Question: Team the world's most accurate instrumentation with the world's most powerful controllers and what do you have?

Answer: Not much. (Unless, of course, they're properly connected via a suitably fast, noise-free communication medium.)

  Wire and cable, and more recently, optical fibers andeven wireless networks are the oft-neglected backbone of industrial control. And whether the application is discrete, batch, or process, bus-based or conventional analog, the same basic questions must be answered, says Neil Maffett,a senior principal engineer with Babcock and Wilcox,Lynchburg, Va. "A system integrator must deal with thesame basic wiring techniques," he says.

  The questions start with application specifics: How fast do signals need to be sent? What are potential sources of electrical noise? Will physical connections require insulation with special chemical resistance? Is there existing wiring that can be reused?

  Then the chosen media--whether copper, fiber, or wireless--must be properly installed and maintained. Adherence to applicable codes and good engineering practice are key, according to Gary Coleman, production manager for Controllink Inc., an Algonquin, Ill.-based system integrator. General installation guidelines include adherence to Joint Industry Council (JIC) standards, the National Electric Code (NEC), as well as local codes, agrees B&W's Mr. Maffett.

  Retrofit applications with existing and perhaps reusable wiring bring with them both opportunities for cost savings and potential complications. "Do not trust existing documentation," Mr. Maffett cautions. "Verify and document the installation before starting any upgrade or expansion work," he adds.

  But in many cases, existing wiring--even up to 25 years old---can be retained, says Bill Southard, president of DST Controls, Benicia, Calif. In these situations, however, good engineering practice dictates that its integrity (both functional and physical) be verified. A thorough check of existing wiring can often eliminate need for removal and replacement. This also helps eliminate the possibility of introducing an error into a properly functioning system. "Surprises always cost money," Mr. Southard says.

  And while a lot of attention has been lavished (and media ink spilled) on the use of fieldbuses and device-level networks, not all users are rushing aboard. "Bus-based control installations have not been a priority with our customers," says Controllink's Mr. Coleman. "As a matter of fact, all of our current projects involve discrete wiring. And, we do not see any bus projects on the horizon," he states. "The companies we do business with are going with tried-and-true analog technology at this time."

  On the other hand, about 10% of system integrator DST Controls' installations are embracing bus technology. While there has been much interest shown by DST's client base, the technology has proven to be either too new or too unproven for most, Mr. Southard says. Although many users and system integrators would like to gain experience in applying device-level networks, short installation schedules and risk-aversion have been limiting factors.

Copper, optics, or no wires at all?

..Which medium is used will depends directly on the application. Choices include metal wire (usually copper), fiber optics, and wireless technologies (e.g., infrared broadcast, radio frequency, and power line carrier transmission--see sidebar, "Where Wires Fear to Tread"). Each has its virtues and weaknesses.

  Although most users and integrators feel at home using standard wire and cable, fiber optics is becoming more prevalent. Intrinsic immunity to electrical noise is a key selling point. Easier and more reliable field splices/termination of fiber-optic cables is also driving their use in industrial applications.

  However, much of the wire and cable available today competes very well with fiber optics in many areas. Insulation and shielding are now available to handle a full range of environmental concerns including temperature extremes, moisture and humidity, elevated pressures, all manner of radio-frequency and electromagnetic interference (RFI/EMI), as well as physical abuse from shock, vibration, and flexure.

  For wire or fiber, choice of jacket material should take into account any chemicals likely to be encountered in the application. Hostile agents can be drawn into the jacketing (causing it to "balloon," soften, and ultimately disintegrate) or draw chemicals from the jacketing material, causing it to become brittle. Specialty jacketing also is available, such as UV-resistant communication cable or hydrocarbon-resistant insulation for wire that must share a transfer line with grease.

Wire alternatives

..Only a few years ago, picking wire was simple. There was either control or power wiring. Even the line dividing them was very soft, since in a 115 V ac control environment, control signals were sometimes strong enough to provide power.

  But the needs of industry have changed. The proliferation of machining centers and robots demanded more flexible (literally) wires and cables. Also, the move to 24 V dc control systems required smaller-gage wire and shielded control wires. These conditions created a new wire product group, electronic wires.

