Takenaka System FS2300DV Instruction Manual page 8

● Recommended timing of asynchronous shutter trigger signal (Vinit signal) for preset shutter/pulse width control
For the case of preset shutter mode, the negative logic pulse is
applied within the width range from 1 H (one horizontal
synchronous time) to 1ms as described below. For this case, the
exposure operation starts in synchronization with the trailing
edge (the leading edge of pixel clock in the case of H-reset
mode) of the internal HD pulse (horizontal synchronous signal)
after and closest to the trailing edge timing of the applied pulse.
For the case of the pulse width control exposure mode, numeric
value of the L level interval of the input Vinit pulse (shown as
Tvinit in the figure) is retrieved in synchronization with the trailing
edge of the internal HD pulse (the leading edge of pixel clock in
the case of H-reset mode), and the integer multiple number of H
(one horizontal synchronous interval) that is closest to the
retrieved Vinit pulse duration is transmitted as nH (the integer
multiple number of pixel clock in the case of H-reset mode) to
the inside of the camera. Then the shutter speed is determined
in response to the time nH.
(Note) In the pulse width control mode (without H-reset), the shutter exposure time is almost equal to the integral
multiple number of the horizontal synchronous time (H) that is closest to the Vinit pulse duration. More
specifically, however, the shutter exposure time is indefinite for the time period corresponding to 1H width in
the case of normal external trigger input (i.e. the case where the Vinit signal is not in synchronization with the
horizontal synchronous timing of the camera). It is improved by being employed in "with H-reset" mode
→ Refer to the timing chart described in another section for the details.
(Note) When the shutter exposure time is very long (i.e. longer than one vertical synchronous time) in the pulse
width control mode, the S/N ratio of the image will be degraded due to the reduction of dynamic range of CCD
by the accumulation of thermal noise components of CCD image sensor in proportion to the shutter speed
and other factors. Therefore, if a long exposure time is employed, it is recommended to conduct experiments
using realistic exposure times in actual conditions to check for the appropriateness.
Example of drive circuit for Vinit1 input circuit
●
[Example of user circuit]
VCC
75
74AC04 or
others
VCC is +5V or +3V
* The Vinit signal should not include unnecessary
noise components such as chattering.
● Polarity reversal of Vinit2 input
The input polarity of the trigger signal (Vinit2) to be applied via CC1 of Camera Link can be inverted.
Some capture boards may have the polarity of the trigger signal input from CC1 that is fixed to positive logic (L level at
normal / H level at active), which is not compatible with the trigger signal of negative logic input (factory preset polarity
of this equipment). In this case, the input polarity of the trigger signal (Vinit2) via CC1 can be inverted to change from
negative to positive logic by the setting of the camera.
→ Refer to "(6-3) How to set operation mode" for the specific setting method.
(Note) The setting of the polarity reversal is valid only for Vinit2. The input polarity of Vinit1 is always negative logic
regardless of this setting.
Vinit1 IN
3.3V
4.7k
Camera 4
100
connector
6.8V
CC1 (Vinit2) input
- 8 -
Tvinit
Vinit
[For the case of preset shutter mode]
1H(horizontal scan time)≤ Tvinit ≤ 1ms
(The shutter exposure time is independent of the Vinit width.)
[For the case of pulse width control mode]
nH ≤ Tvinit <(n+1)H (n is 1 or larger integer.)
(This is the pulse width where shutter exposure time =nH)
Fig. 4-3 Recommended Vinit signal timing waveform
Inside of camera
3.3V
TC74LVX14
47p
(or equivalent)
10k
NORMAL
Setting of Vinit2 polarity
INVERTED
N11A27;8/37
To internal circuit