National Instruments NI 1712 User Manual - page 51
6-2
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Chapter 6
Image Acquisition
(6-1)
where
E
max
is the maximum exposure time without blurring,
R
is the rate of motion of the object either horizontally or vertically,
FOV
is the field of view in the direction of motion, and
N
is the number of sensor pixels in the direction of motion
For many applications that include moving objects, additional lighting is necessary to achieve
good image contrast due to the short exposure time required to avoid motion blur.
Additionally, in many environments, the ambient light conditions vary too significantly to obtain
consistent results without adding dedicated lighting. For example, in a building with windows,
the ambient light can vary significantly with weather. Also, standard fluorescent lighting flickers
at a rate that is perceivable by the NI 17xx Smart Camera. In these situations, the ambient light
must be overridden with a dedicated light source to ensure reproducible results.
Acquiring Images
You can configure the NI 17xx Smart Camera to acquire images based on internal timing or an
external trigger signal. In both cases, the NI 17xx Smart Camera can acquire images at the
camera’s maximum frame rate. Refer to the
Maximum Frame Rate
section for information about
factors that affect the maximum frame rate.
Internal Timing
The NI 17xx Smart Camera features two types of internally-timed modes: free-run mode and
fixed-frame-rate mode.
In free-run mode, the device acquires images at the maximum frame rate allowed by the
configuration.
In fixed-frame-rate mode, you can specify a frame rate that is less than or equal to the maximum
frame rate.
External Trigger
Use the trigger input to synchronize the NI 17xx Smart Camera with an external event, such as
the assertion of a signal generated by a proximity sensor. You can trigger the NI 17xx Smart
Camera at rates up to the maximum frame rate. Refer to the
Maximum Frame Rate
section for
information about factors that affect the maximum frame rate.
To use an external trigger, the trigger signal must be provided on the TrigIn/IsoIn(0)+ and
TrigIn/IsoIn(0)- inputs to the camera and triggering must be enabled in the software. Refer to the
E
max
R
Horizontal
2
×
FOV
Horizontal
(
)
N
Horizontal
(
)
⁄
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