Plan Ahead to Build the Perfect HMI System

Does this still sound familiar? A machine, packaging line, or other process is defined and mechanical designers charge ahead. When mechanical design is almost complete, I/O points are counted. The control engineer figures out what model PLC will handle the load and begins writing ladder logic. Now the project is running behind and someone says, "We need to throw a display in there for ope...

By Gary A. Mintchel, Control Engineering November 1, 2001


Human-machine interface

Industrial computers

Operator interface

Supervisory control and data acquisition (SCADA)

Sidebars: More Tips for HMI Success

Does this still sound familiar? A machine, packaging line, or other process is defined and mechanical designers charge ahead. When mechanical design is almost complete, I/O points are counted. The control engineer figures out what model PLC will handle the load and begins writing ladder logic. Now the project is running behind and someone says, ‘We need to throw a display in there for operator interface.’

One hopes that this scenario only dredges up painful past experiences. More and more OEMs and end-user engineers are taking a more comprehensive view of machine and manufacturing line design. Cross-functional teams including members from product design, manufacturing, quality, service, and even information technology are involved. Often entire production lines are modeled from data derived from product modeling. (See Control Engineering , April 2001, p. 61.)

There will be tremendous dividends if this same degree of comprehensive, up front thought is given to designing human-machine interfaces (HMIs). You can’t just throw a few red pilot lights on the front of a panel anymore.

It is important to consider the complete system when designing HMI,including hardware and software requirements and all facets of communications.

HMI is a system

Today’s HMI systems comprise the areas of operator interface, supervisory control and data acquisition (SCADA), alarming, and serving information to enterprise planning systems. The system must not only gather data from I/O points , and display machine status information to operators, it must also function as an information server for many enterprise-wide systems including manufacturing execution systems, customer and supplier order systems, and maintenance.

These powerful tools have grown so sophisticated that systems can call maintenance on a cell phone and show an alarm on the display. When the maintenance technician arrives at the scene of the situation, drawings and troubleshooting tips in pdf format can be displayed to expedite repairs. This new sophistication requires forethought and planning ahead.

Engineers must consider the type of I/O subsystems and controllers used in the automation system. Can information be polled directly from intelligent, distributed I/O modules? Perhaps web pages can be stored at that level and displayed via browser with information transported via XML. Perhaps a proprietary network is faster and can be used because the entire plant is standardized on a control supplier. Or, perhaps several controller and I/O subsystems must be integrated, so standard technologies like Ethernet TCP/IP and OPC must be employed.

Choosing hardware is not a snap decision anymore, either. Many different types of displays and computers are offered to satisfy needs from computing power to environmental protection. Think about information and interactivity needs before designing. How much information do operators need for efficient process operation? What format is best? Will the operator need to interact with the information? Will a keyboard and mouse be sufficient, or does the environment require a NEMA 4 touchscreen?

If the operator, technician, or engineer needs local computing power, then specify an appropriate industrial computer. A lower cost ‘white box’ computer may be appropriate for applications where the environment is clean or where the PC can be located in an enclosure. Industrial computers with NEMA-rated bezels, designed for mounting on enclosure doors or in special computer enclosures, are a must for typical manufacturing environments.

Use of programming “objects” gives considerable power to HMI softwaredevelopment. Here, USDATA uses Application Objects to define a class,applying parameters from applications like Excel spreadsheets or databases.

Thin clients work

Perhaps the application requires many displays located at critical points along a large installation. A less powerful PC running a web browser is one choice. Another is to choose a thin-client computing solution. In this architecture, a powerful server PC with thin-client enabling software, for instance, Microsoft Windows NT or 2000 Terminal Services. Distributed hardware in this case need only be a display with keyboard and mouse. Advantages of either of these thin-client architectures include lower-cost hardware and having a single repository for the application program, so that updates and backups are easily controlled.

Many operator interface terminals are available, ranging from simpler alphanumeric displays to flat-panel and CRT graphics displays. Some have proprietary networking designed to work with PLCs of the same manufacturer. On the other hand, many now have open networking, such as serial (RS-232, -422, or -485) or Ethernet, which allow designers to choose the best display independently from the PLC and I/O device decision.

This leads to a discussion of connectivity. HMI today serves as a method of two-way communication of operator and technician with machinery or processes. Reaching beyond interface, HMI also serves as a portal of information much needed by enterprise software applications.

The first connectivity that must be considered is physical. This derives from the type of architecture desired. Wiring is different for thin clients than serial or Ethernet. If the architecture calls for distributed client/server computing using Ethernet, then make sure cables, connectors, and physical connections are ‘Cat 5’ (category 5 wiring for 100 Mbps networking). Several manufacturers are coming out with industrializedconnectors to minimize potential problems of typical plastic connectors in an industrial setting.

