University Of East Anglia
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Check Your Security Ltd is an East of England based systems design and build integration company specialising in CCTV/IP-CCTV, structured cabling systems, Fibre cabling, Access control and Intruder security systems.
CCD
What is a CCD?A charge-coupled device (CCD) is a sensor for recording images, consisting of an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to one or other of its neighbours. CCDs are used in CCTV, digital photography and astronomy.
An image is projected by a lens on the capacitor array, causing each capacitor to accumulate an electric charge proportional to the light intensity at that location. A one-dimensional array, used in line-scan cameras, captures a single slice of the image, while a two-dimensional array, used in video and still cameras, captures the whole image or a rectangular portion of it. Once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbour. The last capacitor in the array dumps its charge into an amplifier that converts the charge into a voltage. By repeating this process, the control circuit converts the entire contents of the array to a varying voltage, which it samples, digitises and stores in memory. Stored images can be transferred to a storage device or video display.
CCDs are typically sensitive to infrared light, which allows infrared photography, night-vision devices, and zero lux (or near zero lux) CCTV and video-recording.
The size of the CCD is important as more light can be gathered by a larger device. Common sizes for CCTV CCDs are ¼”, ½” & 1/3”. This together with the technology used with the CCD determines the quality of the picture, the resolution the ability to cope with awkward lighting situations and ultimately the price of the camera it is used in. However, higher density 1/4" and 1/3" CCD chips can now produce as good an image as many older 1/3" or 1/2" chips so it is not always a straightforward choice and bigger is not always better. Better cameras often use CCD produced by Sony or Panasonic and in many cases they are quoted in the specification of cameras from other manufacturers.
The size of the CCD also affects the coverage angle of a given lens. The larger the CCD the wider the angle of view for a given lens
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