[Introduction] The complexity and performance requirements of the application determine the specifications of the controller. In addition to comprehensively considering hardware performance, users should also include the controller programming software in the evaluation process.
Compared to the original purpose of programmable logic controllers (PLCs) , automation controllers now encompass far more than simply replacing relays. They can integrate logic, motion, robotics, and communication with other machines and management systems. Performance ranges from simple devices to multi-core processors.
The traditional distinction between PLCs, Programmable Automation Controllers (PACs), and Industrial Control Computers (IPCs) primarily relates to processing power and performance; however, the lines between them are becoming increasingly blurred. Control software has achieved a degree of standardization due to adherence to the International Electrotechnical Commission (IEC) 61131-3 programming standard. Powerful real-time operating systems running in the background avoid reliance on Microsoft Windows-based systems. Therefore, the term "IPC-based control" might be more accurately described as "Intel- or AMD-based," reflecting the powerful mainstream processors used.
Since modern automation controllers can do much more than just logic processing, PLC may be an obsolete term. Because all automation controllers are programmable, the "P" in PAC also seems redundant. A controller is essentially a computer that can run multiple operating systems (real-time, Microsoft Windows, and Linux) on the same processor. IPCs can be used for control, data acquisition, and emerging tasks such as edge computing.
Traditional PLCI/O communication response time depends on network performance, number of nodes, traffic volume, CPU performance, and CPU load. Adopting a more rigorous integration and open IEC 61131 technology design, with centralized software management and distributed program execution, can improve performance. Image source: B&R.
Considerations for controller functionality
Coordinating the functions of all machines—running on the same processor within the same software environment and with the same program—is becoming a popular trend. This requires synchronized machine functions and a modular code structure, enabling an organized and cohesive approach. However, some domains do not require as much integrated control; for example, simple applications lack expansion plans. The complexity and performance requirements of the application determine the controller specifications. Many factors need to be considered when selecting a controller, and depending on the application, you may need to consider the following points.
logic
The fundamental requirement for logic control is why we continue to refer to automation controllers as PLCs. PLCopen is an organization responsible for maintaining and expanding the scope of the IEC 61131-3 programming standard and managing a vast amount of knowledge, training, and libraries. The organization's activities extend far beyond logic control, encompassing motion, safety, the OPC Unified Architecture (UA), XML, and more.
Multi-axis motion
Depending on the complexity of the application and the requirements for motion synchronization, automation controllers can control dozens or even hundreds of motion axes. With the development of Moore's Law and industry standards, independent motion or robot controllers with dedicated motion networks are no longer necessary.
Cybersecurity
In North America, hard-wired network security remains the preferred choice. The fact that network security infrastructure and control equipment operate on the same network has proven to be an effective control method.
Cybersecurity can be implemented from redundant cores on the control processor, to individual security controllers, and to secure input/output (I/O) in small systems. Cybersecurity also extends to motion safety and robotics functions, allowing machines to operate in a safe mode instead of shutting down entirely, thus providing superior operational efficiency.
Robot Integration
A single automation controller can integrate multiple Delta robots, SCARA robots, articulated and gantry robots, as well as other machine functions. Furthermore, it can perform motion functions in an IEC 61131-3 compliant environment. Thanks to its built-in stacking algorithm to assembly mode, dedicated robot controllers can continuously provide valuable functionality.
The B&R X20 system provides remote I/O, control, and easy network configuration and flexibility for every application.
Machine monitoring
Monitoring machine operation is a key part of predicting maintenance plans and reducing unplanned downtime. Controllers can be integrated with various existing sensors, such as temperature probes and accelerometers, to monitor actual conditions. Machine monitoring also helps detect anomalies before catastrophic failures occur. Energy monitoring can also be applied to compressed air usage, natural gas usage in heaters and dryers, and water usage in process flows, among other things.
Data processing
Automation controllers can be networks, OPCUA servers, and clients. They are capable of collecting Industrial Internet of Things (IIoT) data and can receive instructions from the cloud or endpoints to optimize processes. Automation controllers typically send data to Manufacturing Execution Systems (MES), Enterprise Resource Planning (ERP), Overall Equipment Effectiveness (OEE), Trusted Platform Modules (TPM), and Product Lifecycle Management (PLM) software. In an IIoT environment, receiving useful analytical data is also crucial.
Automatic configuration
Previously, replacing new components (such as drivers) required manually determining and loading the correct firmware version for the device. Now, automation controllers can automatically read the device and alert technicians to make necessary adjustments without human intervention.
communication capability
Today, even low-cost controllers have one or more Ethernet communication ports to communicate with HMIs, management systems, programming, and other non-time-critical tasks. It's common for controllers to support specific types of industrial Ethernet protocols, such as EtherNet/IP, EtherCAT, Powerlink, and Profinet, to build deterministic networks. Unfortunately, there is currently no universally accepted industrial Ethernet standard that provides high-speed, deterministic communication suitable for machine control.
