Use Beam Drift Correction
The beam drift correction can be disabled for use in certain unusual analytical situations. The program will type a warning to the log window if the beam drift correction is disabled.
The beam drift correction calculation is shown here (where beam integration time is taken into account) :
Where
:
is the beam drift corrected unknown intensity
is the
uncorrected unknown intensity
is the
count time for the unknown intensity
is the
count time for the nominal beam current measurement
is the beam
current for the unknown intensity
However, since Probe for EPMA stores and utilizes x-ray intensities in counts per second (already normalized to time), the actual beam drift correction, for direct reading faraday cup microprobes, is quite a bit more simple than the rigorous example above, and is instead shown here:
Where
:
is the beam drift corrected unknown intensity
is the
uncorrected unknown intensity
is the
nominal beam current
is the beam
current for the unknown intensity
This means that if the actual measured beam current for your
unknown decreases over time, the value of the fraction 
,
increases and therefore the corrected x-ray intensity is adjusted
upwards. If on the other hand, the actual measured beam current for your unknown
increases over time, then the value of the fraction ,
decreases and therefore the corrected x-ray intensity is adjusted
downwards.
The beam drift correction essentially normalizes the x-ray intensities to the x-ray intensity that would be expected at the nominal beam current. For example, if most of the x-ray measurements are made at a beam current of 20 nA, then setting the nominal beam current to 20 nA will ensure that the x-ray intensities will appear scaled to readings taken at 20 nA (even if the measurement is taken at a different beam current). In an alternative usage, the x-ray intensities may be expressed in counts per second per nA by setting the nominal beam current to 1.0. See the Count Times dialog in the Acquire! Window to manually change the nominal beam current.