Small PLC for Industrial Automation: Advantages, Applications and Development Trends

What is a Small PLC for Industrial Automation

A small Programmable Logic Controller (PLC) is a compact, cost-effective industrial digital control device designed for small-scale automation systems and limited-space industrial scenarios. Unlike large-scale PLCs that are typically used in complex production lines with thousands of I/O points, small PLCs usually cover I/O points ranging from 10 to 60, striking a balance between size, functionality, and affordability. Modern small PLCs have evolved beyond basic logic control, integrating advanced features such as high-speed pulse output, multi-axis positioning, communication networking, and data processing, making them a core component in today's distributed industrial automation architecture.

Take Inovance's H1S series as an example, a typical entry-level economical small PLC. Despite its compact body, it offers a 16k-step program storage space, eliminating the need for external memory expansion. It supports 3-axis 100K high-speed pulse output for high-precision positioning control and features a built-in real-time clock that can maintain timing for at least one week without external power. It also supports CANlink 3.0 networking and Modbus communication protocols, providing communication configuration functions that were previously only available in medium-sized PLCs. These characteristics demonstrate that modern small PLCs are no longer "simplified versions" of large PLCs, but rather independently designed products tailored to the needs of small and medium-sized automation projects.

The development of small PLCs has been closely tied to the trend of industrial automation decentralization. In the past, large-scale centralized control systems relied on one or two large PLCs to manage all production links. However, with the increase in production customization and modular demand, more and more enterprises are adopting distributed control, where each independent unit uses a small PLC for separate control, and then connects to the upper monitoring system through communication. This model not only reduces wiring costs but also avoids the risk of large-scale production shutdown caused by a single point of failure, improving the overall reliability of the system.

Core Advantages of Small PLCs in Industrial Automation

Small PLCs have occupied an increasingly important market share in industrial automation in recent years, which is entirely due to their irreplaceable core advantages that large PLCs cannot match. These advantages are not only reflected in hardware specifications but also in the overall economic benefits and engineering adaptability they bring.

First and foremost is the space-saving advantage of compact size. In many industrial scenarios, such as small stand-alone equipment, retrofitted projects, and distributed control nodes, the available installation space is often very limited. The small size of small PLCs allows them to be easily installed in compact electrical cabinets, or even directly integrated into the body of equipment, which greatly improves the space utilization of the equipment site. For example, in the transformation of a small packaging machine, the original electrical control box has limited internal space, and a large PLC cannot be installed at all, while a small PLC can perfectly fit into the original space, realizing the upgrade of the control system without changing the overall structure of the equipment.

The second significant advantage is low cost and high cost-effectiveness. For small and medium-sized automation projects, the number of I/O points required is usually between a dozen and dozens of points. Using a large PLC will not only cause a lot of redundant functions and waste of I/O resources but also significantly increase the project budget. The price of a small PLC is usually 1/3 to 1/5 of that of a large PLC of the same brand, which can meet the functional needs while greatly reducing the initial investment of the enterprise. According to the data of a cooling circulating water system transformation project by Siemens, after using the S7-200 small PLC for transformation, the overall hardware cost was controlled within 15,000 yuan, while the annual electricity cost saved exceeded 80,000 yuan, and the investment could be recovered in less than three months, which fully reflects the economic advantages of small PLCs.

Third, small PLCs are easy to program and maintain. Most small PLCs use a simple and intuitive programming architecture, with ladder diagram as the main programming language, which is easy for on-site engineers to master. At the same time, due to the simple hardware structure of small PLCs, the failure rate is relatively low, and when a failure occurs, the replacement process is very convenient, which can greatly shorten the maintenance downtime. In addition, most small PLCs support USB download and online monitoring, which facilitates programmers to debug on-site and modify procedures.

Finally, despite their small size, small PLCs have powerful and comprehensive functions. Modern small PLCs can not only complete basic logic control but also achieve complex functions such as motion control, temperature acquisition, analog processing, and network communication. They can also adapt to harsh industrial environments such as high temperature, humidity, and electromagnetic interference, with the same high stability as large PLCs. Taking the N80 series small PLC of Rectangular Technology as an example, it not only has rich logic instructions but also supports 4-axis motion interpolation control, which can meet the control needs of small CNC machine tools, reflecting the characteristics of "small size but complete functions".

Typical Application Scenarios of Small PLCs

Small PLCs are widely used in various fields of industrial automation due to their unique advantages. Different application scenarios have different demands on small PLCs, and small PLCs can always adapt well and play a great role.

Small stand-alone automation equipment is the most traditional application scenario of small PLCs. In equipment such as textile machinery, packaging machinery, food processing equipment, and small printing presses, the number of control points is not large, but it requires high reliability and a certain degree of motion control capability. Small PLCs can perfectly meet these needs. For example, in a fully automatic packaging machine, the small PLC needs to complete the control of the conveying belt, the positioning of the sealing mechanism, the counting of packaging materials, and the communication with the touch screen. All these functions can be easily handled by a small PLC with 32 I/O points, and the cost is much lower than using a medium-sized PLC.

