10.1007%2F978-3-642-23777-5_97.pdf

D. Jin and S. Lin (Eds.): CSISE 2011, AISC 104, pp. 601605, 2011. Springer-Verlag Berlin Heidelberg 2011 Temperature Monitoring System Based on AT89C51 Xingrui Liu1 and Guohong Gao2 1 Network Management Center Xinxiang University, Henan Xinxiang, China, 453003 49046838 2 School of Information Engineer Henan Institute of Science and Technology, Henan Xinxiang, China, 453003 ggh75 Abstract. This paper presents a low cost temperature detection and control design in composite films of the material production based on AT89C51. The system uses nickel-chromium-nickel-aluminum thermocouple as a temperature sensing element, the ICL7135 as the AD converter, displaying the detected temperature through the LED. This paper focuses on the components of the system hardware, the design method of microcontroller interface circuit and software implementation process. After testing, the system is accurate and reliable. Keywords: AT89C51, Temperature Measurement, ICL7135, Temperature Control, Materials. 1 Introduction Temperature is one of the main accused parameters in the industrial object, especially in metallurgy, chemical industry, building materials, machinery, food, petroleum and other industries, the furnace, heat treatment furnace and reactor are widely used, so stoves and heating fuel are different, such as gas, natural gas, oil and electricity. The process and the temperatures required are different, and thus the temperature sensors and the temperature methods are different. Product process is different, so the precision of temperature control is also different. Thus the precision of the data acquisition (A/D conversion) and control algorithms are also different. But as concerned the dynamic characteristics of the control system, that is basically the lagging part. For such a link, if delay time is shorter, PID control can be used; if a longer delay time, Dahlin algorithm can be used. If the delay time and time constant changes largely (the part of the approved amount of investment varies greatly), adaptive control algorithm can be used. In the plastic packaging (also known as flexible packaging) industry, it is necessary to put an additional layer of pure white or silver aluminum foil on the back of the exquisite designs of printed plastic , which needs to use tape laminating machine. Its main principle is that after heating it to melt raw materials printed on the back attached to form a protective film to avoid scratching patterns. Laminating machines now are generally universal temperature control devices, and have a large range of temperature control and low accuracy. As the response speed and control accuracy are less than technical requirements, general 602 X. Liu and G. Gao temperature control devices on the laminating process will result in the low firm of combined products and poor heat sealing. This design implements a special temperature control device as the temperature control part for laminating machine. To solve the flexible packaging industrys laminating processes propylene melting furnace temperature control is to increase reaction speed and control accuracy, thereby improving product quality and enterprise efficiency. 2 System Design The basic requirements of system design: (1) system should be able to set the desired temperature parameters (the range of parameters: 0-4000C), and be displayed through the LED display; (2) temperature control system should be able to accurately detect the actual temperature of the object and be displayed in the LED display; (3) the system should be able to detect the temperature of the actual parameters of the signal sent to the processor after treatment, the processor should be able to give timely and safe temperature difference between pre algorithm parameters, and give control signals and immediately adjust the temperature; (4) system should be able to store the parameter of the system settings in this value to no re-setting the next time. (5) after the system design is complete, the action should be stable, control action should be correct, control accuracy should be within +5%. To meet the basic requirements above mentioned, temperature control system uses the AT89C51 microcontroller as the main chip to achieve ICL7135 AD conversion, combined with the external MCU clock circuits mature, high-precision voltage regulator, bus drivers and other devices. As showed in Figure 1. Fig. 1. System structure diagram In Figure 1, the melting furnace is the controlled object, the control parameter is the melting furnace temperature (system output) y. Changing the gaining and losing state of single-phase of solid power loop (DC4-32V) can control the heat of hot plate and temperature. The temperature is detected by the thermocouple. The thermocouple output is under 100mv, after a signal conditioning circuit into a 0-2V signal, then the A/D converter transfers it into a digital signal send to microcontroller AT89C51. The Temperature Monitoring System Based on AT89C51 603 microcontroller uses the setted temperature and actual temperature of the furnace system to obtain e, and then uses PID algorithm output to get uk (digital), which is added to the control Line B by the D/A converter into analog amplification, thereby changing the melting furnace temperature. Temperature range: 0-400 0C (technical requirement is 0-400 0C), temperature control accuracy: 0.5%. EPROM is used for storing programs and forms. RAM is used for storing data temporarily. 8255A is used to extend the parallel port for connecting printers and other external devices. Keyboard or display panel is used for inputting and displaying device parameter and the setting amount. Serial port is used for communicating with other computers. As the temperature of melting furnace is 0-400 0C, so the design uses nickel- chromium-nickel-aluminum thermocouple as detection components, sub-degree number is EU, the output signal is 0-41.32mv. Electronic control transmitter uses the transmitter mA, the output is 0-10mA, and then goes through the current - voltage converter circuit to transform into 0-2V signal, then goes to A/D conversion through the A/D conversion circuit. A/D converter adopts double integral A/D converter ICL7135, with a resolution of 1/20000, that is 0.005 0C, fully meeting product process requirements. Heat uses single-phase AC220V, 2500W heating plate to supply heat for melting furnace. The control device uses Single-phase 4-32V DC controlled solid-state relays. System master schematic is showed in Figure 2. Fig. 2. The main control circuit principle diagram 604 X. Liu and G. Gao 3 Software Control Algorithm Design In the design, in order to improve the system precision, the gearshift integral PID control algorithm is adopted. In the hypothesis to keep the temperature for 400C, when the deviation is more than 5%, to abandon integral items totally; when deviation less than 1%, to keep all integral items; when deviation is between 1% to 5%, to increase integral items in diminishing; when the deviation is 1%, equivalent to 4c, corresponding to the binary number B1; when the deviation is 5%, equivalent to 20C, corresponding to the binary number B2. B2-B1=B3. The positional output of increment algorithm of PID controls gearshift integral differential equation is as follows: uk=KPek+NKIek+KD(Ek-2Ek-1+Ek-2) Uk=Uk-1+Uk N=1 |Ek|B2时;N=(B2-Ek)/(B2-B1) B11,1B2; N=0 |Ek|B1 Ek= X-Yk K1=KPT/T1, T is the sampling period (S), T1 is integral time (S), K is scale coefficients.KD = KPTD/T, TD is differential time (S). Ek is the deviation. X is the binary numbers system given. Yk is corresponding to the A/D converters output binary number. Ek-1 is the last system deviation, Ek-2 is the more last deviation. The Uk-1 is the last Uk value calculation result. 4 System Test Analysis After the temperature measurement and control system is completed, the whole system is conducted five tests. It can be shown through the test results, in the system allowed set temperature range (0-400 0C), that the system control precision can be in between -0.5% and +0.5%,which can completely satisfy the product technique requirements. As shown in table 1. Table 1. The test record results of five times Tim es Set temperature (0C) Initial temperature (0C) Display temperature (0C) Response speed (s) Control precision 1 218 214 217 30 -0.4% 2 297 278 296 110 -0.3% 3 342 312 343 65 0.2% 4 359 352 361 56 0.27% 5 384 364 385 125 0.26% Temperature Monitoring System Based on AT89C51 605 5 Conclusion This design, based on the single chip as the key control parts, adopts advanced temperature measuring element and scientific data acquisition and processing technology and advanced heating components and control method, which is helpful for improving temperature measurement and control precision and effectively improving the response speed of system. Whats more, it is beneficial to