The Infrared Temperature Detection System Based On Short Distance Wireless Communication

In modern engineering, scientific research and military field, the newtechnology of infrared temperature measuring is getting more and more extensiveapplication. In practical application, considering the restriction of the on-the-spotcondition and safe factor, there often have suitable distances between the metricalend and observe end, it is very inconvenient to adopt long-line transmission, so itis very important to transmit the temperature signal wirelessly.1. Function of the systemThe goal of this system is the implementation of the whole radiation ofdistrict of low temperature (0～200℃).Using the infrared temperature detectorand modulation pretage amplifier to test the temperature signal, using microcontroller (MC68HC908GP32) to process them and change them into the yard ofvalue, then the short distance wireless data transmission module and PC can bejointed together to implement the communication of people and computer. Thecomputer can change the yard of value of temperature it collected into actualtemperature value and show it out through the visual software programming tocarry on real-time monitor. Code switches are adopted to set up the temperaturecollectors, address in the system, the address range is 0～255. It can observe 256different places at the same time.2. Elements of the systemRS232—485wireless data PC transmission moduleb) the part of the detectionFig.1 The block diagram of the structure for this systemThe system consists of the temperature collectors, short distance wireless datatransmission module and computer mainly. The block diagram of the structure forthis system is shown in fig.1.The unit of temperature collector is composed of infrared temperature sensors,the circuits for signal conditioning and environmental temperature survey, microcontroller (MC68HC908GP32) and wireless data transmission module. It's showin fig.2.MC68HC908GP32 address code settingenvironmentaltemperature surveywireless datainsefrnasroerd consdiigtnioanl i n g transmission modulesignalconditioninginfraredsensorsignalconditioninginfraredsensorbattery MC33997POWER SUPPLYFig.2 The block diagram of the structure for temperature collectorThis system adopts TPML1 infrared sensor. It can normal work at 0～100℃,with the examining warm range 0～200℃ and the typical output voltage is 0～6.639V. There are three infrared sensors in every temperature collector. The signalwill be send to the A/D port of the micro-controller after conditioning. MC33997is been adopts to supply power for each component. The P0 port ofMC68HC908GP32 is connect with the code setting to set the address of thetemperature collector. The micro-controller compares the address signal receivedby the wireless data transmission module with the collector's address, if they aresame it will run the processing program to deal with the data, otherwise it does nothave any response.TDX-1000 little power wireless data transmission module produced inShenzhen Taidaxin communication technology limited company is used in thissystem. It is suitable for many civil, trade and industrial fields, such as wirelesstranscription appliance, industrial remote control, remote test, the system ofautomatic data collect, construction automation, secure protection, the wirelessmonitoring of machine room, device and the plot messenger call. TDX-1000wireless data transmission module is designed by the monolithic radio frequencyreceiving and dispatching chip nRF401, and it works at 433MHz frequency band.3. The communication agreements and the plan of error controlWe need to add the lead code to discriminate the same position code and datawhen TX-1000 is used in the date transmission. After testing, we find it hardlyappears in the noise when 0xAA , 0x55 code follow 0xFF code. So we use the0xFF followed by 0xAA, 0x55 as frame head in the system. Receive agreementstipulates it just receives the package of 0xFF followed by 0xAA, 0x55. We use0x00 as frame tail, it has remarkable differences from the frame head, and it hardlyappears in the information bits. Moreover, in the process of receiving every frame,frame length becomes assistance basis. Because the data of the first bit easily losein the transmission, we add a started bit that contains any content in front of thedata of every frame in the transmission. Fig.3 is the frame format of the system.Fig.3 the frame format of the systemThe started bit contains any content, the frame head is 0xFFAA55 and theframe tail is 0x00. The last frame and next frame have the same format, but theyhave different coded data.As we all know some factors such as the noise of power supply, the change ofthe antenna load and the disturbance of electromagnetism will cause the mistake ofdata flows, especially the data mistake of RF information channel. So the errorcontrol must be carried out in order to improve the quality of communication.Reed-Solomon code can correct not only the burst error but also the random error,and moreover it is more effective for the burst error, so it is applied widely. NowRS code is widely used by NASA and ESA in many fields.RS code is a kind of cyclic code so it has the same coding way. Thepolynomial of information code is:Let's multiply it by , then divide it by making polynomial , the residueis the bound polynomial, put it after , we'll get the RS code. So thecoding of the RS code is a process of getting residue.x n? kg(x)r (x)x n?km(x)∏∑=== +=tiiitjg xxaj 2gx021( )() (2)C ( x)= xn ? km(x)+xn?km(x)modg(x) (3)The process of decoding of RS code as follows: (1) Getting the adjointpolynomial from the receiving polynomial;(2) Get error positionpolynomialS jR(x)σ (x)from the adjoint polynomial;(3) Get the value of the errorposition by gaining the root of σ (x);(4) Calculate the value of the errors andcorrect them according to the error position that has been get.4. Experimentboiling water as it was cooling in atmosphere, both using the system and a precisethermometer. The front figures show the conclusion of the test.From the data we know the biggest error is 1.72℃ without using thealgorithm system of error control, on the contrary, the biggest error is 0.67℃ andthe resolution range is 1℃. The system can satisfy the demand completely, such asthe monitor of the electric cable in transformer substation.5. ConclusionIn this system, infrared temperature measuring, data processed by themicro-controller and wireless data transmission are integrated reasonably, havingrealized the non-keeping in touch with measurement and long-range monitoring oftemperature. After adopting the RS error correcting code algorithm in wirelessdata transmission, the accuracy of data transmission has been improved. It hasbeen proved to be steady and reliable.