By Wayne Labs, Contributing Editor
hile terminal blocks and connectors have always been essential in organizing wiring, the push is on to make faster connections, get them right the first time and to have them work reliably in all sorts of environments. Not all tubing and fittings have to work in nasty environments, but in many cases, theyre called upon to deliver some pretty nasty fluids. Heres a brief update on connector technologiesfor both electrons and fluids.
Screw, clamp, and IDC
IEC terminal blocks are available in three basic types. Knowing when and where to use each type can save costly revisits by maintenance technicians. Screw terminal blocks have been around forever, and typically accept as many as four terminations per block. Spring-clamp blocks require stripping the insulationas do screw typesand they are generally 3050% faster to wire than screw types. The newest type, insulation displacement technology (IDC), requires no stripping of insulation and works with solid and stranded wire, but there is a limit to maximum wire size and types of compatible insulation.
Screw terminal blocks might seem the ideal solution for any application. But PCK Refinery GmbH, which processes over 10 million tons of raw oil a year in Schwedt, Germany, found screw terminal blocks a liability. Every few weeks, screw-type terminal blocks would have problems because of loose screws due to equipment vibrations, says Christian Rada, head of PCKs electro-technical maintenance. PCK is now specifying Wago Cage Clamps for the control equipment. In response to this problem, however, most vendors provide screw terminal blocks with self-locking screws, which will probably solve many of these application problems.
Pluggable Jumpering Saves Time
According to Carlus Hicks, North American product manager for terminal blocks at WeidmÃ¼ller, pluggable jumpering is not a new idea to spring-clamp and IDC blocks, but when combined with traditional screw clamp blocks, the resultwhich replaces wire jumpersis fairly new and can save users a lot of time. How much time can pluggable jumpers save? Brian Delfosse, IEC terminal block manager at Rockwell Automation says, It used to be that everybody used screw center jumpers, and it took forever to install them. And if the installer made a mistake, he had to unscrew every jumper wire and slide them all left or right to the correct position and then screw them all down again. But with pluggable center jumpers, you can plug in about 30 poles in two seconds vs. about 20 minutes installation time to tighten down 30 screws for a screw jumper wire.
One industry trend today is to merge the various connection technologies together side-by-side in a single rail. Todays customer is seeing the need not to standardize on one [rail] technology, says Phoenix Contact terminal block product manager, Larry Freeland.
Customers are realizing that its better to let the application dictate what connection technology is most appropriate. Having a screw clamp, spring cage, auto-spring and IDC product in a single complete system allows the customer a choice to meet his demands for corrosion resistance, speed, clamping force, pull-out force, space, etc.
Another important emerging trend, according to Delfosse, is to add functionality to terminal blocks, and many manufacturers have responded to customer demands with fuse blocks, relay blocks with snap-out relays, transient protection blocks, and plug-in capability for components such as resistors, capacitors, diodes and fuses. Double-level blocks add to the number of circuits a block can handle, and usually include a ground as well. Troubleshooting is another key aspect of using terminal blocks, adds Delfosse. There are great troubleshooting solutions the terminal block industry is offering. They include test plugs, test probes, and test adapterswhich allow a connection to an ammeter, voltmeter, or any test device.
Get the Lead Out â¦
The European Restriction of Hazardous Substances (RoHS) Directive of January 27, 2003 bans the use of certain substances in new electrical and electronic equipment put on the market after July 1, 2006 (exceptions for certain applications are listed in the Annex of the directive). The banned substances are lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE). While this is not an issue in the U.S., Hicks notes that if vendors hope to sell connectors in Europe, the lead will have to come out from any solder (lead/tin) coatings that are currently used on connectors. In addition, hexavalent chromium, which protects against corrosion, is mainly used in the form of chromium layers, in particular on screw connection systems and mounting rails.
Connectors Assume New Roles
As fieldbuses proliferate, the need for connection systems that use junction boxes is displacing the traditional role of terminal blocks. This is not to say that terminal blocks cant handle fieldbus systems, but for localized machinery or processes, cable, and connectors, junction boxes are a viable alternative. What Jim Masterson, vice president of Process Automation at Turck, sees are customers who want to convert from conduit and terminal blocks to quick-disconnect cabling wherever possible, especially for local runs.
According to Masterson, We are [telling customers at process plants] that they can install in general purpose and Class I Div. 2 areas, properly-rated cabling and protected connectors to hook up all their field devices including transmitters, valves, switches, etc., if they follow the right guidelines, which are fairly new relative to the national electric codes. This includes the use of open wiring up to 50 ft (either in trays or hanging in space) if the cable is rated crushproof and meets other guidelines, allowing it to be used outside of conduit.
One company that has employed open wiring in a recent project in Florida is Air Liquide Process & Construction in Houston. The engineering company builds plants that generate hydrogen, oxygen and argon. According to Daniel Thouin, control system manager, a DeltaV system was chosen with Foundation fieldbus. Since it was a small application with about 20 transmitters, blocks and cables purchased from Turck were an easy-to-install, time-saving solution.. Thouin said that a bigger project with about 500 transmitters is in the offing, which may require a mixed environment of terminal blocks and cables/connectors to cover its longer distances.
