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44 ST-133 Controller Manual Version 3.B
Free Run timing
In the Free Run mode the controller does not
synchronize with the experiment in any way. The
shutter opens as soon as the previous readout is
complete, and remains open for the exposure time,
t
exp
. Any External Sync signals are ignored. This
mode is useful for experiments with a constant light
source, such as a CW laser or a DC lamp. Other
experiments that can utilize this mode are high
repetition studies, where the number of shots that
occur during a single shutter cycle is so large that it
appears to be continuous illumination.
Other experimental equipment can be synchronized
to the ST-133 controller by using the output signal
(software-selectable SHUTTER or NOTSCAN) from
the
connector. Shutter operation and the
NOTSCAN output signal are shown in Figure 11.
Shutter opens
Shutter remains open
for preprogrammed
exposure time
System waits while
shutter closes
Figure 10. Free Run Timing Chart,
part of the chart in Figure 9
Shutter Open Close Open Close Open Close
Read Read Read
First exposure
Data
stored
Third
exposure
Data
stored
t
exp
t
c
t
R
Second
exposure
Data
stored
NOTSCAN
Figure 11. Free Run Timing Diagram
External Sync timing
In this mode all exposures are synchronized to an external source. As shown in the flow
chart, Figure 12, this mode can be used in combination with Normal or PreOpen Shutter
operation. In Normal Shutter mode, the controller waits for an External Sync pulse, then
opens the shutter for the programmed exposure period. As soon as the exposure is
complete, the shutter closes and the CCD array is read out. The shutter requires
several msec to open completely, depending on the model of shutter. (Shutter
compensation time is discussed in Chapter 6.)
Since the shutter requires up to 28 msec to fully open, the External Sync pulse provided
by the experiment must precede the actual signal by at least that much time. If not, the
shutter will not be open for the duration of the entire signal, or the signal may be missed
completely.
Also, since the amount of time from initialization of the experiment to the first External
Sync pulse is not fixed, an accurate background subtraction may not be possible for the
first readout. In multiple-shot experiments this is easily overcome by simply discarding
the first frame.