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It is often said that form follows function, if so, it is seems entirely appropriate that the Pelco Spectra dome camera mechanism should look so much like a policeman’s helmet... The US-built Spectra system is available in number of configurations but the key design feature is the fully integrated motorised camera platform, that Pelco aptly describe as a ‘black box’. The compact helmet-shaped unit contains the colour or black and white camera,  mounted on a high-speed pan/tilt mechanism that can be preset to pan at up to 250 degrees per second and tilt through 100 degrees/sec.


The module fits inside an in-ceiling housing or environmentally-sealed suspended pendant enclosure. Both have a quick-release locking and connection system, that speeds installation and servicing. A black plastic shroud or ‘liner’ means it can be used with a transparent outer dome  --- minimising light loss -- without the camera mechanism being too obvious from the outside. That is in addition to more conventional smoked black, chrome or gold mirrored finishes, which are optionally available.


Single or multiple camera units are remotely operated by a Pelco MPT9500 series transmitter/controller unit, of which more in a moment. The main camera/mount features include 360 degrees continuous pan and an ingenious ‘‘auto flip’’ dome rotation function.  This spins the dome through 180 degrees as the camera points downwards, repositioning it, so it can continue to tilt in the opposite direction. Cameras are fitted with an F1.6 (4-48mm) lens with a 12X optical zoom, electronically extended by a further 8X, to a total of 96X. The lens gives a horizontal angle of view of 47 degrees (4 degrees at 48mm, telephoto mode). Focus and exposure systems are fully automatic, though there are manual overrides.


Both cameras use 0.25-inch interline transfer CCD image sensors. The colour model has automatic and manual white balance controls it has a total of 43.7k effective pixels giving a quoted resolution of 460 lines; the mono camera CCD has a 29k pixel array, for a resolution of 380 lines. Low-light sensitivity is in the order of 4 lux (colour) and 0.5 lux (mono), an automatic shutter operates over a range of 1/50th to 1/30,000th second, shutter speed can also be set manually.


Each camera can have up to seven alarm inputs, when activated the camera moves to an associated pre-set position. Communications with the control unit are via the camera output cable, using the proprietary Coaxitron, Intercept or Legacy vertical interval signalling (VIS) protocols, or by 4-wire RS-485 serial link. Using top grade, low-loss cables maximum operating distances can be up to 2,000 feet (VIS) or 4,000 feet (RS-485).


The camera module is mounted on a single bearing, connected to a small stepper motor by a belt drive that turns the camera through 90 degrees. The platform is attached to a turntable, driven by a second stepper motor inside the base, this also uses a toothed belt drive system. The assembly feels very rigid, the design is simple and there’s little to wear out or go wrong.


All of the camera and motor control electronics are contained on a single glass-fibre PCB that’s located in the base of the unit. Connections to the outside world are routed through a pair of sockets, that mate with a corresponding bank of connectors, set into the top of the housing. The camera module is locked into place by a pair of colour-coded lever arms; insertion and removal takes just a couple of seconds. The fixing can be a little temperamental and it pays to heed the warnings in the installation instructions, about double-checking that the latches are secure. The only external controls are two miniature DIP switches, used to set the camera address and communications protocols.


Behind the hinged connector plate on the in-ceiling or pendant mount housings there’s an interface board, for the power supply, video and optional RS-485 communications link. The video connector is quite difficult to get at; it’s a good idea to have a dry run on the ground, before trying to locate and connect the cable with the housing in position. The unit requires a 24 volt AC supply which in addition to powering the camera and motors, also drives a pair of miniature thermostatically controlled fans, and a heater element -- for outdoor operation -- set into the inside rim of the dome. The Pendant housing is suspended beneath a cast alloy bracket, connected to the housing by a 1.5-inch threaded steel pipe.



The MPT9500 series desktop controller is available in two basic versions, with or without time and date generator, and preset tour of up to 64 camera positions. We have been looking at the latter variant. The controller is housed in a sloping cream-coloured console, with a large joystick mounted in the centre of the top panel. Above that there’s a multi-function alphanumeric LED display, this is flanked by two banks of buttons. The group on the left hand side are mostly concerned with routine camera and PTZ operations, they include iris open/close, focus near/far, zoom tele/wide, manual/auto pan, position preset and camera on/off. The buttons on the right side are mainly for programming and function control.


