temperature measurement technology has played an important role in the production process, in product quality control and monitoring, equipment on-line fault diagnosis and safety protection and energy conservation and so on. In the past 20 years, the non-contact infrared human body temperature measurement instrument has been developed rapidly, the performance has been improved, the function has been enhanced, the variety is increasing, and the scope of application is expanding. Compared with the contact type temperature measuring method, the infrared temperature measurement has the advantages of fast response time, non-contact, safe use and long service life. Non-contact type infrared thermometer comprises three series of portable and online or scanning, and various options and computer software, each series and a variety of models and specifications. 2. The principle and characteristics of the infrared thermometer for human body All natural temperature higher than absolute zero ( degrees) object, due to the thermal motion of molecules, in does not stop to surrounding space radiation, including electromagnetic wave 80

2 infrared band,, the radiation temperature dependence of energy density and the object itself with the radiation law. Principle of infrared radiation: 4 4 E ( T T0 ) (1) Formula: E for the radiation of the degree, is Stephen Pozman constant, is emissivity of an object, T is temperature for an object, T0 is ambient temperature for an object. By using this principle, the temperature measuring instrument is called the infrared temperature instrument. This measurement does not need to be in contact with the object to be measured, so it belongs to the non contact measurement. At different temperature range, the wavelength distribution of the electromagnetic wave energy emitted by the object is different, at room temperature (0 ~ 100 degrees), the energy is mainly concentrated in the middle infrared and far infrared wavelengths. 3. Hardware design of infrared thermometer for human body 3.1 System structure The human body infrared thermometer can be measured by pressing the switch, and the result of each measurement is displayed on the display. When the measurement button is pressed, the whole circuit starts to work, surface radiation energy by heat release electric sensor receives the heat radiation signal conversion into electrical signals, via the amplification circuit (caused by the external environment clutter signal after filter) to arrive at a / D digital to analog converter, 89C51 microcontroller as CPU receives the digital signal after a / D conversion, after data processing into the surface temperature of objects displayed on the LCD screen. Working principle is when the infrared detector receives the infrared emitted by the human body, after determining the detection system, in the signal processing unit of the measured signal is amplified, filtering, calculation, analog to digital conversion process is transmitted to a display unit to display the temperature readings. If the processed data is greater than the set of warning data, then the buzzer alarm. If the signal is processed by the signal processing system, the measured data is incorrect, it can be re detected by the controller (button), until the display of the correct temperature. The main function of the circuit is to convert the infrared radiation energy received by the pyroelectric sensor to the electrical signal that can be accepted by the A/D converter. The display (LCD) is driven by the 74LS02 decoder, and the temperature of the surface of the object is controlled by the software of the 89C51 single chip microcomputer. Through the software program can be achieved three effective figures show that 100 degrees of the following two integers and a decimal, 100 degrees above the display of three bit integers. 3.2 Selection of single chip This design uses the 89C51 series single chip microcomputer to carry on the data collection and storage and processing. Since the signal has only one input, in order to avoid unnecessary consumption, the design of the A/D converter using ADC0804. The CLKIN end and CLKR end of the chip can be matched with the clock pulse generated by the chip itself. For measuring the energy of surface radiation heat release electric sensor selection is electric sensor release Nicera sensor Co., Ltd., the PM611 type heat. It effectively regulate the external environment temperature fluctuation influence; selection of liquid crystal display (LCD) is 2 lines 16 characters LCD screen. Microcontroller peripheral circuit is composed of MCU, crystal oscillator circuit and reset circuit. Figure 1 shows the AT89C51 peripheral circuit diagram: 3.3 Temperature sensor The design of the probe is the use of infrared sensors, which can receive the body's infrared emission and make it into a voltage signal. Design and selection is PM611 unit thermal release electric sensor. The sensor although single sensitive element, because he used a receiving element and two parallel compensating element on structure, so it can effectively compensate the environmental temperature 81

