Development Of A Temperature Logger Based On Wireless Sensor Network

In order to ensure the quality of the temperature sensitive products, such as cold medicine, dairy products and agricultural products, they must be kept in cold storage in environmental regulations from sales, storage, transportation, production to consumption. This requires a cryogenic system engineering—"cold chain". Especially, in the pharmaceutical industry, refrigerated drugs related to the health of people, and it needs higher refrigerating condition than general agricultural products. Therefore, to ensure the quality and safety of refrigerated drugs is the main purpose of pharmaceutical cold chain. To maintain low temperature is the core of pharmaceutical cold chain.The pharmaceutical cold chain industry is in the initial stage in China. The development can be summed up as follows:(1) The medicine market demand. And the pharmaceutical cold chain logistics has broad space for development.(2) There is no strong power industry-standard. Nearly79%of the cold medicines in transport have not been monitoring.(3) The information system is not perfect, and the lack of information connection and sharing in upstream and downstream. So, there often appears "broken-chain" phenomenon;(4) The infrastructure is poor and low level of automation. The manual is the main monitor method, so the accuracy is difficult to guarantee.(5) Lack ofprofessional talent. Therefore, the pharmaceutical cold chain is facing a severe test in Chain. And the monitoring and traceability system urgently need to establish. This paper developed a temperature logger based on wireless sensor network for the characteristics and lack of pharmaceutical cold chain in Chain. It based on a large amount of literature and research of the monitoring equipment. The main research contents are as follows:1wireless sensor networkWireless sensor network (Wireless Sensor Network, WSN) is a new high-tech industry, with the unique advantages of miniaturization, low power consumption, ad hoc networks and so on. It is widely used in military, environmental monitoring and forecasting, medical treatment, intelligent home furnishing, large warehouse management. WSN is mainly used in the logistics industry, including warehousing environmental monitoring, monitoring of sports goods, goods in transit goods monitoring and management. If the WSN application in the pharmaceutical cold chain, can meet the need of long time, stable and reliable without manual intervention monitoring features, the logger can effectively of pharmaceutical cold chain equipment for series of on-line and real-time control of temperature, realizes unattended, automatic monitoring real, solution because of cold chain equipment failure, human error, failure problem of refrigerant quality problems caused by blood, vaccines and other cold medicines, pharmaceutical cold chain equipment ensure the continued effective operation, so as to improve the reliability of pharmaceutical cold chain.The topological structure of wireless sensor network has a star network, tree and mesh networks. Star network is a single-hop network, the simplest structure, the easy realization, easy maintenance fault diagnosis, suitable for small range of indoor monitoring. Tree network is hierarchical network centralized control, bw cost, easy to expand the node. But the child nodes of the parent node dependence is strong, if the parent node fails, the node will not work properly. The mesh network is a multi-hop network, can communication between any two nodes, so the network transmission distance, large coverage, high self-healing ability, high network reliability, but the complexity of the network structure, poor maintainability. In summary, all kinds of network structure have its advantages and disadvantages. According to the actual application environment of pharmaceutical cold chain monitoring, monitoring scope is small, the requirements of real-time monitoring of long time without manual intervention. The logger with the star network topology, the monitoring terminal for the network coordinator, construction of low-power, short delay, easy maintenance and efficient network system.2The overall design of temperature loggerThe logger comprises a plurality of wireless temperature nodes and an intelligent monitor terminal. It can be used for monitoring, recording and warning the temperature in the whole cold chain. Nodes collection and pretreatment temperature data, and sent the data to the station monitoring terminal. The monitoring data is mass storage, processing and alarming. The regulatory departments and the user can query the historical data.3The hardware design of temperature loggerThe intelligent temperature logger comprises a plurality of wireless sensor nodes and an intelligent monitor terminal. The node includes a sensor unit, main control unit, communication unit and a battery of four parts, the terminal comprises a main control unit, a touch screen, an alarm unit, a storage unit, communication unit and power supply.1) The node uses ATmega169as the main control chip. The sensor unit is responsible for the collection and pretreatment temperature information in the monitoring regional. And send the processed data to the main control unit. The nodes are waiting for the receiving terminal RF trigger, and the processed data was sent to