line scan camer image display problem (NI 1433, NI 6211)

[Penny001]

These are two images of a static dollar bill. I use NI MAX to grab the image. There is a horizontal line diving both images. Every single time, when clicking the 'grab' button from NI MAX interface, the position of the horizontal line moves. Does anybody know what is the problem? Is that due to the synchronization of the camera or the buffering to display the images?

To be more specific, I am using a NI DAQ 6211 to generate a 8kHz pulse train signal sending to the Pcie 1433 frame grabber via the SMB connector. I have a line scan camera (Basler sprint spl 2048-70km) connected to the frame grabber via the camera link.

Thank you very  much,

Ting