  Still another group of wire products evolved when fieldbus technology came into play. "When wiring a plant, it's now necessary to consider all of the wire categories and how they interact," says Udo Lutze, president of wire manufacturer Lutze, Inc. in Charlotte, N.C. Wires, other than those specialized instrumentation wires (e.g., thermocouple leads) are categorized by Mr. Lutze into five groups:

• Power wires: High-amperage large gage wires against which instrumentation and data transmission wires may need to be shielded;
• Control wires: Medium gage wires used to carry 115 V ac or 24 V dc control signals (possibly shielded);
• Robotic wires: Highly flexible wires designed for constant motion in C-tracks or wire carriers;
• Electronic wires: Low-voltage wires that normally are shielded; and,
• Fieldbus wires: Shielded wires and cables designed to protect and transmit high-bandwidth control signals.

Can't keep a good LAN down

.."As the bandwidth requirements increase, users are looking to fiber technology as the solution." says engineer Eric Bulington, at Belden Wire & Cable Co., Richmond, Ind. "Fiber is becoming the choice because of its versatile construction types and variety of installation possibilities."

  There are three popular myths about fiber-optic cables that traditionally have kept them from wider application:

• Myth: Fiber is fragile. Reality: Today's optical cables offer greater tensile strength than copper or steel wires of the same diameter.
• Myth: Fiber is hard to work with. Reality: While not as straightforward as wire connections, today's fiber connections require fewer parts, and the tools and techniques have evolved to make terminating fiber optics easier and less time-consuming.
• Myth: Fiber is expensive. Reality: For the past several years, fiber-optic cable and related components have been comparably priced to their copper-wire counterparts.

Carrier and conduit alternatives

..When it comes time to actually install the selected communication medium, adherence to applicable codes and good engineering practice become primary. Basic techniques often vary by geographic region, says Controllink's Mr. Coleman. For example, installations in the Northern U.S. tend to use mostly conduit wireways, whereas installations in the milder Southern climates usually combine cable trays with conduit drops. In addition to carrier selection, segregation of power from instrumentation wiring and proper grounding must also be considered.

  Wire and fiber-optic cables are pulled through a variety of mechanical carriers. These include conduit, cable trays, raceways, and cable carriers. Also, bus bars are often used to simplify wiring in enclosures and panels.

  You can't pull many wires through conduit, so it has limited applicability in many industrial situations. When pulling wires in conduit, three different configurations of the wires can occur--triangular, cradled, and jammed. Certain ratios of cable diameter to conduit diameter are more likely to cause problems.

  Cable trays allow many cables to be pulled in the same general area and at different times. Concerns include: correctly calculated data and adherence to the design limits of the cables being installed with respect to tensions, sidewall pressures, and minimum bending radii. Damage occurs most frequently as a result of improper handling before or during installation, or inadequate protection after installation.

  Raceways are basically covered cable trays. In cable trays, cables can be piled on top of each other with little or no concern about stacking height. This is not true with raceways. As in conduit, there's only so much cross sectional space available.

  Cable carriers are flexible, and play an important role in prolonging the life of moving cables. Installing them may seem straightforward, but follow manufacturers' data sheets or catalogs carefully.

  As explained by Greg Binder, senior product marketing engineer, Rockwell Automation/Allen-Bradley Co. (Milwaukee, Wis.), bus bars are metal bars that provide structural support and line side electrical power to motor control components, reducing the number of wires, holes, and mounting screws. Components can be added and removed without extensive rewiring, reducing maintenance costs throughout the life of the control system.

Shield against noise, ground only once

..Wires and cables should also be routed in such a way as to minimize EMI/RFI. Potential sources of data-disrupting noise include electric arc welders, heaters, motors, power relays/contactors, and high-voltage power lines. Some cables themselves create electrical noise while others are susceptible to it. Fieldbus and other control and data carrying cables should be protected against power cables. Shielding helps, but ideally power and data cables should be run in different locations; separate control and power and you're safe.

  In situations where conductors must cross, they should be fixed by clamps or cable ties at 90° to each other to minimize electrical interference caused by the magnetic flux.

