Supervisory control and data acquisition (SCADA) systems are getting a lot of attention these days, primarily on the topics of security, integration with business applications and easy interoperability with large numbers of devices. What gets less attention is the front end of these systems -- the part that real, live operators interact with -- also known as the human-machine interface (HMI). And yet no matter how many devices feed into the SCADA system or how efficiently you route the production and process data they collect, the system is relatively worthless if it doesn't take care of the basics: effectively alerting operators when something goes wrong and enabling them to fix it quickly. Consider that a disruption or malfunction in the refineries, factories and utilities that SCADA systems monitor can be expensive, if not harmful or deadly. "It can end up costing both dollars and lives," says Chris Stearns, product manager at Honeywell International Inc., which makes SCADA systems. Stearns compares it to not being able to quickly find the brakes on a car. "You can't be flipping through graphics trying to figure out how to turn something off," he explains. But until recently, well-designed interfaces have been more afterthought than top-of-mind. "Particularly in larger product engineering companies, it hasn't been taken very seriously," admits Richard Haycock, director at Hexatec, a SCADA vendor in the UK. That may be changing, as groups such as the Instrument Society of America and the Honeywell-led Abnormal Situation Management Consortium (ASM) work on standards and guidelines for HMI. "The first thing you have to think of is human and environmental safety," says Peter Baker, product manager at EPG Companies, Inc. in Maple Grove, MN, which designs and manufactures pollution control systems. "It has to be clear to the operator what action to take when the alarm goes off." Here are some further issues to consider when designing a solid HMI for your SCADA system. (Click here for additional online resources.) Steering Clear of "Flashy"

Today's SCADA HMIs come with lots of bells and whistles, including three-dimensional and animated graphics. But as appealing as these might look, experts say to leave the flashy graphics off the screens designed for operator use. "If you build a 3-D representation of a process, with mixers rotating and tanks filling, and then there's this one little process variable flashing red, the operator may never see it because there's so much noise on the display," Stearns says. The same goes for creating realistic-looking displays, Haycock says. "There's too much detail, and it's difficult to get the scale and projections right," he says."It's very nice to have a picture of a valve, but what's important is whether the valve is open or closed." De-clutter your Displays It's important to maximize the amount of information you can access from the HMI without cluttering the display and confusing the operator, says Tom Muth, director of product and solutions marketing at Wonderware, a Lake Forest, Calif.-based business unit of Invensys Systems, Inc. that makes SCADA/HMI systems. You can do this by tiering the display so that operators can drill down for further detail as they need it. The important thing is to follow conventions that allow for a natural navigation through the screen hierarchy. For instance, instead of relying on screen menus, operators should be able to click on or touch different parts of the graphical representation of the plant to see further details, Haycock says. "You shouldn't need a heavy reliance on the written word," he points out. Another example is using the lower right-hand part of the page for a "next step" button, as well as a back-track capability to the previous display, he continues. Screens should also include a way to return to the top-level display, the equivalent of a home page. Wonderware employs mouse-over tools to supply further detail on particular elements of the plant. So instead of clicking to another screen, operators can just roll over a graphic image of, say, a pump to see further details such as flow rate and key performance indicators. "The data is compactly pulled together in a face plate where operators can quickly see how the system is running and assess whether it's running at peak performance," Muth maintains. Think "Readability"

When designing a SCADA HMI, you need to picture what Stearns calls operators' "standard operating posture" -- feet up, leaning back in a chair behind a console. So even if the system is designed by a 20-year-old systems engineer sitting two feet in front of the computer screen, "it has to be usable by a 50-year-old operator who left his glasses at home and is eight feet away from the screen and is maybe walking around with 10 screens to look at," Haycock says. Simple measures like using a non-serif font in 16-point type go a long way toward improving readability, Haycock notes. You also need to understand color contrasts to know how to make text stand out, especially at a distance. "Equally confusing can be how you represent data -- people will put on decimal points because 'they can,'" he adds. "But why represent temperature as 346.93 degrees?" Careful with Color

The color red is often used for alarms and is generally understood in that context, but color is not the best way to convey plant status on an HMI, Haycock says. For instance, red and green might mean "stopped process" and "running process" to some people but "danger" and "safe" to others. "I've even seen control rooms adjacent to each other where both interpretations are used," he says. In addition, he points out, one out of seven men has some degree of color blindness and may not even be able to distinguish between colors correctly. To indicate status, then, use words such as "running" or "full" or have the pipe or valve change shape. Limit Alarms

According to the ASM, excessive alarms are a problem on HMIs, since they can confuse operators or cause them to miss vital information. Creating a comprehensive alarm management strategy requires operators to work closely with designers to set thresholds. "If not, alarms are set to limits given by the project engineer and aren't given enough rationalized thought," Stearns says. Honeywell uses the ASM's definition of an alarm: If there's no action to take, there's no alarm. Honeywell is also deploying early detection systems that send out alerts hours before a potentially abnormal situation would even occur. Haycock suggests using different sounds to indicate the urgency of the alarm. A high-frequency noise at a high repeat rate will attract people's attention immediately, he says, whereas if you want to convey something less urgent, use a lower frequency sound at a slower repeat rate. "If you get that wrong and cause annoyance, operators will just disable it," he says. And remember that the screen isn't the only interface an operator works with. Many SCADA systems provide remote alarming, which sends signals to phones or other handheld devices. Wonderware enables operators to press phone keys to take actions in response to an alarm. Easy Interfacing

Operators often need to link to historical trend data, diagnostic utilities or step-by-step instructions that are stored in databases or applications within the underlying SCADA system. This kind of data needs to be easily accessible. In the latest release of Honeywell's SCADA system, for instance, operators can review historical trend data such as pressure, temperature or flow, correlated with event data describing actions taken by operators. "So if an alarm for high temperature comes in, they can view the trend data as well as the event data to get a better picture of what may be happening," Stearns says. The event data can be represented by symbols to keep the display uncluttered, with markers to show how it correlates to the historical data. "It gives operators a nice way to visualize both the discrete information and the process information in one window," he suggests. Wonderware provides diagnostic tools that are easily accessible from the operator screen to enable operators to perform root cause analysis. "You don't want to burden the operator with unnecessary information, but he has to be able to drill down to it in an efficient manner," Muth says. Honeywell also plans to add instructional information to its HMI to capture knowledge on how to respond to rare scenarios. "In refineries, there are events that happen once every five years, and you may not have an operator who knows how to recognize and deal with those events," Stearns contends. This can also help companies approach the challenge of training new operators who replace highly experienced staff, who, according to the ACM consortium, are leaving in significant numbers. Prepare for Change

For the HMI to provide a realistic model of the plant and production lines, it has to easily accommodate changes made to these entities, Muth emphasizes. "It's a lot easier to manage something that physically matches what the application represents," he says. "That makes the maintainability of the application an important criterion." The underlying architecture of Wonderware's SCADA application uses an object component model, which Muth says makes it flexible and capable of adding nodes without re-architecting the system. No matter how you design your SCADA HMI, it's important for the customer to specify site design standards, Haycock says, which many companies today don't do. "All too often, it's left to the vendor," he says. "The designer should sit in a room with the operators to understand what these guys do and ask, 'What do they need to know?'"