Teledyne BDS-3960 - Oxygen analyzer - Manual (Page 22)

Operational Theory BDS 3960
Teledyne Analytical Instruments 22
2.2.3 Gas Pressure
The analyzer is equipped with a pressure regulator as shown in
Figure 2-3. To access the pressure regulator, the front panel must be
opened. The inlet pressure should be regulated anywhere between 4 to
50 psig. The sensor is not affected by pressure changes in the inlet 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.
Pressure Regulator
BDS Sensor
Flowmeter
Vent
Oxygen Scrubber
Sample
Inlet
Span
Inlet
Figure 2-3: A simplified BDS Sample System
2.2.4 Temperature effect
The raw output from a BDS oxygen sensor has a temperature
coefficient about 0.25% / °C. That is an average value, it changes as
temperature changes. 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.