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| CCTV MONITORS CCTV monitors are used to view the pictures from CCTV cameras, converting the electrical signal into an optical image to be presented to the system operator. They’re similar to domestic televisions but differ in two respects. Firstly, a monitor has no radio frequency decoding circuitry. Its signal input is ‘base-band’ video as opposed to the aerial input of a television. Secondly, CCTV monitor tubes have a higher resolution than a domestic television. A good quality monochrome CCTV monitor will have a resolution in excess of 800 lines at the centre of the tube; a television is unlikely to exceed 400 lines. Monitors are defined by their tube size, which, like televisions is their approximate diagonal dimension. Common monitor sizes: · Monochrome 9”, 12”, 15”, 17” and 20” When working out which size monitor to use, it is generally regarded that the optimum size for a particular application is between 1/3 and 1/5 of the distance from the screen to the operators position. CCTV monitors are usually equipped with BNC rear-panel mounted connectors for video signal inputs. Brightness and contrast controls are located on the front panel. |
| COLOUR MONITORS Colour monitors have an additional colour brightness control. This should be set to give a true representation of the coloured objects in the scene. Once a monitors controls have been set, it should not be necessary for the operator to further adjust them either when switching between cameras in a multi-camera system or at different times of the day on a single camera. This indicates that there are problems with the camera signal inputs. It could be that termination is incorrect, iris levels have been incorrectly adjusted or video signal levels have attenuated excessively, either by coaxial cable runs being too long or poorly made joints. Later models use TFT LCD displays. These have a number of advantages over conventional CRT monitors: · They’re smaller and lighter. |