The Shocking Truth About Wireless

What You Must Know to Use Wireless Systems in Your Plant

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At least two other companies expect to produce ISA100.11a products by the end of March of 2009.

WirelessHART has somewhat of a lead in this respect. Control’s count shows at least 14 vendors will have WirelessHART-enabled field devices, including sensors, transmitters and control elements (valves, etc.) available for purchase by March of 2009. Six companies (ABB, Airsprite Technologies, Emerson Process Management, Endress+Hauser, Pepperl+Fuchs  and Siemens Energy and Automation) have announced WirelessHART products available by the end of 2008.

ZigBee PRO devices and software stacks are already in manufacture and could appear at a plant near you (probably in the HVAC systems) any day now.

But as the survey respondent quoted above noted, figuring out the wireless field device standard isn’t nearly as important as figuring out how to engineer, specify, purchase and install the devices, and even who will own the networks in the plant.

Start Planning Now

If you are going to install wireless devices, plan ahead, recommends Alan Autenrieth, of Conoco-Phillips’ Sweeny, Texas, refinery. “You have to have a plan, and you have to work to the plan.”

List all the kinds of wireless devices you use and intend to use, not just the wireless sensors that will use WirelessHART and ISA100.11a. Those standards are both evolving to include other sensors, RFID tags and the ability to pass other data. Decide if you are going to include wireless operator stations, wireless-enabled calibrators and bar-code readers, and design your network accordingly.

You also need to decide on a plant-wide or even corporate-wide level who owns the wireless networks. Many respondents to the Control/ISA100 survey indicated that they were involved in discussions with IT over this point.

“We came to an agreement with IT,” Autenrieth said. “They own the corporate LAN, and we own the plant floor. We coordinate with them, but we’re responsible for the wireless network in the plant.”

Design for Scalability and Robustness

You may want to begin with the backbone. Honeywell’s Dave Kaufman urges this method. “You don’t want to get caught with no more bandwidth,” he said, “or with having to rip and replace lots of network because you can’t scale it up any more.” Companies like Apprion, Honeywell, Cisco Systems and others are in the business of providing wireless backbones, not just field-sensor networks.

You may also need to do wireless surveys. Doing the Verizon Man’s “can you hear me now?” walk only works for small systems, like the prototype starter kits many vendors are now supplying for people who want to get their feet wet in wireless.

You also have to design for robustness. “We had to design our antenna towers to withstand 120 mile-an-hour winds,” Autenrieth noted, “and to keep operating when they were swaying.”

Robustness means making sure that the devices you install are suitable for the service. Rob Brooks of PPG, Lake Charles, La., talks about having to remove the first set of network nodes he installed because, although they were designed for outdoor service, they were not designed for outdoor service in a caustic soda plant. The caustic fumes dissolved the rubber grommets around the indicator LEDs and damaged the circuit boards. Robustness means deciding whether you will go with battery power, a combination of battery and line power, solar backup or a combination of all three. In the event of emergencies, it is comforting to know that the wireless network will keep working.

Purchasing and Engineering

Once you’ve gotten beyond the testing phase, you need to move quickly to standardize. “We have an approved vendor list,” Autenrieth said, “and we added the wireless devices and components to it using proper procedures. Now engineering and procurement can work with the same procedures as we use for any sensor or network device purchase.”

This is extremely important if you work with an EPC or a system integrator. By moving quickly to establish standards for wireless networking, wireless sensors and other networking appliances, you run substantially less risk of getting an orphan system that isn’t compatible with the rest of the plant.

ISA Wirelss Survey
In the Control/ISA100 Wireless survey, temperature and pressure measurement are the big key metrics obtained wirelessly.

Do It Yourself

As far as drawings and specifications are concerned, companies are doing it themselves in the absence of best practices, standards and guidelines from ISA.

For example, how do you show a wireless sensor on the P&ID? “We have used the Unguided electromagnetic signal symbol,” Brian T. Smith of INEOS-Nova in Sarnia, Ont., wrote in a post to the Controls Manufacturing Community List. “See ISA5.1, 1984(R1991) page 28, section 6.2.8 Electromagnetic or Sonic (Notguided)... a Sinewave with no center line (not guided), it is a free download for ISA members. This symbol has been used at the individual field Instruments and receiving Instrument symbols. Nothing is shown regarding the radio communications system details. These may be best shown on other types of drawings.”

Control columnist John Rezabek, suggested, “Could you use a “note” to cover wireless devices? (e.g., “Note 3: Wireless connection to host”) . . . and default to the data link symbol to connect transmitter to indicator?”

As a result of this discussion, Bob Szoke, an engineer at Marathon Oil, is using the following approach:

  1. There is no need to show mesh networks, as this would be silly and confusing.
  2. Using the Unguided electromechanical symbology <sine wave> makes a lot of sense, although its not a perfect fit. In the future revisions to ISA symbology, maybe they will expand its usage.
  3. Although we do not typically show junction boxes on P&IDs, the “gateway,” “transmitter/receiver mux” or whatever it’s called, is an active component that currently ties things together, so it should be shown. A single process plant, may have many of these gateways.
  4. There is need now and definitely in the future to distinguish field-mounted instrumentation as wireless.  For this Emerson suggested using two sets of double parentheses’ around a lower case i.
  5. Digital communications between the mux and DCS would be handled by the standard internal datalink symbol of dash lines with dots. This works well for both fiber and CAT 5, 6 or 7 cabling.
  6. Wireless communications between two muxes or gateways can be handled by a combination of the sine wave symbol and digital link, so I propose using the sine wave with dots between each wave.
  7. There can be no such thing as a wired radio signal, so the wired version of the sine wave will not be used for anything other then the electro-mechanical that it was originally intended for.

Get Started Now…or Not

Wireless is here. You’re going to be pushed to get started, and you’ll need to figure out things for yourselves, just like you did with fieldbus.

Deciding to do nothing is a valid choice, and with the multiplicity of standards, incompatibility of device networks, and the lack of good engineering best practices, many end users will make that choice.  

Want MoreCheck out our additional resources:
- Wireless Online Guide
- Defining Coexistence, Interoperability and Compatibility
- Extending the Sensor Network
- Wireless Readiness from an Automation Industry User Perspective
- Listen to The Shocking Truth About Wireless Podcast

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