Reducing dozens or hundreds of wires and cables to one or two makes most control and automation engineers nervous enough. Dropping to no wires at all would probably drive many of them crazy. In fact, wireless technology is still so alien to industrial networking that many potential users say they often can't easily visualize where they might apply wireless capabilities and wind up sticking to t...
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Reducing dozens or hundreds of wires and cables to one or two makes most control and automation engineers nervous enough. Dropping to no wires at all would probably drive many of them crazy. In fact, wireless technology is still so alien to industrial networking that many potential users say they often can’t easily visualize where they might apply wireless capabilities and wind up sticking to traditional hardwired language and concepts.
"Wireless now is a lot like the early days of industrial networking a few years ago. It’s probably still not for everyone, but it definitely has a growing place," says Bill Arnold, Omron Electronics LLC’s product marketing manager. "Wireless is being used for everything from large data file transfers to I/O device monitoring and control, and a lot of technology on the commercial side is dropping down to the factory floor. The $64,000-question is: Can wireless be made secure? The answer is: yes. The price of wireless is down and its reliability is up enough to make it viable in a number of applications.
"Right now, the #1 aid to implementation of wireless on the plant floor is spread spectrum because it prevents electrical noise and intentional jamming, and it matches senders with receivers to let messages get through," says Arnold. "The biggest problem with wireless now is with time-critical, on/off-type controls that still have a delay compared to hardwiring, especially when a wireless system tries multiple times to get its message through. As you add more guarantees that your message will get through, you’re adding more possibilities for delay. There also is an inverse relationship between how fast and far wireless messages will go."
Getting started
Whether wired or wireless, all network project developers must first decide what they’re trying to accomplish; find possible solutions; and analyze all of the benefits, costs, and tradeoffs to pick the best option. To move data via any network, the three basic questions remain: how much, how fast, and how far?
| The numbers above the waveform peaks (1-16) represent a typical frequency hopping pattern, the result of a sequential present algorithm designed to maintain synchronization between the master and the remote radio moderns. |
"To begin thinking using a wireless perspective, it also helps to ask: ‘Is there a signal in this plant that’s traditionally been hard to bring back to the control room?’ or ‘Is there a signal you wish you could add to an existing application, and you haven’t had the budget for it, but you’d try if you could do it for $1,000 or $1,200?’" says Davis Mathews, Phoenix Contact’s marketing manager for wireless and signal conditioning. "These and similar questions can help people think about their plants in new ways. People have to try and consciously think about using wireless on the plant floor before it can become an unconscious option."
| When using direct sequence spread spectrum (DSSS), a pseudo random signal, or Barker code, with a higher clock cycle is superimposed on the useful signal, which spreads its bandwitdth, The useful signal is obtained by applying the same Barker code with the correct phase sequence to the spread signal. |
The main benefit of wireless is that it can reduce material and labor costs, as well as allow control in areas where wires simply can’t go. Some users have used radio frequency (RF) for many years to monitor and control typically long-distance, low-data rate applications that usually aren’t hampered by some interference. However, this field is expanding and diversifying as the cost of wireless components drop and their reliability increases.
For instance, engineers at RiverStone Group Inc. are using ProSoft’s RadioLinx modems and wireless Ethernet switches to monitor tiny changes in pressure and flow as RiverStone’s dredge pumps 6,000 gallons per minute of wet sand through a 2,000-ft pipe to the top of the company’s 70-ft. high classifying plant. RadioLinx communicates with Rockwell Automation’s Allen-Bradley (A-B)
ControlLogix processor and the plant’s 200R industrial PC; data is viewed via A-B’s RSView; and then analyzed using Microsoft Access and Excel. Newly installed sonar on the dredge is also displayed via RSView, allowing operators to see its cutting arm and the underwater quarry’s sandy bottom.
"Our increased data gathering and flexibility have saved us about $100,000 per year," says Mike Gottwald, RiverStone’s corporate engineer. "Also, with the old system, the pipe would get plugged several times a day. Now we can anticipate plugs; and we haven’t had one since the new system went online in May."
