Hach AutoCAT 9000, Instruction Manual

Page: 137 / 176

Manual Endpoint Determination
50081_ManualEndpoint.fm
Page 135
Manual Endpoint Determination
General Guidelines for Manual Endpoint Determination
1.
In the Zoom screen,
move the right and left
cursors as necessary, to
exclude any non-linear
portions at the beginning or
end of the curve, and if
necessary, move the cursors
so that the endpoint will be
roughly centered within the
selected region.
2.
Press
DEL
to enter the
manual endpoint
determination screen.
3.
Move the four cursors
to select one linear region
before, and one linear
region after the endpoint.
Make these linear segment
selections as large as
possible in order to obtain
the most accurate endpoint
determination.
Note: The AutoCAT will draw a
best fit regression line through
the data points between the
two cursors on the left side of
the end point, and a best fit
regression line through the
data points between the two
cursors on the right side of the
end point. The AutoCAT will
use the intersection point of
these two lines as the end point
in calculations.
4.
Press the
CHECK MARK
to calculate the result.
5.
When the sample
oxidant concentration is
high and a predose has not
been selected, the initial
current change may be flat.
6.
By selecting a linear
segment just before the
endpoint, the lines will
intersect at the obvious
endpoint, yielding a correct
Vep.