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Data sampling
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Data storage
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Data
from chromatography system monitors is stored temporarily in data
buffers in the local system controller. Data is transferred from
the buffers to disk storage by UNICORN whenever a chromatogram is
closed, that is when the New_Chromatogram instruction
is issued or the result file is closed.
Data is also saved to disk at pre-set intervals during a run,
thus minimizing data loss in the event of power or communication
failure.
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Data buffer capacity
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The capacity of the data buffer is 16000 points for up to
sixteen monitors.
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Note:
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The data buffer capacity is listed in the Curves group of System:Settings in System Control module.
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Effective sampling frequency
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If
a buffer is filled during a run, i.e. 16000 points have been recorded,
the number of points is halved by deleting every second point, leaving
8000 points on the chromatogram. For subsequent sample points, every
second point is dropped, thus halving the effective sampling frequency.
When the chromatogram again reaches 16000 points the process is
repeated and the effective sampling frequency is halved once again.
Now every fourth sampling point will be recorded.
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Note:
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The real sampling frequency, the sampling frequency of the
card, never changes.
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Initial effective sampling frequency
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The initial effective sampling frequency for each monitor
is set in the system strategy. It can be viewed and changed in the Curves group of System:Settings in System Control.
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Note:
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For ÄKTAxpress systems, the sampling frequency cannot be viewed
or changed.
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Resolution at 10 Hz sampling frequency
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The
table below describes the resolutions that apply for the curves
at an initial effective sampling frequency of 10 samples per second
(10 Hz):
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Duration [minutes]
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Card sampling frequency [Hz]
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Effective sampling frequency [Hz]
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Number of points
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Resolution [seconds/point]
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0-27
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10
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10
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0-16000
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0,1
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27-53
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10
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5
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8000-16000
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0,2
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53-107
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10
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2,5
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8000-16000
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0,4
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107-203
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10
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1,25
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8000-16000
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0,8
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How to ensure maximum resolution
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To ensure maximum
resolution for a part of a run, issue a New_Chromatogram instruction
at the beginning of the part. This empties the data buffers and
resets the sampling frequency to the value specified in the system
settings.
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2005-06-15
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