Spread spectrum basics
The main drawback to wireless is that it’s traditionally affected by electrical noise and interference, usually caused by physical obstacles, operating machinery, or other factors. This can hinder reliability and security. Luckily, many of these potential problems have already been solved by long-time wireless users and standards organizations, while others are now being addressed.
For example, developed during World War II and opened for commercial development in the early 1990s, spread spectrum solves many interference and security issues by dividing its signal among many channels in a preset pattern, and then reassembling or correlating them from identical portions of apparent noise. Likewise, digital packet switching organizes signals more efficiently for faster, high-volume transmissions.
The two main subsets of spread-spectrum are frequency hopping and direct sequence (see Spread Spectrum diagram). Frequency hopping spread spectrum (FHSS) uses predetermined timing on each frequency by transceivers on each end to prevent interference. Direct sequence spread spectrum (DSSS) uses numeric codes that identify units intended to communicate with each other, which prevents communication by anything else that might jump onto the network.
Lingering interference
However, some critics point out that interference is different than being hacked, and that the 900 MHz-to-5.4 GHz Industrial, Scientific and Medical (ISM) bands, including spread spectrum, are still unlicensed and legally unprotected from interference. They add that spread spectrum isn’t inherently secure or reliable because it’s designed to be easy to receive. So, not only is it easy to intercept, its receivers are more subject to intermodulation distortion, blocking, de-sensing and other narrow-band phenomena.
While spread spectrum uses a technique called process gain to reduce narrow-band interference, some observers say that manufacturers apparently don’t care about this, and spread signals at minimally required rates to boost power up to regulatory limits. These spreading rates are sometimes applied below the data transmission rate, which means they have no process gain, and are susceptible to all interference on the band. Process gain is similar to the quieting effect of a wide-band FM signal, and users need to ask about it before implementing a wireless system.
To avoid possible problems, wireless’ supporters say potential users must try out solutions in their own applications and facilities because each setting has its own characteristics. Most wireless manufacturers are more than happy to bring solutions to users for tryouts, and even encourage users to try and make them fail.
Control room in the field
Besides using wireless to lessen trips to the field, some engineers are using wireless to get out into the field more often—by bringing an equivalent of their control room along with them. For example, Iceland-based system integrator Vista Engineering is using National Instruments’ (NI) LabView 7 Express PDA module for Palm and Pocket PC handheld devices at a wastewater treatment plant with 25 pumping stations to communicate input changes, including parameters and control loop tuning, back to a central control system. NI reports that this is the first time wireless technology has allowed PDAs on a plant-floor to perform distributed control functions.
Vista began monitoring the stations more than 10 years ago using LabView with an Ethernet serial port, TNC radio modems from Kantronics, two-way FM UHF radios from Maxon, and a three-element Yagi antenna to secure a 10-mile radius around the 25 stations. This solution cost about $100 per station—far less than the $2,000 per station per year cost of renting two-way telephone lines.
Sewer station data is preprocessed using Schneider Electric’s Type 27 and 37 Telemechanique PLCs, and includes information about alarms, energy use, flow, number of starts and stops, pump running hours and combined use, and total overflow hour and minute calculations per year. "The radio part has always been stable and easy to use. PCs and software are tougher," says Vista’s Andres Thorarinsson. "We’re now on our fourth software version, LabView 6.1. Pump station alarms are received and processed by our central office, or sent via e-mail to our mobile phones. If there is an alarm, we can check it on a secure Web site. We all get to stay at home more."
In fact, Vista’s radio network and its LabView Vista Vision plug-in drivers are so accommodating of other applications that it is now used to monitor: local weather stations using Campbell CR10X dataloggers, building energy use with NI’s FieldPoint 2000, and nearby vehicle traffic using Nu-Metric traffic counters.
