Figure 25. Timing Diagram For External Sync Mode (+ Edge Trigger) - Princeton PIXIS-XB System User Manual

Chapter 6 Advanced Topics 51
The PreOpen {Open Before Trigger} mode is useful in cases where an External Sync
pulse cannot be provided 8 ms (or the length of time a mechanical shutter takes to open)
before the actual signal occurs. Its main drawback is that the CCD is exposed to any
ambient light while the shutter is open between frames. If this ambient light is constant,
and the triggers occur at regular intervals, this background can also be subtracted,
providing that it does not saturate the CCD. As with the Normal Shutter {Normal} mode,
accurate background subtraction may not be possible for the first frame.
Also note that, in addition to signal from ambient light, dark charge accumulates during
the "wait" time (t ). Any variation in the external sync frequency also affects the amount
w
of dark charge, even if light is not falling on the CCD during this time.
Note: If EXT SYNC is still active (in Figure 25, this means that if it is still HIGH) at the
end of the readout, the hardware may interpret this as a second sync pulse, and so on.

Figure 25. Timing Diagram for External Sync Mode (+ edge trigger)

External Sync with Continuous Cleans {Clean Until Trigger} Timing
Another timing mode available with the PIXIS-XB is called Continuous Cleans {Clean
Until Trigger}. In addition to the standard "cleaning" of the array, which occurs after the
camera is enabled, this mode will remove any charge from the array until the moment the
External Sync pulse trigger edge is received.
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