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A Guide To CCTV Equipment And Closed Circuit Television Monitoring

A Guide To CCTV Equipment And Closed Circuit Television Monitoring

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Thanks to doktorjon for helping contribute in the making of this page doktorjon.co.uk

General Questions

1. What is CCTV

Most people think that CCTV is a relatively new invention, but then again, many don"t even know what it is ... so first things first, what exactly is Closed Circuit Television? Well the television bit is perhaps self explanatory; it"s simply about putting a picture onto a television screen, or "video monitor" to give it its correct title. Incidentally, very basic video monitors are essentially televisions, but without the additional circuitry needed, to receive and decode the Radio Frequency signals, which are transmitted through the air.

The "Closed Circuit" bit is actually quite straightforward. Let"s say for example, that you subscribe to Satellite TV. If you watch your favourite television programme, you and perhaps a few million others will be able to receive the transmitted signal through the dish and "set top box". As anyone with a correctly tuned "Telly" can access this signal, we can safely describe this type of arrangement as an "Open Circuit Television" or "OCTV" system.;If a signal is being linked from any source, whether it"s a DVD player, a camcorder, or a surveillance camera, directly to a display device such as a television, this is described as a "Closed Circuit" simply because it is not available to anyone else.

So you can see that in the early days of developing video camera security systems, the pictures from the cameras were almost always sent to a monitor, or a video recorder, or indeed a sealed Control Room under "Closed Circuit" conditions, hence the now widely accepted term "Closed Circuit Television".

2. What you need to know before you buy a DVR

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 thinking about buying a DVR include:

• Frame Rate – The Higher the frame rate the more fluid the playback however also 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 need to delete upto date information

• Image Quality and resolution – The higher the quality and resolution the better picture but however 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)

3. What you need to know about monitors

Their are so many types of monitors, and a wide range of functions available for various applications, but these are really the seven main points to consider....

1) Metal cased monitors are generally far better at reducing and resisting electromagnetic radiation, than plastic cased units.

2) Most industrial monitors provide ‘loop through’ inputs which are terminated. If unconnected, the switch should be set to 75 Ohms.

3) All CRT monitors generate a lot of internal heat. Take special care to maintain good ventilation at all times.

4) If fitted onto a wall bracket, make sure that the monitor is securely fitted, fixed and quite incapable of coming adrift.

5) If the monitor is a multi standard PAL / SECAM / NTSC unit, this can be used to play back recordings using a suitable player.

6) If you leave the same image on a CRT monitor for any length of time, it will eventually ‘ burn in’ to the tubes phosphor coating.

7) Flat screen monitors offer a host of advantages over standard CRT tubed monitors, but the price may still be a limiting factor.

4. Cameras

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 also 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 420 a high resolution is 480 or above however with mono cameras 480 is considered medium resolution and 600 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

Illuminance	Example
0.00005 LUX	Starlight
<1 LUX	Moonlight
10 LUX	Candle at a Distance of 30cm
400 LUX	Sunrise or Sunset on a Clear Day / A Brightly Lit Office
1000 LUX	Typical TV Studio Lighting
32000 LUX	Sunlight on an Average Day (Min.)
100000 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 approximately £500 but 1/3” sensors being considerably cheaper.

• Internal or External

• Does it come with a lens – When buying a camera you should always check whether it is supplied with a lens or not more information can be found in the lens section of this guide.

• Power Consumption

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5. Lenses

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 theirs 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

6. Power Supplies

The amount and type of power your camera will require will vary from camera to camera. Most of the cameras we stock 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. Unlike voltage, you can supply the ampage in excess of what the camera needs as it will only take what it needs. When specifying your installation be sure to make note of what cameras you are installing, what voltage they need to be and how many there are so that you can choose an appropriate power supply . 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 supplys up to 3 Amp suitable for powering multiple cameras. E.g. - An installation with 8 internal colour 12V dome cameras each comsuming 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 you could use a 12V 2Amp metal boxed power supply unit (1202EMC)

Thanks to doktorjon for helping contribute in the making of this page doktorjon.co.uk

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