Servomex NanoTrace DF-760E, Инструкция по эксплуатации

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Theory of Operation DF-760E 141
10 Theory of Operation
10.1
The Oxygen Measurement
10.1.1 The Oxygen Sensor
The sensor in the NanoTrace Dual Analyzer operates on a Coulometric principle. Oxygen
in the sample gas is reduced in an electrochemical reaction that results in a measurable
current flow. The use of this technique is widely recognized for its ability to provide a
precise oxygen measurement. A schematic of the sensor configuration is shown in Figure
143.
KOH
4OH
¯
Sample Gas
Cathode
Secondary
Electrodes
Anode
1.3V Applied
O
2
Stablex
Electrodes
Figure 143: Schematic of NanoTrace Dual Oxygen Sensor
The sample gas is in direct contact with the sensor cathode. Oxygen in the sample gas is
reduced electrochemically at the cathode to hydroxyl ions (OH
-
). The electrolyte solution
contains potassium hydroxide (KOH) which assists in the migration of hydroxyl ions
(OH
-
) to the anode where they are oxidized to complete the reaction. A voltage of
approximately 1.3 VDC, applied to the sensor electrodes, drives the reduction and
oxidation reactions. The current flow resulting from the reaction is proportional to the
oxygen content in the sample gas. The processed signal is then displayed on the front
panel in ppm or ppb units of oxygen.
10.1.2 The Oxygen Electrolyte Conditioning System
The oxygen sensor in the NanoTrace Dual Analyzer is equipped with Servomex’s patented
electrolyte conditioning system and is composed of two specialized electrode pairs.
The patented secondary electrode pair protects the sensing electrodes from the deleterious
effects of trace impurities inevitably found in the electrolyte. The secondary electrodes
attract and trap trace ionic impurities present in the electrolyte, providing a scavenging
function that results in long-term zero and span stability.