National Instruments NI Vision NI 17xx User Manual

Also see for NI Vision NI 17 Series: User manual User manual

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National Instruments NI Vision NI 17xx User Manual Manual pdf 41 page image

Chapter 5 Image AcquisitionNI 17xx Smart Camera User Manual 5-2 ni.comcan be used to calculate the maximum exposure. Assuming the object ismoving horizontally across the field of view, use Equation 5-1 to calculatethe maximum exposure time.(5-1)where E max is the maximum exposure time without blurring,R is the rate of motion of the object either horizontally orvertically,FOV is the field of view in the direction of motion, andN is the number of sensor pixels in the direction of motionFor many applications that include moving objects, additional lighting isnecessary to achieve good image contrast due to the short exposure timerequired to avoid motion blur.Additionally, in many environments, the ambient light conditions vary toosignificantly to obtain consistent results without adding dedicated lighting.For example, in a building with windows, the ambient light can varysignificantly with weather. Also, standard fluorescent lighting flickers at arate that is perceivable by the smart camera. In these situations, the ambientlight must be overridden with a dedicated light source to ensurereproducible results.Acquiring ImagesYou can configure the NI Smart Camera to acquire images based oninternal timing or an external trigger signal. In both cases, the smart cameracan acquire full frame images at the camera’s maximum frame rate.If partial scanning or binning are enabled, the smart camera can acquireimages faster than the full frame maximum frame rate. Refer to theMaximum Frame Rate section for information about factors that affect themaximum frame rate.Internal TimingThe NI Smart Camera features two types of internally-timed modes:free-run mode and fixed-frame-rate mode.In free-run mode, the smart camera acquires images at the maximum framerate allowed by the configuration.E maxR Horizontal 2×FOV Horizontal( ) N Horizontal( )⁄------------------------------------------------------------------------=