  "Because no shielding is 100% effective, filtering is becoming commonplace," cautions Bill Mango, national sales manager of connectors for Richard Hirschmann of America, Inc. (Riverdale, N.J.). Thus, Mr. Mango explains, Hirschmann is getting more requests for connector products to include built-in filters.

  Improper grounding is another potential source of data transmission problems. "Signal wires have the potential for being grounded in more than one location," says Dave Brooks, vp of marketing, Weidmüller (Latham, N.Y.). "Typically, signal wires are grounded at only one location, usually at the input to the bus system. However, this is not always possible. If the ground at the transmitter is different from the ground at the bus system, there is a potential for a 'ground loop.' Because ground is used as a reference point for the signal, problems with accuracy can develop. If there are different grounds, there are different reference points."

  Separation of different grounds can be achieved with isolators, which break the continuity of the loop while isolating the grounds. Signal isolators in the same housing as terminal blocks provide separation without taking up additional space.

A careful pull avoids damage

..When it comes time to actually pull your carefully specified wire or cable, proper handling and planning can prevent problems. Indeed, many failures of low-voltage cables have their roots in damage incurred during installation, says Michael Kopchik, Jr., senior technical consultant, Rome Cable Corp. (Rome, N.Y.). "This damage is usually attributed to improper cable-handling procedures or improper design of the conduit or other raceway system. However, the damage is not always immediately apparent. Undetected, it could result in cable failure months or years after installation. At this point, replacement is usually difficult, prolonged, and quite costly."

  Some advance preparation also can help. "Make sure there are no twists, bends, or kinks in the cable," recommends Gerald Pochurek, director of engineering, Olflex Wire & Cable, Inc. (Fairfield, N.J.). "Lay the cable out for one to two hours before installation to dissipate any stress remaining from cable storage."

  Although rough and improper handling during the pull-in process is often attributed to carelessness, much results from ignorance and inexperience. Adhering to a few basic installation guidelines greatly reduces the potential for damage during the pull:

• Follow manufacturer's guidelines regarding allowable sizes and conductors materials, allowable tension, and number of bends, etc.
  
• Let the cable warm up. Insulation and jacketing lose flexibility and becomebrittle in cold weather. In colder environments, cables should be stored in awarm location for at least 24 hrs before installation.
  
• Clean the conduit/raceway/cable tray before beginning the pull. Waste materials frequently cause physical damage when cables are pulled in. Waste removal can be done by pulling a mandrel or plug through the conduit, while checking at each opening along the route and removing any foreign matter dislodged at condulets or pullboxes. Pulling a clean cloth/swab to wipe out any remaining debris complete the procedure.
  
• When pulling multiple cables, the pulling eye or basket should be equipped with a swivel. Free rotation is vital to accommodate the unequal tensions created by multiple cables.
  
• Use steel lines only in steel raceways. A stranded steel line can saw into aluminum or nonmetallic raceways at bends along the route, leaving sharp edges that can damage the cable. Manila hemp or a synthetic fiber rope that doesn't stretch is best for pulling in nonsteel conduit. Don't use materials such as nylon for pull lines because they stretch, resulting in uneven pulling tension and erratic cable surges.
  
• Lubricate, lubricate, lubricate. An approved lubricant should be applied continuously and liberally throughout the pulling process to reduce friction between the cable jacket and cable tray. For long or difficult pulls, lubricant should also be applied to the in-side of the raceway at all accessible points throughout the pull, such as con-duit bodies.
  
• Plan twice, pull once. The pull should be planned so that a continuous, nonstop pulling rate is maintained. Stopping in mid-pull should be avoided. On long, difficult pulls, use a two-way radios to communicate between the feed and pulling points.

  Finally, once the wire or cable pull is complete, don't neglect the importance of proper connections, cautions Hans Buhler, P.E., a senior electrical engineer with Power Engineers Inc. (Hadley, Ida.). "Do not overlook wire and cable termination. Properly specified provisions for stress relief at the terminations are important. Most failures on wiring and cabling systems take place at termination points," he says. Likewise, positive grounding must be ensured at the termination point. Remember, shielding is useless if not grounded: a wire that comes loose is no use at all.