Industrial system energy-saving transformation is another rapidly growing application scenario of small PLCs. Many old industrial systems have problems such as backward control mode and high energy consumption, and it is necessary to add automatic control to achieve energy saving. In these transformation projects, the original system structure does not need to be changed too much, and only a small PLC needs to be added to complete the automatic control transformation. The aforementioned Siemens 200PLC used in the transformation of the cooling circulating water system of the stamping workshop is a typical case. The original system required manual start and stop of the water pump, which could not adjust the operation of the water pump according to the actual temperature and operating status of the equipment, resulting in a lot of energy waste. After the transformation with a small PLC, the system realizes automatic start and stop linkage with the stamping equipment, automatic switching of water pumps on a rotation basis, and fault flow alarm. According to the actual operation data after the transformation, the transformation saves more than 30% of electricity consumption every year, and the economic benefit is very significant.

Distributed control system nodes are also an important application field of small PLCs. In large-scale production lines such as automobiles and steel, the modern control system usually divides the whole line into multiple independent units, and each unit is controlled by a small PLC, and then connected to the upper industrial computer or SCADA system through the industrial network. This distributed control method has higher reliability. Even if one unit has a problem, it will not affect the normal operation of other units, and it is also more convenient when expanding production capacity, only need to add new units without changing the original control system.

In addition, small PLCs are also widely used in industrial robot control, intelligent transformation of equipment, and industrial Internet of Things projects. In the control of small industrial robots such as welding robots and palletizing robots, the small PLC cooperates with the robot controller to complete precise logic control and signal interaction. In the industrial Internet of Things, the small PLC collects the on-site equipment data, and transmits it to the cloud platform through the IoT gateway to realize remote monitoring and predictive maintenance of the equipment. These applications all benefit from the communication networking capability of modern small PLCs.

Case Study: Siemens 200 PLC in Cooling Circulating Water System Transformation

To more intuitively understand the practical application effect of small PLC in industrial automation, we can analyze the transformation case of the cooling circulating water system of a stamping workshop mentioned on Siemens Industrial Support Center. This case fully reflects the practical value of small PLC in system transformation, and has strong reference significance.

Project Background and Problems

The stamping workshop of this enterprise has 3 large-scale stamping machines, which need to use the cooling circulating water system to cool down the equipment. The original cooling circulating water system consists of an outdoor water tank, 3 indoor water pumps, water pipes, and the original electrical control cabinet. The original operation mode is that the operator starts 3 water pumps manually at 8:30 in the morning and shuts them down manually at 17:30 in the afternoon. This extensive management mode has many problems: First, it causes serious electric energy waste. When only one stamping machine is in operation on a certain day, only one water pump is needed to meet the cooling demand, but the original mode usually starts two or more water pumps. In winter, operators often start the water pump early in the morning when the equipment does not need cooling, resulting in invalid energy consumption. If the operator forgets to turn off the water pump after work, the water pump will run all night, resulting in greater waste. Second, the long-term uneven operation of the water pump causes equipment damage. Since operators often only use one fixed water pump for a long time, the other two water pumps are out of service for a long time, resulting in aging and water leakage of the sealing ring of the idle water pump, increasing the maintenance cost of the equipment.

Transformation Scheme Based on Small PLC

In order to solve the above problems, the enterprise decided to use Siemens S7-200 small PLC to transform the control system. The core goal of the transformation is to realize the automatic linkage between the water pump system and the stamping equipment, reduce manual operation, reduce energy consumption, and prolong the service life of the water pump. The specific transformation scheme is as follows:

1. Add an independent small PLC control cabinet to control the contactor of the original water pump motor, and retain the original manual operation mode as a backup, realizing the switching between manual and automatic modes.
2. Realize automatic start-stop control: when any stamping machine is in working state and the return water temperature reaches 35℃, the PLC automatically starts the corresponding water pump; after all stamping machines stop working, the PLC delays for 5 minutes and automatically shuts down the water pump.
3. Realize automatic rotation of water pumps: the PLC records the running time of each water pump, and automatically switches to the next water pump after 30 days of running of a single water pump, so that the 3 water pumps rotate in turn, avoiding the aging of equipment caused by long-term idle or long-term overload of a single water pump.
4. Add fault alarm function: 30 seconds after the water pump starts, the PLC detects the water flow signal. If no normal water flow is detected, it will trigger an alarm to remind the operator to check for faults such as water pump blockage and water leakage.

