NAC Image Technology SP-642 - 8.13 Frame Straddling (HX and GX-8 Cameras)

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8.13 Frame Straddling (HX and GX-8 Cameras)
With the HX and GX-8 cameras, the frame straddling function enables recording two images with
a very short time separation that is used with PIV (Particle Image Velocimetry). Frame
straddling photography is a method of recording a group of two images that involves shining a
laser at a very short time interval before and after the frame. With GX-8 frame straddling,
recording is performed on two frames (1
st
frame, 2
nd
frame) at the first exposure start signal.
Exposure start
signal
EPO
“Exposure pulse”
Laser pulse
Out
put
Exposure start
1st
Frame
Exposure
2nd
Frame
Exposure
1st
Frame
Exposure
2nd
Frame
Exposure
Exposure start
Out
put
Out
put
Out
put
To use the frame straddling function, set “HX, GX-8 Frame Straddling” under the “Exposure
Timing” tab of “Camera Connection Settings” or “Options” to “ON”. Refer to page 6-7.
It can also be set in “Recording Parameters” in the “List of Camera Settings” window. Refer to
page 4-22.
Internal sync or EST sync can be selected for the camera synchronization.
・ With the camera EPO output signal as a reference, if synchronizing with laser pulse timing, set
the GX camera synchronization to “Internal Sync”.
・ If a reference signal exists separate from the camera, set the HX and GX camera
synchronization to “EST Sync” so the timing of the camera and the laser pulses are
synchronized to the reference signal. The frame rate depends on the frequency of the reference
signal.
The timing to switch the camera from the 1
st
frame to the 2
nd
frame can be adjusted by changing
the 1
st
frame exposure time in the shutter settings.
Also, the 2
nd
frame exposure time depends on the frame size and so cannot be changed.
During frame straddling, only one of either the 1
st
frame or the 2
nd
frame can be shown on the live
video and PC display, which is handy to verify the timing of the laser pulses.
Set “HX, GX-8 Frame Straddling” in “Exposure Timing” (Options/Camera Connection Settings)
(Refer to page 6-7.).
ANY In VIEW/ARM, displays the most recent video or live image without
differentiating between the 1st and 2nd
1st In VIEW/ARM, displays the most recent video or live image in the 1
st
frame
2nd In VIEW/ARM, displays the most recent video or live image in the 2
nd
frame
Refer to the HX or GX-8 camera user's manual for details of the frame straddling function.