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The dramatic effect vision multiplexing has had on multi-camera surveillance is often overlooked and the facility to record the outputs of several cameras on a single time-lapse VCR is now taken more or less for granted. However, the technology required to accomplish this feat -- once only viable on critical, cost-no-object installations -- is now available to a much wider market, thanks mainly to the significant cost reductions in digital video processing microchips.


The Computar CPLEX 16M multiplexer clearly illustrates the progress that has been made in this field. It is manufactured in the US by Robot Research Inc., who have been responsible for much of the pioneering development work in vision multiplexing. This model is very clearly related to several models in their Optima range, the main difference being this one is designed for monochrome cameras, moreover it has a slightly truncated range of features.


Externally the unit is quite compact, it is housed inside a slim, black metal case measuring 432 x 311 x 44mm. On the front panel there are five groups of button with mode and function keys on the left side, and the camera selector buttons on the right. The back panel is populated by two rows of BNC connectors for camera inputs and outputs, a single monitor output, one DB25-S connector for alarm inputs and outputs, and a socket for the external mains power supply.


Up to 16 cameras can be connected to the multiplexer; they can be any type having a CCIR/PAL output. Unlike first-generation multiplexers there’s no need for external synchronisation or genlocking, this is carried out internally. However, one of the most important features on this device is dynamic time-division (DTD). This varies the amount of time each camera output is allocated for recording, according to whether or not there’s any movement in the scene. This makes the most efficient use of a recording VCR, ensuring that critical areas or events receive the most coverage.



Each camera input has it’s own programmable motion sensor facility. This takes the form of a grid of 192 targets (12 x 16), that can be switched on or off, to concentrate on a particular area, or areas within the scene. When movement is detected the multiplexer creates a ‘motion group’, where the output from the camera (or cameras) are repeatedly inserted into the recording sequence, so they’re recorded more often.  


There are four display formats, selected automatically by the multiplexer, according to how many cameras are connected. In addition to a single camera output the screen can show 4, (2x2), 9 (3x3) or 16 (4x4) images, either live from the connected cameras, or on playback from a VCR recording. Incidentally, this is a simplex design, so recording and playback functions cannot be carried out at the same time. A built-in character generator superimposes time, date, video loss, alarm status and camera idents, which can be up to 10 characters long. The initial set-up and routine operations are controlled by a series of  menu-driven on-screen displays, protected against accidental or unauthorised alteration by a control lockout function.


An alarm input is assigned to each camera; contact closure whilst the unit is in the record mode results in the associated camera indicator flashing and the image displayed on the monitor, along with a superimposed alarm message. An alarm indication is recorded on the tape, and the VCR output switches to alarm mode, with the relevant camera prioritised. Alternatively, if the unit is in ‘1-cam’ mode, only the alarm camera will be recorded. During playback the multiplexer responds to recorded alarm indications by flashing the appropriate camera indicator on the front panel and overlays an alarm message on the screen. The system detects and responds to the loss of a video input in a similar manner.



The main set-up menu is accessed by pressing the function and sequence buttons together. This brings up the time/date screen; the following pages cover housekeeping functions for the various display and alarm options, VCR and alarm record times, alarm duration (2-999 seconds), camera dwell time (1-99 seconds), camera titles and set-up screens for the 16 motion detector grids.


On the motion detector display all of the targets are enabled by default, they are switched off using the camera selector buttons, a line at a time, until the area to be covered has been defined. Unlike some other models in the range the CPLEX 16M’s motion detector doesn’t have a separate alarm output, nor are there any indications that it has been activated.



In spite of all the heavyweight digital processing taking place image quality is surprisingly good. Very little additional noise is evident on a ‘live’ full screen display, nor is there any significant loss of resolution or detail. The dynamic range is slightly narrower than a purely analogue signal but it has little impact on image quality; in practice  the recording VCR will usually have a far more detrimental effect.


The quality of multiplexed images is reduced slightly though with a very small reduction in detail and increase in noise though the effects are only really noticeable on test patterns.



Robot’s wealth of experience and expertise in this area are clearly evident on the CPLEX 16M. Construction, design and layout are of a very high standard, and performance is hard to fault. From the installers point of view flexibility and the ease with which it can be incorporated into existing systems are important assets moreover dynamic time division and motion detection are two key facilities, that give this device a significant advantage over most other multiplexers on the market.  




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Ó R. Maybury 1996 2604




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