Ultra Trace Oxygen Analyzer
Operation 4
4-13
Teledyne Analytical Instruments
#### PPM Zero
4 Left=### ppm/s
The zeroing process will automatically conclude when the output is
within the acceptable range for a good zero. Then the analyzer automatically
returns to the
Analyze
mode.
Because the reading of the slope is not very sensitive, it is recom-
mended that zero gas be purging a few minutes before starting the Auto
mode zeroing. This will ensure cell stability on the new Zero settings.
4.4.1.2
Manual Mode Zeroing
Press
Zero
to enter the
Zero
function. The screen that appears allows
you to select between automatic or manual zero calibration. Use the
∆∇
keys
to toggle between
AUTO
and
MAN
zero settling. Stop when
MAN
appears,
blinking, on the display.
Zero: Settling: Man
<ENT> To Begin
Press
Enter
to begin the zero calibration. After a few seconds the first
of five zeroing screens appears. The number in the upper left hand corner is
the first-stage zero offset. The microprocessor samples the output at a prede-
termined rate. It calculates the differences between successive samplings and
displays the rate of change as
Slope=
a value in parts per million per second
(ppm/s).
#### ppm Zero
Slope=#### ppm/s
NOTE: It takes several seconds for the true
Slope
value to display. Wait
about 10 seconds. Then, wait until
Slope
is sufficiently close to zero
before pressing
Enter to finish zeroing .
Generally, you have a good zero when
Slope
is less than 0.05 ppm/s
for about 30 seconds. When
Slope
is close enough to zero, press
Enter
. In a
few seconds, the screen will update.
Once zero settling is completed, the information is stored in the
microprocessor, and the instrument automatically returns to the
Analyze
mode.
4.4.1.3
Cell Failure
Cell failure in the Ultra Trace 3000 is usually associated with inability
to zero the instrument down to a satisfactorily low ppm reading correspond-
ing to a current of 2 nanoamps (approx. 1 ppm). When this occurs, the
