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DIGI-SPEC DS-1 & DS-1PL DIGITAL VIDEO
MOTION DETECTORS
INTRO
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
COPY
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.
PERFORMANCE
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.
CONCLUSION
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.
PRODUCT SPECIFICATION
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
PSI RATINGS DS-1/DS-1PL
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 -/-
Performance
Video quality 9/9
Motion detection 8/9
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Ó R. Maybury 1996 2711
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