Teledyne 3060e - Ultra Trace oxygen analyzer - Manual (Page 85)

Teledyne Electronic Technologies
Analytical Instruments
4-37
Operations Operations Operations Operations Operations Ultra Ultra Ultra Ultra Ultra T T T T Trace Oxyg race Oxyg race Oxyg race Oxyg race Oxygen Anal en Anal en Anal en Anal en Analyz yz yz yz yzer er er er er
Important Notes on Zero and Span Calibration
i. In order to obtain the most reliable results when analyzing sample gases
with oxygen concentrations in the PPB range, the analyzer is programmed
not to offset any background signal exceeding a chosen maximum value. If
you attempt to offset a background signal higher than that value, the system
displays the error message CANNOT ZERO. BACKGROUND LEVEL
MORE THAN THE RECOMMENDED VALUE. The analyzer will
wait until the background signal drops below that value.
ii. The initial zero reading may take up to 48 hours to stabilize. Subsequent
zero readings, however, are usually completed in 5–30 minutes.
iii. The analyzer usually displays a raw background signal equivalent to 20–60
PPB oxygen. During initial start-up, the background signal may be greater
than 60 PPB. The background signal level decreases slowly as dissolved
oxygen is gradually removed from the electrolyte with continued sparging.
iv. If you adjust the zero when the signal is greater than 60 PPB, the zero line
may drift slowly to a negative value. It is recommended that you adjust the
zero frequently during the first 3–4 weeks of operation, preferably once
every day during the first week and then once every two days for the second
and third week. After the third week, adjust the zero once per week.
v. The value of the corrected background signal is stored in the computer
memory. In the Analyze mode, the value displayed is always corrected for
the background signal. However, when you enter the Zero mode, the
previously corrected background plus the current background signal will be
displayed. For example, assume that you offset a background signal of 60
ppb and then return to the analyze mode. After a few days, you are reading
the oxygen concentration in the analyze mode as 5 ppb. You then decide to
rezero the analyzer. As soon as you enter the zero mode, the analyzer will
read 65 ppb and then will settle slowly to a new zero line (usually within
5–10 minutes). This is to ensure that you do not correct the background
signal more than the recommended value at any time. See Figure 4-8.
vi. The maximum raw background signal that can be offset is –10 to 150 PPB
equivalent, and is dependent on the signal output per PPM of the Ultra
Trace sensor, which may vary during operation.
vii. The span of the analyzer is very stable and does not require frequent span
calibration. Therefore, TET/AI recommends that you span calibrate the
analyzer at least once each week during the first four weeks and then once
every two weeks during the next eight weeks. After this time, the analyzer
should be calibrated once a month. TET/AI recommends calibrating the
analyzer in the 0–1 or 0–10 PPM range with a typical span gas value of
500–700 PPB.