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Over the past two decades the PC has proved to be a invaluable tool for the security industry though it hasn’t always been at the cutting edge and in the early days it was largely used in supporting and administrative roles. Gradually, as the technology has developed, it has moved to frontline operations in many different fields, from alarm and access control to more exotic applications like biometrics and image processing. However, in one area the impact of the PC has only just begun to be felt and that’s in video surveillance, where the incumbent technology has proved to be rather more resilient than expected. The bottom line is that when it comes to recording and archiving video images magnetic tape is still the simplest, cheapest and most flexible option, but maybe not for much longer…


Hard disc digital video recorders (DVRs) have been around for at least the past six or seven years and the technology is by now well established. The cost of the hardware, whilst still relatively high – when compared with a mid-range time-lapse VCR -- has fallen dramatically in the past couple of years and picture quality has always had the potential to be at least as good and in most cases, better than that available from analogue video recorders, so what’s the hold-up? 


Cost is obviously a major consideration; there’s no escaping the fact that a hard disc recorder with comparable capabilities to a VCR costs between three and five times as much, though that is usually offset by the fact that HDD recorders usually have many additional facilities, including on-board camera multiplexing and the higher image quality is an important plus. Nevertheless HDD recorders tend to fall down when it comes to archiving recordings, the complexity of installation and use may also be a consideration and then there’s the question of reliability, which on any new technology tends to be a bit variable.


The Plettac Sentio-50 digital video disc recorder and its companion software is a good example of the current state of the art in hard disc video recorders and whilst it’s not going to make analogue VCRs obsolete overnight, it’s yet another nail in the coffin of whiskery old VHS and a tantalising taste of what’s to come. The Sentio-50 DVR is basically a PC, to be precise a 1.6GHz Pentium PC with a 60Gb hard disc drive, (extra hard disc drives can be added if required), 256Mb of RAM, CD-RW drive and Windows 2000 operating system. The key differences between it and a regular desktop machine are the case and expansion cards. Sentio-50 is available in a standard rack-mount housing or a more conventional freestanding PC style case, in both types access to the CD drive and reset button are protected by a hinged and lockable access door and the front panel is virtually featureless, apart from a couple of LEDs that indicate power on and disc activity. The extra expansion cards take the form of video and alarm inputs/outputs occupying PCI slots on the motherboard. Various configurations are available, our test sample was a top-of-the line model fitted with 4 cards, each with 4 inputs giving a total of 16 channels, plus their associated alarm inputs, accessible through a bank of sockets on the rear panel.


Since the Sentio 50 is expected to operate 24 hours a day, 7 days a week cooling has been given a very high priority. In addition to the standard cooking fans in the power supply and on the main processor chip there’s a large cooling fan on the front directing air onto the video boards and three smaller fans fitted to a blanking plate on the back panel. Needless to say six fans on full song make quite a noise, a significant amount of noise in fact and in a quiet environment it could be quite intrusive so some thought needs to be given to location and possibly sound insulation as well. It also puts out a fair amount of warm air too, which might also be a consideration in some installations.


The hardware is only half of the story, keeping everything under control is a suite of programs called Sentio-Review. This is responsible for video recording and playback, display, archiving, motion detection, alarm management, camera control (PTZ), record scheduling and Ethernet network communications. The latter allows the Sentio-50 to connect to a server and lets authorised network users view and record images from any selected camera. Network users with the necessary authority can also alter configuration and alarm settings, and remotely control any PTZ cameras. All of the software is pre-installed and ready to run so all the installer has to do is plug in the monitor, keyboard and mouse and connect up the cameras and alarms. The video inputs are via BNC sockets, in addition to the standard VGA output for the monitor there are also composite and/or S-Video outputs for additional video monitors. The alarm inputs and outputs are via multi-way connectors on the back panel. 


The powerful video motion detection (VMD) utility is called MotionTrack, it is integrated into the software package, this allows the user or operator to specify any number of variable-sized triggers or ‘regions of interest’ (ROIs) for each camera. Sensitivity can be varied to reduce the likelihood of false alerts, caused by changes in light level or natural motion (leaves on trees etc.).




At switch on Sentio-50 boots up to the normal Windows 2000 desktop then after a few seconds the Review software loads and the user screen is displayed. From that point on normal PC functions are disabled and it is not possible to exit the program or access any other programs without going into Supervisor mode. There is a minor security loophole, if the Windows key is pressed before the Sentio software loads it’s possible for the operator to access Windows, however this would be a relatively simple thing to fix and in any case it would be logged by the administrator software.


The main user screen automatically defaults to a live display of connected cameras. A narrow control panel is displayed on the left side of the screen, this shows time and date at the top, below that are three buttons for Supervisor, Live and Playback modes. Underneath are six icons for selecting display mode (single screen, 3 x 3, 2 x 2, 8 + 2, 4 x 4 and 12 + 1) and this sits on top of a list of the available input channels, with green indicators showing which ones are currently active.  It is possible to switch from any display mode to full screen by double-clicking on an image; double clicking a second time changes the display back to its previous state. Images in multi-mode displays can be rearranged by dragging and dropping the picture into its preferred position.


