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Design of RF Heat Therapy System Based on DS18B20 and FPGA [Sensors & Transducers (Canada)](Sensors & Transducers (Canada) Via Acquire Media NewsEdge) Abstract: In the process of research and development of this subject, it compares the three major heat physics technology. According to the organizational characteristics of glioma, it uses radiofrequency capacitive heating method. For conventional temperature sensor's interchangeability and unstable control method faults, it designed an implement RF heat treatment temperature field measure and temperature control system which use high precision digital temperature sensor DS18B20 and programmable logic device FPGA. This system contains temperature setting, temperature display, control algorithm, the FPGA chip configuration, signal power amplifier and the control of DS18B20 function. Finally, this system is used for pork to record the temperature field of heating experiments of center, edge and surface temperature. Copyright © 2014 IFSA Publishing, S. L. Keywords: Temperature sensor, DS18B20, FPGA, Radiofrequency capacitive heating, RF heat treatment. 1. Introduction Tumor thermotherapy uses heat method to treat tumor. Accurately, this kind of treatment is to use a variety of physical energy (such as microwave, radio frequency and ultrasonic, etc.), the sedimentary thermal effect produced in the body's tissues. The tissue temperature rise to effective treatment temperature region (above 41), and maintain a certain period of time to kill cancer cells and does not damage the normal tissue. It is the 5th kind of treatments after surgery, radiotherapy, chemotherapy and immunotherapy, especially for local tumor control, which is much better than other methods [1], The commonly temperature sensor (thermistors such as analog devices) has non-linearity and parameter inconsistency, due to the amplifier zero drift problems, the moment of replace devices need to debug the circuit. In control method of temperature field, most use the CPU or MCU as the core of control system, the control and operation rate base on software method obviously cannot be compared with the hardware method, and the reliability is not excellent [2]. According to these two problems, this paper proposed a new method of measurement and control, high precision digital temperature sensor DS18B20 and programmable logic device FPGA are used to implement the function. DS18B20 is made of the monolithic integrated circuit, it is single digital temperature sensor signal, its outstanding advantage is the temperature being measured directly into digital signal output. Temperature value is subjected to bridge circuit for voltage analog, then it is passed through signal amplification and modulus conversion into a digital signal, it avoids the problem of poor compatibility of traditional sensors. Especially in the occasion of multi-point temperature detection, in dealing with all kinds of error, reliability, and to realize system optimization, etc., DS18B20 has incomparable superiority compared with all kinds of traditional temperature sensors [3]. Using FPGA as controller, because it is pure hardware to realize the control purpose, which is adapted to high reliability requirements of the temperature field. It also can reduce the number of devices of the system greatly, it has advantages on flexible design, field programmable, program debug and small volume [4]. 2. Overall Design of the System This paper design for the treatment of glioma, according to the biological tissue characteristics of glioma, RF signal is chosen as the heating of physical energy, and uses two plate capacitive heating mode, system block diagram is shown in Fig. 1. Rf signal frequency is 0.5 MHz, it outputs control signals by 500 Hz adjustable duty cycle modulation. The FPGA as controller to control the heating process. It sets temperature as FPGA's input by the control panel, DS18B20 measure the temperature of temperature field, and then send real-time digital measurement signal back to FPGA device. The FPGA will compare the measure value with the set value, determine the duty cycle of modulated signal after dealing by the control algorithm. Control signal is added to the work plate by the isolating circuit and driver circuit. The dielectric between plate's heating power can be controlled by adjust 500 Hz modulation signal's duty ratio. 