I still remember my first training session after joining Yiwei, which covered the definition, characteristics, and classification of PLCs. I've benefited immensely from it ever since. Some might think that as a graphic designer, you don't have much direct contact with products and customers, so it's okay if you don't understand the products. But Yiwei doesn't think that way. The automation industry is highly specialized, and regardless of your position, basic product knowledge is essential, and mastering it greatly benefits your work. Below, I'll share some of the training content from that time with all friends who are transitioning from other industries to the automation industry.
A PLC (Programmable Logic Controller) is a digital electronic system designed for industrial applications. It uses programmable memory to store instructions for performing logical operations, sequential control, timing, counting, and arithmetic operations. Through digital and analog inputs and outputs, it controls various types of machinery or production processes. PLCs and related equipment should be designed to easily integrate with industrial control systems and facilitate functional expansion.
I. Characteristics of PLC:
1. High reliability and long service life
2. Strong environmental adaptability
· 3. Flexible and versatile
4. Easy to use and simple to maintain
5. The entire connection process can be completed with just one screwdriver.
II. Classification of PLCs
PLCs arose from the needs of modern large-scale production, and their classification must also conform to these needs. Generally, programmable controllers can be classified from three perspectives: first, by the size of the control scale; second, by the performance level; and third, by their structural characteristics.
1. Classification by control scale: It can be divided into large-scale machines, medium-scale machines and small-scale machines.
(a) Mini-computer: Mini-computers generally have 256 control points, which are suitable for single-machine control or small system control.
(1) Japan's OMRON Corporation CQM1
Processing speed: 0.5~10ms/1k words
Storage: 3.2~7.2k
192 digital inputs and 44 analog inputs
(2) German SIEMENS S7-200
Processing speed: 0.8~1.2ms
Memory: 2k
Digital inputs: 248 points, Analog inputs: 35 channels
(ii) Medium-sized machine: The control points of a medium-sized machine are generally no more than 2048 points. It can be used to directly control the equipment and monitor multiple lower-level PLCs. It is suitable for the control of medium or large control systems.
(1) OMRON Corporation of Japan C200HG
Processing speed: 0.15~0.6 ms/1k words
Memory 15.2~31.2k
1184 points
(2) German SIEMENS S7-300
Processing speed: 0.8~1.2ms
Memory: 2k
1024 digital inputs, 128 analog inputs
Network: PROFIBUS, Industrial Ethernet, MPI
(iii) Mainframe computers typically have more than 2048 control points, enabling them to perform not only complex arithmetic operations but also complex matrix operations. They can be used not only for direct control of equipment but also for monitoring multiple downstream programmable controllers.
(1) Fuji Electric F200
Processing speed: 2.5ms / 1k words
Memory: 32k
I/O points: 3200
(2) Japan OMRON CV2000
Processing speed: 0.125ms / 1k words
62k I/O points in memory 2048
(3) German SIEMENS S7-400
Processing speed: 0.3ms / 1k words
Memory: 512k
I/O points: 12672
(4) German AEG A500
Processing speed: 1.3ms / 1k words
Memory: 62k 64k
I/O points: 5088
2. Classification by control performance: It can be divided into high-end machines, mid-range machines and low-end machines.
(a) Low-end machines
These types of PLCs have basic control functions and general computing capabilities. They operate at relatively low speeds and can support a limited number of input and output modules. For example, the S7-200 manufactured by the German company SIEMENS belongs to this category.
(ii) Mid-range machines
These types of PLCs possess strong control functions and powerful computing capabilities. They can perform not only general logic operations but also more complex trigonometric function, exponential, and PID calculations. They operate at relatively high speeds and can support a large number and variety of input/output modules. For example, the S7-300 manufactured by the German company SIEMENS belongs to this category.
(III) High-end machines
These types of PLCs possess powerful control functions and strong computing capabilities. They can perform not only logic operations, trigonometric function operations, exponential operations, and PID operations, but also complex matrix operations. They operate at high speeds and can support a large number and variety of input/output modules. These PLCs can handle large-scale control tasks. In networked systems, they are typically used as master stations. For example, the S7-400 manufactured by the German company SIEMENS belongs to this category.
3. Classified by structure: It can be divided into integral type, modular type, and stacked type.
(a) Integrated type
A PLC with an integrated structure integrates the power supply, CPU, memory, and I/O system into a single unit called the basic unit. A basic unit constitutes a complete PLC. Expansion units can be added when the number of control points is insufficient. The integrated structure is characterized by its compact size, low cost, and easy installation.
(ii) Combination
A modular PLC divides its components into several functional modules, such as a CPU module, input modules, output modules, and power supply modules. (Today's forwarding code is: Yiwei Company's values: Integrity, Responsibility, Cooperation, Innovation.) While each module has a relatively simple function, the variety of modules is increasingly rich. For example, some PLCs, in addition to basic I/O modules, also have special function modules, such as temperature detection modules, position detection modules, PID control modules, and communication modules. The characteristics of a modular PLC are that the CPU, inputs, and outputs are all independent modules. Modules have uniform size, neat installation, flexible I/O point selection, and are convenient for installation, debugging, expansion, and maintenance.
(iii) Stacked type
The stacked structure combines the compactness, small size, and easy installation of an integrated structure with the flexible I/O point configuration and neat installation of a modular structure. It is also composed of a combination of individual units. Its characteristic is that the CPU is an independent basic unit (consisting of the CPU and a certain number of I/O points), while other I/O modules are expansion units. During installation, no baseboard is needed; only cables are used to connect the units, which can be stacked one by one. This makes the system flexible in configuration and compact in size.
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