Oxygen Analyzer Operational Theory
Teledyne Analytical Instruments 23
Figure 2.4 Typical Purge-down Curve After Air Saturation
S h or t e n i ng t h e ai r exp o s u r e wi l l al l o w a f a s t e r se ns o r r ec o v e r y.
A ty p i c a l BD S se n s o r wi l l re c o v e r t o 1 pp m i n ap p r ox i m a t el y 25
m i nu t e s , t o 10 0 pp b af t e r 80 m i n , an d 10 pp b i n ab ou t 8 ho u r s , af t e r
s u f f e r i n g a t e n- m i n u t e ex p os u r e to ai r .
2.2.6 Background Gas CompatibilityT he BDS oxygen sensor wi l l work in i ner t gas backgr ounds,
i ncludi ng ni t rogen, hydr ogen, ar gon, heli um and ethane. The sensor
out put, however, i s dif fer ent in di ff erent backgr ound gases. For exam pl e,
t he sensor output i n a hydr ogen background is twi ce as much as it woul d
be in a ni tr ogen background. Therefor e, i t is recom mended to cali br ate t he
analyzer wit h an oxygen standar d that has a sim il ar background as the
sam pl e gas. If an oxygen st an dar d is unavai l able for a par ti cul ar
background, a Gas F act or which is det er mi ned at TAI coul d be used t o
cor rect the sensor out put in dif f er ent backgr ound (see sect ion 4.3.9) .
Note: the gas flow meter in the analyzer is calibrated for air. The
error for measuring nitrogen is usually negligible. But for