A Reader Writes:
We've been providing wireless communications solutions as alternatives where additional device-level nodes are needed in difficult-to-wire locations. We've not been involved with hazardous locations until now. Can we use wireless in Class I, Div. 1 and Class I, Div. 2 areas?
-From May 2003 Control Design
Use Spread-Spectrum Monitoring
New technology is enabling greater use of spread-spectrum radio for monitoring and control in industrial environments. Today, spread-spectrum can securely move small amounts of sensor and control information from a transmitter measuring flow, level, pressure, temperature, etc., even transmitting mission-critical information through heavy interference. The most efficient interference-tolerating technology for such applications is frequency hopping, a part of spread-spectrum.
...The maximum allowable transmit power according to the FCC is 1 W for a frequency-hopping spread-spectrum device. The devices can be connected directly to a transmitter located in a Class I, Div. 2 hazardous location and can send the signal 600-1,000 ft. in a plant in harsh industrial conditions, eliminating the need for wire, conduit, trenching, and all associated labor. No setup, configuration, or software is required. Simply plug in, power, wire the transmitter or signals to it, and get it out on the other end.
...However, the 1 W maximum transmit power and the circuitry around it is used to achieve the distances and to tolerate interference levels, which pose a problem in a Class I, Div. 1 area. For applications in a Div. 1 area, the device can be mounted in a supplied explosion-proof housing with a clear window. The propagated radio signal penetrates through the clear window, while maintaining an explosion-proof rating. The receiver is placed in the safe area or Div. 2 area by the controller. This method eliminates the need for additional explosion-proof conduit systems, seals, glands, and associated labor.
Davis Mathews, Instrumentation Product Manager
Phoenix Contact, Harrisburg, Pa.
It's All About the Label
In addition to the UL ordinary locations/general purpose standards that may apply and the installation requirements per the local Authority Having Jurisdiction (such as ANSI/NFPA 70, "National Electrical Code" Article 500), the node(s) should be evaluated in accordance with the following UL hazardous locations standards and their protection method philosophies briefly described below. Readers first may wish to refer to www.ul.com/hazloc to familiarize themselves with the different protection methods, standards. and area classifications noted in this article.
...It may be difficult to place the node, antenna and all, inside an explosion-proof enclosure and have it perform as desired with other nodes. But it could be possible to evaluate the node's enclosure as explosion-proof, or obtain an appropriate UL-certified explosion-proof enclosure suitable for the location, so the node could be placed inside. This enclosure most likely would be evaluated to ANSI/UL 1203, "Explosion-Proof and Dust Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations." In this scenario, any atmospheric ignition caused by the node would be contained within the enclosure and not propagate into the surroundings. (The same argument would apply to Class I, Zone 1 Flameproof protection in accordance with ANSI/UL 2279, "Electrical Equipment for Use in Class I, Zone 0, 1 and 2 Hazardous (Classified) Locations."
...A more viable choice for Class I, Div. 1 hazardous locations may be to have the node evaluated as intrinsically safe per standard ANSI/UL 913, "Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Div. 1 Hazardous (Classified) Locations." The intrinsically safe method achieves its protection by evaluating, and more importantly limiting, the potential energy of the node under electrical fault conditions so that the specific atmosphere or group of atmospheres the node is located in are not capable of being ignited by a possible spark from the node. An evaluation per UL 913 also would allow the node to sit openly and transmit without the interference of being in a thick-walled enclosure. (The same argument would apply to the consideration of using the Class I, Zone 0 or 1 Intrinsically Safe protection methods in accordance with ANSI/UL 2279, "Electrical Equipment for Use in Class I, Zone 0, 1, and 2 Hazardous (Classified) Locations.")
...In addition, the possibility of the node being used only in Class I, Div. 2 hazardous locations should be addressed. In this case, the protection method used for evaluating the node would be Non-Incendive per UL 1604, "Electrical Equipment for Use in Class I and II, Div. 2, and Class III Hazardous (Classified) Locations." Though this method of evaluation would also evaluate the potential energy in the node as in the above intrinsically safe method, it does not limit the energy nor does it consider the potential energy under the electrical faults introduced during the intrinsically safe evaluation. Instead, this method evaluates the normally sparking parts as well as the possibility of shorting or grounding exposed electrical circuits (such as the antenna), and their ability to keep the ignitable atmosphere out of the electrical contact area, or by the parts not having enough energy under normal conditions of use to ignite the hazardous atmosphere.
