Points to note before purchasing CCTV cameras :
1.IMAGE SENSOR
First thing you have to note is the Image Sensor of the camera(which is responsible for transforming light into electrical signals). 2 types are available in the market :
a) CMOS type (Complimentary Metal Oxide Semiconductor)
b) CCD type (Charged Couple Device)
CCD sensors are costlier compared to the CMOS counterpart.Image quality from a CCD sensor is far better than that from a CMOS.
CMOS cameras of image sensor size 1/4” are widely used commercially.Even though their image quality is limited ,they are very much cheaper & it is possible to produce smaller size cameras.They also consume little power.
CCD cameras with image sensor size 1/3” are available in the market with either Sony chip or Sharp chip.The quality of image produced by these cameras are superior .
You may make a note that the image sensor in a common mobile phone camera or a
webcam is of size 1/6”.
So 1/3” is superior to 1/4” or 1/6”.
2.RESOLUTION
Next thing to consider is the Resolution of the camera which is defined by the number of horizontal TV lines (TVL).A normal television image is produced from 625 TVL.Todays LCDs are digitized & the picture is made up of pixels & not TVLs.The more pixel you have the better the image.
A camera capable of 300 to 400 TVL is a Low resolution camera. 400 to 500 TVL is Medium resolution.Above 500 TVL is high resolution.
A 1/3 ” Sony CCD camera has normally 420 TVL and that of a Cmos camera is 380 TVL.
Night vision cameras fitted with IR LEDs are also available,which is suitable for places with less lighting.
3. FPS Frames Per Second
Another feature to look into is the FPS of the camera.
A still photo is nothing but capturing a moment at a time,and a motion picture is capturing an extended moment of time.i.e., a video is a collection of pictures or frames taken at a given rate.You get an impression of motion video,when you see the pictures taken in rapid succession.
If the FPS of a camera is lower,then you see jerky picture or a picture with hiccups.DVD movies you see generally take 30 fps,which is the maximum frame rate possible.A human eye can register up to 30 fps only.
A camera with as low as 15 fps still can show you a good quality video.The smoothness of video suffers when fps is below 10.
A camera with Sony CCD of image sensor 1/3” , resolution 420 TVL & 20 FPS is considered the best quality camera with highest value for money.
DVR
A DVR is a digital video recorder (DVR) that records motion video in a digital format to a hard disk. This can include various models such as stand-alone, USB DVR ,capture board plugged inside PC. . Software enables personal computers to extract segments of video for playback from the hard disk.
Before making a choice of CCTV DVRs you need to look into some important details such as the resolution and quality that you want, the recording options, footage accessibility, audio recording options,ability to view footage on mobile phones,ability to be monitored over internet,capacity of Hard disk supported,types of output supported VGA/RCA,motion detection recording,etc..
Basic two types of DVRs:
- Stand Alone DVRs (does not require a PC)
- DVR Cards (require a PC)
- DVR capture boards are available and are simplest to install in the PCI slot of your existing Desktop computer.A standalone DVR is like a set-top box with elegance & style.USB DVRs are also available,but not preferred because of poor resolution recording and no smoothness or real time recording.
DVR Digital Video Recorder receives the analog signals from the cameras and convert them to Digital (LCD monitors do the same function).So a DVR is going to limit the resolution of the recorded video to certain extent.
Even if a camera is capable of delivering more than 540 TVL of resolution, the DVR IS NOT GOING TO RECORD AT THE RATE ABOVE 540 TVL. So a camera with resolution more than 540 TVL is really not going to benefit the user.
alselectro 