3. Hardware Design Hardware circuit mainly constitute of FPGA and the configuration circuit, power circuit, optical coupling isolation circuit, drive circuit, control panel and the display unit. Block diagram as shown in Fig. 2. The FPGA chip used in this design is Altera Corporation's ACEX1K Series EP1K30TC144-3. The special configuration of chip is Altera EPC2 which used to data configuration. External 20 MHz vibration semiconductor provides the clock signal for FPGA. ACEX IK's 2.5 V and 3.3 V voltage is from external 5 V power supply circuit. Control panel is made up of dip switches and buttons, dip switches is used to control the digital display, buttons is used to set temperature as FPGA's input. To avoid driving circuit interference to control circuit, a 1 MHz highspeed optical coupling isolation 6N137 is used. 4. Software Design DS18B20 temperature measurement program design flow chart is shown in Fig. 3. All software functions are implemented in the Quartus software platforms, the design method is mixed editing, Functional block diagram as shown in Fig. 4. Two external push buttons are used to input Specified temperature. The two keys are processed to eliminate the bounce inside the FPGA, so it can be used to count. Dip level switch 'Set' used to control temperature Settings, and 'Show set' is temperature display switch selector. System clock is provided by external 20 MHz semiconductor vibration, and it pass frequency division processing to obtain 500 kHz duty ratio for 50 % of the RF signal and 500 Hz adjustable duty ratio from 0-40 % of modulation signal, at the same time it provides synchronizing signal for DS18B20 [5]. The specified the temperature and the actual temperature which DS18B20 measured are processed into four decimal values, then display the temperature values in digital tube. According to the specified temperature and actual temperature, we get the corresponding duty ratio of the two ways with dead area complementary modulation signal by the control algorithm. Rf signal is modulated by signal modulation, then passes through optical coupling isolation circuit and driver circuit, finally added to the work capacity [6]. 5. Choice and Design of Control Algorithm 5.1. One-dimensional Fuzzy Controller of Single Input Single Output In the traditional control system, control algorithm is getting by the system mathematical model. In this paper, the controlled object is the patient's body temperature, because each patient's situation is different, such as tumor in the body parts, tumor size and the height of the patients themselves fat are factors that affect heating temperatures, obviously the determination of such uncertain object to establish a mathematical model is difficult. So this heat treatment system adopts the fuzzy control as the control algorithm of the system. In theory, the higher dimension the fuzzy controller of fuzzy control system has chosen, the higher control precision of the system get. But the higher the dimension chosen, the fuzzy control rule is too complicated, so the control algorithm based on fuzzy synthesis reasoning get by computer implementation is more difficult. After weighing accuracy and complexity of the two factors, in the RF heat treatment temperature control system of this topic, two kinds of control scheme is designed. First, the temperature deviation is input, 500 Hz modulation (PWM) signal the duty of the score for the output of one dimension fuzzy controller structure. Second, uses the temperature deviation and deviation change rate as input, uses 500 Hz modulation (PWM) signal the duty of the score for the output of the twodimensional fuzzy controller structure [7]. Set temperature deviation error=set temperature To-measuring temperature Tt, assume quantity deviation error and output control (the empty score wire theory domain) E and R, respectively. Because the set temperature (treatment temperature) in the range of 40-45, while the measuring temperature in the range of 25-45, suppose overshoot temperature range in -5 - +5, then the error of the basic theory of domain is [-5, +20], the basic theory of the domain of R is [0, 40 %]. E can be divided into seven fuzzy subset, fuzzy subsets and the temperature difference of the value is shown in Table 1 [7]. R can be divided into six gears and form 6 fuzzy subset, fuzzy subsets and the corresponding relationship between the outputs as shown in Table 2. Among them, N, 0, P0, PI, P2, P3 and P4 represent negative, zero, positive zero, small, middle, large and very large [8]. Use 'If E then R' fuzzy control rules, so we can get the corresponding control rules table, as shown in Table 3. 