Wednesday, July 13, 2011

CCTV Multiplexer




A CCTV multiplexer or Closed Circuit TeleVision Multiplexer allows more than on camera to be connected to the unit but only one output at a time is allowed through the unit.  Most Digital Video Recorder or DVR units have this function built right in to the DVR.  Another way to describe a multiplexer is by its function which is to combine various input signals and generate only one output signal.  You can almost think of a CCTV Multiplexer as being similar to a computer router.
For digital video security and surveillance systems, the multiplexer is what allows the display of 8 cameras simultaneously.  Eight video transmission cables from eight individual cameras connect to the multiplexer.   The multiplexer then takes the 8 individual camera inputs and combines them into one.  This how you are able to view 8 digital video security and surveillance system cameras on one monitor.
A CCTV multiplexer works by allocating bandwidth; this highly refined process insures that the transmission medium is used efficiently.  There are actually four different methods of multiplexing:
* Space division;
* Frequency division;
* Time division; and,
* Address multiplexing.
Generally speaking, digital transmission uses time division multiplexing and analog transmissions use frequency division.
In applications like cable TV each channel the user visits is broadcast on the input cable at a different frequency.  But with a CCTV application however, since the cameras are all on a closed circuit, all use the same frequency.  With each camera broadcasting at the same frequency there would be no doubt of the signals getting jumbled up, interference, and cross talk.  Literally, about the only way to handle that situation would be for every camera input to have its own monitor.  In other words, a 16 camera system would require 16 separate monitors.  CCTV multiplexers were designed to put as many cameras as possible on one monitor and reduce the user’s cost by relieving the need for the same number of monitors as there are cameras.
Multiplexers are available in a variety of sizes.  Since the DVR often contains the multiplexer, the multiplexer can be custom designed within the DVR unit itself via the manufacturer of the DVR.  However separate, external multiplexers are still available and used today in about three different configurations based on the number of cameras (channels) that are being used.  Common sizes for stand alone multiplexer units are 4, 8, 16 and 32 channels (camera inputs).
Setting up a multiplexer is rather easy and doesn’t require much prior knowledge of digital video security systems.  Some multiplexers do have a few different features that you will need to activate if you want to use them.  These may include the ability to view one channel at a time or all or multiple channels at the same time.  Some units may also have a “dwell” setting.  Dwelling is the term applied to multiplexers that describes the ability to display a particular camera for a certain period of time before showing the next cameras.  This process is repeated cyclically as the multiplexer moves through each individual camera one at a time.  This is also known as “dwell time.”
Some CCTV multiplexers not only can dwell, but some also come with a hand held remote control that allows the user to stop or move-on a particular camera in the system.  Setting the multiplexer up for use with these features is usually accomplished with On Screen Displays or OSD that make the set even quicker and easier.
In the past, CCTV multiplexing was not an option but was a definite requirement if you wanted to see more cameras than just one on a monitor.  Today, with LCD and LED monitors multiple camera viewing is very easy.  Now the only question is how many cameras do you want to view at once?  Of course this is dependent on your DVR which ultimately means, dependent on the multiplexer built into your DVR.

Source : http:// www. security cameraking .com/ securityinfo /

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