3 fluctuation, vibration and interference effects. His working temperature is -20 degrees C C, particularly suitable for measuring the temperature of the human body. And PM611 index is relatively good, so choose it to do the probe temperature instrument. The PM611 pyroelectric infrared sensor is a kind of sensor which can detect the infrared light emitted by human or animal. The internal pressure of two bipolar transistor IR1 and IR2, when receiving an infrared rays emitted by the human body, internal gas heating expansion, under pressure, piezoelectric crystal deformed, charged particle relative displacement occurs, thus appeared on the surface of the crystal are positive and negative bound charge and potential of the property is called piezoelectricity produce piezoelectric pole at the two ends of the shaft. 3.4 Design of amplifier circuit C1 30pF 30pF C2 SW-PB C uF X1 Y1 12MHz X RESET 9 31 R1 29 Res XTAL1 XTAL2 RST EA/VPP PSEN ALE P3.0/RxD P3.1/TxD P3.2/INT0 P3.3/INT1 P3.4/T0 P3.5/T1 P3.6/WR P3.7/RD VSS AT89C51 Fig.1 AT89C51 peripheral circuit P0.0/AD0 P0.1/AD1 P0.2/AD2 P0.3/AD3 P0.4/AD4 P0.5/AD5 P0.6/AD6 P0.7/AD7 P1.0/T2 P1.1/T2EX P1.2 P1.3 P1.4 P1.5 P1.6 P1.7 P2.0/A8 P2.1/A9 P2.2/A10 P2.3/A11 P2.4/A12 P2.5/A13 P2.6/A14 P2.7/A15 Because the sensor detected by the human body infrared signal is weak, when the need to be converted to voltage through the amplifier amplification voltage signal. Because the signal detected by the detector may be doped with some factors of the external environment, so the amplifier circuit to add a low-pass filter circuit to filter out the excess signal. The main function of the circuit is to convert the infrared radiation energy received by the pyroelectric sensor to the electrical signal that can be accepted by the A/D converter. The display (LCD) is driven by the 74LS02 decoder, and the temperature of the surface of the object is controlled by the software of the 89C51 single chip microcomputer. Through the software program can be achieved three effective figures show that 100 degrees below the display of two integers and a decimal, 100 degrees above the display of three bit integers. As shown in Figure 2 for the amplifier circuit: 3.5 Analog to digital conversion circuit Because the sensor detects infrared light is amplified by analog signals, but it needs to be displayed on the LCD liquid crystal display, so the design of the use of analog digital converter to achieve this function. Because only to an input signal, so in order to save unnecessary cumbersome, the use of ADC0804 to convert the analog signal into a digital signal, and finally displayed. ADC0804 is a step by step analog to digital conversion chip made by CMOS integration technology. Resolution 8, the input voltage range is 0-5V, increase some of the external circuit, the input analog

4 voltage is + 5V. The chip has an output latch, and when the computer is connected, the output of the conversion circuit can be directly connected to the CPU data bus. This design adopts the CLK r port and the CLK in port complexes, chip itself generates clock pulses method, a / D converter VIN (+) port received by processing of the analog signal in the internal A / D conversion. Chip select port CS and WR write signal input port with low usually start conversion, because 0804 internal output latch, the converted digital signal existing latches in. When the CS, RD is low at ordinary times, can read the output digital signal conversion, by the A / D converter D0~D7 output, P1.7~P1.0 access AT89C51 SCM P1 port, the program firing to display on the LCD panel. A/D analog to digital conversion circuit connection diagram as shown in Figure 3 below: Fig. 2 amplifier circuit P3.7 P3.6 P CS RD WR INTR DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 A D ADC0804LCN CLK R CLK IN VIN+ VIN - VREF/ IN0 7 D pF Fig. 3 ADC0804 analog to digital conversion circuit 1K LS1 470K Buzzer P K Q1 2N3906 Fig. 4 alarm circuit diagram 83

5 3.6 Circuit in the warning system The measured signal after amplification, filtering, calculation, analog digital processing may be greater than the set of warning data, you can alarm circuit through the alarm, this design uses buzzer alarm. Buzzer, commonly known as a speaker, is widely used in a variety of electronic products, a component, it is used for prompt, alarm, music, and many other applications. As shown in Figure 4 for the alarm circuit: 4. Design of software The idea of software design is the first system initialization, and display subroutine, temperature reset each port, press the switch, switch on the power to determine when the power supply is turned on the A / D converter VIN (+) input read after amplifying and filtering calculation data analog to digital conversion, end of the chip select CS and WR write ends at the same time is set to a low level, when the chip itself produces a pulse and start the conversion. Then the CS converter RD, A/D at the same time for the low level 0 read the conversion output data, converted data into the analog digital converter own latch, the output port D0~D7 input to the microcontroller P0 port. Read the three data, the full three times after the correct reading of the microcontroller EEPROM memory. At the same time the counter plus 1, continue to read the next set of data. If the data is not correct after reading the full three times, it should be clear to the microcontroller, reset after the re measurement. The main program to achieve the following functions: (1)Boot or reset to automatically initialize the device, the correct implementation of the boot program. (2)Boot or reset after the start A/D conversion, the ambient temperature of the sample, and the display on the display of the current environment temperature. (3)To keep the temperature display at the same time, to cover the heat release electric detector field of view of the object surface infrared radiation conversion and sampling, and the sampling value, until the sampling value for heat release electric detector response peak voltage. 5. Conclusion Due to ordinary infrared thermometer is limited to measure the temperature of external objects, it is not convenient to measuring objects and obstacles of temperature, so you can add a section of optical fiber in the detection head, and at the front end installed a small angle of the lens, so the measured radiation of objects to the lens into the interior of the optical fiber. In the optical fiber which is reflected many times to the detector. Because the optical fiber can be freely bent, so that the radiation can be free to turn, which can solve the problem of measuring the internal temperature of the object, can be measured with obstacles blocking the corner and other places of temperature. Reference [1] Zhicun Liu, Key Technology to Measure Micro-Resistance, Physics Examination and Testing, 2005, pp [2] Yong Xia, Study of Instrument for Testing the Internal Impedance of Battery on Line, Telecom Power Technologies, 2003, pp [3] Changqing Gui, Impedance Parameters and State-of-Charge of Valve-Regulated Lead Acid Battery, Telecom Power Technologies, 2002 pp.1-4. [4] Zhang Y, Cai Z, Bi Y. Measurement and implementation of battery internal resistance based on AD630[C]//2011 2nd International Conference on Artificial Intelligence, Management Science and Electronic Commerce (AIMSEC). 2011: