At the North America Emerson Exchange in October, I'm conducting a workshop on "Everything You Wanted To Know About Wireless But Were Afraid to Ask". This is designed to be a technical discussion and will include questions (sometimes obscure) that we get asked. For example:
Laura,
Based on my conversations with customers regarding wireless, here are a few frequently asked questions:
What are the differences between the wireless plant network (WPN) for Mobile Worker and wireless pervasive field network (PFN) for WirelessHART devices?
Both the wireless plant network (WPN) and pervasive field network (PFN) operate in the unlicensed 2.4 GHz spectrum. However, interference is minimized by the WIrelessHART protocol's use of Frequency Hopping Spread Spectrum (FHSS) and Cisco's use of Dynamic Frequency Selection (DFS). These technologies select the least congested channels for transmission. The WPN utilizes the ubiquitous 802.11b/g/n protocol for client communications and 802.11a for mesh member backhaul traffic. The PFN uses the industry standard WirelessHART protocol for communication between devices. The WPN is composed of a mesh of wireless access points relaying data back to a central root access point hardwired a plant ethernet network. The PFN is composed of a mesh of WirelessHART devices relaying data back to a DeltaV WIreless I/O Card (WIOC) or 1420 Wireless Gateway.
Is WirelessHART secure?
Similar to the WPA2 key authentication in your home or office 802.11 network, WirelessHART devices may only participate in a network in which they have the correct Network ID and Join Key. Communication between authorized devices will not be disrupted by the presence of unauthorized devices in the same physical space.
Can I use an iPad as a wireless client for DeltaV?
In theory, any device that can host a Remote Desktop Protocol (RDP) session can connect to a DeltaV Remote Session on a ProPlus or Application Station. The Mobile Worker solution utilizes Remote Access Server (RAS) and not RDP. One reason for this architecture is to preserve your DeltaV session credentials if the wireless signal is temporarily lost. If you lose connectivity in an RDP session, you must relogin to DeltaV even if the RDP client automatically logs you back in to the Windows session. The RAS client machine is running DeltaV natively inside of Windows.
Do I need separate physical wireless networks for the WPN and PFN?
No! Per the Mobile Worker Product Data Sheet: (www2.emersonprocess.com/.../WPN%20Service%20DS%20Mobile%20Worker.pdf) "Field Data Backhaul. Using the same Wi-Fi MAPs
for your mobile worker, Emerson can wirelessly connect your remote Smart Wireless field instruments back to your central control room."
You can also use the wireless mesh network for carrying wireless video traffic that can be integrated into DeltaV or other Plant systems. When possible, WirelessHART devices are incorporated into DeltaV using Wireless I/O Cards (WIOC), but the Rosemount 1420 Wireless Gateway may be used for remotely located wireless I/O.
Lara,
It seems that the questions that I get have to do with what is unique to wireless, mostly on how the network works and how to manage the batteries.
Some questions on the battery anxiety front:
Q: For wireless transmitters, how long will the battieries last?
A: The life of power modules in Smart Wireless transmitters is primarily dependent on the wireless update rate that is selected. When our wireless transmitters are shipped they are set to update every 60 seconds. At this update rate, for many of the transmitters, the power modules will not need to be replace for ten years.
Q: Power is critical for wireless transmitter, why are they not each equipped with a solar panel, so that they can be powered by sunlight, or ambient light in the factory?
A: We have found that the economics of solar power just does not work out over the life of our transmitters. Even at faster wireless updates, it is cheaper to replace the power module every few years, than it is to purchase and maintain a solar power system. In many cases, the rechargeable batteries that are required as a part of the solar system need to be replaced every couple of years. The power modules that we use, which contain non-regargeable batteries, simply provide a lower life-cycle cost.
Tracy Niebeling | Product Marketing Manager, Wireless | Rosemount Inc. Emerson Process Management | 8200 Market Blvd. PL18 | Chanhassen | MN | 55317-9685+1 952 949 7201
In reply to Tracy Niebeling:
Tracy, You make a good point about the economics and logistical issues using solar power for wireless transmitters. A much more viable technology for extending the battery life of the transmitter, even at the fastest update rates, are vibration energy harvesters. My company is working with Rosemount to offer a Vibration Energy Harvester (VEH) power option for the Smart Wireless transmitters. At a 2 second update rate it will extend the life of the batteries by 3.5X. At 4 second and slower update rates, no battery changes would be required for 10+ years. They are robust & reliable, hazardous zone certified, eliminate or minimize battery chage maintenance logistics and can lower life-cycle costs with a good ROI.