Simplifying real-time I/O integration with panel PCs
29 July 2011
The latest Windows-based industrial panel PCs address a common platform developer’s need – that is, to integrate real-time I/O for deterministic process control without incurring the technical challenges or development costs associated with building custom drivers. Ian Ritson reports.
Modern industrial automation and processing environments demand robust, application-specific systems that combine a variety of measurement, sensing and control capabilities with intuitive and easy-to-use interfaces. The capabilities required tend to be project specific, demanding customisation at many levels from basic I/O channels to the human-machine interface.
Historically, process automation systems have tended to be expensive and essentially one-off developments, designed to meet a specific set of requirements and demanding a significant commitment from both the equipment provider and the customer. In today’s economic climate, there is intense global competition to win manufacturing business and this is driving a reduction in development costs and turnaround time.
SCADA systems have traditionally been used in large systems and are capable of managing thousands or even tens of thousands of channels distributed over a wide area. And while there are now smaller and lower-cost implementations of these systems to satisfy the requirements of today’s agile, down-sized manufacturing facilities, choosing a suitable SCADA from the wide variety of systems on offer carries risks and can be confusing.
Under pressure to reduce costs and deliver results more quickly, developers are finding PC architectures and technologies to be a more attractive option.
Enter the panel PC
New generations of Windows-based panel PCs are enabling developers to build their own applications using Windows tools, and so avoid using SCADA altogether in smaller systems requiring up to several tens of channels. Significantly, with customers needing to modify the ‘look and feel’ of touch screen interfaces and front panels, some of these new panel PC options are offering significant opportunities for customisation, even in relatively small quantities.
With their PC architecture, Windows-based development and built-in industry-standard interfaces such as Ethernet, Gigabit Ethernet, mini-PCI, RS-232 and USB, panel PCs offer flexibility, wide connectivity, processing power, durability and reliability. But in order to realise panel PC based industrial process control, the developer must also overcome some specific I/O-integration challenges - particularly those relating to applications that demand a deterministic response.
One such challenge is to write suitable drivers that will enable the external I/O boards to be controlled from the application program. Commercially available I/O boards typically ship with drivers for standard desktop systems such as Windows XP or Windows 7. Windows CE, however, which offers real-time performance, is a far better choice for applications requiring a deterministic response.
Windows CE is a hard real-time operating system featuring support for many levels of thread priority for flexible scheduling, nested interrupts allowing immediate servicing of interrupts at high priority levels, the ability to adapt scheduling to match changing application demands, and the ability to speed up completion of low-priority threads to release resources quickly when needed. These in-built features of Windows CE, combined with the timing and tracking tools provided, enable developers to measure and control latencies accurately and manage resources to ensure that time-critical demands placed on the system are met.
Unfortunately, few off-the-shelf I/O modules come with Windows CE drivers, and so developers are faced with the prospect of building their own drivers or buying in proprietary software - either route adding to development time and costs. But there is an alternative approach.
‘Driverless’ I/O modules are available that free the developer from these software-development challenges. By implementing their own command sets, comprising standard ASCII character strings, they can be driven by any panel PC application capable of sending signals to a serial output port.
Modules such as these can be connected via an RS-232 port or USB port, thus integrating easily with a system based on an industrial panel PC. Together, the driverless modules and customisable Windows panel PC provide an economical data acquisition and control platform.
The simple interactions between the modules and the PC allow developers to re-use existing software, if available, to communicate with the modules. Alternatively, custom code can be created quickly and easily using accompanying software development kits.
An additional advantage of this approach is that industrial control can be scaled quickly and cost-effectively, since more I/O can be added simply by connecting extra modules end-to-end. The cost of adding any extra I/O is seen only in terms of the purchase price of the additional modules. These can serve a variety of device inputs, from digital units providing general-purpose I/O to function-specific connections, including tachometer, quadrature encoder and event counter inputs, as well as analogue inputs from thermocouples.
The modular Windows panel PC described in the panel opposite, with its modular open architecture supporting Windows CE and extensive HMI customisation, provides an ideal platform for control and data acquisition using driverless modules.
Not only does the PC present a rich selection of I/O ports, including serial interfaces for connection of driverless modules, but there is also the physical capacity to incorporate the modules directly into the chassis. So one or more driverless I/O modules can be incorporated neatly alongside customer-specified functions such as an optical hard drive or Wi-Fi module, creating a self-contained system. And with high-voltage input protection also provided, these modules can be connected directly to external circuitry without risking damage to the PC arising from events such as ESD strikes or power faults.
The open-architecture modular panel PC is liberating many smaller-scale industrial automation projects from expensive, bespoke software and hardware design that is the province of much larger systems. Developers are able to take advantage of the familiar PC environment and tools to customise their HMIs quickly and cost effectively, and to streamline application development.
Simplifying the integration of real-time I/O – arguably the final obstacle to wider adoption of panel PCs for low-cost industrial automation – is now within reach using a combination of simplified driverless I/O modules and the flexible real-time panel PC.
Ian Ritson is managing director, Hoffmann + Krippner UK
An open, industrial panel PC architecture
Windows-based industrial panel PCs such as Hoffmann + Krippner’s flex-IPC family illustrates the trend for open, industrial panel PC architectures that can provide high levels of flexibility in terms of configuration and customisation. Featuring membrane keypads, resistive touch screen technologies and HMI customisation capability, these panel PCs can be sealed to IP65/NEMA 4X for field use.
The units feature 49 function keys and an integral alphanumeric keypad, combining a 10.4in resistive touch screen with extensive I/O connectivity and a variety of processor and memory configurations. System integrators can specify turnkey front panel designs to meet customer-, application- or environment-specific requirements. Options include the addition of company branding and logos, the specification of colour schemes and the labelling of individual keys.
The Flex-IPC M modular open-architecture panel PCs can be specified with Windows CE version 6.0, for a deterministic performance, and have their own software development kit, which provides a suitable environment for building embedded applications.
A choice of processor specification and RAM and Flash densities include the 500MHz AMD Geode LX combined with 512Mbyte RAM and 1Gbyte HDD/Flash, and the 1.6GHz Intel Atom plus 1Gbyte RAM and 1Gbyte HDD/Flash.
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