PLC ladder diagram design and programming method - Database & Sql Blog Articles

Ladder diagrams are common programming languages ​​for various plc. Although the instruction symbols used by PLCs of various manufacturers are not consistent, the design and programming methods of ladder diagrams are basically the same.

First, determine the number of each component, assign I / O address using ladder programming, you must first determine the programming component number used, PLC is to distinguish the operating components by number. The FX2N model PLC we selected has the internal component address numbers as shown in the following table. It must be clear when using it. Each component can never assume several roles at the same time. Generally speaking, the configured PLC has the number of input points corresponding to the number of input signals of the control object, and the number of output points and the number of control loops output are also corresponding (if there is analog quantity, the number of analog channels and the actual number are also To be equivalent), the I/O allocation is actually to assign the PLC's in and out points to the actual I/O circuit. When programming, the logic or control relationship is established according to the point number. Sit" to wire. The I/O address allocation of the FX2N series and some other memory allocations have been introduced before. Students can also refer to the programming manual of the FX series. Second, the ladder programming rules 1, the coil of each relay and its contacts are the same number, each component's contacts are used without a limit. 2. Each line of the ladder diagram starts from the left and the coil is connected to the far right (no contact points are allowed on the right side of the coil). 3. The coil cannot be directly connected to the left busbar. 4. In a program, if the coil of the same number is used twice, it is called double coil output, it is easy to cause misoperation and should be avoided as much as possible. 5. There is no real current flow in the ladder diagram. In order to facilitate the analysis of the periodic scan principle and logical causality of the PLC, it is assumed that there is a “current” flow in the ladder diagram. This “current” can only be unidirectional in the ladder diagram. Flow - that is, from left to right, the level of change can only be from top to bottom.