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1. Introduction Programmable controller is a new type of general automation control device. It integrates traditional relay control technology, computer technology and communication technology. It has the advantages of strong control function, high reliability, flexible and convenient use, easy expansion and other advantages, and is used more and more widely. However, due to the harsh working environment of industrial production sites, there are many interference sources during use. For example, the starting or stopping of high-power electrical equipment causes interference in the grid voltage, and the power frequency interference generated by electromagnetic coupling of welding machines, EDM machine tools, motor brushes, etc. will affect the normal operation of PLC. Inutetsu Group has also accumulated some experience in the use of PLC systems. For example, in some of the company's main plants such as iron plants, sintering plants, power plants, steel plants, rolling mills, and air separation plants, PLC or DCS automatic control systems have been used earlier, and they are familiar with the installation, debugging, and maintenance of new systems. However, the coking plant started using PLC systems late. First, it is acquainted with new technologies. * The other reason is that due to the particularity of the technology and environment of the coking plant, a very cautious attitude was adopted when using the PLC system. Careful and detailed feasibility studies were conducted in terms of equipment selection, cable selection and cable installation methods, and the design of the main control room. Detailed design and implementation plans were made to ensure that each system achieved a successful test run and the continuity of safe production when applying new technologies. The following is a brief introduction to the operating environment of the coke cart PLC system: The installation environment of the PLC system on the focus push truck is different from that in other workplaces. Since the coke push cart is a large-scale movable device, the PLC on it needs to be installed and fixed regularly._I * Working in an operating environment that keeps moving back and forth, this is far from the ideal operating environment of the PLC system. In an industrial site with a large number of people, controlling PLC_[Working environment can effectively improve its working efficiency and life, meet the requirements of safe production, and thereby improve the economic and social benefits of the factory. When installing PLC, avoid the following places: 1. The ambient temperature exceeds the range of 0-50 degrees; 2. The relative humidity exceeds 85% or there is dew condensation (caused by sudden changes in humidity or other factors) 3. Direct sunlight 4. Corrosive and tender gases 5. Frequent or continuous vibration, vibration frequency is 10-55Hz. Amplitude is 0.5mm (peak to peak) 6. A large amount of dust 7. Impact exceeding log (gravity acceleration) Proceedings of the 4th National Automation Technology Exchange Demonstration Conference in Metallurgy, Electric Power, Petroleum and Chemical Industry_The control sequence must be s7- However, these requirements cannot be met in the working environment of the coke pusher. The working environment of the coke pusher is roughly as follows: 1. The ambient temperature is high (the temperature in the main control room above the coke pusher rod sometimes even exceeds 70 degrees). 2. Vibrations caused by the movement of the coke pusher, the coal rod, the coke pusher, door removal, door installation, door clearing and frame cleaning are frequent. At the same time, the amplitude of the vibration is relatively large, far exceeding the amplitude prohibited by the PLC. 3. The gas produced by the coke oven is a mixed gas containing many components. Some of the components of these gases are highly corrosive, and at the same time it is a flammable gas, which is the source of factory production and household gas. 4. Due to the harsh production environment, the dust on site is also quite large. 5. Since the system is installed in the main control room of the coke pushing car, it is a moving environment, so the requirements for the connection quality of all cables are naturally relatively high. At the same time, it also requires system spare parts to have high vibration resistance. 6. There are many interference factors. For example, large equipment movements such as the movement of the cart, the advancement and retreat of the coal leveling rod and the coke rod are all driven by the motor. The large motor itself is a large source of interference. The noise generated by these arcs directly affects the normal work of the system and the safety of the system itself, which may in turn cause other safety accidents. B. The main control objects of the coke pusher PLC system: The coke pusher is a relatively complex large-scale equipment, which includes the following main subsystems: 1. Travel control; the movement of the coke pusher is driven by a motor, and the movement of the motor is controlled by a frequency converter, which is centrally controlled by the PLC system. The PLC system ultimately controls the movement speed and direction, starting and stopping of the traveling motor by outputting a 4-20mA control signal to the frequency converter. 2. The starting, stopping, forward and backward speed of the coal leveling rod. The coal leveling rod is also driven by a motor. The motor is controlled by a frequency converter, and the control method is almost the same as that of the traveling control. 