0 Introduction In recent years, the cold chain logistics industry has developed rapidly in China. Cold chain logistics refers to the systematic project that the frozen and frozen products are always in the low temperature environment in the production, storage, transportation, sales, and all stages before consumption to ensure product quality and reduce the loss of articles. It is suitable for fruits and vegetables, eggs, and water. Products, frozen foods, dairy products, flowers, medicines and other fields. If the environmental indicators at a certain point do not meet the requirements, it is easy to cause quality accidents. The traditional method can not continuously record environmental parameters, and can not give an alarm signal in time to respond, which may cause economic losses. On the other hand, it also causes difficulties in the identification of accidents. In order to solve these problems, it is necessary to have a system that continuously records the environmental data of the items and sends them to the monitoring center for storage and analysis.
This paper designs a cold chain logistics environment monitoring system based on Radio Frequency Identification (RFID) and sensing technology. The system can monitor the environmental parameters of the articles in the storage and transportation phases in real time, and judge whether the standards are met by the monitoring center, so as to adjust in time to reduce losses.
The temperature and time in the cold chain stream are two risk factors that must be considered, and temperature is important, both of which run through the entire process of storage and distribution. If not handled properly, it may cause cumulative and irreversible quality degradation until it affects the safety of the product. This article replaces the traditional environmental monitoring method with RFID tags, which are equipped with antenna RFID chips, temperature sensors, humidity sensors and light sensors. After the tag is placed in the proper position, the sensor will collect the temperature, humidity and illumination information of the environment in real time, and write the information into the chip of the tag to transmit the information to the reader at regular intervals. The reader reports to the monitoring center through the wired/wireless network, and the monitoring center stores and analyzes the received data. If there is an abnormal situation, it will promptly report the alarm and take measures.
1 Environmental Monitoring System Design The system consists of a monitoring center, a cold storage monitoring subsystem and a refrigerated truck monitoring subsystem. Each subsystem is connected to the monitoring center through a network. The overall composition of the system is shown in Figure 1.
The refrigerator monitoring subsystem consists of RFID sensor tags and readers. Depending on the size of the freezer, you can place multiple tags or place the reader at the door of the freezer. Each tag and reader has a unique number. Before use, the card issuing department of the monitoring center writes the information about the refrigerator to the tag and associates the number of the reader with the number of the refrigerator. In addition to recording temperature and humidity information, the sensor tag collects changes in the light sensor and sends the information to the monitoring center through the reader. The monitoring center can analyze whether the temperature and humidity in the refrigerator meet the requirements. According to the data of the light sensor, the opening time and duration of the refrigerator door are calculated, and it is judged whether it is illegally opened.
The refrigerated truck monitoring subsystem consists of an RFID sensor tag and a car reader. The goods to be transported are packed, and the cargo information of the monitoring center is written into the RFID tag, and then the tag is attached to the goods to establish a correspondence between the car reader and the cargo information and the driver information. Before entering the dedicated refrigerated truck, the goods read the information on the label and record the initial temperature and humidity information. During transportation, the sensor tag records the environmental information in real time and transmits it to the on-board reader. The car reader has a GPS positioning function, and the reader reads the positioning information together with the environmental information in the compartment where the tag is collected. Report to the monitoring center via the GPRS network. The monitoring center stores and analyzes the received data, draws a curve of temperature and humidity, and records the opening of the door. If it is found that the environmental indicators do not meet the requirements of the goods, promptly contact the driver and take remedial measures.
The monitoring center is responsible for data storage, analysis processing and alarms. The specific main functions are as follows:
(1) Collection of temperature and humidity information of goods out of the warehouse: When the goods are loaded out of the warehouse, the initial information of the temperature and humidity of the goods is collected, and the correspondence between the batch of goods and the ID of the vehicle reader is established;
(2) Receiving and receiving environmental information: The management center receives the information sent by the on-board reader and parses the information into the database;
(3) Matching of environmental information: matching the received temperature and humidity information with the batch of goods;
(4) GPS information receiving and storage: the management center receives the GPS positioning information sent by the car reader, and parses the storage into the library;
(5) GPS information matching: matching the received GPS positioning information with the cargo batch (vehicle);
(6) Display of the temperature and humidity curve of the goods in transit: The user inquires about the temperature and humidity information of a certain batch of goods in the way, and displays them in the form of a line chart;
(7) Query of the location of the goods: the user can query the physical location of a batch of goods;
(8) Whether the goods arrive at the inquiry: the user can check whether a batch of goods has reached the destination;
(9) Cold storage environment information collection and processing: periodically collect the environmental information of the storage warehouse and match the stocks in the warehouse;
(10) Data backup and export: The data that is queried can be backed up and exported.
2 System core equipment The environmental monitoring system designed in this paper is different from the traditional monitoring system. The two core devices are RFID sensor tags and RFID readers. The performance of these two types of devices has become the key to the performance of the entire system. Recently, several frequency bands commonly used in RFID systems include low frequency, high frequency, ultra high frequency and microwave. The identification distance, transmission speed and environmental sensitivity of each frequency band are different. Considering the practical application, the system adopts tags and readers supporting the air frequency of 2.40~2.48 GHz in the air interface. The band has a long recognition distance and is less affected by metal. In addition, RFID tags are divided into active tags and passive tags according to whether they are powered internally. Passive tags rely on the energy of the reader to wake up the work, and the recognition distance is short. Therefore, the system uses active tags. The tag has a battery voltage detection function that can read the battery power: the tag antenna is circularly polarized, and the direction selectivity is weak, so as to cope with the random placement of the tag in the car: the tag temperature range is -20 to +50 °C, the measured humidity range is 0% to 100%. The reader is required to store a certain amount of temperature and humidity information, and has GPS positioning function and GPRS wireless data transmission function.
3 Conclusion The cold chain logistics environment detection system designed in this paper integrates advanced RFID technology, sensing technology, wireless network transmission and GPS positioning. The system can effectively solve the real-time monitoring of environmental information in the refrigerator. When the temperature and humidity exceed the tolerance of the item, an alarm will be given to prompt timely control. The system solves the problem of real-time monitoring of environmental information in cold chain transportation. The system can sense the temperature and humidity information of the goods through the sensor and report it to the background application system through the reader device. In addition, the system also solves the problem of illegal unpacking monitoring in cold chain transportation. Cold chain transport is a closed system. If an illegal unpacking action occurs during transportation, the change of light will enable the system to monitor and report the action. The system captures the location information in real time through GPS and reports the location information through the wireless transmission network, thereby solving the problem of route monitoring in the cold chain transportation. In summary, the system can solve the key environmental information such as temperature, humidity and light changes in the storage and transportation of cold chain logistics in real time, realizing real-time monitoring and traceability of the cold chain logistics system.
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