Figure 16. Mechanical Shutter Operation And Not Scan Signal; Figure 17. Winx Detector Temperature Dialog - Princeton PIXIS-XB System User Manual

Chapter 5 Operation 37
Exposure Time
Exposure time (set on the Experiment Setup|Main tab { Common Acquisition
Settings expander}) is the time between start acquisition and stop acquisition commands
sent by the application software to the camera. In combination with triggers, these commands
control when continuous cleaning of the CCD stops and when the accumulated signal will be
readout. The continuous cleaning prevents buildup of dark current and unwanted signal
before the start of the exposure time. At the end of the exposure time, the CCD is readout and
cleaning starts again.
Because PIXIS-XB cameras do not incorporate an internal shutter, some signal may
accumulate on the array while it is being readout. This continuous exposure of the array
during readout may result in some smearing. However, exposures that are significantly
longer than the readout time can be performed without a shutter, as the amount of
smearing will be low.
If smearing or other factors require a shutter-like operation, the NOT SCAN { Not
Reading Out } or the SHUTTER { Shutter Open }signal at the LOGIC OUT connector
on the rear of the PIXIS-XB can be used to synchronize the x-ray source or an x-ray
shutter with the exposure-readout cycle so the CCD can be read out in darkness (see
"LOGIC OUT Control", on page 56 for more information). Figure 16 shows the action
of a mechanical shutter with respect to the NOT SCAN signal.

Figure 16. Mechanical Shutter Operation and NOT SCAN Signal

CCD Temperature
As stated before, lowering the
temperature of the CCD will generally
enhance the quality of the acquired
signal. When WinX is the controlling
software, temperature control is done
via the Detector Temperature
dialog (see Figure 17) accessed from
the Setup menu. When LightField is
being used, temperature control is
Figure 17. WinX
done on the Sensor expander.
Detector Temperature dialog
Once the target array temperature {Temperature Setpoint} has been set, the software
controls the camera's cooling circuits to reach set array temperature. On reaching that
temperature, the control loop locks to that temperature for stable and reproducible
performance. When temperature lock has been reached (temperature within 0.05°C of set
value), the current temperature is Locked . The on-screen indication allows easy
verification of temperature lock.
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