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Servomex’s non-depleting Coulometric sensor technology enables the measurement of oxygen at percent or ppm levels - without the requirement for periodic replacement or false low readings associated with fuel cell sensors.

The sensor operates on a simple coulometric process whereby oxygen in the sample gas is reduced in an electrochemical reaction. 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.

The Coulometric sensor responds very quickly to changing oxygen concentrations: The 0-1,000 ppm range sensor can be exposed to air and in less than a minute will measure <10ppm on pure nitrogen – beneficial for users who have upset prone applications. And in addition to fast response to changes in O2 concentration, the performance of the sensor is unaffected by reasonable changes in flow rate.  Because the non-depleting sensor is not consumed when exposed to O2, it has a long lifespan and does not require a purge gas to protect it when it's not in use.

Coulometric sensing complements Paramagnetic O2 sensing by being able to measure ppm level measurements, where Paramagnetic lacks sensitivity at these levels. There are some limitations however: the sensor cannot be used with gases containing alcohols, aldehydes and solvents. 

Products featuring Servomex Coulometric technology:

  • DF-140E


    Reliable oxygen measurement in a wide variety of environments

  • DF-320E


    Trace / percent oxygen measurements in Div 2 / Zone 2 hazardous area locations

  • DF-340E


    High-sensitivity trace / percent Coulometric oxygen analyzer certified for hazardous area use

  • MonoExact DF150E

    MonoExact DF150E

    Touch-screen Coulometric ppm/ppb oxygen analyzer

  • MonoExact DF310E

    MonoExact DF310E

    Touch-screen ppm oxygen analyzer for IG applications

  • DF-550E NanoTrace

    DF-550E NanoTrace

    Leading ultra-middleweight oxygen analyzer designed for monitoring ppt level semiconductor UHP gas

  • DF-560E NanoTrace

    DF-560E NanoTrace

    Ultra-trace coulometric Oxygen measurements in ultra-high purity electronic grade gas for quality control

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