Ethernet actually refers to the physical media and, often, to the first level of firmware. There are several ‘protocols’ in the firmware stack that enable communications. TCP and UDP/IP are the common carrier protocols. On top are information packet protocols. Sender and receiver must be using the same protocol. If more than one protocol is needed-say because the server must communicate with I/O devices with one protocol and enterprise systems with another-don’t despair. One of the beauties of Ethernet is that multiple protocols can run on one wire. Firmware at the specified address seeks the protocol it likes, and then downloads the data.

Communication choices

Communication with I/O devices can be proprietary, via a device or field network, or Ethernet, Modbus over TCP/IP; or CIP, a protocol promoted by Open DeviceNet Vendors Association and ControlNet International.

HMI designers must work with their Information Technology (IT) departments to ensure manufacturing contributes to overall company goals. Many companies have installed various types of supply-chain management software. These involve automating purchase orders to vendors or production scheduling and customer service generated by customer purchase orders.

It is essential to know what the corporate database needs. SQL server may be required, or perhaps ODBC (open data base connectivity). Many manufacturing databases contain OPC drivers. OPC has become a standard for industrial information passing, and its new DX specification is designed to make OPC easier to use with Ethernet and with other open networks like DeviceNet and Profibus.

There are many elements to building a successful HMI system. Careful planning up front will ensure all elements work together. Lost time due to incompatibility of parts will be eliminated. Correct and complete information will flow to those people and applications where required. Automation’s contribution to corporate bottom line will be enhanced.

What happens when something doesn’t fit, or the correct configuration just doesn’t seem to appear on the menu? Who does the local sales engineer call to get a specific application question answer? The person at the other end of the telephone usually has a title like product manager or product marketing manager. These are technical people who are factory trained by the product design team and bring years of application experience. These people, often through bitter experience, have gathered many clues to a well-defined system and about potential pitfalls. The panel of experts below offer a wealth of tips to keep HMI designers out of trouble.

Identify actual needs

Kris Davis, Mitsubishi Electric’s (Vernon Hills, Ill.) product marketing manager, says, ‘One of the first things a designer should do is identify actual needs, that is, do I need a full HMI package for this application or can a simple operator-interface terminal do the job? Also, drivers are a potential problem. Be sure the package you buy has all the proper drivers. Be leery of vendors who say they’ll develop a special driver just for you since that may lead to project delays.’

Kevin Tock, Wonderware’s (Irvine, Calif.) vp, states, ‘People now have options. Take a look at Terminal Services Edition from Microsoft. With it, there may be no need to reinvest in the base software when expanding a system. This will lower the total cost of ownership. Another important consideration is how much it costs to do the integration. A shrink-wrapped package may be more adaptable to upgrades than custom written code in Visual Basic.’

Advantech Automation’s (Cincinnati, O.) product manager, George Liao, suggests evaluating the application before determining the PC operating system for HMI. ‘If the HMI is just used as a PLC terminal or performing simple control, Microsoft Windows CE/embedded NT should be fine. Otherwise, Windows 98/NT could be the alternative. Also consider cost versus required viewing space when choosing a display. The bigger LCD provides better viewing quality and larger viewing area, but the cost is relatively higher.’

Mitch Vaughn, chief technology officer of USDATA (Richardson, Tex.), offers, ‘HMI/SCADA systems often require importation of massive quantities of configuration data. These data may be PLC address lists, PLC program, or pre-existing configuration data already in electronic format. Usually this information is in an Excel spreadsheet. If this is the case, use an HMI package that can import from Excel to cut project time and avoid potential transcription errors.’

‘Design your database up front,’ says Daryl Walther, Rockwell Software’s (Mayfield Heights, O.) product marketing manager. ‘Structuring and organizing data in both the controller and HMI allows more effective data transfer. Also, base displays on a saved template. Consistent layouts and naming make it easier to use the system.’

Use reasonable graphics

Chris Batch, Rockwell Software’s applications engineering manager, says, ‘Use VBA [Microsoft Visual Basic for Applications] intelligently. Use it only when needed to perform functions unavailable in the core system. Be reasonable with 24-color bitmaps and use of ActiveX controls as they have significant impact on system resources.’

‘Look for a multi-screen adapter,’ notes Elyse Mintz, Colorgraphic’s (Atlanta, Ga.) vp, ‘to allow several separate screens from a single PC to help users make fewer operator errors and gain a faster critical response time.’

Jerry Koch, CTC Parker Automation’s (Milford, O.) product manager, relates, ‘Modular design allows HMI scalability from basic pushbutton panel to high-performance applications by adding trending, recipes, reporting, and network modules. Bundling enables cost economies and an integrated development environment.’

