Welcome to the
"Technical Section"
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Doktor Jons
Guide to Closed Circuit TV (CCTV)

CCTV Camera Operation - in a little more detail

CCTV Camera Scanning Techniques (continued)

Historically, with older technology switchers and multiplexers (or high speed frame switchers), it was considered advantageous to synchronise all the cameras to a common signal (a bit like a repeating starting pistol); if you consider the start of a Formula 1 motor race, when the lights go out all the cars start racing, and hopefully there's less chance of them crashing togethor.

In much the same way, if CCTV cameras are told to start scanning their pictures (i.e. externally syncronised), when the pictures are switch displayed, there is then little if any roll or break up in the images, and they don't crash togethor.

However, with the advent of modern 'digital' multiplexers (that sample images at very high speed) there are now hardly any security related situations, where the significant additional costs involved in wiring up every camera in the system to a common synchronising signal, can be reasonably justified.

That said, it was previously possible (particularly with smaller CCTV systems) to 'daisy chain' the cameras togethor, such that the sync. signal from camera one drives number two, and the output from two triggers three, and so on .... but again, this technique has almost certainly been consigned to the dustbin of yesteryear!

Purely on a technical level, the 'time base correction' required to enable various signals to be sampled at maximum efficiency, are now comfortably incorporated into most quality multiplexers, so in that sense at least, whilst external syncronisation sockets can still be found on the back of a very few quality 'box' cameras, this technique has in practical terms, ceased to be of any relevance to the modern installer.

Camera output connections>

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