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Selection and use infrared illuminators

The importance of choicing Infrared Illuminator is the compatibility

of  the camera and illuminator, lens, cover, power supply etc.  In the

design of programmes for the integrated system, the engineer should

considered to design the whole sets of equipment  as a low intensity

infrared night vision surveillance systems. It is incorret for people who

first buy cameras, lens, covers, power supply and even install them before

purchase the infrared illuminator,  People should pay attention to the

following issues.

1.Use black and white cameras, color cameras or special transformed

ordinary colour cameras
CCD image sensors have very wide spectral range photosensitive, the

photosensitive spectrum includes not only the visible area, but also

extended to the infrared area. To use  this feature, the camera could be

use under  invisible conditions at night, and the infrared illuminator

will support the CCD image sensor to get  clear image. Ordinary colour

cameras can transmit colour signal from the CCD output signal devices

separate from the three green-blue-red base color video signals, and then

synthetic colour television signals. The photosensitive can only be

installed in the visible spectral region, if it is possible to achieve the

transformation of its infrared light region sensory functions through its

CCD infrared filtering glass, the front infrared can penetrate into the

850nm infrared filtering glass or without infrared filtering glass.

(attention! Without infrared filtering glass color change may lead to

cameras.)

With the advances of technology, the current market colour day and

night conversion camera is used a cut-over two CCD or a CCD digital

circuits used for the cut over, but the existence of black and white

illumination is higher, some of the shortcomings effects of colour will

gradually be eliminated. The infrared sensitive of Low intensity colour

and infrared camera is four times higher than normal camera.  With the

tend of lower costs,  it will become the trend.

2. To select an 850nm infrared camera with low intensity respondent
Low intensity means that  the optical brightness degree when the light

of sence and the video signal output electricity balance of the camera

reach a special low range. To measure the parameters should specified the

size of the camera's aperture F. For example, using a F1.2 lens when the 

illumination is 0.02Lux, the scope of the video camera output signal is

50%-33% of  the standard scope 700mv, we say that the camera with the low

illuminance of  0.02Lx/F1.2. Some camera manufacturers give different

aperture F, the lowest illuminance. When the low illuminance of the camera

is higher than infrared illuminator requested, the effective distance

infrared lights will be affected. Users should be reminded that the sale

of camera technology in market marked the low illuminance with two

unnormal ways, one is that the camera manufacturers marked the low

illuminance target surface, which is the illuminance of CCD image sensor, 

and it features with low illumination more than 10 times more than the

scenery; Another one is the false illuminance quoted by some camera

manufacturers or distributor. Currently, some economical black and white

video cameras have the low illuminance of  0.01~0.02Lx, but in fact

0.1~0.2Lx only. If the infrared illuminator require a camera with 0.02Lx,

it will affect the effective irradiation distance, and purchase a 0.02Lux

camera will need twice cost of a 0.1~0.2Lx cameras. In this case there are

two options, to spend more money in camera, but less in infrared

illuminator; or on the contrary. Experimental verification that the former

option is more economical for outdoor long distance.

3.The size and specifications of CCD camera

The size of a CCD camera is becoming smaller, and in the current

market there are 1/2 ", 1/3 ", 1/4 " CCD cameras. The bigger size of the

camera, the more transmition of light. For example, the effective infrared

lights distance is tested with the 1/2 " CCD camera, if you use 1/3 " CCD

or 1/4 " CCD camera, the distance will be effective. The light transmition

of 1/3 " CCD camera is only 44% of the 1/2 "CCD camera. Choose colour

black and white clock automatic conversion should particular paying

attention to the selection of the camera with 1/3 " CCD, because tmost

camera in the market is with 1/4" CCD.

4. Selection of lens

The smaller of the aperture F of the lens, the greater the effects

footage - ray hole.

5. The required functions of cameras and lens

With automatic electronic shutter function, AGC functions, and

automatic aperture of the lens, the cameras can accommodate large range of

illuminance changes in day and night.

6. Power supply

Fronter video survaliance system equipment should be integrated into

the power supply design. The working current of the infrared illuminator

is sensitive with the power supply voltage and different length of cables

determined different decay of DC voltage. When you are using a number of

infrared light with various distance between the control room, a focus

power supply of DC12V may cause a high voltage of the infrared illuminator

whichi is near the control room and low voltage which is far away from the

control room. In addtion, the deviation of adjusting supply voltage will

cause over high voltage and the life time of infrared illuminator  will

shorten or burn off; low voltage infrared illuminator will find power

shortage. It is proposed that adapt a AC22V supply or a one to one DC

voltage power supply. This kind of DC supply has stable output of current

in some DC voltage power net or  voltage fluctuations with a voltage

stabiization of  AC100V-245V to assure the reliable and stable power of

the radiation of  infrared illuminator.

In addition, please take into account the following factors, to choice

a good distance of radiation of infrared illuminator.

1.The low intensity of the cameras. What is the lowest intensity mean

here? The video signal value of camera is 1V, the standard value is 0.7V ,

and the video signal value of lowest intensity is 1/3-1/2 of the standards

for planting. In this case, camera cannot see as in bright day light under

a lowest intensity situation.

2.The image horizontal of Camera under the lowest intensity situation

is examed by the measure cark of video signal, the black and white

alternate with the code for black reflectivity is near 0%, 89.9% more than

the rate of white reflection. But in fact we do not have such conditions,

such as : the reflection rate and contrast of leaves and grass is low, we

cannot have a clear image.

3.Low intensity is given by the camera while also providing relative

value of F requirements. The zoon lens generally be with a maximum

photography 1:F only, which is the minimum at aperture F (f actual size of

the apetrure), F=f/D, if  D for the constant vatio, when f focal length

widen 10 times,  F is becoming big (f actual size becomes small).

Transmition of light will be greatly affected.

4.In the use of automatic aperture lens, AGC or automatic electronic

shutter camera, the aperture F of lens will be changed. For example, there

are features near  the camera, reflecting llight back to the camera glare,

or light exposures the cameras, this camera's sensitivity will be reduced

at that time and the automatic aperture size will become small,

transmition of light will be greatly affected. Therefore, the application

shall be automatically fitted accurately adjust its automatic current

balance, DC automatic control mode in the camera's lens aperture scale

resistance video automatic control mode, aperture lens adjustment.

5.Defensive cover also have an impact on the effectiveness of infrared

illuminator. Infrared light  transmit through different media,

transmissivity and reflectivity are also different. Different window

glass, especially automatic defrost coated glass, will attenuate the

infrared radiation, so they should choose the Windows layer glass.

6.Some manufacturer and distributor giving power only without infrared

lights irradiated distance which is a very vague concept. Beside the power

consumption that transfer into the infrared light energy, there are losses

of heat and power, circuit, light source, infrared light filtering glass

efficiency, and so on. The same power infrared illuminator, the radiation

distance may be great different.

With the rapid development of infrared night vision systems, the

number of infrared illuminator suppliers will increase, but this kind of 

products are not be produced as easy as people imaging. The technology,

instrumentation of facilities conditions are vary from them, so I hope the

buyer and user can compare these, choose your need and want professinally.

To use infrared illuminator firstly is to read the user mannual

carefully, especially to ensure the personal safety equipment attention

matters. Inspection the point I told previously such as the compatibility 

and the interfering impact of factors.

Users should not arbitrarily increase supply voltage, Infrared

illuminator is designed to considered the full play of their irradiance

and its security reliability. Increase supply voltage, may burn out the

it. Also arbitrarily break up is not allow. If so, the manufacturers may

not be responsible for maintenance. If infrared light problems you should

contact with the manufacturers or supplier first.

 
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