4 Operation Model 3000TA-XL-EU
4-16 Teledyne Analytical Instruments
sufficiently stable.) Once Enter is pressed, the Span reading changes to the
correct value. The instrument then automatically enters the Analyze func-
tion.
4.4.3 Span Failure
The analyzer checks the output of the cell at the end of the span. If the
raw output of the cell is less than 0.5 uA/ppm O2, the span will not be
accepted. The analyzer will return to the previous calibration values, trigger
the System Alarm, and display in the VFD:
Span Failed!!
This message will be shown for five seconds and the instrument shall
return to the Analyze mode. In the upper right hand corner of the VFD
display “FCAL” will be shown. This message flag will help the operator
troubleshoot in case calibration was initiated remotely. To reset the alarm
and the flag message, the unit must be turned off by cycling the standby key
. It will not reset if the next span cycle is correct.
A trace cell is unlikely to fail span. As explained before, when the
sensor reaches the end of its useful life, the zero offset begins to rise until the
analyzer finds the zero unsatisfactory. Nevertheless, feeding the wrong span
gas or electronics failure could set this feature off at the end of the span.
Consider this before replacing the cell.
4.5 Switching of Sample Streams
The Model 3000TA-XL may be used to monitor more than one type of
sample gas, such as nitrogen and helium, or two streams of nitrogen contain-
ing low (less than 1 ppm) and high (5000 to 10,000 ppm) concentrations of
oxygen.
For these applications, we recommend the following parameters and
conditions be followed:
1. While switching streams, such as between nitrogen and helium, both
the gas streams must be made to flow continuosly even through only one
stream is going through the analyzer at one time. Failure to do so may result
in spikes in output when the dead-ended stream is switched in. For more
discussion of this, read the Technical Bulletin - TB00001, dated 3-98. This
Bulletin is available upon request from TATAI.
2. The analyzer is capable of handling the switching of streams without
effecting the sensitivity of the cell. This switching of streams between