| Recently a large number of low-cost surveillance systems have come on the market. One with four cameras and a hard drive capable of holding a month or more of video clips costs about $300. Cameras are unobtrusive and can be easily hidden. However, there are a number of problems of which users should be aware. When an infra-red illuminator is part of the camera, they cannot see outdoors from behind windows indoors. The reflection from the window blinds the camera. Another consideration is that when the problem is outdoors, the cameras must be outdoors. Cameras have a limited range of operating temperature, typically 150 F down to 4 F and must be kept dry. They must not be placed where they will become overheated; and, more importantly, in northern climates, they must be heated in the winter. Similar cameras used for truck and bus backup viewers are made self-heating by suitably insulating them and keeping the infra-red illuminators operating even when the vehicle is parked and turned off. Unfortunately, some surveillance cameras contain a sensor that shuts off the illuminator in the daytime to improve image quality. Camera heaters can be user-fabricated, however. They can be wrapped around the camera. The required heating power per camera is small when the camera is insulated. An excellent design tool for calculating the required heating power for your own climate is a program suitable for a programmable desk calculator, "Estimating Electronic Box Surface Temperature is BASIC" [Paul Coniglari and Matthew Conigliari, Electronic Packaging, February 1984, 163-167]. |