‘Decide on naming conventions before starting,’ suggests Craig Thorsland, GE Fanuc Automation’s (Charlottesville, Va.) visualization manager. ‘Decide on function or geography. Is it more important to know where it is or what it does? Consider your software, too. We have a field in the configuration to describe which machine this tag is for. Know what information your software requires and how to get the most out of it.’

Dean Evans, GE Fanuc’s software technical support help desk manager, says, ‘Device configuration mapping, alarm management, project architecture, troubleshooting, status monitoring, and change control are considered too late in the game. One customer had 200 alarms on a machine. They went off so often that it was like the little boy crying wolf.’

Bill Jameson, GE Fanuc’s software solutions program manager, chimes in, ‘Modern software allows you to monitor more than one machine, so, think bigger. Then, you’ll need to filter and sort alarms to keep the entire system from being overwhelmed. Further, many organizations fail to get feedback from production and IT. For instance, an operator may have to go down eight screens to see something, then back up, then down another eight to see a second machine. Get IT’s input, and they will have some ownership in the system and use it.’

How to upgrade

Jon Giardina, Omron Electronics’ (Schaumburg, Ill.) product marketing manager, offers this advice for OEMs. ‘Consider how you will send downloads, fix bugs, and provide upgrade to your customers. We have memory modules that can store a full screen or a firmware upgrade. Do you ship machines to multiple countries? If so, look for software with language translation support to make your life easier.’

Scott Kortier, Xycom’s (Saline, Mich.) product manager, also provides pointers to OEMs. ‘OEMs build a machine, run it off, tear it down, ship, and rebuild at the customer’s site. HMI screens are developed for the customers only. Try building some screens for the set-up technicians to assist in the machine rebuilds. That will save a lot of time at the end of the project.’

Xycom’s Ralph Damato, industrial PC business unit manager, considers rethinking during retrofits. ‘Users should look at how and why they go about a retrofit. Instead of just replacing something, ask what they were trying to do at the time and if there is a better way to do it now.’

Marsha Cross, Eaton Cutler-Hammer’s (Columbus, O.) product manager, says, ‘Be sure to configure the system for responsiveness. The operator needs information in real time in order to make accurate and efficient decisions. Further, designers should consider hardware with enough rugged features to avoid downtime.’

Considering a thin-client solution? Automation Control Products’ (Alpharetta, Ga.) director of engineering, Randy Cannady, provides three benefits of this solution: PCs can be a theft risk, software version concurrence is tough, and occasional use of application software in many locations makes licensing costs high.

Rick Tohmforde, president of Christensen Displays (Preston, Wa.), says, ‘Open technologies allow for lower cost, higher performance HMI solutions. Four distinct, yet related, trends can benefit the designer of smaller HMI systems: cost effective, smaller LCD monitors; continued decline in cost and size of PCs, PLC and I/O device connectivity over Ethernet; and open, PC-based software design tools.’

Jim Elwell, president and ceo of QSI Corp. (Salt Lake City, Ut.), cautions to specify products appropriate to industrial settings. ‘For mid-range HMI units, simple polydome keypads are inadequate for most industrial applications. Consider minimum specifications of steel dome on PCB under polyester. Even better is elastomeric with carbon pills (not carbon ink) or hard-cap over steel domes. Regarding NEMA rating, ask for a copy of an independent test report before believing the rating.’

Watch out for complexity

Stefano Zanetti, National Instruments’ (Austin, Tex.) HMI software product manager, notes, ‘The development of an HMI can increase in complexity as the number of channels to monitor increases. An open programming language can certainly offer flexibility. A configuration-based system offers a better approach for large channel counts. In such a system, the I/O subsystem is treated as an inherent part of the system.’

Roberto Penso, director of technical support at Iconics (Foxborough, Mass.), offers further advice regarding system scalability. ‘OPC technology is the best solution for providing a flexible system to connect to any PLC, and yet it’s robust enough for a reliable base.’

Adept Technology’s (San Jose, Calif.) Adeptmodules business manager, Tim DeRosett, while showing off a new Palm-based robot interface, points out, ‘Don’t overlook simple tools like this interface built on a Palm platform. Dedicated purpose and small, clean screens combined with low cost can be just the answer.’

HMI consultant and Siemens Energy & Automation (Alpharetta, Ga.) integrator, Bob Meads, president of iQuest (Atlanta, Ga.), notes, ‘What works today has to work tomorrow as well. Anyone can do great graphics; I look for a package that is based on standards: ODBC, flexible networking, built-in OPC, and standard scripting.’

With all these tips, how can you go wrong in your next HMI design? Just remember to plan, do your homework, and choose wisely.

More Tips for HMI Success

Optimize device communications

Manage alarms

Choose naming conventions

Define security levels

Avoid animated graphics

Always have something changing on screen

Document every step

Source: Control Engineering with input from GE Fanuc and Wonderware