Is that old wire up to fieldbus?

..Preparing for the day of digital fieldbus communications, but not sure if your wiring is up to snuff? Because virtually all versions of the fieldbus concept's physical layer already are specified in the ISA's SP50 standard, Bob Crowder, president of Ship Star Associates (Newark, Del.), suggests the following test to determine the suitability of your old wire:

  Connect the wires into a "chicken foot" at the junction box and install terminators (100 {OMEGA} ±1% resistor in series with a nonpolarized 2 µF ±20% 50 V working voltage capacitor). Direct current leakage through the terminator should be less than or equal to 100 µA and the terminator should be nonpolarized.

  Use an impedance tester to verify 100{OMEGA} ±20% over the frequency range from 8 to 50 kHz. (SP50 calls for a maximum dc resistance of 22 {OMEGA}/km at 25 °C.)

  If the existing wiring is within the above specifications, Mr. Crowder is confident that it shouldn't have to be stripped out and replaced in order to run fieldbus protocols

Schematic software jumpstarts design work

Electrical design packages help improve productivity, cut down on tedious work, and keep wires from getting crossed in the process.

..Still using a mechanical computer-aided drafting (CAD) package to execute electrical schematics? Want to have more fun on the job? Deliver more accurate work in less time? Well, it may be time to go beyond generic CAD in favor of a software package specifically designed to help streamline electrical schematic development.

  "AutoCAD itself is not made for what we do," explains John Holland, a project engineer for system integrator and panel builder K&R Automation Corp., Warren, Mich. AutoCAD, from San Rafael, Calif.-based Autodesk, is the industry standard mechanical CAD package for PCs. "It's a great drawing package, but it doesn't help you think," says Mr. Holland.

  Instead of using AutoCAD alone, K&R uses Promis-e, anAutoCAD add-on package from ECT International (Brookfield, Wis.), that customizes AutoCAD's primitive mechanical drawing strengths (lines, arcs, etc.) to the needs of electrical controls designers.

  "It makes our jobs much more interesting," says Mr. Holland, who once spent an entire year error-checking the schematics for an automated conveyor system--a task that is now performed automatically as designs are developed. "The software does the things that everybody hates to do. Plus, accuracy and consistency go way up," he remarks.

Beyond mechanical CAD

..So just what do these packages do that AutoCAD doesn't? First and most obvious are the built-in tools designed to make drawing electrical schematics easier. Libraries of icons represent electrical control entities as well as specific vendors' parts. "We had to keep log books of parts, but now we just let the software do that," says Jeff Shellenberger, electrical designer and system administrator for IPEC/Planar, a Phoenix, Ariz.-based builder of semiconductor processing machines. Drag-and-drop, snap-to connections are automatically assumed to be wires and numbered accordingly. Estimates of savings in drawing time alone range from 15% for sophisticated AutoCAD users to as high as 70% for the uninitiated.

  Beyond drawing time, the real payoff comes in taking advantage of the design data that underlies the schematic. "Electrical controls design is not about pictures, its about information," says Steve Bernier, an applications engineer with EPLAN/Wiechers & Partner, a software developer that markets a standalone (AutoCAD independent) package from its offices in Brookfield, Wis. "A circle with a line on each side may represent a coil, but that coil has a manufacturer, a part number, contactor cross references, and connecting wire information that CAD packages do not capture," he says.

  "The real productivity comes from the extraction of information from those drawings," adds Jamie Howe, marketing manager for VIA Development Corp., a schematic software developer based in Marion, Ind. VIA user Sherry Wolfe, a supervising design engineer at Armstrong World Industries, Lancaster, Pa., concurs, identifying "automatic extraction of reports such as a bill of materials" as the software's key benefit. "We can extract data from any drawing that has attributes," she says. Underlying information also can be used to automatically generate wire lists, cable layouts, wire labels, panel layouts, and even purchase orders for accounting.

