Hello everyone! I am your old friend, Wang, a seasoned author of microcontroller/PLC tutorials! Today we will embark on the journey of PLC programming together! Don’t worry, I will guide you through the basics of electrical work to become a PLC programming expert in the most down-to-earth way! Just think about it, you will be able to easily control various automation devices in the future, and that feeling is fantastic!
1. What is PLC? What does it have to do with the light switch at home?
Many people feel overwhelmed when they hear PLC, thinking it is very profound. In fact, it is just a sophisticated “light switch”! Your home light switch controls a light bulb; while PLC controls thousands of devices, such as machines on assembly lines, valves in factories, and so on.
Basic Concept Explanation: PLC, short for Programmable Logic Controller, is a type of digital electronic device that can control various industrial devices according to pre-written programs. Simply put, it is a programmable “super switch”.
Hardware Circuit Diagram or Ladder Diagram: Beginners don’t need to worry about complex circuit diagrams; let’s start with the simplest. Imagine a button (input) controlling a light bulb (output). In PLC, this can be represented using a ladder diagram, where one button corresponds to one input contact, and one light bulb corresponds to one output coil. (Here, a simple ladder diagram should be inserted, showing the connection between the button and the light bulb, and labeling the input/output points)
Code Example: Different PLC programming software may vary slightly, but the basic logic is consistent. Below is a simple example (assuming using Siemens STEP7 software):
//Network 1
I 0.0 //Input point 0.0, corresponding to the button
Q 0.0 //Output point 0.0, corresponding to the light bulb
This code means: When input point I 0.0 is activated (button pressed), output point Q 0.0 is activated (light bulb lights up).
Practical Application Case: This is like a simple automatic door control system. When someone approaches the sensor (input signal), the door opens automatically (output signal); when the person leaves, the door closes automatically.
Common Problems and Solutions: The most common problem is wiring errors! Be very careful, always check the circuit diagram carefully before wiring to confirm the correspondence between input and output terminals. If the light bulb does not light up, first check if the power supply is normal, then check if the connections between the button and the light bulb are correct. Using a multimeter can help you quickly troubleshoot.
2. Relay: The “Good Brother” of PLC
Relay is like the “good brother” of PLC, an indispensable partner. It can help you control high-current devices and protect the PLC from damage.
Basic Concept Explanation: A relay is an electromagnetic switch that uses a small current to control the on and off of a high-current circuit. Imagine it as a remote control that uses a small signal to control a powerful device.
Hardware Circuit Diagram or Ladder Diagram: (Here, a simple circuit diagram should be inserted, showing the PLC controlling the relay, and the relay controlling a high-voltage lamp, labeling the PLC output point, relay coil, and high-voltage lamp)
Code Example: This part of the code is similar to the previous example, but the output is controlling the relay coil.
Practical Application Case: Many large motors in factories need to be controlled by relays to protect the safety of the PLC.
Common Problems and Solutions: Relays can easily burn out, always pay attention to choose the appropriate relay, with a rated current greater than the current of the controlled device. If the relay remains energized or does not release, check the coil voltage and whether the relay itself has issues.
3. Timer: Let PLC Work on Time
Timers are commonly used function blocks in PLCs that allow you to control devices to work in a time sequence.
Basic Concept Explanation: A timer is like an “electronic timer” that can set a time to perform specific operations when the time is up.
Hardware Circuit Diagram or Ladder Diagram: (Here, a simple ladder diagram should be inserted, showing the timer controlling the switch of a light bulb, and labeling the timer’s setting parameters)
Code Example: Different PLC programming software may have slightly different timer instructions; here’s a general example:
//Timer Setting
TON T1 10s //Timer T1, set time to 10 seconds
//If the timer completes counting
IF T1.Q THEN
// Perform operation
Q 0.1 := TRUE; // Output point 0.1 is activated
END_IF;
Practical Application Case: For example, an automatic filling device needs to control the filling time periodically; a traffic light needs to control the switching of red and green lights at intervals.
Common Problems and Solutions: Incorrect timer parameter settings are a common issue. Be very careful about the timer’s setting unit (seconds, milliseconds, etc.) and the judgment of the timer completion flag.
4. Counter: The “Counter” of PLC
Counters can help PLC record the number of occurrences of events.
Basic Concept Explanation: A counter is like a “counter” that can record the number of pulse signals.
Practical Application Case: For instance, counting products on a production line, counting the floors of an elevator, etc.
(Subsequent content needs to be supplemented with hardware circuit diagrams, code examples, common problems, and solutions regarding counters, while maintaining a consistent article style)
Conclusion: Alright, that’s it for today’s PLC introductory tutorial. Remember, practice makes perfect! I recommend everyone to try building a simple PLC control circuit, like controlling a light bulb with a PLC. The more you practice and summarize, the more you can become a PLC programming expert! Don’t forget, safety first! Before conducting any circuit experiments, please ensure your safety and take protective measures. Let’s continue exploring the world of PLC together!