Teledyne 3000TB-XL - Trace oxygen analyzer - Manual (Page 51)

Trace Oxygen Analyzer Operation 4
4-11 Teledyne Analytical Instruments
To show negative oxygen readings on the display:
- Press the System key
TRAK/HLD Auto-Cal
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- Use the Right or Left arrow keys and select More. Press Enter.
Version Self-Test
Show_Negative=NO
- Use the Right or Left arrow keys and select
“Show_Negative=NO”.
- Use the Up or Down key to toggle from NO to YES.
- Press the Escape key twice to return to the analyze mode.
This preference is stored in non-volatile memory, so this configuration
is remembered after a power shutdown. If the instrument is cold started, it
will go back to default (not showingg negative oxygen readings).
4.4 The Zero and Span Functions
Although the instrument can be spanned using air, a span gas with a
known oxygen concentration in the range of 70–90% of full scale of the
range of interest is recommended. Since the oxygen concentration in air is
20.9% (209,000 ppm), the cell can take a long time to recover if the
instrument is used for trace oxygen analysis immediately following
calibration in air.
Connect the calibration gases to the analyzer according to the instruc-
tions given in Section 3.4.1, Gas Connections, observing all the prescribed
precautions.
The B-2CXL cell has a zero offsetzero offset of less than 0.2 ppm oxygen.
Normally, the offset slowly decreases during the first 7 to 10 days of operation, and is
expected to reach a steady value after this time.
Generally, the value of the zero offset is part of the oxygen reading of the sample
gas as shown by the analyzer readout. As an example, a reading of 0.5 ppm oxygen may
include 0.4 ppm oxygen in the sample gas and a 0.1 ppm zero offset.
The determination of the zero offset requires the use of oxygen free gas to the
analyzer. We recommend the use of nitrogen gas with a scrubber to assure oxygen levels
below 0.02 ppm.
The user may decide to eliminate the zero offset for improved accuracy. If the
low range accuracy needs to be better than 100 ppb, a zero calibration should be
performed. Thus, the analyzer is equipped with a zero calibration function. However, we
do not recommend carrying out the cal zero during the first 10 days of the operation of the
cell.