  Automatic cross-referencing and error-checking, whether performed continuously, upon file-saving, or as a separate subroutine, also can help schematic software earn its keep. "The later errors show up, the more expensive they are," says Felicia Moore, Mayfield Village, Ohio-based program manager for Rockwell Software's RSWires. (To date, the company's RSWires software is largely based on a private-label agreement with ECT International, with Rockwell Automation's extensive global distribution and support network the key differentiator.)

What to look for

..In addition to the typical laundry-list of bells and whistles that stack up slightly differently from package to package, several overarching issues need to be considered when selecting an electrical schematic software package. Primary among these are open hooks for integration with other software packages and databases, flexibility for individual customization, and ease of use and implementation.

  In terms of openness, import and export compatibility with accepted graphics and database formats are essential. "A computer-aided engineering package should be able to draw information into the design through ODBC from your parts library," says EPAN's Mr. Bernier. "It should also be able to take virtually any project information and export it to an ASCII file, to feed into downstream systems such as PLC [programmable logic controller] programming software or a manufacturing resources planning system for ordering."

  Links with PLC programming software are an especially (ahem) logical synergy for electrical schematic software developers. "There are overlaps in the information involved and sometimes it's tough to make sure they match," says Rockwell Software's Ms. Moore. For example, if the wire list documentation is lost, several packages can recreate an I/O list from the programming logic itself. Growing compatibility with PC-based logic engines as well as design tools tailored to device-level networks are other trends to watch.

  Schematic software should also provide sufficient flexibility so that users don't have to change the way they develop their documentation. "Few companies appreciate being told that they must do things a certain way, and standards differ from one company to another," reports VIA's Mr. Howe. "Flexibility is key," says Harold Jezierski, president of Aucotec, Buffalo Grove, Ill. "for example, you need to be able to generate wire lists that match the user's manufacturing practices."

  "Inevitably, there are little things they want to customize," adds Tom Stawicki, TCS president. "For these situations, it's important to have a high-level, controls-specific language for developing custom functions."

  The final major considerations are ease of implementation and ease of use. Few new ways of doing things are faster overnight: How long will it take to get back to and exceed a break-even level of productivity? Drafters and designers who use the tools everyday are one thing, but for the engineer or other occasional user who may shift from design to implementation, then back to design, intuitive use is especially important.

AutoCAD add-on or standalone?

..The best answer to this question may well be in the eyes ofthe beholder. On one side, many users currently evaluating electrical schematic software are AutoCAD users. For example, ECT president Arthur Sawall estimates that 90% of his company's inquiries come from the already AutoCAD-initiated. "Standalone is a tough sell," he says, "I'm convinced that Autodesk drives the market."

  On the other hand, "A big feature that people like is the true Windows interface,' says EPLAN's Mr. Bernier of his company's stand-alone offering.

  "It depends on whether users are engineers or designer and drafters," admits Rockwell Software's Ms. Moore. "Designers and drafters are familiar with AutoCAD, but engineers may be more familiar with Excel--they're more used to the Microsoft environment," she says. As a result, AutoCAD-based developers such Rockwell and ECT continue to hone the overall usability of their software, attempting to balance the best of both worlds.

  In the not-too-distant future, however, this may prove a nonissue. After a decidedly late move to Windows from DOS with its AutoCAD 13 release, Autodesk and Microsoft now appear to have a much closer working relationship that should be reflected in AutoCAD 14, currently under development.

  For most of the electrical schematic software alternatives, pricing ranges from $5,000-$10,000 for a full-featured version. Limited functionality, view-only licenses also are available typically starting at $500. But for most users, pricing is a distantsecondary consideration to features and platform familiarity.With the exception, that is, of companies that are looking beyond their "core" CAD users to "adjacent" users who could benefit from technical schematic technology. For those users, whomay outnumber core users 10 to one, a full-blown electrical schematic package (much less a $3,500 AutoCAD license) simply isn't feasible.

  That's where a new breed of mass-market schematic software tools such as Seattle-based Visio Corp.'s Visio Technical may be suitable. Not a drawing package, but not an electrical controls package either, the $399 Visio is designed for a broad range of design/drafting applications that employ a high degree of predefined symbol content.

