Are PCs Ready for Control and HMI?

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Suggestions on How to Save Some Money and Gain Functionality by Combining Control and HMI into One PC-Based Platform

We currently use PLCs for control and a PC-based HMI for operator interface on our packaging machines. We would like to save some money and gain functionality by combining control and HMI into one PC-based platform. Last time we looked a few years back, we were concerned with the ruggedness and reliability of industrial PCs. Has anything changed for the better?

—from May ’08 Control Design

Answers

Time Changes Everything, Hardware Too

In the 1980s and 1990s, there were huge concerns over PC stability in general, and industrial computers at the time simply added cost to a generally unstable platform. There were problems with the hardware, the OS and the software. The hardware all required fans. The dust in industrial environments would clog the fan filters and reduce the cooling ability, or it would get into the systems, build up on components and cause heat and signal quality issues. Additionally, the rotating drive media available was not conducive to industrial environments due to heat and vibration found in those environments. The OS was either some proprietary code or it was Windows-based. The proprietary code usually would perform well but left the owners in a tough spot when they needed to upgrade or make changes. The Windows OS was very new and took several years to become stable.

EXTREMELY RUGGED Extremes of heat, moisture, vibration and shock require a PC and HMI durable enough for any environment. GLACIER COMPUTER

Now, we have very powerful systems using mobile-based, low-power, single-core and multi-core processors without the need for fans. These hardware systems remove the issues related to dust and heat buildup and usually can be put in case structures that keep all the dust out.  Solid-state drive media are now at a price point that makes it a viable replacement for rotating media and solves the heat and vibration issues seen in rotating media. The available and prominent Windows OS, as well as the industrial software products that run on it, have been around for 10-25 years. The quality has improved greatly over this time.

With this level of stability in the OS and environmental readiness in the hardware, quality industrial computer systems can be found.

David Gardner, product manager,
Wonderware

In the Heat of the PC

Product requirements for manufacturing computers differ widely based on industry and application. Using computers to do control and HMI tasks on one unit realizes significant cost savings.

Engineering costs can be reduced greatly since they often share the same database. Since both HMI and control are critical to an efficient manufacturing process, obvious care must be given to reliability. There have been significant advancements in recent years to increase the reliability of industrial PC systems.

The primary points of failure in a PC are the moving parts, basically the fan and the hard drive. Different mounting configurations and motherboard design changes help reduce these potential points of failure. Current industrial designs must have shock-absorbed hard drives.

Also check to see if there is a single fan or multiple fans to extend operating temperature from commercial grade PCs. Air flow is critical to disperse heat. The microprocessor should have special thermal designs to dissipate the heat generated by today’s high clock speeds. Extensive heat sinks have been developed to dissipate the heat.

To ensure corrective actions can be taken if problems develop, make sure the PC has built-in software capability for monitoring overheating.

All data and programs can run off compact flash and since the CPU requirements for the operating system are reduced, fans no longer are required. Keep in mind industrial-grade compact flash with 2M write cycles, will cost more than commercial, 100K-write-cycle, grade. Commercial grade shouldn’t be used for control or HMI.

Harold Muma, product marketing manager–HMI,
Siemens Energy & Automation

Cables and Connections

Another technological improvement is industrial displays that can withstand up to 50 °C. For rugged applications, these would be an ideal solution over a commercial display.

On the design side, machine builders should seek out industrial computers with the fewest number of cable connections to the computer, as well as cable connectors that lock in place. Gold plating on cables helps improve connectivity and stands up better to corrosion.

One advantage of industrial computers versus commercial PCs is component stability that benefits hardware longevity. Manufacturers that use commercial computers start with one product and one hardware platform. However, if they want to add another PC a few months later, chances are high that the hardware will be different. This means that they will have to make changes to the software image already loaded on the first product to make it work on the new product. Industrial computers are managed for longer periods, making maintenance much easier and significantly reducing development efforts.