Displays’ Future Looks Flat – Panels That Is

As greater responsibility and authority gravitate to operators in manufacturing, information must be available to them quickly in an easy-to-understand format. Software suppliers continue to improve information presentation in more ways than just the famous tank-filling example. Multiple windows with highlighted error messages that automatically boot a screen containing control logic requ...

By Gary A. Mintchell, CONTROL ENGINEERING August 1, 2000


Human-machine interface

Computer peripherals

Display devices

Graphic displays

Operator interface

Sidebars: Monitor integrates keyboard and mouse Technology behind the display

As greater responsibility and authority gravitate to operators in manufacturing, information must be available to them quickly in an easy-to-understand format. Software suppliers continue to improve information presentation in more ways than just the famous tank-filling example. Multiple windows with highlighted error messages that automatically boot a screen containing control logic require high definition displays to enhance readability.

So far, the answer has been CRTs. That’s CRT as in cathode ray tube—the same thing that powers your TV set at home. CRTs have proven reliable over the years, but they are heavy and large. Look at a typical desk. Wouldn’t a thin, stylish flat-panel look much better? Think of the heat generated, not to mention electricity consumption. So, until everyone is wearing goggles like the ones shown here from Olympus America (Melville, N.Y.), flat-panel displays will soon be everywhere.

Explains Cutler-Hammer (Westerville, O.) product manager, Marsha Cross, “Customers and OEMs are shifting to flat-panel displays as a result of improved brightness, color, viewing angles, narrow profile, and declining prices. Also, demand for color is increasing as prices decline and downtime is minimized due to better operator feedback.”

Enable operators

Reflecting on actual users of these products, Rick Tomfohrde, Christensen Display Products (Preston, Wa.) vp, says, “The reason for this upgrade from CRT to flat panel is as exciting as the upgrade itself. Operators have a new attitude toward both their work and company success versus a decade ago. They are empowered to change things for the better. There is a huge amount of skill and experience at the operator level and giving them the proper tools and motivation to do the job is the right thing to do. Expanded HMI devices with more information and associated monitoring equipment is a key ingredient in continued worker productivity and product quality enhancement.”

Designers are tackling just about every display component to tweak better performance at a lower cost.

Jim Higgins, Advanced Development manager for Rockwell Automation Industrial Computer Business (Duluth, Ga.), discerns three seed technologies that are influencing flat-panel monitor acceptance: enhanced scaling engines, improved CCFL and inverter technologies, and LCD panel technologies.

“Enhanced scaling engines with advanced auto-calibrate algorithms and superior phaselock loop performance have brought analog interface to a level rivaling CRTs,” explains Mr. Higgins. “Although nothing can compare with video quality of an LCD in native mode with a TMDS (transition minimize differentiated signal) interface, newer analog interfaces offer surprisingly good quality levels. By integrating high performance A to D converters and advanced digital signal processing technologies at the silicon level, chip suppliers have inexpensively solved an extremely complicated problem. Although we believe new displays will ultimately migrate to TMDS via DVI (digital visual interface), there will still be many legacy systems.

“Improved CCFL (cold-cathode fluorescent lamp and inverter technologies are now enabling long life, stable, and bright displays over wide dimming ranges. Peak light output of TFT panels now exceeds CRTs by a wide margin and the half-life of bulbs is close to that of a CRT. Dimming problems of early displays have been solved with innovative inverter techniques that yield wide dimming ranges and temperature stabilization.

New LCD panel technologies offer wide viewing angle, high light output, increased speed, and expanded temperature range,” he continues. “A steady evolution continues to improve quality and decrease prices. Viewing angles are wide enough on new 17- and 18-in. panels that this is no longer considered an issue. Fine tuning has reached a point where previous show-stoppers are routine.”

Leverage commercial technology

Like many components used in manufacturing automation, flat-panel display designers are leveraging price and performance advantages from the commercial market. The early driver for flat panel growth and development was notebook (now laptop) computers. There was sufficient volume to justify large development expenditures as well as huge capital outlays for TFT manufacturing equipment.

