Embedded control: Automation’s fastest growing segment

15 April 2009

This growing technology is bridging the gap between conventional modular programmable controllers on the one hand and PC-based control systems on the other. The boundaries are increasingly fluid, and the power density continues to increase.

The heart of embedded control is a specialised, rugged PC that is capable of being mounted directly on the machine. An example of this is Siemens’ Microbox, an ultra-compact box PC without fan or hard drive, realtime-capable controller software and its own visualisation system.

The latest advancement in this embedded control platform is the addition of real-time Simatic WinAC RTX PLC software and, optionally, the WinCC flexible visualisation system.

With the on-board software, the device can be operated entirely without visualisation—supported by several built-in diagnosis options (LED) directly on the housing—or with a remote control unit.

An extremely low-cost method utilises one (or more) of the new Thin Clients, which can be operated via Ethernet and the WinCC flexible/SmartAccess option at low engineering costs. And this at a distance of up to 100 m from the Microbox, with the switch located even farther away. This type of remote operation is useful, for example, when the application cannot be stopped, even when the operator panel is replaced.


The high computing power of the Microbox is based on Intel M processors that are more than twice as fast as their predecessors. The user has several options, up to the 1.4 GHz Pentium M processor with 1 GB RAM. The thermal power dissipation of the CPUs has been optimised for safe operation without fans, even under extended maximum load.

Instead of a conventional hard disk, a CompactFlash (CF) card serves as the storage medium. There are, therefore, no moving parts—one of the most frequent sources of errors of PC-based systems. This makes the Microbox virtually maintenance-free and suitable for continuous 24-hour operation at temperatures of up to 55° C.

Flash cards, now with capacities of up to 4 GB, offer spacious storage for the software, as well as for formulations, process, product and other customer-specific data. Siemens recommends the use of its own very high-quality industrial-grade CF card capable not only of unlimited startup but designed for a significantly higher number of write cycles—over two million, rather than the conventional 100,000—even at increased temperatures. A battery-backed NVRAM with a capacity of 128 KB meets the automation industry’s demand for a certain level of redundancy. In the NVRAM, important control data, configurable by the user, is secured against loss—with no need for an extra uninterruptible power supply.


The most visible difference between this model and its predecessors is four new multi-coloured LEDs, which signal crucial operating states without the need for a control unit. They include LEDs for Power and for Watchdog as well as for system fault and RUN/STOP for the controller software.

There are three PC104 expansion slots, enabling cost-saving integration of fieldbus connection modules or even input/output modules. Of the latter, the most important is the PC I/O central expansion card that provides up to 320 digital inputs and outputs in 24-volt technology, up to 48 analogue I/O or up to 12 incremental encoder inputs, depending on the model. Fault-tolerant subsystems can be integrated via the Simatic Distributed Safety option package.

The Microbox also comes equipped with the kind of extensive connectivity demanded by the industry: a serial port, 1 DVI -I interface (DVI and VGA combined), four USB ports, and two Ethernet connections. It also sports an integrated Profibus DP interface. Its compact dimensions of 262 x 134 x 47 mm (W x D x H, excluding expansion frame) are suitable for the most space-challenged industrial applications.

Siemens Simatic Microbox 4278
Siemens Simatic Microbox 4278


But what good is the most rugged hardware when the software isn’t also ready for the day-to-day harshness of the industrial environment? Siemens answers this question with the Windows XP Embedded (XPe) operating system. Lightened by unnecessary ballast such as games, fonts, etc., the ‘embedded‘ version requires only 250 to 400 MB RAM, instead of the 1 to 1.5 GB in the full version. This allows the CF card to be booted safely and quickly.

Unlike a dedicated operating system, a standardised system is well-suited to the use of low-cost standard software and custom-tailored special applications. This openness and the large storage capacity for process data are the strengths of PC-based systems.

If the system is to be used in the familiar arena of classical PLC—controlling time-critical, deterministic processes with precisely defined cycling times—a real-time expansion is a must. The Microbox with the real-time Simatic WinAC RTX meets the demand of a growing number of industrial applications for shorter cycling times. With the open real-time extension and the integrated Profibus interface, even distributed automation tasks on the clock-synchronous Profibus are feasible.


In the Microbox 427B HMI/RTX version, the Visualisation Software Simatic WinCC flexible is preinstalled on the CF card, giving this compact embedded solution the power to perform demanding visualisation tasks. The system contains all the functionalities necessary for comfortable operation and monitoring, as well as efficient machine and process control, including alarms and messages, archive and formulations, secure access protection, as well as up to 16 online languages for use worldwide.


In the midst of all this passion for innovation, one thing has never changed: the universal engineering environment of the Simatic Manager with Step 7. The same familiar tools used to program and configure Siemens’ conventional control units are also used with the Microbox. When you know these, you can begin the engineering immediately. Naturally, this includes seamless integration of WinCC flexible into Step 7—Totally Integrated Automation also applies to Simatic Embedded Automation.

The development objective now for the Simatic Embedded Automation is communication via the Profinet standard, the rising star in automation.

— Giuseppe Favata and Dipl.-Ing. Thomas Laudenberg, Siemens AG Industry Automation, Industrial Automation Systems, Nürnberg, Germany

See also Control Engineering Europe's article "Sleek and elegant: New touchscreens for embedded control" by CLICKING HERE

LEDs signal operating states without the need for a control unit
LEDs signal operating states without the need for a control unit

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PC-based solutions typically include technological tasks such as image processing, measured value acquisition and numerical controls.

The WinAC option Open Development Kit (ODK) allows flexible use of all PC resources from the control program via three different interfaces in order to provide high performance expansion of the PLC functionality.

All the operating system functions and system resources of Windows are available to the programmer for this purpose, also providing access to external hardware and software components.

An ODK application is developed with a standard development environment for C-/C++ programming, such as Microsoft Visual Developer's Studio. This provides the application developer with the familiar environment tailored to Windows applications. C++ programming knowledge is not required for integrating such applications into the WinAC control program. The ODK applications can be used like normal system functions in the STEP 7 program.

WinAC ODK offers three interfaces for the following applications:

1. Custom Code Extension Interface (CCX) for calling your own C/C++ programs from the WinAC control program

2. Shared Memory Extension Interface (SMX) for high-speed WinAC data exchange with Windows applications

3. Controller Management Interface (CMI)for integrating the WinAC Panel functionality into a Windows application

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