Teledyne BDS-3960 - Oxygen analyzer - Manual (Page 49)

Oxygen Analyzer Maintenance
Teledyne Analytical Instruments 49
Filter 5 minutes
Gas Factor 1.00
Temperature Coef. 0 ppb/degree centigrade
Alarm 1 setpoint 1000 ppb
Alarm 2 setpoint 100 ppb
Pressing the Set Defaults button brings up a confirmation dialog
box. Press Yes to reset to the defaults or No to keep the current values.
4.4 Calibration of the Analyzer
The analyzer must be calibrated prior to use. For most applications
where the desired range of measurement is 0 to 10 ppm, or less we
recommend the analyzer be calibrated using a span gas with a
concentration between 7.0 to 9.0 ppm oxygen in nitrogen. This will
require that calibration be performed in the 0-10 ppm analyzer range.
Before the cell is ready for calibration, it must be purged with
sample gas to a low oxygen level—preferably below 0.1 ppm. If the
oxygen content of the sample gas is higher than 0.1 ppm, a zero gas such
as nitrogen having an oxygen concentration below 0.1 ppm may be
required.
4.4.1 Zero Cal
The BDS Sensor has a zero offset of less than 5 ppb oxygen.
Normally, the offset slowly decreases during the first 7 to 10 days of
operation, and is expected to reach a steady value after this time.
Generally, the value of the zero offset is part of the oxygen reading
of the sample gas as shown by the analyzer readout. As an example, a
reading of 5 ppb oxygen may include 0.4 ppm oxygen in the sample gas
and a 5 ppb zero offset.
The determination of the zero offset requires the use of oxygen free
gas to the analyzer. The BDS 3960 has an oxygen scrubber as an
integral part of its sample system. The software and electronics
automatically re-route the sample gas through the scrubber to provide
the sensor with oxygen free gas. Best results as well as prolonged
scrubber life is attained when the oxygen concentration of the sample
gas is below 1 ppm oxygen.