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 image from the same camera and performs a comparison for change. Depending
upon the sensitivity (larger models can view up to 64,000 individual points
on a CCTV picture) and alarm threshold (a selectible preset number of points
which must change), if a change is detected, an alarm is declared. The
operator sees the reconstituted digital image (versus real time) picture on
a monitor. Successive movement produces successive alarm images ("ghosts")
on the monitor which remain there, even if the motion stimulus leaves the
camera's field of view, until operator reset. Figure 24 depicts the
image(s) produced. Models by various manufacturers are available which can
handle one, two, four, eight or sixteen cameras. Any CCTV camera can be
used, but the sharper the camera image, the better the performance of this
sensor. This type of sensor is highly susceptible to nuisance alarms from
extraneous motion within the camera field of view. Some models permit
"desensitizing" image points which cover nuisance alarm sources, while
others provide sensitized squares or rectangles which can be placed over
specific areas or objects to be protected. The following considerations for
application and installation apply to CCTV motion detection sensors:
a)
Fixed-focus CCTV cameras are most suitable for use with this
sensor.
b) Stable fixed CCTV camera mounting is critical. Any camera
movement will be perceived as an alarm state by the sensor.
c) Cost-effectiveness is a serious consideration compared with the
application of conventional volumetric sensors with a CCTV assessment
system. In addition, within the sensor type, lower cost CCTV motion
detection sensor
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