  Wayne Bandy, an electrical and instrumentation systems consultant based in Squaw Valley, Calif., has been involved in an Exxon project where Visio Technical was used to bridge the gap between the field technicians installing control systems and the professional engineers who designed and approved them. "Full AutoCAD wasn't feasible for the field, so we put Visio on industrial computers; technicians could make as-built changes to the drawings right there and then." The changes were then reviewed and stamped by the legally responsible professional engineers. "Visio is good for keeping separation between the technical and professional sides of the house," Mr. Bandy says.

  Generic technical schematic tools like Visio also hold the promise of becoming a more suitable platform alternative to AutoCAD for niche products such as electrical controls. "We know the mass market, but because the technology is so programmable, third parties have the power and flexibility to do develop their own custom libraries," says Dirk Meyer, Visio Technical product marketing manager.

Objects are cost of entry

..Essentially all of the reasons for using electrical schematic software instead of a mechanical CAD package derive from the concept of object orientation. Pictures must retain the properties of the devices they represent, and connecting lines must behave like real-world wires.

  "I need attributes in my CAE tools," summarizes an engineer working for one of the Big Three car-makers. "Instead of a dumb drawing, I need objects that have attributes."

  In part because it already has charted a course independent of AutoCAD, EPLAN already uses an object-oriented database engine. But Autodesk (following Microsoft's lead) and all of the AutoCAD-based electrical controls suppliers (following Autodesk's lead) will incorporate increasing amounts of object technology into their next-generation packages.

  "Currently, users are forced into a top-down approach to control system design, starting with the schematic," comments TCS' Mr. Stawicki. "Users now want to be able to attack the design problem from a number of different angles." For example, to start with a function chart or parts list and work toward a schematic. "Object-oriented databases make this possible."

Where wires fear to tread

..The relentless advance of networking technology has lead to the emergence of wireless communication options that can be used to connect remote parts of the process to the rest of the plant. They're used in those cases where it's impractical or impossible to connect nodes using wire, cables, or fiber optics. Radio frequency data links, infrared data links, and powerline communications techniques are already in use daily in many industrial applications.

Radio frequency

..There are several types of radio frequency (RF) data transmission systems on the market. Some use the tried-and-true, and well-understood amplitude or frequency modulation techniques. However, new families of digital techniques have entered the market. These are commonly grouped under the heading "spread spectrum."

  Spread spectrum (SS) RF networks are playing a growing role in the connection of today's sensors, actuators, and control systems. Essentially, SS is a technique in which a transmitted signal is spread over a frequency range that is greater than the minimum bandwidth normally required for information transmis-sion. The purpose is to improve the bit error rate in the presence of noise or interference. Other advantages of the SS approach include reduced interference with other signals, resistance to jamming, improved privacy, and the ability for multiple users to share the same channel.

Infrared

..We're all familiar with the infrared (IR) remote controller so commonplace for television and stereo components. Less known is the use of the infrared spectrum for data transmission.

  Applicable to both stationary and semimobile uses, infrared data transmission converts electrical data pulses into light signals, and back into electrical pulses on the receiving end. Such a network is contactless since the transmission is optical instead of electrical.

  Optical data links are very real. Taking an example that's close to home, RDI Software, a software development company headquartered in the building next to Control Engineering, has expanded, taking space in the same building where this magazine is produced. The offices in the two buildings are connected by a laser-driven, high-speed, infrared data link that spans a distance close to that of a football field. This saves the on-going expense of using a dedicated phone line to interconnect the two sites while enhancing the security of the data transmission. The only interruption might be due to an occasional bird flying through the beam.

Powerline

..Many industrial applications already are supplied with electrical power. The idea of powerline communications is to use this wire to send data, too. "Reliable data communications with rates to 100 kbps over existing power lines is possible using a patented spread-spectrum technique," says Eric Hughes, marketing manager for Adaptive Networks, Inc. (Brighton, Mass.) "The signals can be transmitted over ac or dc power lines from 110 to 480 V, 50/60 Hz and can be carried by multiphase lines as well. Distances up to four miles are practical and up to 65,000 nodes can be connected to the same network."