Design And Implementation Of Intelligent Sensor In Cold Chain Traceability System

The cold chain system refers to the system engineering that requires strict control of temperature and humidity for certain special foods and medicines in all stages of transportation or storage.With the rapid development of China's cold-chain logistics industry,the inadequate monitoring of temperature and humidity has led to frequent incidents of deterioration of food and medicine,which seriously threatens people's health.Therefore,it is very urgent to develop a complete set of cold-chain equipment.Based on the field of cold chain traceability,a smart sensor is designed in this thesis,which can collect temperature and humidity data in real time and send the data to the host computer through a wireless network.The monitoring center can check the temperature and humidity values of the refrigerator during transportation or storage at any time and analyze and save the data.If the value exceeds the threshold,the host computer interface will send an alarm message.The sensor nodes in the same channel connect to the network through a polling algorithm and implement data transmission.Finally,the algorithm was transplanted into the hardware and tested under the actual transportation environment.The test results show that the sensor has the advantages of low power consumption,strong penetration,long-distance data transmission distance and low packet loss rate,and the performance index in cold chain traceability environment can be achieved.The main contributions of this thesis are emphasized below:(1)This work studies the network layer of wireless sensors and describes the functions of each layer of the network.On this basis,the wireless sensor network architecture designed in this thesis is established.(2)The performance indicators that the intelligent sensors need to achieve in the cold chain traceability environment are analyzed,and a detailed solution is proposed for the low power consumption problems in the requirements of performance index.Then the hardware schematic and PCB design were completed,and the electromagnetic compatibility issues involved in the design process were summarized.After the hardware design was completed,the embedded software code was written in a modular way.(3)Considering the jamming and blockng problems of data transmission in the process of transportation and warehousing,a polling control algorithm is proposed,and the concepts of average queue length and average waiting time are introduced.The algorithm is modeled by the method of Markov chain and probability generating function.The mathematical expressions of these two physical quantities were calculated by the method of solving the equations in a circular way,and the curves were drawn in MATLAB.The method of porting TinyOS based on STM32 is introduced.At the same time,the polling algorithm is implemented in TinyOS operating system.The actual values measured by experiments are compared with the theoretical values and the results show that the errors are within a reasonable range.(4)The experiment was designed to test the energy consumption,penetration ability,distance and integrity of data transmission of sensor nodes.The test program was written in Labview,and the joint debugging of hardware and software was performed by connecting the node and software.After the test was passed,we applied the sensor node to the cold chain traceability environment to verify the feasibility of the sensor node designed in this thesis.