New Ways to Use Wireless SensorsOctober 18, 2013 By: Todd Hanson, Honeywell Sensing and Control
What happens when you take networking cable out of the equation when developing a communications infrastructure for an industrial facility? Many of the obstacles hampering network expansion go away, and the potential for greater operational visibility increases. Just look at the rapid growth of wireless networks in factories and assembly plants worldwide. Leveraging a wave of advances in reliability, robustness, and flexibility, plant managers are increasingly turning to wireless networks to connect switches and sensors to a variety of controllers and machines. By eliminating the need to install, maintain, and troubleshoot cable, companies cut capital expenditures and accelerate their ROI. With these benefits in mind, users are seeking out and finding new and unique uses of the technology, propelling wireless into a broader range of applications and sectors.
You can find some of these new uses of wireless networking in large, outdoor warehousing, trucking, and aviation facilities. In these applications, harsh operating conditions make deploying and maintaining underground cables prohibitively expensive. Constant heavy traffic breaks cables and connectors. Underground water corrodes cabling. And in regions with extreme climate variations, the ground's annual freezing-thawing cycles stretch and break cabling.
These very obstacles play to the strengths of wireless communications, which offer a practical, cost-effective alternative to installing underground cables. In fact, the advantages that wireless networking brings to the table are driving the technology's migration beyond the confines of the production line into remote and harsh environments.
For example, some large truck fueling stops have experienced customers taking diesel fuel from the pumps without the station's operators realizing it. To combat this theft, the operators are installing switches on the pumps that wirelessly send an alarm when a pump has been opened. Cable connections from the pumps to the station's office would be expensive to install and maintain, especially with heavy trucks constantly rolling across the underground cables. Not only is wireless less costly, but the radios and receivers for this kind of network can be up and operating in a matter of hours.
You can find a similar application at airports. Only in this case, you have heavy aircraft rolling across runways and jet ways. Here, facilities managers are using wireless sensors to indicate when hanger doors are open or closed. In these situations, many hanger doors also have smaller pocket doors that provide access to the hanger interior. A pocket door enables airport operators to reduce air conditioning and heating costs.
Because the pocket doors are mounted inside the large hanger door, the challenge is to connect the position switches that indicate if the pocket door is open or shut. Using cable is problematic. Every time the larger door is opened and closed, the data cables are stretched and twisted, reducing their life span.
One operator's solution was to use Honeywell's Limitless 802.15.4 radios to provide reliable connectivity. A 35 dB link margin ensures that minor obstacles or even heavy precipitation will not compromise communications. The allowable operating range of these radios is greater than 1000 ft. In extreme conditions, such as heavy precipitation, the range may be reduced by as much as 75 ft., but by using battery powered wireless switches, maintenance costs are greatly reduced or eliminated.
Another interesting new application is the use of wireless alarms on emergency industrial showers and eye washes. In some facilities, a wireless switch is embedded in the shower or eye wash mechanisms so that the system automatically sends an alarm when the mechanism is activated. In many locations, however, these "emergency" showers are also used for nonemergency applications, such as cleaning boots, headgear, and clothing. In these cases, it is more effective to simply attach a wireless push button switch that can be activated only in case of a true emergency.
Wireless Health Checks
Wireless switches are susceptible to interference from a variety of sources. In industrial applications, for example, vehicles or large objects occasionally move between the switch and the controller, temporarily blocking the transmission.
Wireless switches often use a "health check" monitoring system to determine when this situation arises so that transmissions can be repeated until the signal is received. If after a period of time the remote switch's signal is not received, an alert is sent to the central controller to allow a plant operator to respond.
The health check also monitors battery strength. If the switch's diagnostics recognize that the battery must be charged or replaced within a week or two, it sends an alarm, providing the facility operator with plenty of time to attend to the issue.
There are many benefits to using wireless sensor networks instead of relying upon a cabled system. Not only does wireless eliminate the costly maintenance, troubleshooting, and repair costs associated with cabling, but it also provides an effective and easy-to-reconfigure network that does not require extensive training or highly skilled technicians to implement.
When plant and facility managers evaluate the advantages and drawbacks of wired versus wireless networks, they should consider cost savings, maintenance issues, ease of installation and configurability, uptime, and security. In many cases, installing a new wireless network is less expensive in both hard costs and installation time than trying to replace an existing wired network.
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