Teledyne BDS-3000 - Oxygen analyzer - Manual (Page 68)

Operation BDS 3000
Teledyne Analytical Instruments 54
Press ENTER to enter the span value into the system and begin the
span calibration.
Once the span has begun, the microprocessor samples the output at
a predetermined rate. It calculates the difference between successive
samplings and displays this difference as a slope on the screen. It takes
several seconds for the first slope value to display. Slope indicates the
rate of change of the span reading. It is a sensitive indicator of stability.
#### % Span
Slope = #### ppm/s
When the span value displayed on the screen is sufficiently stable,
press ENTER. (Generally, when the Span reading changes by 1 % or less
of the full scale of the range being calibrated, for a period of ten minutes
it is sufficiently stable.) Once ENTER is pressed, the span reading
changes to the correct value. The instrument then automatically enters
the Analyze function.
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 1.5 nA/ppb or more than 13.5
nA/ppb O
2
, 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 analyzer must be properly
spanned.
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 The Alarms Function
The Model BDS 3000 is equipped with 2 fully adjustable
concentration alarms and a system failure alarm. Each alarm has a relay