The back panel has just five sockets, an RJ-14 6-pin modular phone-type socket is used for the RS-485 communications cable; there are three BNC sockets for the video/VIS feed from the camera, monitor output, and video loop-through. On the far right there’s a socket for the mains supply cable.



The first step is to select the control protocol, Coaxitron is set by default and requires no further adjustment. For RS-485 operation a camera address and simplex or duplex (actually half-duplex) modes have to assigned, using options shown by the on-screen display and DIP switch settings.  Routine camera operations are largely self-explanatory. The joystick has progressive action, pressing the button on top of the stick puts it instantly into top gear or ‘turbo’ mode, though the fastest speeds are reserved for automatic preset operation. The tele zoom button goes to a maximum of 24X on the first press, pressing the button a second time -- within one second -- extends the zoom to the maximum of 96X. Zoom and focus speeds are set using the on-screen display, along with the time and date.


The main camera functions have their own set of menus. At this point the otherwise reasonably well-written instruction manual become quite difficult to follow. The procedure for accessing the main camera on-screen menus is not very clearly explained, in fact it took a fair amount of trial and error to figure out exactly how to get the display on the screen. Once there the options include auto focus (on/off), AGC (auto, on/off), gain, backlight compensation, shutter speed, auto iris (auto mode, level or peak metering), white balance (auto, red/blue and magenta/green) and line synchronisation. Selections are made using the joystick, and selected by the iris open button. It’s not especially logical or intuitive. 


The on-screen display is also used to program camera presets. This takes only a few moments. The camera is first moved to the required position and zoom setting, then the position number is entered on the keypad, and the preset button pressed. Each position can be given an ident. Preset tours are programmed in a similar manner, the dwell time for each location -- 1 to 99 seconds, and its position on the tour are set using the function keys. Care need to be taken to avoid pressing the button on the joystick as this erases tour data. Random scanning is also possible (3 -second scan followed by a 3 second pause), and frame scanning, with the limit stops defined by the controller.



The colour camera is a high-performance device, our sample managed to resolve more than  420 lines without any difficulty.  In natural light noise levels were very low indeed. Colours looks clean and well defined. With the white balance system switched to automatic accuracy was good in natural and tungsten light. Minor adjustments were necessary on scenes lit by predominantly fluorescent light. The exposure controls and systems are very efficient. They were able to cope quickly with a wide variation in lighting conditions, producing a usable image from bright sunlit exteriors to subdued interior lighting.


There is a small but perceptible change in the texture of the image as the zoom shifts from optical to electronic enlargement, though up to the first stage 24X setting the loss of detail is quite small. From 24X to 96X the image becomes progressively coarser and beyond 60X the increase in pixelation makes it difficult to identify all but the largest features.


Pan and tilt controls are very smooth indeed, resolution is very good and it is possible to track very small movement by light pressure on the joystick. The turbo function is sufficiently fast for most situations, tracking at around 150 degrees/sec. The PTZ mechanism is almost silent, though the two cooling fans emit a continuous noise, that’s just about audible in quiet surroundings.



The lightweight mechanical construction undoubtedly contributes to the fast smooth action of the motorised mount.  Build quality is generally good and it looks as though it will last the course. Weatherproofing on the pendant housing should also be satisfactory, assuming the installation procedures are closely followed. 


The only real quibble concerns the instructions and the control software for the on-screen displays. Both could do with an overhaul as neither are especially well laid out, or easy to follow. Together they conspire to make some parts of the system quite difficult to set-up and program. It’s mainly a question of presentation; instead of one seamlessly integrated control system it creates an impression of two quite separate devices, that happen to share the same box. The lack of co-ordination spills over into the instructions, with some procedures tangled up in jargon and inappropriate terminology.


Camera functions are faultless, it produces a clear, bright and well defined image under a wide range of conditions. Features like the electronic zoom increase its functionality significantly.



Design and design features              ****

Circuitry and components                  ****

Ease of installation and wiring    ****  

Range and variety of functions            ****    

Accompanying instructions                   **                                

Technical advice and backup            ****     

Value for money                         ****                           




Ó R.Maybury 1997 1509



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