Posts Tagged ‘ digital video surveillance systems’



CCTV Multiplexer

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Tuesday, July 5th, 2011

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.

Be sure to check the specifications of the DVR or CCTV multiplexer to make sure that everything is compatible before making your purchase.  If you have any additional questions on multiplexers, please contact one of our security experts via on-line “Live Chat” or by telephone at 866-573-8878 Monday through Friday from 9AM to 6PM EST.

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Surveillance DVR

Written By:
Wednesday, March 2nd, 2011

The backbone behind any good digital video security system is the surveillance DVR or Digital Video Recorder.  It processes the video transmissions sent by the digital video cameras, controls the video cameras, stores the recorded surveillance video footage, and transmits the real-time and recorded video images to the monitor, the internet, or some other output device.  In essence, the surveillance DVR is actually the brain of the security and surveillance digital video system.

The surveillance DVR can be directly wired or cabled to the digital video cameras or the cameras can communicate with the DVR wirelessly.  In many covert (hidden or disguised) digital video surveillance systems the DVR and camera are an all-in-one compact system.

Another method of communication between the DVR and the cameras uses the Internet for the vehicle of the cameras’ transmissions.  This means that cameras can be easily placed in a variety of locations that have Internet connectivity and their signal can be sent all the way around the world via the Internet to a Network Video Recorder or NVR (essentially a surveillance DVR designed to work on the Internet with Internet Protocol or IP ready cameras).

Regardless of the method used to transmit and receive the video transmission signal from camera to surveillance DVR, the DVR’s chief responsibility is to digitally process the information.  It does so by using a unique computer processor Integrated Circuit or IC chip called a Digital Signal Processor or DSP.

Digital video consists of nothing more than digital photographs.  However, these photographs are taken at a high rate of speed and when presented to the human eye at the same rate, trick it into thinking that we are seeing fluid motion video.  Typical high-quality video rate is about 30 photographs, also called frames, per second or 30 fps.

Considering how large a typical digital photograph file can be, you can imagine the amount of digital information in a digital video file.  Hence, the need for the high-speed specialized processor called the DSP.  Consider that a typical high quality photograph may easily contain enough data to make a digital file approximately 1 Megabyte (MB) in size.  For a video file that is 30 minutes long that would be 30 fps x 60 seconds x 30 minutes x 1 MB or a file that is 54,000 MB or 54 Gigabytes in size.  Multiply this times 8 cameras and in one half hour typical 8 channel surveillance DVR has processed over 432,000 MBs or 432 GBs.

Considering the tremendous volume of digital data, one can appreciate very readily why a DSP is superior to an average computer processor since it is designed specifically for the purpose of handling digital video data.

The surveillance DVR’s responsibility doesn’t end here though.  The DVR processes this data into a digital video file. However, the DVR uses a COmpression/DECompression or CODEC utility to make the file just a fraction of the original size without sacrificing much quality of the digital video.

Security Camera King’s surveillance DVRs currently use the latest, most efficient CODEC called “H.264.”  The DSP creates the file using H.264 then saves the compressed digital video file on a recording medium, such as a hard disk drive or some sort of portable memory medium like a Thumb drive or SD card.  In addition, it may make the file immediately available for viewing in real-time on a monitor connected to the system.

If the surveillance DVR makes the video available for viewing over the Internet, it also has further processing to do.  The DSP now has to either download the digital video file to the requesting computer, or more commonly, convert the digital file once again into a different type of file called a streaming file, suitable for transmission over the Internet.

In addition to all this digital data and file manipulating, the surveillance DVR must also handle the responsibility of coordinating the control of the cameras.  Some cameras have Pan-Tilt-Zoom or PTZ functions and the DVR usually instructs the camera what to do with these movements.  Other cameras may have audio recording as well that the DVR must also process.

In addition to the camera processing, the surveillance DVR is also responsible for the display of the video image, live or recorded.  Considering all of these responsibilities, the importance of a high-quality surveillance DVR in a digital video security system becomes readily apparent.  And that’s why Security Camera King only offers the highest-quality DVRs in its digital video security systems.

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