American Dynamics SpeedDome Ultra VII Operator's Manual page 32

In this example, the dome receives information about the color of the traffic light. While the
light is red, the image is relatively static. With the shutter limit set to 1/4 second (250
milliseconds), updated red light information is transmitted at 1/4-second intervals. When the
light changes from red to green, updated light color information becomes available. The
dome must now transmit information about the green light. This update occurs as soon as the
green light information is available. This may occur before the 1/4-second interval elapses. In
this example, the light changed to green after 180-milliseconds. Thereafter the green light
information is transmitted at 1/4-second intervals until new light color information becomes
available.
If the light were to change from red to green halfway through the field integration interval
(125 milliseconds), it may appear that both the red and green lights are lit simultaneously.
This situation is illustrated in Figure 3-2.
Figure 3-2: Mixed field integration
Red Light
Adjusting the Shutter Limit sets the update time used to maintain the image quality. If you
want to videotape an incident in low-light conditions, you may find that tape quality is not
acceptable. To ensure that the videotape quality is acceptable for possible prosecution
purposes, you may want to test the Shutter Limit settings under the expected lighting
conditions.
The Relationship between AGC and Open Shutter Settings
Table 3-1 explains which settings may be changed based on the current AGC/Shutter setting.
Table 3-1: AGC Maximum Gain and Shutter Limit settings
AGC/Shutter Setting
AGC Off
AGC On
Open Shutter
3-6
Red Light
250
msec
Max Gain
N/A
0-28dB (NTSC)
0-28dB (PAL)
0-28dB (NTSC)
0-28dB (PAL)
Red/Green Light
125 125
msec msec
Limit
N/A
N/A
1/2-1/60 (NTSC)
2/3-1/50 (PAL)
SpeedDome Ultra VII Operator's Manual
Green Light