...This type of evaluation would most likely also require an evaluation of the combination of the node and the device it is installed with, not just the node itself. The same argument would apply to the consideration of using the Class I, Zone 2 Non-Incendive protection method in accordance with ANSI/UL 2279, "Electrical Equipment for Use in Class I, Zone 0, 1, and 2 Hazardous (Classified) Locations."
...There are currently many radio/modem devices that are UL-certified under the intrinsically safe and non-incendive protection methods. Many of these devices involve process control applications located near pipelines, furnaces, etc., gathering temperature and pressure information and relaying it back to a central computer via antennas.
Jason Frieders, UL HazLoc Project Engineer
Underwriters Laboratories, www.ul.com/hazloc
Built Our Own Antenna
We have run into this problem frequently and decided to develop an antenna that would pass the rigorous certification tests.
...We chose the 2.4 GHz Mobile Mark body-mount antenna because of its rugged construction for vehicular applications. This antenna can be manufactured with a solid two-piece aluminum mounting base and radome containing the radiating element.
...The antenna was redesigned to reroute a coaxial cable through the mounting base and was internally sealed using fibrous packing and approved conduit-sealing compound. The bottom side of the base has a plug that further seals and secures the coaxial cable. This is an accepted method of preventing gases from leaking inside the housing through the antenna-mounting base.
...A radome containing the radiating element of the 2.4 GHz or 900 MHz antenna is threaded and securely screwed onto the aluminum base section with a proprietary sealant cement securing the two pieces. The base of the antenna has a 3/4-in. NPT fitting, containing the feedthrough, for assembly into a hub on the top of the housing. The figure shows the prototype explosion-proof antenna attached to an Adalet explosion-proof enclosure.
Ed Rasmussen, President
Certifications Are Invaluable
Industrial wireless modems typically carry some form of UL certification. Our line of wireless industrial communication solutions carry multiple hazardous certifications, including UL1604, Class I, Div. 2, Groups A, B, C, and D for the U.S. This certification is also regarded as an acceptable certification for much of the rest of the world. The products are cUL (Canadian Standard CSA) Class I, Div. 2, Groups A, B, C, and D for use in Canada. For Europe, we are completing the testing process for ATEX certification.
...UL1604, Class I, Div. 2, Groups A, B, C, and D, is the most common certification, permitting wireless modem operation in locations where flammable or explosive gases, fluids, or vapors are possible, but are not necessarily part of the normally operating environment. Class I, Div. 1 is essentially for industrial locations where there is an ongoing risk of explosion due to the presence of combustible gases, liquids, and vapors. A key requirement here is that enclosures must be explosion-proof. For a work-around for using Industrial wireless products in a Class I Div I area, the devices can often be placed in containers that meet Class I Division I standards."
...Getting these certifications can be expensive and time consuming for the manufacturer, however, the benefit to the customer of having this certification is that a company can standardize wireless networks on a single type of device, and use it for many applications, regardless of the environment."
Wally Gastreich, Wireless Application Engineer
Kevin Zamzow, RadioLinx Specialist
ProSoft Technology, Bakersfield, Calif.
Screw or IDC--Which Works Better?
Until recently, for better or worse, we used screw-clamp terminal blocks for connections. Now, we have customers that prefer and sometimes specify insulation-displacement connectivity. They argue that IDC means lower installation costs and reduced cabinet space as a result. That's fine, but I'd like to hear what real users know about increased likelihood of having to run down loose connections in the field later on. We sell into global environments with varying degrees of vibration, repetitive motion, etc.
Send us your comments, suggestions, or solutions for the problem. We'll include them in the November 2003 issue. Send visuals, too,a sketch is fine. E-mail us at CDTheAnswer@putman.net or mail to The Answer to Your Problems, CONTROL DESIGN, 555 W. Pierce Rd., Suite 301, Itasca, IL 60143. You can also fax to 630/467-1124. Please include your company, location, and title in the response. Have a problem you'd like to pose to the readers? Send it along.