Question

The programmable logic controller is classified into

Answer 1

Programmable Logic Controller (PLC) is a digital computing and operating electronic system designed for industrial environments. It uses programmable memory to store instructions for performing logical operations, sequential control, timing, counting and arithmetic operations, and controls various mechanical equipment or production processes through digital or analog input and output. There are many ways to classify PLC. The following is a classification from several main perspectives:

Classification by structural form

1. Integral PLC (box-type PLC)

- Features: The core components such as CPU, I/O interface circuit, memory, and voltage-stabilized power supply are encapsulated in a housing to form a unified whole.

- Advantages: compact structure, small size, light weight, and relatively low price.

- Application scenario: Suitable for small and simple control systems, such as single-machine control, small production lines, etc.

2. Modular PLC (combined or building block PLC)

- Features: CPU, I/O interface circuit, memory, power supply and other components exist in the form of modules and are connected through bus slots. Users can select and install the corresponding modules according to their needs.

- Advantages: strong flexibility, good scalability, easy maintenance and upgrade.

- Application scenarios: suitable for large and complex control systems, such as automated production lines, intelligent warehousing systems, etc.

Classification by control scale

1. Micro PLC

- I/O points: generally less than 64 points.

- Memory capacity: small.

- Application scenarios: suitable for simple control tasks, such as small stand-alone control, simple production lines, etc.

2. Small PLC

- I/O points: generally between 65\~128 points.

- Memory capacity: moderate.

- Application scenarios: widely used in various industrial automation fields, can adopt integral structure or modular structure.

3. Medium PLC

- I/O points: generally between 129\~512 points.

- Memory capacity: large.

- Application scenarios: suitable for medium-sized control systems, usually using modular structure, with high flexibility and scalability.

4. Large PLC

- I/O points: generally above 513 points.

- Memory capacity: large.

- Application scenarios: suitable for large control systems, such as large production lines, intelligent warehousing systems, etc.

5. Giant PLC

- Features: I/O points and memory capacity have reached extremely high levels.

- Application scenarios: suitable for ultra-large control systems, such as large industrial projects, aerospace and other fields.

Classification by function

1. Low-end machine

- Main function: logical operation, suitable for simple control tasks.

2. Mid-range machine

- On the basis of the low-end machine, analog quantity processing, communication networking and other functions are added, with higher control accuracy and data processing capabilities.

3. High-end machine

- On the basis of the mid-range machine, data processing, intelligent control, remote monitoring and other functions are further added, with powerful data processing capabilities and advanced control functions, suitable for high-end industrial automation and intelligent manufacturing fields.

In summary, there are various ways to classify PLCs, and users can choose the appropriate PLC type according to actual needs and application scenarios.

Answer 2

A programmable logic controller (PLC) is a specially designed computer that works reliably in harsh industrial environments and performs various automation control tasks. 

The classification of PLCs can be divided from different perspectives. The following are some common classification methods:

Classification by structure

1. Fixed PLC: The CPU board, I/O board, display panel, memory block, power supply, etc. of this PLC are fixedly installed in a chassis, with the characteristics of compact structure, small size and low price. Small PLCs generally adopt this structure.

2. Modular PLC: Modular PLC is also called combined PLC. Its various components, including CPU module, power module, I/O module, etc., are all separate modules. 

Different modules can be selected and installed on the rack as needed, thus forming PLC systems of different scales and functions. Modular PLC has flexible configuration and convenient expansion. It is generally used in large and medium-sized PLC systems.

Classification by function

1. Low-end PLC: It has basic functions such as logic operation, timing, counting, shifting, self-diagnosis, monitoring, etc. It can also have a small amount of analog input/output, arithmetic operation, data transmission and comparison, communication and other functions. It is mainly used for single-machine control systems of logic control, sequential control or a small amount of analog control.

2. Mid-range PLC: In addition to the functions of low-end PLC, it also has strong analog input/output, arithmetic operation, data transmission and comparison, number system conversion, remote I/O, subroutine, communication networking and other functions. 

Some can also add interrupt control, PID control and other functions, which are suitable for complex control systems.

3. High-end PLC: In addition to the functions of mid-range PLC, it also adds signed arithmetic operation, matrix operation, bit logic operation, square root operation and other special function operations, tabulation and table transmission functions. 

High-end PLC has a strong communication and networking function, which can be used for large-scale process control or to form a distributed control system to realize factory automation.

Classification by I/O points

The I/O points of a PLC refer to the sum of the input and output signals that the PLC can accept, and is an important indicator for measuring the scale of the PLC. According to the different I/O points, PLCs can be divided into small, medium and large PLCs.

* Small PLC: The I/O points are generally less than 256 points, mainly used for single-machine control or small control systems.

* Medium-sized PLC: The I/O points are generally between 256\~2048 points, which can be used for complex single-machine control or small production process control.

* Large PLC: The I/O points are generally above 2048 points, which can be used for large or complex production process control and distributed control systems.

Classification by output type

The output types of PLC mainly include relay output, transistor output and thyristor output.

* Relay output: suitable for AC loads, but the response time is long and the action frequency is low.

* Transistor output: suitable for DC loads, with short response time and high action frequency, but small load capacity.

* Thyristor output: Mainly used for AC loads, especially high-power AC loads, with advantages such as fast response speed and strong load capacity.

In summary, there are many ways to classify PLCs, and you can choose the appropriate PLC type according to different needs and scenarios.