National Instruments ISC-1783, User Manual

windows, the ambient light can vary significantly with weather. Also, standard fluorescent

lighting flickers at a rate that is perceivable by the ISC-178x. In these situations, the ambient

light must be overridden with a dedicated light source to ensure reproducible results.
The Lighting Strobe starts after the Trigger Delay is satisfied. Use the Exposure Delay if your

lighting source requires time to reach a stable intensity so that your images are consistent and

your lighting does not fluctuate. The Exposure Delay can only be specified in units of time,

and defaults to a value of 0. The Exposure Delay can be adjusted by setting the Exposure

Delay control in Vision Builder AI, setting the Exposure Delay attribute in LabVIEW, or by

setting the Exposure Delay in the attribute tree in MAX. The exposure begins once the

Exposure Delay is satisfied. Both the Lighting Strobe and the Exposure signals end once the

Exposure Time is satisfied.

Related Information

Field of View

 on page 17

Determining the Maximum Frame Rate

 on page 22

Image Readout

The image readout phase begins immediately following the completion of the image exposure

time. During image readout, the sensor transfers the acquired image data to the CPU of the

ISC-178x.
The image readout duration is primarily dependent upon the image size and the image

decimation because these settings directly influence the amount of data that must be

transferred. The length of time required for the image readout directly affects the maximum

frame rate that can be achieved because only one image can be transferred at a time. There can

never be an exposure that ends during the image readout for the previous image. The

relationship between the triggering, exposure, and readout of the image is determined by the

Trigger Overlap feature.

Related Information

Field of View

 on page 17

Determining the Maximum Frame Rate

 on page 22

Trigger Overlap

The Trigger Overlap feature determines whether to allow the exposure phase of a triggered

image acquisition to occur while the previous image is still being transferred to the host. If

Trigger Overlap is disabled, the exposure phase and the image transfer phase will occur

sequentially. If the exposure phase ends before the previously acquired image is transferred to

the host, enabling Trigger Overlap can lead to dropped frames. If, however, the exposure phase

ends after the previously acquired image is transferred to the host, enabling Trigger Overlap

can increase the speed of your application.
When Trigger Overlap is disabled, the start of the exposure phase is highly deterministic

because the exposure and image readout occur sequentially. When Trigger Overlap is enabled

and the exposure begins during the readout of the previous image, the exposure signal must be

synchronized with the sensor. This introduces additional offset and jitter to the start of the

exposure.

ISC-178x User Manual

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