Surveillance systems : the technical features
Video surveillance systems consist of cameras, monitors and recorders and the most basic system involves a direct connection between each of these components using just one camera. While this may be fine for some situations most businesses and homes require more than one camera to cover their surveillance needs. More complex systems can involve hundreds of cameras linked to a number of monitors and digital video recorders (DVRs).
This basic guide is aimed at giving you some insight into the technical features of surveillance systems and what to look for when shopping for surveillance systems.
Home digital video cameras: what to look for
Color vs. black & white:
It used to be that black and white cameras were cheaper and more light sensitive than color cameras but that is no longer the case. Color cameras can now cope with low light conditions just as well as black and white cameras. However, color cameras with a low light sensitivity rating can still be expensive but cheaper models are able to automatically switch to black and white when required. Some vendors no longer even sell black and white cameras.
Resolution refers to the sharpness of the image and is important where good image quality is required; particularly where footage may be used as evidence or for identification purposes. Resolution is measured in one of two ways: TV lines (TVL) and pixels.
The number of lines determines how sharp the image is. TVL is the measurement that is used most often as it is considered to be the most reliable although pixels are used to measure the resolution on digital equipment. You should only rely on pixel measurements if the entire system, including the cameras, is digital. Otherwise it is best to stick with TVL.
Generally 400 lines is considered acceptable resolution and 500 lines or more is excellent. Also, make sure the resolution on all components of the surveillance system match. It's no good spending extra money on a monitor with 500 lines of resolution if the camera only records 400.
This is a term referring to the level of light that a camera can operate at and still produce images of an acceptable quality. Light sensitivity is measured in 'lux' and the lower the lux rating the more light sensitive the camera. The importance of this rating depends on where the cameras will be positioned. If the area to be monitored is prone to low light conditions it is a good idea to get a light sensitive camera.
Lenses are sometimes sold separately to the rest of the surveillance system although most complete systems will include them. There are two types of lenses: fixed focal length and variable focal length.
Fixed focal lenses offer only one, fixed field of view (as the name suggests) and changing the focal length means changing the lens. This may be fine for monitoring areas such as hallways or various rooms in a home but for larger applications it may not be sufficient.
Variable focal lenses are more expensive than fixed lenses but may be necessary for certain surveillance needs. In larger areas such as car parking lots, malls or department stores having a zoom function could be useful.
Signal to noise ratio:
The signal to noise ratio or s/n refers to how much signal is transmitted by surveillance system cameras in relation to how much 'noise' or interference there is. Noise presents itself as 'snow' or static on the image and can affect image quality. As a general guide 30db or below represents poor picture quality, 40db is good and 60db is excellent.
It is important to note that wireless surveillance systems are more prone to noise interference than wired systems. Read the page on wireless surveillance cameras to learn more about this.