However, the development of Time-Sensitive Networking (TSN) has brought great expectations. Together with OPCUA and OPCUA publish-subscribe (Pub-Sub), TSN will bring more certainty to the IEEE 802 series Ethernet standards. The Industrial Internet Consortium has built a testbed for it, with several industrial automation suppliers participating to demonstrate the feasibility of TSN in machine-to-machine communication.
TSN is important, primarily because for IIoT to function, interoperability between different control platforms is required across factories, enterprises, and the cloud. If a serial interface is needed, it should be specifically defined, as serial communication is currently less commonly used.
Installation method
The following are the three most common installation methods for automation controllers.
1. IP20, rack mounting: This is a common installation method for traditional PLCs. It has a separate HMI and usually uses integrated, backplane/rail mounted I/O, or remotely mounted I/O modules.
2. IP65/67/69K sealed, base or front panel mounting: This type integrates the HMI and controller and adopts a rocker arm type mounting, which can give full play to the ergonomic advantages of the device, and is therefore becoming increasingly popular.
In addition to control, this form factor can also integrate PC functionality to run various Microsoft Windows applications, such as HMIs, although the trend towards web-based HMIs is becoming increasingly apparent. Compared to similar controllers, base-mounted controllers tend to be more expensive than panel-mounted ones, requiring stainless steel baffles and higher sealing requirements.
Some people prefer to mount the PLC and HMI separately on the panel to avoid having to replace both components if one fails. However, this is no longer necessary, as integrated devices with freely detachable HMIs are now available. This makes replacing the screen with a larger one easier, or upgrading to more powerful control hardware without needing to replace the screen.
3. IP20, rack-mount industrial PC with a standalone HMI: Similar to the integrated form, this configuration can also function as a controller with a real-time operating system, various computer operating systems, and network services. The controller can be standalone, and the industrial computer can be dedicated to non-control tasks such as edge computing, fog computing, or cloud computing. Historical databases, serialization, and visual inspection are also common applications.
Advanced automation suppliers can offer users a range of PLC products to meet diverse needs, from micro PLCs with fixed I/O configurations to mid-range PLCs and modular PLC systems capable of handling thousands of I/Os. Image source: AutomationDirect
Scalability
While software development environments are typically hardware-dependent (ultra-small, micro, medium, and large PLCs), it's also possible to work in hardware-independent development environments. This means programming the project first, and then selecting or changing the control hardware. This flexibility extends to motor and drive types. Low-end stepper motors or frequency converters can share the same programs as high-end servos. Scalability is especially critical when a range of devices is designed to allow for the reuse of key software elements.
CPU performance
There are various types of processors available, ranging from low-end to multi-core, but their performance can overlap. Therefore, it is recommended to work with the technical support and sales engineering teams of your technology provider to select the best cost-performance solution for your expected application needs, as they have a better understanding of their products.
Ideally, the processor should be scalable so that the control software is compatible with all products in the controller product line. Automation technology suppliers maintain sufficient inventory of key components to ensure product availability and provide migration services for alternatives.
In addition, it's necessary to determine whether silent operation is required and the expected ambient temperature for installing the controller. Other cooling options include fans, air conditioning, radiators, and water cooling.
Memory
Solid-state memory (SSD) is already very popular in automation controllers, removable media (such as C-Fast cards), and applications where cost is more critical for permanent installations. The advantages of removable memory include easy replacement, ease of creating and storing backups, and easy expansion of memory capacity.
However, caution is needed when using industrial memory cards, and it's crucial to ensure the media meets the application's specifications. Different storage types have different lifespans, depending on the read/write cycle. This is also a topic that needs to be discussed with the automation supplier.
Differences between different types of controllers
Choosing a controller for factory automation involves more than just whether to use a PLC, PAC, or IPC; it also requires defining the application requirements, including basic control needs and future scalability. The selection of a programmable software platform, in particular, is just as important as choosing the right hardware and should play a crucial role in the decision-making process.
Whether for machine or process control, typical controller families include PLCs, PACs, and IPCs. Although there are many differences between different controllers, their features and functions are constantly converging.
Considerations for Controller Selection
Key considerations when selecting a controller include:
Automation experience of factory personnel;
The number and type of I/O;
The required control functions, such as closed-loop proportional, integral, derivative (PID), motion, and speed;
Communication options;
Data collection requirements;
Special functional requirements.
Easy to program;
Preferences and comfort zones;
Time and cost investment;
Available training resources;
Data logging and remote access.
