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Guide to Closed Circuit TV (CCTV)

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All the bolt on bits of equipment ...
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Time and Date Generators (TDG)

The earliest open reel time lapse video recorders didn’t have them; the first generation VHS cassette time lapse machines had them as an optional plug in module, and all the current VCR’s and DVRs used for security recording have them built in as standard.

We are of course talking about a Time and Date Generator.

The need to imprint an accurate chronological reference on any video recordings that may be used as evidence in a court of law, almost goes without saying, but what about those specialist video machines, or indeed domestic recorders, that may on occasions be used for a range of everyday applications, including of course scientific research.

Well there are still a limited number of Time and Date Generators (TDG) which can be bought seperately, then connected up between the camera (or ancillary item like a switcher) and the video recorder.

They all provide for the display of Time and / or Date in varying formats, and usually to the nearest second.

With some video recorders, you can connect a 'Master' clock signal , so that a common TDG will generate the time / date information for all the units connected into the system. Almost without exception, an industrial TDG will have a low voltage battery 'back up' as standard, so once the correct information is programmed in, the unit can be moved around or powered down for short periods, without having to be re programmed.

For specialist high speed applications where events need to be timed down to an hundredth or perhaps even a thousandth of a second, there are specific ‘Time Code’ units which act a bit like a free running stopwatch to overlay a precise point in time, wherever positioned on the picture.

Just recently, a very few DVR manufacturers have developed TDG radio modules, which when connected to the recorder, allow an accurate time to be displayed, courtesy of a radio transmitted signal from an atomic clock. This has the benefit of both providing a time reference accurate to an n'th of a second, but even more importantly, the time display changes automatically with the seasonal clock shift (e.g BST / GMT ); so for some larger system operators, there is no service call required to alter all the time settings on the equipment.

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