Similar to adoption of PCs in manufacturing where an off-the-shelf “white box” PC is often not an appropriate choice, engineers should match products to applications. States Russell Yost, Industrial Computers manager for GE Fanuc Automation (Charlottesville, Va.), “Many industrial automation companies manufacture consumer-grade flat-panel displays for use in industrial environments because they are less expensive. However, some displays are manufactured expressly for industrial/medical applications. These displays can withstand higher temperatures, generate less heat (which provides a longer MTBF), and offer better viewing angles.”

Mr. Yost further notes that improved mechanicals allow easy mounting in smaller panels with clips.

Yet another factor in the “buyer beware” category is matching the flat-panel display to the computer’s video driver explains Andy Zuidema, an engineer with Computer Dynamics (Greenville, S.C., a wholly owned subsidiary of GE Fanuc Automation), “Since there is no standard for how an LCD is driven, one of the key technology enablers is interface circuitry design needed to drive the display for each application. Engineers should look for products that allow the computer to connect to any flat panel, or the other way around.”

Another way to enhance interoperability of displays is embedded software. Omron Electronics’ (Schaumburg, Ill.) Jon Giardina, MMI product marketing specialist, reports that software embedded in some displays enables communications with PLCs from other manufacturers, like Allen-Bradley SLC 500s and GE Fanuc 90-20/90-30. Further, an embedded Programming Console, a touchscreen emulation of Omron’s hand-held programming device, allows users access to an Omron PLC control program and data table.

Digital interface

Nematron (Ann Arbor, Mich.) product engineering vp, Roberta Zald, notes another benefit of new designs, “Our new designs are less prone to magnetic interference than CRT-based systems. We also have recently announced a line of digital monitors. A typical monitor’s signal is converted from digital to analog at the computer, then converted back to digital at the monitor. Our monitors are completely digital, meaning that there is never a signal translation. This provides better clarity, ensures there is no signal degradation, and eliminates need for user adjustment.”

Think that advancements end with LCD technology and electronics? Harold Muma, Siemens Energy & Automation (Alpharetta, Ga.) HMI product business manager, sheds light on another essential component. “We have incorporated new technology into our backlight design increasing luminosity by using six fluorescent tubes, rather than the typical two. The lamps are coated with a special pigment that, in conjunction with color filters, causes white light to approach sunlight in spectral distribution.

“Most flat panels install backlights directly behind the screen,” he adds. “The new Siemens design employs a complex optical system that positions them laterally in the glass matrix. At the back of the light guides, there are dispersion centers in a calculated distribution. On the front there is a diffuser film through which the light is emitted with a high degree of homogeneity producing more even brightness distribution. No part of the screen will become illegible even if a lamp should fail.”

Are these technology and price advances reflected in how computer technology is installed in a factory?

Larger and lighter

Ralph Damato, Xycom Automation (Saline, Mich.) product manager, industrial PC products, says, “Customers are increasingly requesting the ability to separate the PC from the display. The PC is mounted in a control cabinet, and they want a compact, lightweight display mounted in a more convenient location, perhaps on a swing-arm. Flat-panel monitors now permit this type of installation.”

Mr. Damato reports the industry trend is toward larger screens, citing a Venture Development Corp. study that estimates that industrial market share for LCDs 10-in. or smaller, now over half, will drop to about one-third by 2004.

Most LCD manufacturers are in Asia, however, the United States Display Consortium would like to see more manufacturing at home. To that end, it recently awarded a development contract to CHA Industries (Fremont, Calif.) to develop a roll coater for depositing materials required to fabricate TFTs on plastic webs. This would lead to development of flexible flat panels. Think of the possibilities for products built with this technology!

Is there a flat-panel display in your future? Better bet on it.

Monitor integrates keyboard and mouse

Touchscreens are widely used as the operator interface mechanism for displays. In fact, Xycom Automation reports that over half of its current product line has touchscreen interfaces. Users still need keypads, however, so Xycom is introducing a 15-in. LCD flat-panel monitor with keypad and mouse.

