Wireless Can Fine-Tune Your Access Business
Smart Design Means Preparing to Contend With Multiple Obstacles
To begin the design phase, reference Figure 2, which illustrates a typical first-floor layout with offices on the perimeter of the building and an open atrium in the middle. The building measures 275 feet by100 feet with 16 doors that need to be secured. Coincidently, there are PIMs that can support up to 16 doors with select access control systems. Therefore, only a single PIM will be needed, right? Not necessarily.
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Refer to the two squares marked with Xs in the center of the atrium in Figure 2. Those are elevators. And guess what? Elevators usually have stainless-steel doors and metal panels, causing an RF “shadow” or an area where RF transmissions won’t propagate.
It’s always smart to design around such obstacles. In this application, placing PIMs on either side of the elevator will eliminate the shadows entirely. This is an example of how to prevent potential intermittencies. Let’s review why.
With a single PIM configuration, the system will work when the elevator car is on an upper floor. But when the elevator lands on the ground floor, the metal content in the cab will block the signal. That could cause a momentary RF shadow, which could appear as an intermittent problem. With the PIMs placed on either side of the elevator, the problem has been solved.
Repeaters Are Handy Tools When Clear Line of Site Is Not Available
Remember, line of sight is the unobstructed transmission path between your wireless access point modules and the PIM to which they are linked. Figure 3 makes this clear. While referencing Figure 3, see how Building B and the tree obstruct the signals coming from Building A.
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You’ll recall a cell has a 200-foot coverage radius for indoor applications. Outside, however, free from obstructions such as trees, fences and walls, a 1,000-foot line of sight can be achieved. What happens if a stand of trees is in the way or when the acc
ess point is farther than 1,000 feet? No problem. Look at Figure 4, which shows a building and two vehicle entrance gates, along with a stately tree in the northeast corner of the building. You could cut down the tree to eliminate the obstacle, but that isn’t a likely or an appropriate option.
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The most advantageous option is to use a repeater. When looking at Figure 4, you will see that there is a clear line of sight between the main building and Gate 1, and the distance is less than 1,000 feet. This is the perfect scenario for a wireless gate kit, comprised of a PIM, an outdoor wireless reader interface (WRI-OTD), and an indoor/ outdoor remote antenna. Such a solution allows you to mount the PIM indoors, mount the remote antenna outside, and mount the WRI at the gate, as shown in Figure 5.
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However, Gate 2 creates a new quandary since the tree proves to be a transmission obstacle. The remedy? Take advantage of the clear line of site between the building and Gate 1, and from Gate 1 to Gate 2. If we place a repeater at Gate 1, we can link it to the main PIM and also link the repeater to the WRI at Gate 2, as shown in Figure 5. When compared to a wired solution, this saves hundreds of feet of costly trenching and weeks of disruption.
Take a Conservative Approach to Ensure 100% Coverage
Before we apply some of what we learned above, it is important to note: keeping a meticulous site survey worksheet can be a great help in recording and tracking all needed equipment, leaving nothing to chance and providing a basis for getting a quote on doing the job.
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Now let’s proceed by protecting the 150 foot by 150 foot L-shaped building in Figure 6. Using the PythagoreanTheorem, the distance between the two corners is 212 feet, which is pretty close to our 200-foot rating. However, if you put the PIMs in Room 14, you should be able to cover the entire floor. That’s because the RF can cut across the open courtyard between the building’s two wings.
But, there is a problem. You don’t have control over the courtyard. The blueprint shows only the building dimensions; you need to plan for the unexpected. How will the space be utilized in a year or so? What happens, if after building completion, landscapers install trees, shrubs, flowers, picnic tables and a walking path, as shown in Figure 7?
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Using Murphy’s Law, you can expect the trees will eventually impede the signal from reaching Doors 1, 23, and 24 as shown in Figure 7. And, you’ll get that call at 10 p.m.! That’s why it is best to be more conservative in your planning as in Figure 7, where you split the PIMs between Rooms 6 and 14 to ensure 100-percent coverage.
Lester LaPierre is marketing manager for Schlage, an Ingersoll Rand Security Technologies company based in Forestville, Conn.He can be reached at (866) 322-1237 or [email protected].
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