5.2. Double Input and Single Output Fuzzy Controller The structure diagram of the controller is shown in Fig. 5. Input signals are respectively temperature deviation and deviation rate of change, the output signal is 500 Hz duty score of PWM wave [9]. Same as above, the temperature deviation error = set temperature To-measuring temperature Tt, and temperature deviation rate = (measuring temperature at the moment-measuring temperature at last moment)/time interval, set the time interval of 1 s, Because of the time interval is a fixed value, so use measuring temperature the moment-measuring temperature at last moment. To measure the magnitude of the temperature change, so the rate of change in the temperature deviation=measuring temperature (Tt) at the moment-measuring temperature at last moment (Tt) [10]. Deviation of the error of the basic theory of domain is [-5, +20]. Define the error of domain in fuzzy sets theory is E, and divide it into 10 fuzzy subsets, the relationship of fuzzy subsets and the temperature difference value is shown in Table 1. Among them, N, 0, P0, PI, P2, P3, P4, P5, P6 and P7 represent negative, zero, positive zero, positive 1, positive 2, positive 3, positive 4, positive 5, positive 6 and positive 7 [11]. Rate of the basic theory domain is [0.25, +0.25], define the rate domain for fuzzy theory is RT, and it can be divided into nine fuzzy subsets. The relationship between fuzzy subsets and the corresponding temperature difference change rate values as shown in Table 4. Among them, NL, N, P, NS, PS and PL represent negative large, negative, negative small, zero, positive small, positive, positive large. Output control quantity duty ratio (basic theory domain [0, 40 %]) fuzzy set theory domain R can be divided into nine fuzzy subset, the relationship between the fuzzy subsets and the corresponding temperature difference change rate values is shown in Table 5. Among them, 0, P0, PI, P2, P3, P4, P5, P6 and P7 on zero, positive zero, positive 1, positive 2, positive 3, positive 4, positive 5, positive 6 and positive 7 [12]. Using the If E and RT then R fuzzy control rules. So can get the corresponding control rules table, as shown in Table 6. 6. Temperature Measurement and Control Experiment 6.1. Experimental Results Experiment 1: Heat object and specify temperature 40, record the center and the surface of the heating temperature, the results data are shown in Fig. 6. In Fig. 6, in the 7th minute when the temperature of center of A already reaches the specified temperature 40, but the temperature continues to rise to 40.7, temperature gradually decline later, in the 12th minute, temperature keep stability, it changes between 39.9 and 40.0. And the surface temperature is not changing with heating, the temperature is still 25. Experiment 2: Heat object to specified temperature 41, record the center and the surface of the heating temperature, the results data is shown in Fig. 6. In Fig. 6, in the 6th minutes the specified temperature of center reached 41, but the temperature continues to rise and in the 7th minute it reaches to the highest temperature of 42.1, since then the temperature begins to decrease, in the 9th minute it reached to its minimum of 40.7, then the temperature rises, it kept in 41 stability in 12th minute. The surface temperature still not change, it kept in 25. Experiment 3: Heat the object, set temperature 41, 42, 43, 44, 45 respectively, records the center, edge, surface of the heating temperature, the results is shown in Fig. 7 and Fig. 8. In Fig. 7 and Fig. 8, at a specified temperature for 41 and 42 and 43, the center temperature had overshoot phenomenon, but the overshoot volume is small, all within 0.2. The Edge temperature along with the center temperature rising, the highest edge temperature is 27.1 (When the center temperature is 45.0). Surface temperature did not change at 25. Experiment 4: Specified temperature of 41, 42, 43, 44, 45 respectively for the object, record the center, edge, surface heating temperature, the results is shown in Fig. 9 and Fig. 10. In Fig. 9 and Fig. 10, the center temperature overshoot, the largest amount of overshoot is 0.5, and after the temperature overshoot, temperature drop again fast. The highest edge temperature is 32.7. Surface temperature did not change at 25. 