the intelligent monitoring terminal by the JTT4432RF module real-time. The power is two seven alkaline battery. The design of node should have miniaturization, low power consumption, low cost, extended and high reliability.2) High accuracy measurement circuit. For best linearity, the RTD sensor element requires a stable current reference for excitation. In this circuit, a voltage reference, along with two operational amplifiers, are used to generate a floating1mA current source. The voltage signal is filtered with a2nd order. It reduces noise and prevents aliasing of higher frequency signals. And then12-bit A/D converter gives a nominal temperature resolution of0.1℃.3) Monitoring terminal adopts a master-slave control mode. The master K_AE050was connected with the slave ATmega128through RSR232. HMI trigger the Atmega128communication with nodes through the wireless module JTT4432. ATmega128storages and analysis the data from the node. When the temperature exceeds the limit, the alarm message was sent to the user through the GSM module TC35. The power supply use220V power, output dual isolation voltage AC-DC power module LH10B24.4The software design of the loggerThe software mainly includes the main program, temperature data acquisition subprogram, RF program and display subroutine. Firstly the node was initialized, and then it was in sleep. The sensor unit collects and pretreatment the temperature information in the monitoring regional, and sends the processed data to the main control unit.The terminal sends command by the address of nodes at set intervals. And then it is waiting for the receiving the data, and according to the node address storage for one by one. Terminal with touch screen, can display the topology map, running state diagram, monitoring results and rich information in real time, and setting parameter. In the system, when the data exceeds a threshold, the touch screen can be used to protect data and an alarm message was sent to users at the same time by the real-time GSM. This ensures that the staff can arrive at the scene in the first time, and minimize losses.5The design of HMIFriendly interactive environment is one of the most important elements in instrument design. A touch screen is an industrial man-machine interlace (HMI, Human Machine Interlace), it can display the operating parameters and running state of vivid, intuitive, and easy to operate. The features of this logger include user login, node topology, parameter setting, data display, high temperature alarm and historical data query. It can be divided into two parts:man-machine interface screen design configuration software based on SKWorkshop4.0.0; MODBUS protocol to write and single-chip communication program based on.6The performance testThe performance was test in the experimental platform. It mainly includes the temperature measurement precision, the reliability of communication experiment.The results show that, the logger in this paper achieves the desired design goals. It can effectively solve the pharmaceutical cold chain monitoring process of high precision, low power consumption, recording, real-time alarm and historical traceability requirements. Through the application of the wireless temperature logger, realize the real time control of temperature of cold chain equipment, greatly improve the reliability of blood, vaccines and other cold medicines, on the basis of the record data validation of cold chain logistics performance, reduce the labor intensity of workers, avoid the equipment work or abnormal operation error caused the valuable drug damage due to temperature problem. The recorder all-weather monitoring, recording, warning, multi-directional cold chain abnormal information acquisition, to realize unattended cold chain online real-time monitoring function, improve the reliability of the monitoring efficiency and monitor the medicine storage, timely warning.In summary, the main achievements and innovation in this paper are as follow:1High precision temperature measurement circuit. The key is to design high precision constant current source and a2nd order low-pass filter, parameter optimization, matching design, improve the anti-interference ability.2Design of wireless communication node. RF system was based on the transmission line theory, so the device layout, PCB design, the antenna have high requirements. The design of high efficient RF channel is the key in this system.3The friendly HMI. The terminal with touch screen is friendly interface, and easy to use.Although the logger in this paper has been basically achieved the expected design goal, but also has the shortcomings in design, need to be further improved. The work in future might have:1Optimize network structure. This paper adopts the star network structure, which is relatively simple. It suitable for small range of monitoring site, but not for the field with large quantities. Using high precision, high reliability, mesh network, to improve the network structure.2Combined with the internet of things. With the development of science and technology, the internet of things was watched by more and more people. It can consider to add nodes positioning function, and integrate RFID technology. To further improve the recorder in the cold chain of mobile field work ability. And to improve the information management level of pharmaceutical cold chain.