Presentation is everything with operator panels

Field Editor Kevin Russelburg reports on the tough decisions we face when choosing an industrial PC or an operator panel for a particular machine control application in this edition of Specmate.

By Kevin Russelburg, Field Editor

THE DECISION to choose an industrial PC or an operator panel for a particular machine control application is more complex today. Lower-end to mid-range displays often are selected because the control system designer needs a smaller display due to machine size.

"Traditional panels have increased speed as well as memory," says Jay Coughlin, manager HMI products, Siemens Energy & Automation. "They usually include built-in communications for networks such as Ethernet.

“Industrial PCs also have increased memory capacity and processing speed in smaller footprints. The decision usually is based on the capability of the software applications that will run on the device, as well as the amount of information that will be required. Some of the newer panels provide capabilities once reserved for Industrial PCs, but as a general rule, the more data and software intensive the application, the more the Industrial PC is a better fit.”

Text-only displays are well-suited for simple, repetitive machine operations. "Instead of blinking lights or alarm sounds, the machine will have a text display indicating a problem," says Haroon Rashid, HMI product manager, Schneider Electric. "For example, a machine might have push buttons that do repetitive jobs such as, start, stop, jog, etc., but all that hardware and wiring can be replaced with a text-based terminal display. This provides space and cost savings.” Previous system designs had to connect to a PLC or hard or programmable relays, but now those outputs can come directly from the HMI.

"If a user needs to run numerous operations within that process, a higher-end system can offer a single interface that simplifies the whole process."

When machine builders require more capability, the displays offer larger graphics, which typically means moving up in complexity and price. These products can communicate with multiple PLCs or drives, and have more elaborate programs. They also offer multiple communication protocols. "They can accept additional instructions when the application becomes more complex, and offer more interface features like buttons, keypads, or additional function keys rather than display-only," adds Rashid.

Industrial machine builders often choose an electronic display instead of pushbuttons because they want the flexibility to change or add new functions. Touchscreen functionality provides graphically rendered functions that the operator can manipulate. With graphical displays, machine builders simply can add another graphical component or page of interactive information.

One advantage of a graphical display is that its machine might need other capabilities in the future. A more sophisticated display gives the system flexibility and options. "When applications change and the display needs to provide new functions, the machine builder might choose to simply add a new screen," says Rashid. “The builder doesn’t have to add additional boxes or counter displays to add more buttons or switches. Many machine OEMs want this type of flexibility. They want the ability to add options at the lowest possible cost.”

More complex graphical displays are especially suitable when even more features are required. If a user needs to run numerous operations within that process, a higher-end system can offer a single interface that simplifies the whole process.

"These displays also can be used for logging and storing data for future reference,” says Coughlin. “Customers who want to monitor what failures occurred and log that data to review later to improve their process will specify this type of functionality." Features can include the ability to manipulate the application with a script and have multiple alarm locks.

“All these tasks are added to more complex applications, and the high-end displays have the ability to handle these tasks,” adds Coughlin. “These complex displays are not necessarily common in any particular industry, but are more dependent on the complexity of the application.”

Similar to other fields, the machine building industry has moved to open-architecture and open-standards-based hardware and software. Many display manufacturers started with proprietary solutions, but, as needs change, there have arisen increasing numbers of interchangeable HMI terminals and displays from various vendors. This trend also includes digital communication standards-based open protocols. "There now are HMIs that have built-in web servers, so they can act as browser-enabled devices, and have built-in ftp servers,” adds Rashid. “This offers the customers cost savings and great flexibility. For example, if the system is connected to an http server, a user can connect remotely to the HMI. They don’t have to go to the factory floor where that machine has the HMI installed.”