Section 6
Page 97
UVTOCOperation.fm Calibration Menu
(0,y
1
) and is called the baseline. The higher point (x
2
,y
2
) is normally called the
span reading, though it is not always done at the full scale of the analyzer.
The slope of the interpolated/extrapolated line is the gain of the analyzer
in ppm/mg/L (gas/TOC). See Figure 31.
Figure 31 TOC Concentration vs. CO
2
ppm
For example, if a 0–1000 mg/L analyzer is calibrated with 800 mg/L the
calibration might be defined as (0, 25) and (800, 7602). This would give a
gain of (7602-25)/800 i.e 9.475 ppm/mg/L. The gain of each analyzer will vary
slowly with time due to aging of peristaltic pump tubing and also the aging of
the UV lamps. Following any manual calibration or auto-calibration, this aging
can be identified by the % in the Pri v cal screen (see section 6.7.3.1 on
page 93). An online TOC measurement of a sample is produced by
measuring the CO
2
gas ppm and using the straight line to mathematically look
up the TOC mg/L. If the calibration set (0,y
1
) and (x
2
,y
2
) are being used as the
two point active calibration:
Where:
y
s
is the CO
2
ppm being produced by the sample.
At any point in time, four distinct calibrations are stored separately in the
database of the analyzer. Only one is used at any time to calculate the online
Gain
y
2
y
1
–
x
2
------------------ -=
TOC µg/L or mg/L
CO ppm
2
0
20%
20%
40%
60%
80%
100%
40%
60% 80%
100%
0
(0, y )
1
(x , y )
Span
22
Zero or Baseline
Online sample TOC (mg/L)
y
s
y
1
–()x
2
•
y
2
y
1
–()
----------------------------------- -=
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