Teledyne BDS-3000 - Oxygen analyzer - Manual (Page 28)

Operational Theory BDS 3000
Teledyne Analytical Instruments 14
water) inside the sensor is gradually concentrated during the sensor
operation. It typically takes about four months for the electrolyte level to
drop from the Max line to Min line. When adding water to increase the
electrolyte level from the Min line to the Max line, it is typical that the
oxygen reading will drift down about 10 ppb in an hour. If the oxygen
content in the sample gas is very close to zero, the analyzer may display
a negative reading during this period. The sensor will recover by itself
during the following week. This drift-down then recover-back
phenomenon is caused by the quick dilution of the electrolyte and re-
establishment of a new equilibrium inside the sensor. To minimize this
effect, add a small amount of water each time and do this before the
electrolyte level reaches the Min line.
2.3 Sample System
The sample system delivers gases to the BDS sensor from the
analyzer rear panel inlet. Depending on the mode of operation either
sample or calibration gas is delivered.
The Model BDS 3000 sample system is designed and fabricated to
ensure that the oxygen concentration of the gas is not altered as it travels
through the sample system.
The sampl e syst em for the standar d inst rument incor porates 1/4" VCR
fit tings for sample inl et and swagelock fittings for outl et tube connections at
the rear panel. The sample or cal ibrati on gas that flows through the system
is monitored by a flowmeter downstream from the sensor .
Figure 2-6 represents the flow diagram of the sampling system. In
the standard instrument, calibration gases can be connected directly to
the Sample In port by teeing to the port with appropriate valves.
Figure 2-6: Flow Diagram