Princeton 4411-0097 ユーザーズマニュアル

54 

PI-MTE System Manual 

Version 4.C 

Shutter opens

Shutter remains open

for preprogrammed

exposure time

System waits while

shutter closes

Shutter opens

Controller waits for

External Sync pulse

Controller waits for

External Sync pulse

(shutter preopen)

(shutter normal)

 

The PreOpen mode is useful in cases where an External Sync pulse trigger edge cannot 
be provided 5–28 msec (shutter open time) 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 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

w

). Any variation in the external sync frequency also affects the amount 

of dark charge, even if light is not falling on the CCD during this time. 

Note: If EXT SYNC is still active (in Figure 18, this means that if it is still LOW) at the 
end of the readout, the hardware may interpret this as a second sync pulse, and so on.