Embedded controllers: defined, differentiated and applied

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Embedded controllers: defined, differentiated and applied

Embedded controllers have emerged as the next generation of controllers for discrete and batch processes. These controllers derive the best characteristics of a long line of technology advances from PLCs and PC-based control systems. Sometimes referred to as programmable application controllers, they combine the power of a PC-based controller with the reliability and ease of maintenance of a traditional proprietary PLC to integrate control functions and provide scalability.

Embedded control schemes are not new to the industry, but previously this type of controller was usually a custom-designed single board computer or VME system with various operating systems. In addition, all of the functionality was developed in 'custom code,’ such as the C programming language or Visual Basic, and the earlier generations were developed in-house by either a systems integrator, machine builder or OEM.

These early embedded controllers were tightly 'closed’ systems that could be programmed, modified and maintained only by the equipment supplier. They were especially prevalent in high-speed applications such as semiconductor machines and high-speed sorting equipment, but they were widely rejected by most industries in favor of systems that could be maintained and modified by plant personnel.

The emerging generation of embedded control is being developed by traditional global control systems manufacturers and typically embed (but do not expose) Microsoft Operating Systems and more accepted control languages such as flow charts or relay ladder logic. Some of the main differences are that like PLCs, the operating system is hidden to the user and the systems are much more scalable than before. Most also include a tightly integrated graphical HMI, which can also be maintained and modified by the end user (Fig. 1).

With the accelerated acceptance of Ethernet communications for control, such as EtherNet/IP, ProfiNet and Modbus TCP, the new generation of embedded controllers does not require additional hardware other than the basic system for interfacing to plant floor devices or plant communications. Almost every offering of the newest controllers is designed for high reliability and low maintenance with diskless storage and fanless cooling requirements. This provides PC-based power in a PLC form factor (Table 1).

While the definition of the new generation of controllers certainly highlights many of the differentiators, there are several other reasons to choose embedded controllers instead of – or in addition to – the more traditional PC-based systems or PLCs.

These machines combine PC technology, communications and reliable hard real time operating systems to bring increased power, easier implementation and larger capacity for handling manufacturing data requirements, while providing the security and reliability of a PLC. The embedded controller’s advanced instructions are well suited for retrieving data from the process, manipulating the data with advanced mathematic and String Parsing commands and directly providing the data to various database formats (Access, SQL, Excel) to the plant network and systems via Ethernet. This is a significant advantage now that process and manufacturing data are requirement in most applications.

The demand by many companies for FDA approvals, web-based order tracking, part validation and assembly 'birth certificates’ to satisfy end user and government demands has elevated process data to the same level as quality of control. Embedded controllers also allow tight integration of required functions on the system such as I/O interface, logic control, HMI and based on various vendor implementations, specialized functions such as motion control (Fig. 2).

While capitalizing on the ease of installation, reliability and form factor of the traditional proprietary PLC system, the embedded controller still offers significant differences and advantages over these solutions. For example, the new generation of embedded controllers offers measurably more application, program and data storage capacity. At the same time, most offer superior performance for higher complexity applications combining logic, control, HMI and communications, while performing these critical functions on a single hardware platform.

The single and scalable embedded controller hardware approach not only facilitates the tight integration of all data associated with the applications, but reduces costs by 40% to 50% compared to a PLC-plus-HMI approach, and 30% to 40% over industrial PC systems.

Another significant difference between the PLC and an embedded controller is communication flexibility. While most PLC systems are limited to the I/O systems and protocols from the PLC manufacturer, the new generation of embedded controllers usually support the more 'open’ approach inherited from the larger IPC systems. Embedded controllers have also adopted a more configurable approach to device and plant connections to support the ease-of-use requirement. The open communications capability of the embedded control technology is popular for retrofits of existing equipment where preserving the investment of the installed devices is critical. The industries that have used this advantage include textiles, automotive and electronic assembly equipment.

Almost every industry has applications that benefit from this control technology. Certain applications have adopted this approach very early and with measurable success. Many forms of material handling – from letter sorting to distribution systems to transporting automobile sub-assemblies on production lines (engines, transmissions, axles, mirrors, etc) – require speed and accurate data tracking. As described, the embedded controller performs these tasks better than many solutions.

Applications requiring very high speed, such as semiconductor equipment, spinning or winding equipment or very precise machining are also typical users of the system. Embedded controllers also are deployed in the water industry (water/waste water) for the ease and distance of multiple communications for control, peer-to-peer communications and plant data collection.

Embedded controllers combine improved data manipulation capacity, database and open I/O communications, 'PLC-reliable’ real-time control and HMI functions into a single cost effective platform.