How to learn PLC from scratch

Introduction: PLC is the core of automation equipment development and a commonly used controller in industrial control. How to learn it systematically? Learning in stages from simple to difficult can be divided into switch quantity learning, analog quantity learning, and communication control. At the same time, you need to master the design of the host computer (human-machine interface).

How to learn PLC systematically from scratch? I will use my own experience to illustrate. For fresh graduates, they have the basics or theory, but lack practice. When you first start working, the company will definitely not have big projects or new projects for you to do. Generally, you will use the old machines to modify and practice. You must seize this opportunity. There is no pressure at this stage. Here you can remove each electrical component at will and learn how to control it separately.

I have also gone through this stage. To be honest, this period was very difficult or helpless. No one would help you to look up all the relevant information on the Internet and look for instruction manuals, operating manuals, etc. What you learn here is your own.

PLC is the core of automation equipment development and a commonly used controller in industrial control. How to learn it systematically? Learning in stages from simple to difficult can be divided into switch quantity learning, analog quantity learning, and communication control. At the same time, you need to master the design of the upper computer (human-machine interface).

1. Switching quantity

Switch quantity is the simplest, with two states, ON and OFF. The basic unit of PLC is switch quantity control, whether it is input or output. Input can be divided into low-frequency and high-frequency input switches according to the switching frequency. Low-frequency switches → various switch buttons such as buttons, knobs, travel switches, proximity switches (can also be high-frequency), various relays, etc. High-frequency switches are very fast switching frequencies such as pulse input → encoders. Output is also divided into high and low frequencies. Low-frequency output often controls some switches such as relays and contactors, and high-frequency output is generally high-speed pulses. You need to understand and master the wiring methods for these things, including two-wire, three-wire, four-wire, etc., and also pay attention to the type PNP or NPN.

2. Analog

The input and output of the equipment are not only switch quantities, but also analog signals. For example, the output of various sensors (displacement, temperature, electrical signals, pressure) is given in the form of analog signals. The control of various equipment requires analog control, such as frequency converters, rectifier cabinets, pressure valves, etc. Analog signals are generally composed of voltage and current signals, commonly used 0~10v, 0 (4)~20ma. These signals are the expressions of various quantities. You need to perform data conversion in the PLC. For example, if the frequency of the frequency converter is 30.00Hz, you cannot directly let the PLC output this frequency value. You have to convert it into a digital quantity first. The digital quantity is converted into an analog quantity through the DA module to control the frequency converter. Speaking of this, the basic unit of the PLC generally does not have analog quantity, and expansion modules such as AD and DA modules need to be added.

3. Communication

After you have mastered the switch and analog control of PLC, you also need to know communication control. The way of industrial control is to learn until you are old, and constantly learn new knowledge. Communication is simply to use a certain communication protocol to connect PLC and equipment. All signals of the equipment can be controlled by sending instructions through PLC, without switches or analog quantities. For example, the start and stop of the equipment, the size of the control quantity, and data monitoring can all be completed through communication, and the wiring is simple. Here you need to master the relevant communication protocols, as well as the function codes of the equipment, and have a certain computer foundation, including the conversion of various types of data.

4. Host computer (touch screen)

The host computer is the status display and control of your PLC. Using a host computer can save many buttons on the control panel and it is also beautiful. The important thing is that for equipment controlled by PLC, you can directly control and modify equipment process-related parameters on the host computer. You need to master the programming of the host computer, including interface design, PLC status and value settings to cooperate with PLC for control.

Basically, after mastering these four categories, you can start developing automated equipment. This is a gradual process. Don't be impatient. Be patient and persistent. You can basically master it in about a year.