As the blood of modern industry, petroleum occupies an important strategic position in the national economic life. As an important means to ensure national energy security, petroleum reserves make the safety of petroleum reserve banks particularly important. The safety issue of oil storage tanks in petroleum reserves is the core of its safety issues. All kinds of technical parameters of tanks (temperatures inside and outside the tank, temperature of the main shaft of the oil pump, level of oil tanks, etc.) are fully implemented in real time. Monitoring is necessary. Here we introduce an oil depot real-time monitoring system using RS-485 bus technology as a communication network.
Because of the special nature of oil reserves, the oil depot has a large area, and the distribution of oil storage tanks is very scattered (mainly to prevent the storage tanks from being isolated in a timely manner in case of accidents, so as to prevent chain reactions from occurring), so that the transmission distance of data signals is far away. The real-time monitoring system of oil storage tank adopts distributed control system. Because of temperature, pressure sensors generally use current, 4-20ma signal, voltage signal 0-10V signal or 0-5V transmission, but due to the wide range of oil depot, mutual Between the distance, the current voltage signal transmission is not stable, and RS-485 bus can reach 1200 meters because of its transmission distance. By using the switch module and the analog module, the current and voltage signals are converted into RS-485 bus data signal transmission. The oil depot monitoring system adheres to the design principle of “dangerous dispersion, decentralized functions, load decentralization, and centralized managementâ€. The RS-485 bus is used as the data communication line, and relevant parameters are collected to the monitoring center computer to ensure the stable and real-time acquisition of the monitoring system. Data is managed in a unified manner.
Here, we adopt the MD-108 analog-to-485 acquisition module of Shenzhen Guoke Weiye Communication Technology Co., Ltd. and the ND-1084 switch-to-485 acquisition module to collect the relevant temperature and pressure parameters and switch quantity alarm signals, due to the storage tank The distribution is distributed in a grid-like manner. Routing the daisy-chain bus topology in hand-to-hand mode can cause wiring troubles and complicated post-maintenance. Therefore, we use the N-1204 type 485 hub for laying out the RS-485 bus network with star topology.
The temperature data generated during the operation of the storage tank pump, the temperature data outside the tank, the level data in the tank, and the tank pressure parameters are converted to 4 to 20 mA by the system's temperature sensor, level sensor, and pressure sensor. Analog current data signal, MD-108 analog input module can simultaneously collect eight 4 ~ 20mA current analog signal, which provides 12-bit resolution, accuracy can reach ± ​​0.2%, the analog module built-in microcontroller using Modbus RTU protocol The relevant signal is encoded, and the digital signal is transmitted over the RS-485 bus over a long distance. The communication speed of the RS-485 bus is set to 9600 bps.
The on/off status of the same oil tank pump and the switch signal formed by the alarm of the oil tank are connected to the digital input port of the ND-1084 digital input/output module. The ND-1084 module provides eight switch inputs and Four-way switch output status, the built-in MCU program can encode the collected switch signal according to Modbus RTU protocol, transmit related data to the remote computer via RS-485 bus, and the four-way switch output adopts built-in The relay drive can drive the 220V/3A power switch. It is mainly connected to the oil pump and other electromechanical equipment of the oil storage tank. After the computer analyzes the collected switch signal and analog signal, it sends the corresponding command to the N-1084 switch. The quantity module, its four-way switch output port according to the issued instructions to make the appropriate action, thereby controlling the mechanical and electrical equipment / relay connected to the action.
Since both the switch module and the analog module use Modbus RTU as the communication protocol and the RS-485 bus as the communication line, we connect all related equipment in the same RS-485 bus communication network. The computer sets the program for each module. Give a unique address code to facilitate the computer software to identify the corresponding module and obtain the relevant conditions of the various oil storage tanks through various modules and to control the relevant equipment. However, the RS-485 bus must be used in a daisy chain bus topology. In-situ cabling, and because the tanks are widely distributed and dispersed, and bus-type cabling is very complex, a star topology is decided. However, if the RS-485 bus is simply wired with a star topology, signal reflection and other problems will occur. Causes the communication to be unstable, affects the system communication quality, needs the 485 hub here to solve the corresponding question.
The 485 hub is mainly used to solve the star-type wiring problem of the RS-485 bus network. Its RS-485 interface is driven independently, using optical isolation and power isolation between each other, which can effectively avoid the 485 signal reflection problem. Each RS-485 port has a lightning protection function of 600W, which can effectively prevent lightning interference from affecting the equipment. The specific use of the 485 hub is as follows: It is divided into multiple levels of cascading connection, that is, a N-1208 type 485 sharer is placed in the monitoring center, a N-1204 type 485 hub is placed in each storage tank, and the monitoring center The serial port of the computer is connected to the RS-232 serial port of the N-1208 of the monitoring center. The eight-way RS-485 bus provided by the computer is connected to the upper 485 port of the N-1204 of the oil storage tank, and the four RS-channels provided by the N-1204 are downward. The 485 interface is connected with the analog module and the switch module. Through the above configuration, the problem of one RS-485 node will not affect the normal communication of other nodes and ensure the normal communication of the entire RS-485 communication network.
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