Transformation Effect Benefit Analysis

After the completion of the transformation, the system has been running stably for more than two years, and the effect is very significant. First of all, the energy saving effect is remarkable. According to the statistics of the enterprise's electricity consumption, the annual electricity consumption of the cooling circulating water system has decreased by 32%, and the annual electricity cost saved is about 82,000 yuan, which is much higher than the total investment of the transformation of less than 15,000 yuan. Secondly, the labor intensity of operators is reduced. After the automatic control is realized, the operator does not need to pay attention to the start and stop of the water pump every day, and can put more energy into the core stamping production. Finally, the service life of the water pump is prolonged. Due to the scientific rotation operation, the wear and tear of each water pump is balanced, and the number of maintenance and replacement of the water pump sealing ring is reduced by more than 60% compared with that before the transformation, which further reduces the maintenance cost.

This case fully proves that the small PLC can bring significant economic benefits to the enterprise in the industrial automation transformation, with the characteristics of small investment and quick effect, which is worthy of promotion in similar transformation projects.

Mainstream Small PLC Product Lines in the Market

At present, many well-known automation brands at home and abroad have launched mature small PLC product lines, and different products have their own characteristics, which can meet the needs of different industrial automation scenarios.

Inovance Technology's H1U/H1S series small PLC is a representative product of domestic economical small PLC. The H1S series is positioned as a simple and economical model, with I/O points covering 14 to 60 points, which is especially suitable for small automation equipment that pursues cost performance. This series of products has large program capacity, supports 3-axis 100K high-speed pulse positioning, supports CANlink expansion of remote modules, and is equipped with two independent serial communication ports, which is convenient for system integration. It also provides complete encryption functions to protect the intellectual property rights of equipment developers, and is very popular in the domestic equipment manufacturing industry.

Siemens S7-200 SMART series is a classic small PLC product that has been widely recognized in the market. This product has a stable and reliable hardware design, a complete software programming environment, and a rich ecosystem. It is very popular in system transformation projects and small and medium-sized automation projects. It supports Ethernet communication, can be easily connected to the touch screen and upper computer, and has a wealth of function library instructions, which can quickly realize various complex control logics. Although the price is higher than that of domestic products, its stability and brand reliability are recognized by the market.

Wuxi Xinje Electric has a very rich product line of small PLC, with 6 major categories and more than 400 product models, which can easily cope with various control scenarios. Xinje's small PLC not only has basic logic control functions but also can match the company's own servo system, frequency converter and human-machine interface to form a complete automatic control solution. It also supports industrial Internet of Things related functions, and can connect to Xinje's industrial cloud platform through the IoT gateway to realize remote debugging and online monitoring, which is very suitable for the current demand of intelligent manufacturing.

Rectangular Technology's ELink wireless small PLC and N80 standard small PLC also have their own characteristics. Its wireless small PLC integrates wireless communication functions, which can solve the wiring problems in some special scenarios, and is very convenient to use. The N80 series standard small PLC is cost-effective, has rich instructions, and supports a variety of communication methods, and is widely used in small automation equipment and distributed control sites.

In addition, international brands such as Mitsubishi FX series and Omron CP series are also very popular small PLC products in the market, with the characteristics of high stability and rich expansion modules, and occupy a high share in the high-end small PLC market.

Future Development Trend of Small PLC in Industrial Automation

With the continuous development of industrial automation and the Internet of Things technology, small PLCs are also constantly evolving, and their future development trend mainly presents the following directions:

First, the degree of networking and intelligence will continue to improve. More and more small PLCs will integrate Ethernet, wireless communication, and even 5G communication functions, which can directly access the industrial Internet platform, realize remote collection of equipment data, remote debugging, and predictive maintenance. In the future, small PLCs will not only be a control terminal but also an important data node in the industrial Internet of Things system, providing data support for enterprises' production management and optimization.

Second, the integration will become higher and higher. Future small PLCs will be more closely integrated with HMI, motion control modules, and IoT modules to form an integrated control solution. For example, the integrated controller that integrates PLC and touch screen can further save installation space and reduce the cost of the whole machine, which is very suitable for small stand-alone equipment.

Third, the application field will continue to expand. With the increasing demand for intelligent transformation of traditional industries, small PLCs will be applied in more fields, such as intelligent agriculture, environmental protection equipment, intelligent building, and other non-manufacturing fields. These fields do not require a large number of I/O points, but have high requirements for cost and reliability, which is very suitable for the development of small PLCs.

Finally, the ease of use will continue to improve. With the development of programming technology, the programming of small PLCs will become simpler and more convenient. More visual programming methods and rich application instruction libraries will reduce the threshold of use, allowing more small and medium-sized enterprises to easily use small PLCs to achieve automation upgrades.

In general, small PLCs have become an indispensable core component in the field of industrial automation. With their unique advantages of small size, low cost, and powerful functions, they are widely used in various industrial scenarios, bringing huge economic benefits to enterprises' automation upgrades and system transformations. In the future, with the development of industrial Internet of Things and distributed control technology, small PLCs will have a broader development space and will play a more important role in the process of industrial automation.