Welcome to the
If it's video switchers
When CCTV systems get large they generally scream for a video switching matrix thats man enough for the job.
Most manufacturers (and there really are only a relatively few) design their systems to be modular in structure, so by using an industry standard 19 rack mount enclosure, the system can be built up in stages.
Smaller matrices may only accept a few dozen cameras, whereas their 'big brothers' are easily configurable to accept thousands of inputs (cameras), switching to hundreds of outputs (monitors or videos).
Using a specific system control module, and a power supply that can support a certain number of 'cards', the unit can be configured for an appropriate number of video sources, and still have room for future expansion.
Whilst the specific configuration of a matrix will vary between manufacturers, the principle remains pretty much the same.
The cameras are connected to Video Input Cards, which usually accept between eight and sixteen camera signals. So obviously, the more cameras in the system, the more cards are needed to handle all the signal feeds.
Likewise, Monitor Output cards are capable of routing a selected signal to any number of connected monitors. Again these cards are usually configured for six to twelve monitors per card. Seperate ancillary circuit boards are also used for audio, and whatever control protocol is adopted by the system control unit(s).
Overall, the biggest problem (apart from the risk of total power failure, sabotage or a lightning strike!), is simply trying to remember all the correct codes for each individual camera .... bit of a nightmare. but that's where touchscreen systems come into their own (more later!).
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