Similarly, North Carolina-based Metrolina Greenhouses uses a Cimtec automated watering system controlled by GE Fanuc Automation’s Series 90-30 PLCs and Cimplicity software running on wired and wireless Ethernet. The system previously used a fiber-optic backbone running though hoses, but it was taking the growers too long to get to each Cimplicity server to control the automated system. Cimtect installed mobile Cimplicity PalmView, which uses GE Fanuc ThinView running on Compaq iPAQ PDAs, allowing the growers to wirelessly program, use, and maintain their system from anywhere in their 30-acre section of Metrolina’s 80-acre greenhouse. Besides time and costs savings, Metrolina has better control of its environment and can add automation components and parameters on the fly.
Honeywell Industrial Solutions’ Mobile Station Process Knowledge System (PKS) uses 802.11b and a thin-client format to allow users to carry a complete operator console into the field. John Tillotson, product manager for Mobile Station PKS, claims it’s being used mainly in petrochemical applications, and is tied to Honeywell’s PlantScape and Experion PKS solutions.
"Most people are afraid of wireless because they’re worried that signals can be backtracked by hackers, but this can easily be prevented with a software firewall for 802.11 and/or by using encryption. Neither of these will significantly affect today’s network speeds," says Tillotson.
4-20 mA keeps wireless simple
Instead of approaching wireless using a fieldbus or Ethernet-based strategy, Phoenix Contact and Omnex Control Systems Inc. are focusing their wireless efforts on plant-floor users who may be less concerned with programming than they are with simply getting a signal back. Phoenix’s Mathews says his company sought FHSS to wirelessly imitate the pure I/O gathering and transmitting abilities of its wired 4-20 mA signal conditioners, which are mounted directly on an I/O device’s terminals.
"We accept 4-20 mA data at the devices and then give it back on the other end of the radio link. So, to the electrician, wireless now looks the same as a wired network," says Åke Severinson, Omnex’s president. "However, it seems as if everyone in engineering and control and automation is from Missouri. They have to see it work, and so we do a lot of demos. They start to become convinced when they see how hard it is to make wireless fail in their own environments." It also helps that Omnex’s solutions typically cost about 1/10thas much as wire and cable.
Working with Trusted Wireless I/O and data radios from Omnex, Phoenix developed its Measurement Control Regulation-Radio Analog Digital (MCR-RAD), which transmits small packets, usually 16-18 bits at 96 baud and at relatively high power, up to the 1-watt maximum allowed by federal regulations. This allows MCR-RAD’s signals to penetrate objects better and transmit over longer distances.
"There’s no programming or protocol needed, and we don’t need big packets because this is just raw 4-20 mA data," says Mathews. "Because MCR-RAD doesn’t need a bus system, it can be used with any digital or analog signal just by wiring the transmitter directly to the device whose performance you want to measure. We’re still working point-to-point, it’s just that one of the points is a wireless multiplexer."
Marc Pedrotti, of R.E. Pedrotti Inc., says his company has used MCR wireless modules for system integration in several municipal water treatment facilities in Kansas. For example, when a new road recently cut the line between the supervisory control and data acquisition system and the pumping station in Olathe, Kansas, the municipality decided to use an MCR radio to send signals across the 1,000 ft. span, rather than install the usual wires and conduit.
On the strength of the savings already generated, Olathe and Pedrotti may soon use the MCR modules in a sewer monitoring application, which would involve checking the ultrasonic flowmeter on a Parshall flume. Pedrotti says a telephone-based modem monitoring the 4-20 mA signal has proven to be unreliable and another proposal using a radio, radio terminal unit (RTU), and a PLC would reportedly cost $3,500 to $4,000. Phoenix’s MCR-based solution would cost about $1,300 to $1,400 and wouldn’t generate a $10-80 per month phone bill. MCR modules may also be used on another town’s water tower, so 4-20 mA signals can be sent back to city hall, eliminating the need for manual monitoring.
Because the initial MCR-RAD was unidirectional and only able to monitor data, Phoenix recently launched a bi-directional radio transceiver, MCR-RT, that lets users perform control and actuation via four analog or eight digital I/O points. Omnex and Phoenix have also announced that they’re developing a point-to-multi-point device.
