Справочник Пользователя для Pelco MD2001-X
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Pelco Manual C616M-B (11/97)
4.8 DETECTABLE TARGETS
The ability to detect a moving object is determined by its size, contrast with the
background, and speed of motion. Once an object appears larger than approxi-
mately 3% of the monitor screen dimension, or 0.1% of the screen area, its ability to
be detected will not increase greatly. Therefore, the best trade-off of area coverage
against sensitivity occurs when the lens and camera position are selected to give
this size for objects of interest. When maximum detection probability is desired, a
slightly longer focal length lens may be used.
background, and speed of motion. Once an object appears larger than approxi-
mately 3% of the monitor screen dimension, or 0.1% of the screen area, its ability to
be detected will not increase greatly. Therefore, the best trade-off of area coverage
against sensitivity occurs when the lens and camera position are selected to give
this size for objects of interest. When maximum detection probability is desired, a
slightly longer focal length lens may be used.
An object must have some visual contrast with the scene background in order to be
detected. Contrast may be enhanced by improved lighting and by positioning the
camera so that detection targets appear against a background of contrasting color.
For most targets, a light background provides the highest contrast.
detected. Contrast may be enhanced by improved lighting and by positioning the
camera so that detection targets appear against a background of contrasting color.
For most targets, a light background provides the highest contrast.
A target may move so slowly that its motion is not perceived by the unit. This prob-
lem may be corrected by using a longer focal length lens to magnify both the size
and apparent speed of motion of the target.
lem may be corrected by using a longer focal length lens to magnify both the size
and apparent speed of motion of the target.
A target may move through the scene so rapidly that its presence is missed by the
camera and the system. This condition is very unusual, but often may be corrected
by camera positioning and lens selection.
camera and the system. This condition is very unusual, but often may be corrected
by camera positioning and lens selection.
In any given installation, these factors should be determined during installation
planning. If necessary, experiments under actual operating conditions should be
conducted.
planning. If necessary, experiments under actual operating conditions should be
conducted.
4.9 FALSE ALERTS AND MISSES
Common causes of excessive false alerts are:
a.
Sensitivity control set too high
b.
Loose or defective coaxial video connectors or cables
c.
Spurious moving objects or lights in the camera field-of-view
d.
Camera ALC set too high
e.
Unnoticed shadows
f.
Flickering fluorescent lights, etc.
Common causes of excessive misses are:
a.
Sensitivity control set too low
b.
Object in motion is too fast or too slow
c.
Object in motion is too small to create sufficient video change
If false alerts and misses continue to be a problem, the entire installation should be
reexamined. Installation changes to improve performance may be possible. Such
changes may include:
reexamined. Installation changes to improve performance may be possible. Such
changes may include:
a.
Relocation of the camera
b.
Change of lens
c.
Change of lighting
d.
Addition, at different locations, of other cameras and motion detectors to cover
a wider variety of motions
a wider variety of motions