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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.

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Video Loss Alarms (VLA)

For most general CCTV applications, the loss of a particular picture may not necessarily be a routine occurence, but unfortunately it does happen from time to time.

In mission critical applications where the loss of cameras for even the briefest of periods may seriously compromise the sites overall security; one obvious option is to fit a Video Loss Alarm (VLA) unit.

These devices constantly monitor the video signal coming from the camera, and in the event of a power, equipment or transmission failure, an alarm will automatically trip to provide a visual and audible indication of which camera has gone down.

Some more advanced items of equipment such as top end multiplexers and quads, also have VLA circuits built in, so in the event of a breakdown or sabotage, they may well display the last available image along with an alarm status indication, and indeed in some cases, an automatically updated electronic log indicating what happened and when.

Under certain operating conditions, this type of loss alarm can become a security risk in itself

For a CCTV control room operator, the failure of a key camera, to be replaced by the last frozen image from the disabled unit, can easily be overlooked as the significant problem it undoubtedly has become.

Wherever there is a significant risk of individual cameras being deliberately disabled, and thereby causing a major breach in security, a seperate low cost Video Loss Alarm device can significantly increase the integrity of the CCTV system. So if anyone does try to disable a camera, or inject a static video image into the record / display system, the VLA should create an immediate alert, which hopefully a well trained operator will recognise as something other than simply an equipment malfunction..

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