There is a big demand for industrial networking systems with hardened cordsets says Masterson. In the process world, Foundation fieldbus is the most prevalent system, much of which uses armored cable for really nasty environments. Most applications call for junction bricks with quick-disconnect options that also must fit into Class I Div 2 environments.
Industrial Tubing and Fittings
For certain applications where nasty fluids need to be moved from point A to point B, metal piping is out. Polymersbetter known as plasticsare in. Rockwood Electronic Materials (Riddings, UK) developed a new silicon etchant for its customers in the semiconductor industry. While the conventional chemicals for silicon etching are hydrofluoric acid and nitric acid, the new product improves process stability and surface quality in addition to reducing the amount of post-treatment.
We have used George Fischer Piping Systems products for the last 20 years, says Andrew Hutchinson, facilities manager. Over this long period of time, their valves have proven to be the most suitable for our applications. Even though we put them into a harsh chemical environment, they tend to last the longest. The valve and piping tolerate more than 300 different chemical mixtures in the plant, and work in ambient temperatures from -10Â° to 50Â° C and maximum pressures to 6 bar.
Harsh and caustic flows need special piping. Temple-Inland, a pulp and paper producer in Silsbee, Texas, pumps large volumes of green liquor throughout its process. With a pH of 14, green liquor is an aqueous solution of sodium carbonate, sodium sulfide, sodium hydroxide and sodium sulfate. The solution has a tendency to quickly form carbonate scaling in pipes, reducing flow rates. George Pemble, a project engineer-group leader, found that the process was down 50% of the time due to scaling. We were using basic carbon steel pipe, and were required to shut down our density control system for green liquor every other day and flush it for long periods.
Working with a Plastic Lined Piping Systems local rep, Pemble made the decision to design the density control system around Halar (ECTFE)-lined pipe for three reasons. First, ECTFE has anti-stick characteristics and a smooth finish. Second, it handles the caustic liquor, and third, it can operate at 180Â°190Â° F. Pemble installed several hundred feet of ECTFE lined pipe and fittings in 1.5 and 3.0 in. line sizes.
Pemble says that since the installation, the scaling problem is basically gone. He flushes the system briefly every other week to remove soft sediment that collects in the pipe.
NeSSIAn Evolving System
Instrumentation systems that take samples and conduct analyses online used to be rather large and often took several months to build. Today, NeSSI systems let engineers put together sampling systems that look like stainless steel versions of Lego blocks. Originally, the system was conceived as a plug-and-play system for valves, sensors, and tubing, but newer versions of it will include built-in fieldbus as well.
Rick Ales, marketing engineer at Swagelok and NeSSIs secretary, explains, NeSSI can be thought of as a two-rail concept. One rail is the fluid interface and the other rail is the electrical interface. Sample systems that implement the fluid interface or mechanical rail as defined in ANSI/ISA 76.00.02 are considered NeSSI Generation I systems. Adding the electrical rail or the NeSSI Bus interface to a NeSSI Gen I system gives us a NeSSI Generation II system. The latest draft specification for NeSSI Gen II systems is available on the CPAC website.
Swagelok released the first NeSSI Gen I-compliant platform, MPC, in January of 2003. Since then we have seen industry acceptance building and the proliferation of third-party components. End-users are asking suppliers to deliver completely assembled systems rather than supply individual components as the number of NeSSI systems in service continues to grow. In fact, at many companies where it is in service, NeSSI is beginning to be thought of as a best practice.
According to Ales, Getting Generation II moving has been a challenge, with the biggest hurdle being settling on the right NeSSI Bus technology. From the beginning, a Controller Area Network (CAN) had been the preferred bus technology, but unfortunately CAN does not meet the NeSSI Gen II requirement for intrinsic safety. Two milestones happened in 2004. First, the NeSSI Gen II spec was adjusted to identify Foundation fieldbus as an acceptable technology for NeSSI Bus. Second, the technical committee for Sensor Technology of the Instrument and Measurement Society (IEEE) sponsored a draft standard, IEEE P1451.6, that would provide a Smart Transducer bus based on CAN technology. One of the goals is to have an intrinsically safe bus option that is designed to meet the NeSSI Bus requirements.
NeSSI is getting the support of major companies, several of which are working together. Parker and Honeywell recently announced an alliance to provide the process industry with an advanced system for sample analysis. The alliance combines the Parker IntraFlow line of surface mount flow control components with Honeywell pressure, temperature, and flow transducers. An early user of the system, Michelle Cohn, senior manager of the advanced characterization area in exploratory and fundamental research for UOP LLC says, The modular flow system from Parker and Honeywell improved the productivity of our skilled staff responsible for developing and delivering new technologies in our labs and pilot plants. She adds, Total project time to install this system was reduced by two-thirds compared to conventional systems and only required half the normal amount of time by our professional staff.
Faster to set up and the ability to handle nasty environments are the watchwords for modern connector technologieswhether they carry electricity or fluids, and in the case of NeSSI, both. Both can save plant engineers money in the long run.