Teledyne BDS-3000 - Oxygen analyzer - Manual (Page 25)

Oxygen Analyzer Operational Theory
Teledyne Analytical Instruments 11
2.2.3 Gas Pressure
The analyzer is equipped with a flow restriction tube (from the
back panel of the analyzer to the left side of the BDS sensor) as shown
in Figure 2-3. The sensor is not affected by pressure as long as the
analyzer vents to atmosphere. If the analyzer is not vented to
atmosphere, the downstream pressure must not exceed 10 inch of water.
A clogged or restricted vent or excessive pressure will force gas into the
electrolyte and cause damage to the BDS sensor.
Figure 2-3: BDS Sample System
2.2.4 Temperature effect
The raw output from a BDS oxygen sensor has a temperature
coefficient about 0.25% / °C. This temperature effect is compensated by
the software throughout the operation temperature range (5 – 40°C).
2.2.5 Recovery from High Level Oxygen Exposure
The ambient air contains about 210,000,000 ppb (2.1 x 10
8
)
oxygen. Figure 2.4 is a typical purge-down curve for a new BDS sensor
which had been air saturated. It is normal to take several hours, even
days for an air saturated BDS to purge down to a low ppb level.