Teledyne BDS-3960 operating instructions Sample System

Oxygen Analyzer Operational Theory

There is a Max line and Min Line clearly marked on the BDS sensor body. It is a good practice to check the electrolyte level every month and add de-ionized water into the sensor whenever it is convenient.

When running dry gas through the sensor, the gas carries out moisture from the sensor. Therefore, the electrolyte (10% KOH in 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.

2.3Sample 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 3960 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 sample system for the standard instrument incorporates 1/4" VCR fittings for sample inlet, span inlet, and vent and Swagelock fittings for instrument air tube connections at the rear panel. The sample or calibration 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, span gases can be connected to its own separate inlet port. Solenoid valves are controlled by the software to switch the proper gas when the analyzer enters the span mode. Zero gas is generated internally when the sample gas is re-routed to go through an oxygen scrubber before it is fed to the sensor. The life of the oxygen sensor depends in two main factors: flow rate, oxygen impurity being scrubbed. Thus, the life of the scrubber can vary depending on the sample gas being used to zero the analyzer. It is recommended to change the oxygen scrubber every two years. Use this as a guideline only.

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