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sufficiently stable.) Once Enter is pressed, the Span reading changes to the correct value. The instrument then automatically enters the Analyze func- tion.
4.4.3Span 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.
4.5Switching of Sample Streams
The Model
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
2.The analyzer is capable of handling the switching of streams without effecting the sensitivity of the cell. This switching of streams between
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