CCTV Systems Guide
Abbion Fire and Security Systems appreciates that purchasing a new CCTV system is an expensive and technical issue. Here on this page, we will try and help you understand a little more about CCTV Systems and what they involve. Please keep checking back as we will always try to keep you updated of new developments wherever possible. Any further questions or queries will be answered as soon as possible by contacting us.
DVR'S - Digital Video Recorders
Unlike the ‘Analogue’ VCR (Video Cassette Recorder), a Digital Video Recorder (DVR) is very different and often totally misunderstood. Firstly in terms of conventional CCTV, with very few exceptions, the camera signals are being input into the recorder via a standard composite video (CVBS) analogue input (BNC connector). The individual images (fields or frames [each comprising of two interlaced fields]) are converted to a standard recognised protocol, such as MPEG-4, M-JPEG, JPEG2000 or Wavelet, which are unique and totally incompatible compression formats, that allow data rich images to be stored as a stream of ‘slimmed down’ coded files. Some of the main things to consider when purchasing a DVR based CCTV system are:
Frame Rate – The higher the frame rate, the more fluid the playback however a higher frame rate will use up more hard drive space. (Real-time recording is 25FPS)
Maximum Hard Drive Capacity – The bigger the hard drive the more you can record without the need to delete up to date information
Image Quality and Resolution – The higher the quality and resolution the better picture but, again, just like frame rate the better the quality, the more hard drive space will be used so a compromise must be made.
Backup Facilities – There are several different methods of backup such as CD, DVD or over a network. CD backup is the most common form of backup for DVR’s however DVD’s have larger storage capacities so can store more footage per disc. The other method of backup is via a network which involves streaming the data onto a computer using specific software and then converting previously recorded data as its being played back into a specific file type such as AVI.
Networkability – If you want to view what’s happening over a network or the internet you will need a DVR that has the ability to network. There are also several other points to consider when networking such as the speed of the network, for example if you are connected on a Local Area Network you will receive almost real time streaming. However over the internet with a 512kb upload speed you will get between 1/2-5 frames a second this varies depending on the compression algorithm and internet speed of each user (The DVR and the person viewing)
There are three main types of cameras to consider; mono, colour and colour/mono. All have their own advantages and disadvantages. The advantage of mono cameras are the cost effectiveness of them and as they don’t display colour they are able to achieve higher resolution for a cheaper price. Colour CCTV cameras are better for evidence purposes as they display in colour where things may be more difficult to make out on mono cameras. Colour/Mono cameras have an advantage as you get the full quality of colour during the day and then can still receive mono images during the night.
Other than the type of camera you require there are several other important factors to consider when buying a camera these include:
TV Lines – The higher the TV Lines the better the quality of image on the camera. An average amount of TV Lines is 420TVL, a high resolution is 480TVL or above. With mono cameras 480TVL is considered medium resolution and 600TVL considered high.
Minimum Illumination – Light is measured in LUX. Below is an example which should help you in choosing what the minimum LUX you require is
|10 LUX||Candle at a distance of 30m|
|400 LUX||Sunrise/sunset on a clear day/brightly lit office|
|1000 LUX||Typical TV Studio Lighting|
|32000 LUX||Sunlight on an average day (min)|
|10000 LUX||Sunlight on an average day (max)|
CCD Image Sensor – there are various sizes of image sensors ranging from ¼” to ½” the larger the size of the chip the better the picture quality however the larger the chip the higher the price of the camera with ½” cameras costing a lot more but 1/3” sensors being considerably cheaper.
Lenses determine the angle of view of your camera. Lenses with longer focal lengths give a narrower angle but further viewing distances (see the image below)
There are several types of lenses, the two main types of lens are fixed focal lenses and vari-focal lenses.
Fixed focal lenses only have one aperture whereas with vari-focal lenses the aperture can be changed within a certain range for example 2.8-12mm. Secondly there is the choice between fixed iris, manual iris and auto iris lenses. Fixed iris lenses stay in a fixed position and always let in the same amount of light so if it get too bright for the camera the picture will become too bright. Manual iris lenses have the ability to change the size of the iris however this must be done manually by the user. Finally auto iris lenses work as the name suggests by changing the lens depending on the brightness.
The amount and type of power your camera will require will vary from camera to camera. Most cameras require a 12V DC power supply although some have dual voltage 12/24V adapters built in and some cameras require 230V AC power. The voltage of the camera you need will vary depending on the installation but most of our customers use 12V DC cameras due to the fact that high voltage 230V cameras require a qualified electrician to provide a link to the mains. It is very important that you do not supply a higher voltage than the camera is rated for as this will blow the board and the camera will be useless. Once you have found out the voltage of your cameras you will need to find out their power consumption. Power supplys are needed whenever you are using a 12V or 24V camera to transform the 230V from the mains to the appropriate voltage. The PSU's are available as individual plug in units up to 1 Amp (1000mA) suitable for single cameras and as metal boxed power supply’s up to 3 Amp suitable for powering multiple cameras. E.g. - An installation with 8 internal colour 12V dome cameras each consuming 200mA would require the power supply to be able to provide 200mA to each of the 8 cameras. Therefore you would need at least 1.6Amp (1600mA) to power all the cameras. In this case we would use a 12V 2Amp metal boxed power supply unit (1202EMC)