Meshes and fabrics
Wireless’ flexibility and its need to provide sufficient coverage have inspired some developers to enable their nodes to move beyond sending and receiving messages and to begin serving as routers for neighboring devices. This strategy creates a mesh or fabric of wireless devices that Ember Corp. calls a Wireless Mesh Network. Developed by the MIT Media Lab and manufactured by Ember, this wireless mesh can also be defined as point-to-point-to-point or an ad hoc, multi-hop network. This routing through intermediate nodes is not only rapid, about 100 msec, it’s also self-configuring and self-healing because data packets will automatically reroute through an alternate path if one link fails.
| In a wireless mech network, if one node fails then messages will automatically be routed via alternate paths. |
A manufacturer of tank and pipe heaters for refineries, Tyco Thermo Controls LLC, recently implemented Ember’s Wireless Mesh Network to replace wiring and avoid repeated line-of-sight adjustments required by its former point-to-point wireless solution.
"The rigidity of point-to-point was hard to commission to site specifications, and it was difficult to maintain. The wireless mesh approach made a lot of sense because individual nodes just need to see their neighbors, instead of requiring the whole network to predetermine all its pathways," says Ken McCoy, Tyco Thermo’s electronics business unit general manager. "We tested it and it works great for us, even among heavy extrusion equipment, cement walls, and power switches. In an older facility without a local area network (LAN), you’d just have to drop in a few nodes, tap a little power and, without any wiring costs, you could bring all your temperature points back to a central panel. This really allows a new technology to monitor an older one."
Turning on Wireless Security
"Wireless is just as safe and secure as wire and, in many cases, wireless is even more secure," says Palmer Greene, Pexx Inc.’s VP and COO. Bold words, but only if you don’t know what security is available for wireless networks and applications. Greene has several suggestions:
Turn it on. Implement the security features that are usually already installed in most products and systems, but which most users don’t take the time to activate. This includes basic security features in most wireless access points, and the 128-bit and 152-bit encryption capabilities that also come with most wireless equipment.
Use the IEEE 802.1x security scheme to log on using a name, password, and certificate. This feature is also already built into many wireless devices and enables a dynamic security encryption scheme. It is based on per user, per session, and can be changed on a timed basis.
Use intelligent switching, which is similar to Ethernet switching. Many wireless devices can include or exclude users/clients based on their media access control addresses (MAC), and this can be used to prevent unauthorized access.
Secure a professional opinion, both to help assess the relative exposure of the wireless system being considered, and to help implement the most appropriate solution. Also, use common sense and conduct a value assessment about your data. How risky is it if someone accesses your network? If all they can do is access the Internet, then that access is just an irritant. However, if broadcast data can be used to actuate or control, then the potential risk is high and multiple authorizations are likely needed.
Consider implementing a virtual private network (VPN) with secured routing, allowing communication down one route that can’t be intercepted.
Wireless Types and Profiles
| Type | Band | Bit rate | Name | Facts/applications |
| Source: Control Engineering with data from Matric and IEEE | ||||
| IEEE 802.11 | 2.4 GHz | 1-2 Mbps | 100-m max., all types | |
| IEEE 802.11a | 2.4(5) GHz | 54 Mbps | ||
| IEEE 802.11b | 2.4 GHz | 11 Mbps | WiFi | 14 years old |
| IEEE 802.11g | 2.4 GHz | 54 Mbps | Zigbee | Approval expected 6/03 |
| IEEE 802.11h | 5.4 GHz | 54 Mbps | Under development | |
| IEEE 802.11e | Being developed at media access control (MAC) layer for better quality of service and to allow for more efficiency for voice and video. | |||
| IEEE 802.11i | Also being developed at MAC layer to better address security and encryption. | |||
| IEEE 802.15 | 2.4 GHz | 722-784 kbps | Bluetooth | 10-m max. |
| Wireless application protocol | WAP | Based on wireless markup language (WML) and managed by WAP Forum | ||
| Third-generation | 2 Mbps | 3G | 384 kbps in mobile applications; administered by the International Telecommunications Union (ITU) | |
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