|
|
About CCTV
So What is Closed Circuit Television?
Closed Circuit TV (CCTV) is a television system which operates on a 'closed loop' basis. Unlike broadcast television which is available to anyone with a suitable receiver, CCTV pictures are only available to those directly connected to the loop.
CCTV was first used in the 1950s and has since become an essential part of any professional security system.
In most CCTV installations, the loop is a physical link, a cable, which carries the picture from a camera to the viewer. However, over long distances, e.g. town centres, fibre optic transmission has become very popular. This can be very expensive and a cheaper alternative is ISDN (Integrated Services Digital Network).
CCTV has a wide variety of applications:
Monitoring Theft or criminal damage
Deterring would be offenders
Access to secure areas
Personal safety
Traffic control
Alarm verification
Crowd control
Insurance claim assessment
Public access
Staff control
Car Park security
Shopping Precinct security
Industrial Process control
CCTV offers increased efficiency and the faster detection of problems. Other benefits include: reduced security running costs, faster response to problems, peace of mind, simplicity and reliability, improved quality of environment for owners, operators and the public, easier identification of suspects and increased management control.
back
About Cameras
Monochrome vs Colour
Generally Monochrome Cameras have a higher image resolution than colour cameras. In low light conditions a monochrome camera will produce better results. In addition, Colour Cameras are not sensitive to Infra Red Light.
High Resolution
Camera resolution is measured in the number of TV Lines, the greater the number of TV Lines the more detail the camera is capable of transmitting.
Back Light Compensation
Many cameras are now equipped with a Smart Control which automatically adjust to the level of background light. This enables the camera to pick-up detail which would otherwise be missed.
1/2" or 1/3" Format
1/3" and 1/2" refers to the size of the imaging area of the CCD sensor in the camera. Generally speaking the greater the sensor area, the higher the resolution of the camera. Although more recently high performance 1/3" CCD imagers have improved in resolution considerably.
Sensitivity
Choosing a more sensitive camera will improve picture clarity. This sensitivity is measured by the minimum amount of light (Lux) required to produce a picture.
back
Lenses
C Mount and CS Mount Lenses
C and CS Mount lenses can be differentiated by the flange back focal lengths as shown below.
C Mount Lenses = Rf’ 17.526mm
CS Mount Lenses = Rf’ 12.5mm
Fixed Focal Lenses and Varifocal Lenses
The varifocal lens is a zoom lens. The magnification of a focused image may be changed by varying the focal length of the lens. The focal length (f) has a direct relationship with the view field, which is calculated by the ration between the focal length of a lens and the size of the image pickup devices.
Focal Length
The focal length represents the distance from the optical centre of the lens to the point at which the image is in sharpest focus and where the pick-up device in the CCTV camera is located. The smaller the focal length is set, the wider the view field grows, while the larger the focal length is set the narrower the view field becomes. Lenses with focal lengths between f12 and f16mm are typically referred to as standard lenses, while those with focal lengths below these values as wide-angle lenses and those above these values as telescoping lenses.
View Field
A view field is defined as the largest angle in a certain size of an image pickup device. The view field can be obtained by the equation opposite, with a given focal length and size of an image pickup device.
Particular attention should be paid when selecting lenses and cameras, since the view field is not only determined by the focal length of a lens but by the size of the image pickup device of a camera.
back
About Light
Light
The Human eye and the camera operate on completely different lines. The human eye can adjust automatically to the various lighting conditions around it. The camera is inherently less flexible.
In a CCTV system, the lighting has to be considered from the beginning if the best results are to be obtained. The type of lighting used, as well as its positioning is vital if your system is to provide maximum security.
Everyday ‘White’ light is actually a mixture of colour of different frequencies of light. CCTV is more susceptible to certain colour combinations than others. The best results are usually obtained by matching the spectral response of the camera to the light illuminating the scene.
The amount of light reflected from an object determines how ‘bright’ it appears.
Lux
Lux is the metric unit of measurement of light. The table below describes some of the average lighting conditions which could be associated with certain Lux values.
Lux Description
50,000 British Summer sunshine
5,000 Overcast sky
500 Well lit office
300 Minimum for easy reading
50 Passageway/outside working area
50 Good main road lighting
10 Sunset
5 Typical Roadside lighting
2 Minimum Security risk lighting
1 Twilight
0.3 Clear Full Moon
0.1 Typical moonlit/cloudy sky
0.001 Typical starlight
0.0001 Poor starlight
back
About Housings
All Camera Housings, whether for internal or external use, are given an IP rating. This is a measure of weatherproofing governed by European and British manufacturing standards.
The First Digit determines the degree of protection from solid objects, the second protection from the ingress of water.
Solid Object Protection
Liquid Protection
1st Digit
Degree of Protection
2nd Digit
Degree of Protection
0
No Special Protection
0
No Special Protection
1
Protected against solid objects greater then 50mm in diameter
1
Protected against dripping water (vertical drops will have no effect)
2
Protected against solid objects greater then 12mm in diameter
2
Protected against dripping water when tilted to 15 Degrees
3
Protected against solid objects greater then 2.5mm in diameter
3
Protected against spraying water
4
Protected against solid objects greater then 1mm in diameter
4
Protected against splashing water
5
Dust Protected (Ingress of dust is not totally prevented, but dust does not enter in sufficient quantity to interfere with satisfactory operation of the equipment
5
Protected against water jets
6
Dust Tight (No ingress)
6
Protected against heavy seas
7
Protected against effects of immersion
8
Protected against submersion
back
About Monitors
Size
Monitors are available in a range of sizes from the very smallest portable and LCD screens to the largest of plasma display panels. When choosing a monitor, the correct size obviously depends on its use, e.g. how many pictures are to be displayed at any one time, viewing distance and the available space. Monitors are measured in inches or cm, being the diagonal length of the tube from corner to corner
Monochrome & Colour
Colour Monitors usually accept only composite colour signals. Where extremely high quality images are required monitors with Y/C (luminance and chromiance) input should be used.
back
|
|
| | |
