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Video motion detection has rapidly evolved from an exotic and temperamental fringe technology into a mainstream surveillance tool. We’ve been testing the Digi Spec DS-1 and DS-1PL, two of the latest generation motion detectors, designed to integrate easily with small and medium-scale installations



The DS-1 and DS-1PL are compact video motion detectors (VMDs) from DigiSpec in the US; they’re both designed to integrate with a wide range of video surveillance equipment. Functionally the two units are fairly similar, though the more advanced DS-1PL is aimed at more demanding applications, including multi-camera systems and monitoring areas of high activity.


Both devices are housed inside a small black plastic cases with extendible feet, the boxes measure 110 x 30 x 220mm. On the front of both units there are four push-buttons and a power-on LED; all four buttons are illuminated on the DS-1PL, only the alarm and menu buttons light up on the DS-1. On the back there are two BNC sockets, for composite video input and output, a 9-pin D-socket for the alarm connections and serial (RS232) communications with a PC or remote device, plus a DC supply socket. Power in both cases is provided by a plug-in mains adaptor module.


In most types of installation the DS-1 will be the second component in the video chain, i.e. it connects between the camera any switching, multiplexing, recording and display devices downstream. The DS-1PL can process a quad display, which makes it more suitable for multi-camera systems.  Whilst both VMDs are stand-alone devices, in that they operates independently of any other video components, the DS-1 may need to be linked to an external timer or clock, if it’s required to work in areas or situations where there’s a sudden change in day and night lighting levels. The DS-1PL has a built in timer facility, that can be programmed to switch the unit on and off up to three times in a 24 hour period and it has an internal day/night switch. They have internal sounders -- the DS-1 ramps up with an increase in activity; alarm outputs are normally connected to a time-lapse VCR, external audible warning device, or used to trigger an alarm system.


The success, or otherwise, of a VMD system entirely on the degree of control the installer has over detector sensitivity and the care taken during the set-up procedure. In that respect they’re both off to a very good start. The image area is divided into 262,000 sensor elements which Digi-Spec refer to as ‘pixels’; the DS-1 instruction manual suggests they’re analysed 30 times a second but that sounds very much like what would happen on a NTSC video signal; since our test samples were PAL models it’s more likely motion analysis is carried out 25 times a second (the field rate of a CCIR/PAL video signal).


All operating functions are controlled from menu-driven on-screen displays. The DS-1 is the simpler of the two with four screens covering motion detection set-up, alarm configuration, motion effects, zone pattern mask and camera/channel ident. The DS-1PL is more extensive. The first menu page has 8 selections that cover motion detection set-up, zone pattern, alarm configuration, timer set-up, on-screen data and motion effects, a simple display titler, date/time adjust and serial port set-up.


In both cases the motion detection menus contain the most important adjustments, that will ensure maximum reliability, and immunity to false alarms. The DS-1PL is the more complicated of the two with 8 definable ‘areas’  labelled A to H, each one with preset and user-defined values for trigger level, sensitivity level and tracking. The trigger level establishes the threshold for motion activity, in other words the number of ‘pixels’ that are triggered in the display at any one time. The range for the DS-1 is from 1 to 256,000; on the DS-1PL each mode can be set from 1 to 65,535.


On both units the sensitivity level defines the relative deviation between active and reference pixels, required to trigger an alarm; this operates over a range of 1 to 100, with the factory default set at 50. Tracking is arguably the most critical adjustment on both VMDs, this sets the length of time that motion must occur, in order to activate an alarm. It’s a highly effective filter, that can be set to ignore predictable or inconsequential movement, that would otherwise result in a false alarm. For example, they can be set to discriminate between fast-moving traffic, and someone walking across the field of view, the random movement of branches on a tree, lightning or simply camera shake.


The Zone Pattern mask on the DS-1 generates a grid of 20 x 18 ‘zones’, the DS-1PL has 24 x 12 trigger points, all of which can be individually switched on and off. The DS-1PL goes one stage further, each zone cell can be assigned one of the 8 ‘areas’ of sensitivity. The DS-1PL Alarm menu defines how the unit responds to various types of trigger, sets entry and exit delays, alarm duration and reset times. The timer menu on the DS-1PL is also responsible for setting start and stop times for the three timers, enabling an external timer and setting times for day and night operation.


On-screen data generated by the DS-1PL can be positioned anywhere on the screen and displayed on a single line, or ‘stacked’ in rows, so that it doesn’t obscure important areas of the image. There are also presets for the time display format and motion display.


Both VMDs have an image trace facility, which shows the track of a moving object; this can also be made to flash on the DS-1PL, or ‘sparkle’ on the DS-1. The track can be highlighted and memorised. Various other effects are available, including a black-screen display, that will show the outline of a moving object. This is especially useful on installations with multiple monitor displays, where the operator’s attention will only be drawn to a screen when there is any activity. In this mode a counter displays a constant readout of pixel activity, which can be used during the set-up procedure, to determine the optimum level of sensitivity.


All alarms are automatically logged by the DS-1PL which has the capacity to store up to 160 events. Additional facilities common to both models include a video loss alarm and the RS-232 serial communications port, that enables remote control and configuration on a PC.



Neither VMD has no significant effect on video signals passing through the units. Noise levels are unchanged and it has no noticeable impact on resolution, luminance or  colour levels, so from that standpoint it can be regarded as virtually transparent.


Both motion detection systems are extremely versatile, overcoming most of the inherent problems associated with most rival devices. The additional facilities on the DS-1PL means it is possible to virtually eliminate spurious triggering, though it could take some doing as there are so many variables to contend with. Nevertheless, this is one of the few motion detectors capable of handling a busy outdoor scene, containing a lot of random or unexpected movement.



They’re both good, but not quite perfect  -- no system is -- and they can still be fooled by things, like large insects crossing or landing on the camera lens, and severe weather conditions, such as hail or snow.  However, until now motion detection systems have been largely confined to indoor applications and environments where spurious activity and movement is either predictable, confined or controlled. The comprehensive motion detection facilities on these devices frees motion detection of many of those constraints, broadening their scope considerably, making them suitable for a wide range of indoor and outdoor installations.  




Video format                  PAL/CCIR

Video input                    0.5-2v pp composite, 75 ohm termination

Digitisation                    256 grey scale

Zone pattern                  20 x 18 (DS-1) 24 x 12 (DS-1PL)

Alarm contacts            30 VDC, 3A

Backup                         non-volatile memory

Sys set-up                    programmable via on-screen menus or PC via RS-232 serial port

Power supply                 7-15 VDC (mains adaptor module supplied)

Weight              0.5kg

Dimensions                   110 x 30 x 220mm




Product             8/8

Product design            8/9       

Build quality                  8/8

Ruggedness                  8/8


Operation                      8/9

General functions            8/9

CCTV functions            8/8       

Ease of use                   8/8

Instructions                   8/8

Manuf. support            -/-                    



Video quality                 9/9       

Motion detection             8/9       



Ó R. Maybury 1996 2711





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Copyright (c) 2005 Rick Maybury Ltd.