Princeton Instruments PhotonMAX System, Руководство пользователя

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Chapter 6 Advanced Topics 57
Fast and Safe Modes
Introduction
The PhotonMAX has been designed to allow the greatest possible flexibility when
synchronizing data collection with an experiment. The fundamental difference between
the Fast and Safe modes is how often the acquisition start and acquisition stop commands
are sent by the computer for a data collection sequence. With Safe Mode, the computer
sends a start and a stop command for
each frame of a data sequence. With Fast Mode,
the computer sends only one start and one stop command for each data sequence . Once
the start command is sent, the selected timing mode and the shutter condition determine
when charge will be allowed to fall on the CCD array.
In WinView/32 and WinSpec/32, the choice of
Fast
or the
Safe
data collection is made
on the
Experiment Setup|Timing
tab page. The flowcharts in Figure 46 show the
differences between the two modes.
Fast Mode
In Fast operation, the PhotonMAX runs according to the timing of the experiment, with
no interruptions from the computer. Fast operation is primarily for collecting "real-time"
sequences of experimental data, where timing is critical and events cannot be missed.
Once the PhotonMAX is sent the start command by the computer, all frames are collected
without further intervention from the computer. The advantage of this timing mode is that
timing is controlled completely through hardware. A drawback to this mode is that the
computer will only display frames when it is not performing other tasks. Image display
has a lower priority, so the image on the screen may lag several images behind. A second
drawback is that a data overrun may occur if the number of images collected exceeds the
amount of allocated RAM or if the computer cannot keep up with the data rate.
Safe Mode
In Safe Mode operation, the computer processes each frame as it is received: the
PhotonMAX cannot collect the next frame until the previous frame has been completely
processed. Safe Mode operation is useful when the camera is operated from a slower
computer that cannot process the incoming data fast enough. It is also useful when data
collection must be coordinated with external devices such as external shutters and filter
wheels. As seen in Figure 46, in Safe Mode operation, the computer controls when each
frame is taken. After each frame is received, the camera sends the stop command to the
camera, instructing it to stop acquisition. Once that frame is completely processed and
displayed, another start command is sent from the computer to the camera, allowing it to
take the next frame. Display is therefore, at most, only one frame behind the actual data
collection. One disadvantage of the Safe mode is that events may be missed during the
experiment, since the camera is disabled for a short time after each frame.
Note:
Safe Mode must be used whenever the system is set up for the optional Kinetics
Readout Mode. See "Kinetics Mode (Option)" , page 60, for more information about this
type of image acquisition and readout.