The operator has full access to Playback mode, when selected a new control panel appears at the bottom of the screen displaying a timeline, there’s also a time and date readout, VCR type controls, a set of replay ‘speed’ buttons (1x, 2x, 4x & 8x), two Event buttons and an Export button, for ‘burning’ a CD-R disc or printing a still image. The timeline shows the duration of the current recording as a white band, yellow markers indicate VMD events and red markers show alarm triggers. By clicking on the timeline or an event marker it’s possible to go more or less instantly to any part of a recording, or times can be entered manually from the keyboard.


Incidentally, when archived recordings are burnt onto CD-R discs the system automatically includes a player utility on the disc, so that the recording can be viewed on any Windows PC.


Critical settings can only be accessed from the password protected Supervisor mode. This opens a tabbed dialogue box, there’s also buttons for configuration settings, exiting to user mode or closing the application and returning to the Windows 2000 desktop.


Tab 1 is labelled Cameras and this includes fields for composing camera titles, specifying record mode (Always, Never Default), record speed (1 to 25 images per second), image quality/compression (level 1 = high quality/low compression, level 11 = low quality/high compression), Alarm enable, VMD enable, Data Archiving enable/disable, Archive record speed and quality. Tab 2 deals with the alarm settings, specifying recording speed and quality, duration, pre-alarm recording time, alarm inputs and output states. Video motion detection is handled on tab 3, the selected camera input is shown on a sub screen and the Region of Interest (ROI) is defined using the mouse. There are three sensitivity settings (low medium and high) and buttons to show and deselect targets. The Preview tab provides access to image quality settings for normal recording and archive recording, showing the effects of different compression settings in an inset sub screen. The Patrol tab is used when one or more PTZ cameras are connected.


Tab 6 ‘Hard Disk’ displays a pie chart showing the amount of space being used by each camera channel, and space remaining. There’s also archiving information and an estimate of disk usage. Tab 7 ‘Time Zones’ is used to schedule recordings for regular events such as cash collections and deliveries. It displays a grid with days of the week divided into 96 15-minute slots, there’s provision to skip holidays, set recording speed, image quality and enable alarms and motion detection. This particular aspect of the setup is slightly convoluted and it pays to keep the manual (on CD-ROM) close to hand. Tab 7 is for managing any additional hard disc drives fitted to the system, Tab 8 is the Event Log that record all system activities and tab 9 is for managing the User list and changing passwords.


There are a couple of relatively small operational annoyances. Firstly the maximum 8x search speed is not fast enough for skimming through a recording and it would have been helpful to have some way of changing the timeline scale. As it is it displays a 13-hour time segment and finding a particular event without alarm or VMD indicators would be a lot easier if the scale could be compressed, to say, an hour or 30 minutes. Lastly, when switching between Play and Live modes the display always reverts to the default 4 x 4 layout, it would be more convenient if it returned to the previously selected display mode. 



Picture quality and recording times are dependent on a number of factors including the amount of compression, recording interval or speed and the number of camera channels being recorded. At the lowest picture quality setting and slowest interval (1 image per second) the output from a single camera the 60Gb drive can hold a little under 30 days worth of recordings. Increasing any of all of those values has a big impact on duration. For example, changing to the mid quality setting and using a recording speed of 25 ips the output from a single camera will fill the drive in a little less than 36 hours.


Picture quality on settings between 3 and 5 are comparable with the best that high and low band analogue tape has to offer with a fair amount of detail and reasonably natural-looking colours. The picture is rock solid and it really comes into its own during replay, with the facility to step forwards or backwards through a recording a frame at a time or in search mode at the click of a mouse and without any picture disturbance or noise bars. Quality settings 1 and 2 are noticeably sharper than S-VHS and noise levels are very low indeed.


Quality settings of 6 and over are marred by block noise and poor contrast giving the picture a slightly gritty texture so they are really only suitable relatively undemanding tasks where recording duration takes precedence over image quality.


The quality of archived recordings transferred to CD-R is comparable with standard VHS, there is a fair amount of processing noise, especially in static backgrounds and colours are somewhat muted but, depending on the settings, the image retains a fair amount of useful detail, and the facility to be able to replay the disc in any Windows PC is a definite bonus.



There’s much to admire about the system but also some room for improvement. Firstly it would have been useful to have a digital zoom facility on full-screen displays. Second, why not make use of the PC’s audio facilities, at the very least it could generate the odd ‘ping’ for VMD or alarm events, to draw the operator’s attention, and – this is a old gripe with PC-based hard disc video recorders – why not have a provision for recording audio as well?  Compression schemes like MP3 require very little disc space and it would definitely add to the system’s versatility.


On the plus side it is very easy to set up and use and configuration is reasonably straightforward. The desktop displays are clear and simple and critical settings are well protected. Video performance can be very good though we suspect that extra capacity may well be necessary in a lot of multi-camera installations.


Hard disc recording is improving in leaps and bounds and the Sentio-50 demonstrates that the DVR is a big leap forward in video recording technology but for the moment at least cost and recording capacity remain critical issues.



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                         ??                          



ă R. Maybury 2002



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