PLC Basics Tutorial: Master Core Knowledge to Become an Automation Expert

Hello everyone, I am Lao Wang, an experienced engineer in the automation industry. Today, let’s talk about PLCs, which are the core of the automation field, just as important as the light switch in our homes. However, instead of controlling a simple light bulb, it controls various complex industrial devices. The goal of this article is to help you quickly get started with PLCs and become an ‘expert’ in the automation field. Of course, let’s not take the term ‘expert’ too seriously; we will take it step by step, starting from the basics and gradually accumulating experience.

1. Introduction to PLC: What Is It?

Imagine the light in your home; to control it, you need a switch, right? A PLC is like a super powerful ‘switch’ that can control a variety of devices, such as motors, valves, sensors, and so on. Moreover, it is not just a simple switch; it can also make logical judgments based on different conditions. For example: if the temperature exceeds the set value, the motor will stop running; if the pressure is below the set value, the pump will start, etc. This might sound abstract, so let’s think of it as an ‘industrial brain.’ It receives information from various sensors and controls actuators to complete various tasks based on pre-set programs. The core of PLC is its program, which is the ladder diagram we write.

2. Introduction to Ladder Diagram Programming: Draw Your First Program from Scratch

PLC programming mainly uses ladder diagrams, which use simple graphical symbols to represent logical relationships. Even if you have never learned programming, you can easily get started. Let’s look at the simplest example: controlling a light switch.

1. Basic Concept Explanation: A ladder diagram is like a circuit diagram; the left side is the power source, and the right side is the load (which is our light). The contacts in the middle are the input conditions, such as a push button switch. If the button is pressed, the contact closes, allowing current to flow, and the light turns on; if the button is not pressed, the contact opens, and the light turns off.

2. Hardware Circuit Diagram or Ladder Diagram:

(Ladder Diagram)
[----[Button1]----]---|----[Light]---|

1. Code Example: (The statements here use Siemens PLC syntax; different brands of PLCs have slightly different syntax.)

// Simple PLC program to control the light switch
IF Button1 THEN
    Light := TRUE;
ELSE
    Light := FALSE;
END_IF;

1. Practical Application Case: The simplest application is controlling an indicator light based on a sensor signal to determine whether the light is on or off. For example, a water level sensor; when the water level is too high, the indicator light turns on.

2. Common Problems and Solutions: The most common issue is programming errors, which prevent the light from being controlled properly. Be sure to carefully check the ladder diagram and program to ensure the logic is correct. Also, pay attention to hardware connections and ensure the PLC is correctly connected to the light.

3. PLC Input and Output: Interaction with the Real World

The input of the PLC is like our eyes and ears, receiving signals from external devices; the output is like our hands and feet, controlling external devices. The input usually connects to sensors, such as temperature sensors, pressure sensors, proximity switches, etc.; the output usually connects to actuators, such as motors, relays, solenoid valves, etc.

1. Basic Concept Explanation: The input and output of the PLC are implemented through I/O modules. The I/O module acts as a bridge between the PLC and external devices, converting external device signals into digital signals that the PLC can understand.

2. Hardware Circuit Diagram: (Here is a simple example of input and output)

(Circuit Diagram)
+-----------------+     +-----------------+
|   Sensor        |---->|   Input Module   |---->|   PLC   |---->|   Output Module  |---->|   Motor     |
+-----------------+     +-----------------+     +-------+     +-----------------+     +-----------------+

1. Code Example: (Assuming the input signal is I1 and the output signal is Q1)

// Check input signal I1
IF I1 THEN
    Q1 := TRUE; // Turn on the motor
ELSE
    Q1 := FALSE; // Turn off the motor
END_IF;

1. Practical Application Case: Control a motor; when an object is detected nearby, the motor starts; when the object leaves, the motor stops.

2. Common Problems and Solutions: Check that the I/O module connections are correct, ensuring that the sensors and actuators are properly connected to the PLC’s I/O module and that the signal’s voltage and current meet the requirements. Check that the program is correct, ensuring that the program runs according to the expected logic.

4. Practical Suggestions: Start Small and Accumulate Experience

I suggest starting with simple projects, such as controlling an LED light switch, gradually increasing the difficulty, and trying to control multiple devices while learning to use different sensors and actuators. Remember, practice is the only standard for testing truth. During the learning process, be sure to practice more, encounter problems, look up information, and consult others. Safety first! Before conducting any experiments, ensure safety measures are in place to avoid accidents.

Alright, today’s PLC introductory tutorial ends here. I hope this article helps you quickly get started with PLCs and embark on your automation journey! Next time, we will continue to learn more advanced knowledge, such as timers and counters. Remember, learning PLCs is like learning to ride a bicycle; it may be tough at first, but with persistent practice, you will master it!