First, example analysis The control function of the PLC is determined by the application program prepared by the user. If the PLC is to complete a complicated control task, the corresponding application program is also complicated. How to clearly organize the various parts of the program, and choose and determine the appropriate program structure is critical. SETP7 provides linear programming, partially structured programming, and structured programming methods. When developing S7-300 PLC applications, structured programming methods are usually used. On the one hand, SETP7 programming software itself provides users with a wealth of common functional blocks (SFB, SFC), on the other hand, the user can according to actual needs to prepare some specific function blocks (FB, FC), by assigning the corresponding entry parameters, the user program You can call these instruction blocks repeatedly. To support structured programming, SETP 7 divides the instruction blocks of the user program into three types: OB organization blocks, FB function blocks, and FC functions. In the example of program design, we take a typical "process development of industrial stirring process" as an example, that is, further study and application of S7-300 PLC from the task description, PLC system configuration, application program structure design and software programming. The method of product realization industrial control task. 1. Task description Both ingredients (Fundament A and B) are mixed together by a stirrer in a mixing tank. The mixed product exits the tank through a discharge valve. Block diagram for the process. The stirring system can be divided into 3 zones. Components A and B have the same equipment. When describing tasks and areas in the mixing process, not only the actions of each zone but also the different elements of the zone are controlled. This information includes the following. 1) Electrical, mechanical, and logical inputs and outputs for each task. 2) Interlocking and interdependencies between tasks. 2. Create a description of the action The stirring system uses electrical appliances and control equipment such as pumps, motors, and valves. Prior to the control system hardware selection and software programming, a clear description of the operating characteristics of each read preparation and the interlocks required in operation is required. Describes the operation of the equipment in the mixing system. An in-depth understanding of the operation process of these devices is of great benefit to hardware selection and software programming. 3. Create input/output diagrams After the physical description of the control object, you can create an input and output logic diagram for each device and task area. 1) Establish the input/output logic diagram of the pump The stirring process uses two pumps. Each pump requires four inputs, the start switch, the stop switch, the interlock to start the pump, and the feedback input to interrupt pump operation when a fault is detected. This control block has two outputs, one to control the motor running and the other to inform the CPU pump to stop working. 2) Create the input/output logic diagram of the stirring motor Similar to the pump in this example process, the agitator motor has four inputs, the start switch, the stop switch, the interlock to start the pump, and the feedback input to interrupt the agitator motor when an error is detected. This control block has two outputs, one to control the operation of the stirring motor and the other to inform the CPU that the pump has stopped working. 3) Establish the input/output logic diagram of the valve The coil-actuated discharge valve control block has only 3 inputs, the open switch, the close switch, and the operation interlock, which controls the discharge valve coil (ie, the valve opens/closes). 4. Description of safety requirements Based on statutory requirements and overall decision-making, decide which additional units are needed for the safety of the process, and add the effect of the security unit on the various areas of the process in the description of the user task. In the stirring process, its safety circuit uses the following logic. (1) An emergency stop button is used to stop the following devices that are independent of the programmable controller (PLC). 1A component pump. 2B component pump. 3 Mix the motor. 4 Discharge valve coil. (2) Emergency stop button on the console. (3) The status of the emergency stop button must be entered in the controller. 5. Description of operator station (operator station) In general, each control process requires an operator interface that allows people to intervene in the process. Operator interface forms can be varied, such as button/indicator console, PC, OP, touch screen, etc. In this mixing process example, the operation and stop of each device follow the actions of the buttons installed on the console. The console includes indicators that show the status of the operation. It also includes an emergency stop button to stop the process immediately. 6. Determine the hardware configuration of the control system After all control requirements have been determined, the control equipment used for this project is determined. This includes determining the input/output modules The type, number of input/output physical points (that is, the number of input/output modules) determine the hardware configuration of the S7-300 PLC system. In the PLC hardware configuration section, you should pay attention to the following matters. (1) Cost-effectiveness of system selection. (2) Take proper account of the margin of the PLC hardware device. The hardware configuration of the stirring process. Valve Stems,Aluminum Snap-In Car Tire Valve Stem,Car Tire Valve Stem,Rods Valve Stems Wenzhou Xinzhan Valve Ball Co. , Ltd. , https://www.xzfmqt.com