Experts, please explain PLC statements

You’re learning Siemens’ PLCs, right? Haha, this requires knowledge of instruments and electrical systems, so it’s not something that can be explained in just a short time.

FB has its own background DB, while FC does not. FB is more convenient to use than FC, as it has the additional background DB; FB’s static variables are also stored in this DB. OB1 calls FC or FB; programming in FC or FB will suffice. OB35 is an interrupt block, and the interrupt duration can be defined by oneself. The timing interrupt of 400PLC is more than that of 300. OB100 is the initial speech parameter block. For more detailed information, download it from Siemens’ website: www.ad.siemens.com.cn. This post was last edited by faner on 2009-3-27 02:50.]

The three most commonly used OB100 blocks as initial parameter blocks are those that are executed only once; they are used to assign certain data and parameters during PLC operation, with the initialization statements placed here. OB1 is executed continuously; it doesn’t care about the execution time and will start executing again immediately once it is finished. OB35 is a time interrupt, and the timing can be set; for example, you can set it so that the program runs once every 1 second. It can be used for counting, or for programs that do not require fast execution. Their execution order and priorities are as follows: when the PLC is powered on and set to RUN, OB100 executes OB1 while OB35 does not execute. After OB100 finishes executing, OB1 is executed; however, OB35 has a higher priority than OB1. If both OB35 and OB1 need to be executed, OB35 will be executed first.

Thank you for ZZLLYP’s answer; it was excellent. Thanks :) Unfortunately, I don’t have many points to give, so I’ll award the highest score to you. This post was last edited by hijosen on 2009-3-27 08:50.]

You still need to use it more; the more you use it, the more you’ll remember it

Previously, when programming, it was done in the form of ladder diagrams; I haven’t seen the approach you mentioned very often. You might want to take a look at the sections on relays in the book \"Motors and Electrical Apparatus\" first, which should make programming easier for you. :victory:

I’m also new to this area; even after installing the simulation software, I find it quite confusing and don’t know where to start. Let’s explore and learn together.

A PLC is just a tool; what’s important is having an understanding of the field and the manufacturing process. As a starting point, I suggest you download some books from Siemens’ website – once you’ve read them, you’ll be an expert. “300CPU specifications, 300C technical features, 300LAD, 300STL, 300 module data, 300 hardware and installation manuals, 400CUP specifications, configuration and instructions for 300/400 expansion racks, hardware configuration and communication, system software for S7-300/400 systems and standard functions. Good luck to you.

Before writing a PLC program, it is first necessary to analyze the characteristics and operating process of the system. In typical industrial production processes, each device within the system starts in its initial state. The initial conditions include: a. The power supply for the equipment is functioning properly. b. The equipment should be set in automatic mode, that is, under PLC control. c. The protection, control, and signaling of the device have been reset. After confirming that each device is in its initial state, the operator issues a start command, and the entire system proceeds from its initial state into the startup process. If any device fails to meet the initial conditions for startup during self-check, the startup operation cannot be carried out. During the startup process, the status of each device keeps changing; the individual devices start operating in sequence according to the process flow, moving toward a stable operating state until they finally reach it. The duration of stable operation is determined based on production conditions. Once a production cycle is completed, either by the operator’s action or automatically as a result of shutdown conditions, the system enters shutdown mode. Once the last device has stopped operating, the entire system returns to its initial state, ready to start the next cycle. 1) In the initial stage, faults that occur during the self-check of various system devices: a. Abnormal power supply or device. b. Whether the device control mode is set to automatic. c. The fault has not been eliminated. 2) Starting faults: The most common starting fault is a starting timeout fault, meaning that the relay driven by the PLC activates, but the motor fails to start within the normal time frame. 3) Operational faults: During system operation, sudden events or faults may occur, such as motor overload tripping, manual alteration of the automatic mode, or activation of the emergency stop switch to protect the safety of personnel and equipment. Should either of the above faults or signals occur, the PLC program should immediately be switched to the execution stop command phase, thereby stopping the production process as programmed. Such faults that require an immediate suspension of the production process are classified as Category 1 faults. In actual production, there is another type of fault that does not require an immediate halt to the production process. For example, dust collectors are auxiliary devices in the overall production process; their absence does not affect the normal progression of production. When such a device fails, the PLC system can first shut it down and send audible and visual alarm signals to the operator. Maintenance personnel are then assigned by the control room to repair the device, while the PLC system can continue to execute the main production procedures. Such faults can be classified as type II faults.

Find a book that explains the S7300 in simple terms to read

PLC startup is further divided into warm startup and cold startup; accordingly, the initial OBs for startup are also different