3. Control of the coke pushing rod. Motor driving, variable preheater control, the control method is almost the same as that of flat coal pole. 4. Door removal and door installation operation control. Hydraulic transmission control, the working direction is controlled by the solenoid valve, which is centrally controlled by the PLC system. 5. Door clearing and frame clearing control, etc. 2. Some measures taken during design and installation: 1. Create an environment and try to meet the working environment temperature requirements of the PLC system: transform and improve the working environment in the main control room, strengthen the sealing and insulation of the house, and add air conditioning equipment to ensure that the temperature in the main control room where the PLC is installed is controlled at around 25 degrees all year round, with a maximum of no more than 30 degrees. 2. In order to ensure that the system reduces internal and external interference, three suppression measures are taken from the design stage: cutting off or attenuating the propagation path of electromagnetic interference; improving the anti-interference ability of the device and system. In order to reduce the electromagnetic interference of power cables, Especially for the feeder cable of the frequency conversion device, copper-tape shielded power cables are used in the selection, thereby reducing the electromagnetic interference generated by the power line. In the PLC control system, the power supply occupies a very important position. The main way for grid interference to enter the PLC system is through the power supply (UPS) of the PLC system. Therefore, during engineering construction, the power supply of the PLC system should be separated from the power supply of other field instruments such as transmitters to reduce the interference of the power supply to the system. 3. Improve the grounding system. In order to ensure safe production and better suppress interference, a complete grounding system is one of the important anti-interference measures for PLC control systems. System grounding methods usually include: floating ground method, direct grounding method and capacitive grounding method. For the PLC system, it is an adjustment low-level control device and should be directly grounded. Due to the influence of the distributed capacitance of the signal cable and the filtering of the input device, the signal exchange frequency between devices is generally lower than 1 MHz. Therefore, the PLC system grounding wire adopts one-point grounding and series-connected one-point grounding methods. The series connection method adopted in this project uses a large-section copper busbar to connect the central grounding point of the cabinet of each device, and then directly connects the grounding busbar to the grounding electrode. The grounding wire cross-section is greater than 22mm2, and the grounding resistance is 3 ohms. 4. In order to ensure the continuity of production and improve production efficiency, it is recommended to change the travel switch in the design to a proximity switch. In the past, travel switches were all mechanical contact type and were easily damaged during frequent operations. This will interrupt production or cause accidents, which is incompatible with the high reliability and accuracy of PLC. Changing all limits to proximity switches will directly improve the overall efficiency of the system, reduce the amount of maintenance, and increase social benefits. * * Improved. 4. Main functions of the PLC system: All control functions of the automatic control system can only be realized through the PLC. The PLC processes all the signals collected from the field through the signal input template and turns them into digital signals and sends them to the CPU for processing. At the same time, the various control commands issued by the CPU change the digital signals into signals that can be recognized by the field equipment through the output template. For example, the analog remote output template converts the commands sent by the CPU into 4-20mA analog signals and sends them to control the equipment on site. The communication template realizes the communication between the PLC and the host computer, and exchanges various data required for control with the host computer. 5. The host computer software and its main functions: The host computer uses Kingview as the monitoring software. This software is used to make all human-machine dialogue screens, including true reflections of all actions of each subsystem of the coke pusher. This allows the original instrument panel and operating console to be eliminated, reducing the operator's work. At the same time, it saves space and reduces many fault points and maintenance. The operator screen provides the operator with various data such as oil pressure, oil temperature, specific position of the coke push rod, etc., as well as the working status of each part of the coke push car equipment and control switches (the configuration software includes various user-favored buckwheat shapes). The programmer can select the switch that satisfies the user according to actual requirements. Each switch replaces the original electrical device on the operating table. Since the operation control is realized by software, the reliability is higher. * * Reduce control system failures. Programmers can make the picture very realistic, and the operator can understand the real status of the field equipment in a timely manner by observing the shape of the equipment displayed on the screen. The operator only needs to click the corresponding switch on the screen with the mouse to control the switches of the on-site equipment. At the same time, the operator can grasp the working status of the system in a timely manner by observing various data displayed on the screen.