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Vertical timing: High speed/Pulse width control/Asynchronous shutter/Without H-reset/Without Fast-dump
●
Vertical timing
Ｖｉｎｉｔ
ＨＤ
(Internal horizontal
synchronous signal)）
Exposure time
Camera Link
ＦＶＡＬ
Image output
ＳＴＲＢ
ＢＵＳＹ
Unless otherwise specified, the time unit of the values in the vertical timing chart is H (=3156 PCLK =1920
※
(Note) The width of Vint must be larger than 1H (Horizontal synchronous time). However, for the following reason, the output
level becomes unstable due to uncertainty of exposure time corresponding to 1H in the case of short exposure time,
if the trigger pulse which is out of synchronization with the horizontal timing of the camera is given.
(Note)
Strictly speaking, even if the same pulse width of Vinit is applied, the shutter speed differs for the period
corresponding to 1H width when the asynchronous shutter operation is executed in the pulse width control mode
(indefinite for 1H width).
Although an equal pulse width (value between 2Hs and 3Hs) is applied both for (A) and (B) in the figure below, the
phase relationship with the internal horizontal synchronous timing makes their shutter speeds different from each
other: (A) shutter speed = 2Hs and (B) shutter speed = 3Hs.
Example of 1H difference with same Vinit signal
Vinit (A)
Vinit (B)
HD
(Internal horizontal
synchronous signal)
Because of the above reason, consideration must be given to the fact that the exposure time becomes indefinite for the
period of 1H shutter speed when a Vinit signal that is not in synchronization with the internal horizontal synchronous
signal (HD) is input from the user side. Some of the countermeasures to be taken are as follows:
(1) Use only with the shutter speeds that do not have serious impact even if the shutter speed is indefinite for a period of
1H.
••• No practical problem may be caused when the shutter speed is fairly long, say 100H width or longer because the
impact of 1H difference in exposure time over the signal level is relatively small.
(2) Use with H-reset
••• The duration time where the exposure time is indefinite falls within up to 1 clock because the internal HD timing is
reset (initialized) by inputting the trigger signal.
(Note) Since n does not have an upper limit, the exposure time can be prolonged to be more than one frame time. The
maximum exposure time to be employed, however, should be determined after implementing experiments based on
the conditions of the actual operation because a longer exposure time is accompanied by the degradation of S/N ratio
due to the accumulation of CCD thermal noises.
(Note) It is necessary to set "PWEN=ENABLED" in flag register(FR) and to set (hypothetical) shutter switch (or externally
specified shutter SW position) to "9" for enabling the settings of pulse width control mode.
ｎ
474×PCLK
1100×PCLK
ｎ＋２
1
0.13
The period where it is regarded invalid to newly input trigger signal
0.13
1
2
1
2
3
1
End of exposu re (Sen sor gat e)
10
Effective image duration
(Shutter time:2Hs)
(Shutter time:3Hs)
- 48 -
M10510B;48/58
20 54
（1960）
1/32.50MHz = 97.11 μ S).
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