This NEMA 4/4X/12 panel mount 3015KPM uses standard PC cabling and interfaces to the host PC. With high quality interconnect cables, distances of 100 to 250 feet from computer to monitor/keypad/mouse are possible. To accommodate graphics that use touchscreen, one will be available as an option.

In some situations, safety switches are required, for instance, when both hands are needed to be clear and away from dangerous situations. The product contains up to eight contacts to enable interface to these switches. Class 1, Division 2 Hazardous Location approval will be standard. Shipment is expected to begin in 4Q00.

Technology behind the display

The leading technology today for higher end graphic displays are AMLCD (active matrix liquid crystal diode) and TFT (thin film transistor—they mean the same thing). Dramatic improvements in quality and cost reductions have all but eclipsed the need for the lower performing passive or ‘dual scan’ technology.

This technology is practical for displays from 5- to 20-inches diagonal. TFT enables high-density pixels (picture elements) and a lower ‘pitch’ number. This is great for computer monitors, handheld appliances, or anything else where a high quality image is required.

For large format distant viewing, plasma display panels are more appropriate. Plasma sizes start in the mid-20-in. range, with 40-in. most common. Products up to 60-in. diagonal have been announced. Large trade show monitors and wall-mount flat TVs use these panels today. Resolution and pixel pitch is far less than TFT panels, but that is not obvious to the user at long distances. For instance, a large screen projection TV system looks great across a room but is virtually invisible when close up.

Not all TFT displays are created equal. There are approximately 20 companies in the world, most in Southeast Asia, which operate LCD foundries. A primary LCD fab is on technical and cost parity with a microprocessor fab, costing about a billion dollars. Performance and costs vary greatly among models and most vendors do not specify which brand of LCD is used in their end computer or monitor products. Graphic parameters to evaluate when choosing a display include brightness (measured in ‘nits’ or candelas per square meter), viewing angle (measured in degrees from center—not all directions are always the same), response time (measured in how many milliseconds to change from all black to all white and back again), and color depth (how many colors in the true color spectrum can any pixel represent). Of course, the best bet is to request a live demo since graphic performance, like beauty, is in the eye of the beholder.

Before we go on, let’s understand a bit more about LCD technology and how it works. LCD (liquid crystal display) defines that what you look at, while AM (active matrix) and TFT (thin film transistor) are the primary means of controlling the crystal’s brightness and colors.

An LCD panel is comprised of thousands or even millions of individual liquid crystals, enclosed in glass, all working together to control the amount of light to a user’s eyes. The basic premise of a liquid crystal is that it conducts light much like a very short piece of fiber-optic cable. If you bend or twist the crystal, the light will bend or twist with it. A white light source, commonly called a “backlight” and a fixed polarizer are located behind the array of liquid crystals. This generates polarized light that enters all crystals evenly. Active transistor devices control the amount of twist in each crystal. Another fixed polarizer is used on the front where the light exits. Crystals that are twisted one way have the light oriented with the second polarizer, hence the light passes through and is visible. Crystals twisted the other way have the light oriented perpendicular to the second polarizer hence the light does not pass.

Ability to control just how much twist is applied yields degree of brightness. Ability to control color comes from a color filter in the front. A combination of red, green, and blue used to give the full color spectrum. The big trick is to pack as many of these crystals and transistors as possible into a small area to give high viewing resolution. It takes three crystals and transistors (they are called subpixels) to make up one color pixel as used to measure screen resolution.

Unlike most electronic technologies, LCD and other flat- panel displays have a natural boundary to continued performance enhancements—the human eye. Once performance is at the limit of this instrument—and it’s just about there now—improvements will focus more on quality and cost reductions, as opposed to functionality. This is good news to users, who can now make long-term LCD monitor purchase decisions.

—Rick Tomfohrde is vice president of Christensen Display Products.