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42 of 50 Specifications - 3650 Portable O2 Analyzer
Operator Manual
ORBISPHERE
7.2 Theory of Operation
The sensor circuitry performs four functions:
• Applying a constant voltage to the anode
• Measuring the current flowing through the sensor
• Compensating this current for sample temperature variations
• Converting these resulting signals into a scaled current or voltage
The anode is held positive with respect to the cathode. Current flowing through the
sensor due to oxygen reduction at the cathode is converted to a voltage by an amplifier,
the proportionality between voltage and current being determined by the feedback
resistance of this amplifier.
The output voltage is essentially a function of oxygen activity (partial pressure),
temperature and membrane permeability. Corrections for variations in membrane
permeability are made when the sensor is calibrated. The temperature compensation
circuit accounts for temperature variations. Hence the output voltage varies only with
oxygen concentration.