6.2. Experiment Result Analysis Overshoot problem: From the experimental results of one-dimensional control algorithm (experiment 1 and experiment 2) it can be seen that the temperature overshoot amount is larger, beyond the 1. The experiment results from two dimensional control algorithms (experiment 3 and experiment 4) it can be seen that the temperature overshoot volume is small, within 0.5. From heating surface temperature and edge temperature of experiment 1, experiment 2 and experiment 3 we can see: in the heating process, the surface temperature does not changed, kept in 25. When the heating temperature is different, the edge of temperature is different, and edge temperature changes with center temperature. When the heating temperature is same, three different volume object's edge temperature is different, it reflects the temperature of the heat treatment temperature field distribution from the center to the surface of gradient distribution. The possible influence factors of the experimental process: three pieces of pork meat, such as water content differences. Plate with medium (pork) do not match the contact close degree, will cause electromagnetic field impedance difference. 7. Conclusions From data and temperature-time curve and compare the two kinds of controller, we can see that one-dimensional controller's control precision is not enough, so the temperature overshoot is higher (1), the two-dimensional controller temperature overshoot is lower (0.5 ). Therefore, the design of RF heat field of temperature measurement and control method meets the requirements of heat treatment. For achieve better temperature field control effect, the RF heat therapy system should also add four or six plate electrode method and further optimizer control algorithm. Acknowledgements It is a project supported by Natural Science Foundation of He Nan Province (122102210416) and Foundation of office of education, He Nan Province (12A470007). References [1]. Zhou Runjing, Jia Lanping, Liang Zhian, Design of Measure and Control of Heating Field in the Radiofrequency Heat-therapy System, in Proceedings of the 7th International Conference on Electronic Measurement and Instrument (ICEMI'05), 2005, pp. 255-260. [2] . Li Qingxiang, Combination of Microwave Heat Therapy and Interventional Chemotherapy in Treating Mi-term and Advanced Peripheral Pulomonary Cancer, in Proceedings of the 5th China International Congress on Thoracic and Car diovas culal Surgery, 2000, pp. 120-124. [3] . Wang Shao, Tang Ju-ming, Science Letters: Radio frequency heating: a potential method for postharvest pest control in nuts and dry products, Journal of Zhejiang University Science, Vol. 1, Issue 10,2004, pp. 10-15. [4] . Fen Ping Zhou, Hong Tao Ma, Bing Dong Sui, Temperature Detecting System of Beer Fermentation Based on DS18B20, Advanced Materials Research, Vol. 108- 111,pp. 898-902. [5] . Li Kangkang, Jia Yuming, Jin Changxin, Design of a Kind of Combined Temperature Sensor, in Proceedings of the 3rd International Symposium on Test Automation Instrumentation, 2010, pp. 169-174. [6] . Jinquan Hu, Qing Guo, Study on High-speed Hightemperature Adaptive Fuzzy PID Control System, in Proceedings of 9th International Conference on Electronic Measurement & Instruments (ICEMI'09), 2009,pp. 114-119. [7] . Shen Hongyao, Fu Jian, Embedded System of Temperature Testing Based on DS18B20, in Proceedings of International Technology and Innovation Conference, 2011, pp. 561-565. [8] . Huang Bang-Yan, The Reading Data Error Analysis of 1-wire Bus Digital Temperature Sensor DS18B20, in Proceedings of 4,h International Conference on Modelling, Identification and Control (ICMIC'12), 2012, pp. 211-215. [9] . Yuliang Zhang, Liyi Zhang, Design of Temperature Measurement System Based on Embedded ARM & Linux, in Proceedings of International Conference on Economic Management and Engineering Technology (EMET'12), 2012, pp. 355-358. [10] . Yi Feng, Ke Xiao, The Distribution Temperature Sampling Based on FPGA, in Proceedings of The 2nd Asia-Pacific Conference on Information Network and Digital Content Security (APCID'l 1), 2011, pp. 210-214. [11] . Guo Zong-Liang, Pei Xiao-Gen, One Kind of the Temperature Control Circuit Simulation Design Based on Programmable Component FPGA Temperature control circuit design of the new method of system simulation, in Proceedings of International Conference on Management Science and Intelligent Control (ICMSIC'l 1), 2011, pp. 354-358. [12] . Zhipeng Xu, Jun Wei, Jianwei Li, Design of a Temperature Control system Using Incremental PID algorithm for a Special Homemade Shortwave Infrared Spatial Remote Sensor Based on FPGA, in Proceedings of the Advanced Sensor Systems and Applications Conference, 2011, pp. 353-358 Liangyu Su School of Electrical and information Engineering, Xu Chang University, Xu Chang, 461000, China Tel: 13298231568, fax: 0374 2962013 E-mail: [email protected] Received: 13 June 2014 /Accepted: 29 August 2014 /Published: 30 September 2014 (c) 2014 IFSA Publishing, S.L. |