The quest for quality quads.
PICTURE YOURSELF AS RESPONSIBLE for guarding valuable items that are moved in and out of a 20,000-square-foot building. You use a sequentially switching, eight-camera, single-VCR recording system to monitor the site. Inventory control suggests that an item has been stolen within the last 24 hours.
Before playing back the videotape, you conclude that five of the eight camera zones have to be reviewed. The theft occurred between noon and 6 pm.
The tape is now playing back, and the fun begins. With the cameras switching during playback, it is difficult to follow any movement, so you slow down the playback mode. Hours later you notice the item in question is recorded by camera 2. A shadow indicates that someone is approaching the package. You advance the VCR to the next frame, and--oh, no! Camera 3 appears, then 4, and so on. By the time camera 2 appears again (16 seconds later), the room is blank: no item, no suspect.
Despite the existence of alternatives, sequential switchers dominate existing CCTV recording and monitoring systems. Costs and the fact that most existing CCTV systems were installed in the 1980s account for this dominance.
But security managers have been demanding more efficient recording and monitoring controls. More than 15 manufacturers have responded with four-, eight-, and in a few cases 16-position quad multiplexers, all of which are generally known as quads.
Most quads have four or eight camera inputs and one main output for recording and monitoring multiple cameras on one VCR and monitor. Simply put, four cameras are viewed on one monitor simultaneously. The eight-position quad first views cameras 1 through 4 simultaneously, then switches (in one- to 10-second intervals) to cameras 5 through 8, then back to 1 through 4, and so on. Many models have additional outputs for remote monitoring and recording. GIVEN THE SWITCHING SYSTEM'S FAILURE to detect the thief, what can you do? A CCTV dealer suggests two four-position quad systems to replace your single eight-camera switching system. The current cameras can stay; however, the quads replace the switcher, and an additional VCR and monitor are needed. Labor costs are minimal, so for $5,000 you can eliminate the problem of the 16-second recording gap of each camera. The money is approved, and the new system installed.
Soon the same theft situation occurs. This time your incident report notes the recovery of the item plus a decrease in overall shrinkage due to shoptalk about how the new system works. After your glowing report, the controller pulls you aside and asks about these new eight-position quads that would have cost only $2,000 because they would have worked with the existing VCR and monitor.
Let's back up to the mid-1980s, when four-position quads first made a presence. Poor picture quality and a staggered, jerky motion was the price paid for choosing quad over sequential switching. Not only did the quads cost more, but the overall system costs increased by over 30 percent due to the extra VCRs and monitors needed.
Fortunately, the options improved with new eight-position quads in the late 1980s. An eight-position, real-time-refresh-rate quad introduced at that time eliminated the jerky movement and worked well with virtually any camera whether it was line-locked (synchronized to keep the picture from rolling during switching) properly or not. A mixture of 12-volt DC and line-locked 24-volt AC cameras was permissible. NO TWO SECURITY MANAGERS HAVE THE same needs. Therefore, system recommendations should be made on a case-by-case basis. More than 30 models of quads are available from over 12 manufacturers under 20 different labels. If you are recording information for both internal investigations and criminal prosecutions, the following guidelines may be helpful when you are choosing a new system:
Refresh rate. Try to avoid quads with refresh rates of 15 or 30 fields per second. A 60-field-per-second refresh rate provides smooth, real-time playback and monitoring. Typically, models with that rate are more expensive and provide better picture quality than models with slower refresh rates.
Ease of installation. Although equipment costs have been declining, the costs of labor, cable, and conduit always increase. It is common for a CCTV system involving fire-rated cable to have a labor-to-cable cost ratio of one to four.
Let's consider labor as the combination of labor, cable, and conduit. Labor costs can never be traded in. In most cases, conduit and cable, once laid, are rarely reinstalled. Doesn't it make sense to keep labor costs down?
Replacing a sequential switcher with a quad and keeping the cameras will work flawlessly with some quads. If the cameras are 12 volts DC and not gen-locked (another form of synchronization), some quads will not work. If the cameras are 24 volts AC, some quads will work only if they are perfectly line-locked. Power-over-the-coax (single-cable) quads will always work as long as you replace the cameras with ones made specifically for that quad.
If you have old, burned-out tube cameras, most dealers would recommend replacing them with chip cameras. If you use a gen-locked system, three cables will have to be run per camera. With a 24-volt system, two cables must be run per camera, and with a power-over-the-coax system, only one cable has to be run per camera. Needless to say, a single-cable system uses less cable and therefore a smaller conduit diameter size and less labor.
Record four, play back one. Is this feature the sizzle or the steak? Some four-position quad manufacturers promote the fact that their quads can play back any individual camera on the full screen. If such a feature adds to your cost of the quad, then it is not worth it. This feature simply blows up the picture by four times and reduces picture quality by four times.
It is not difficult to concentrate on one camera while the others are playing back simultaneously because no switching is involved. If you cannot concentrate on one quadrant, cut a quadrant-size square out of a piece of cardboard and cover up the other three quadrants. The ability to record four and play back one is definitely sizzle and not a significant benefit.
Record eight cameras, play back two. All the sizzle of the four-position quad applies, plus an additional drawback. In the playback zoom mode of one individual camera, you must bring an unwanted other camera into the playback mode. You will see the view that appeared in, say, the lower left quadrant, but keep in mind that in an eight-position quad, each quadrant switches back and forth between two images.
Remote monitoring quads. In many cases, security managers need to monitor all or part of the recording quad system from a remote location. With a four-position quad you can simply loop out of the recording monitor.
If you want individual cameras monitored, then a looping quad gives you the most flexibility. One coax cable is needed for each camera that is to be monitored individually.
The same holds true for an eight-position quad, except that remotely monitoring more than four cameras through the monitor produces switching that is difficult to follow on a monitor. In any event, eight-position undedicated quads require one or more cables to be run for each camera to be remotely monitored.
With power-over-the-coax dedicated quads, you need run only one cable to the remote site, and with one monitor there you can see any combination of cameras. You can also view any individual camera by controlling the submonitor output on the quad.
The submonitor does not affect recording. Remote controls are available that give the remote monitor attendant control over which cameras are viewed. Such a set-up requires one 12-conductor cable and one coax cable.
Color. Most quads do not handle color. The ones that do allow for a mixture of monochrome and color. Some monochrome quads pass color if they are programmed to switch from quad to full screen. In those cases, only the full-screen picture is in color.
Security managers are waiting for color systems to come down in price before they order them. Manufacturers are waiting for more color orders so they can produce color quads in quantity and lower the price.
In sum, when choosing a quad system, consider the labor costs involved with each model. Think about your options for future additions. Always insist on 20-gauge, solid-copper coax cable with 95 percent copper-braided shielding. These considerations will help you in the long run.
Remember that on cable runs of 1,500 feet or more, a thicker cable may be needed, and that some cable runs are simply too long for a quad to work effectively.
Nevertheless, despite the loss of picture quality, especially with 15- or 30-second refresh rates, quad multiplexers can significantly increase your chance of retrieving information.
Joseph Gabriszeski is CCTV director for A-Com Inc., a security electronics contractor and distributor in Chantilly, VA.
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|Title Annotation:||theft monitoring equipment|
|Date:||Aug 1, 1991|
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