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Guide to Closed Circuit TV (CCTV)

So would you like to play "Spot the CCTV Camera?". Eagle eyed visitors may recognise the profusion of street furniture, surrounding a single heritage dome camera keeping watch over part  of Londons' prestigious Oxford Street shopping area.

If you need to handle
multiple images ....

Recording Multiplexers

Although early display and recording multiplexers were built as seperate units, the modern designs are highly engineered to provide both functions ‘in the same box’. Whilst this approach undoubtedly provides a convenient and more affordable package, in one respect it again places a high level of reliance on a single piece of equipment, which can so easily fail and compromise the integrity of the entire system. In practice, a recording multiplexer fulfils a very specific, and in most situations absolutely essential function, which is to send the images from all connected cameras, direct to tape (or single channel DVR).

It does this by sequentially ‘grabbing’ an image from each connected camera, and then passing the processed image to the video recorder (whether analogue tape or DVR); when all the cameras are recorded, it repeats the process continuously, for as long as is required:-

(e.g. 1,2,3,4,5,6,7,8, then 1,2,3,4,5,6,7,8,then again 1,2,3,4,5,6,7,8,...etc. ).

On playback, the unit can be instructed to replay all the images from an individual camera, or reconstitute a number of cameras on screen, as a replay mosaic.

In general terms, the picture quality of modern multiplexers is very good, with some now achieving resolutions at around 520 horizontal lines, so there really is little excuse for not producing impressive quality images.
With the current designs of multiplexer, they are often described by the manufacturers as offering ‘duplex’ or triplex’ operation, which simply means that they can do two or three different things at the same time.

This might be record to tape and display independantly, or record to one machine, and replay from another; in fact as the designs develop in sophistication, there are various permutations of what can be achieved within the confines of a simple box of electronics (okay so it’s not really that simple!).

The most recent designs of Digital Video Recorder (DVR) are now offering built in duplex or triplex operable multiplexers, and there is no doubt that the industry will embrace this technology over the next few years; but Doktor Jon would still have some reservations about the risk to system integrity, in the event that a tiny component fails, and the whole box of tricks has to be sent away for repair.
These expensive yet impressive tools should only really be used, provided adequate safeguards and back-ups are incorporated into the overall system design.

Computer based Multiplexers >>

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