DF-550E an ultra-trace Coulometric oxygen analyzer.

Coulometric - Our Coulometric sensors provide high-sensitivity measurements of oxygen

Used to measure oxygen (O2), Coulometric sensing is based on a simple, non-depleting process that responds quickly to changing O2 levels. The heart of our DF-500 range of oxygen sensors, it delivers the low-level detection that is essential for UHP gas applications.

Our Coulometric technology enables the measurement of O2 at percent or parts-per-million (ppm) levels. It is non-depleting, so there is no requirement for periodic cell replacement and it avoids the false low readings associated with standard electrochemical sensors.

It operates through a simple Coulometric process where O2 from the sample gas is reduced to hydroxyl ions at the sensor cathode.

The resulting current flow is proportional to the O2 content in the gas, and the process signal can be displayed in ppm or parts-per-billion (ppb) units of O2.

Coulometric sensors respond very quickly to changing O2 concentrations. For instance, a 0-1,000ppm range sensor can be exposed to air and in less than a minute will measure <10ppm on pure nitrogen. This is highly beneficial for users who have upset-prone applications.

Additionally, 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 not in use.

Related and alternative technologies

Coulometric sensing works alongside Laser Moisture technology in our DF-760E and DF-760E ULTRA analyzers, for a highly sensitive dual measurement of oxygen and moisture at ppm levels. Coulometric sensors should avoid sample streams that contain acidic gases. For applications involving these gases, a Paramagnetic or TDL sensor is recommended instead.

Key applications


Solder reflow ovens

Reactor process control

Key benefits

Industry-leading lower detection limits

Fast response and rapid recovery

Non-depleting sensor with a long lifespan

Ideal for

Sensitive, parts-per-million measurements of O2, for example in impurity monitoring for UHP semiconductor gases

Explore the Coulometric analyzers we have for your process

Learn more about all our gas analyzer solutions that use this sensor technology.

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DF-550E NanoTrace


An ultra-trace Coulometric oxygen analyzer, the DF-550E is optimized for quality measurements in ultra-high-purity electronic gases.

DF-550E an ultra-trace Coulometric oxygen analyzer.
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DF-560E NanoTrace ULTRA


A superior quality control solution for ultra-high-purity (UHP) electronic grade gases, the DF-560E Ultra delivers an industry-best detection of 45 parts per trillion for oxygen (O2).

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Designed for quality control applications in UHP bulk gases, the compact DF-760E analyzer is a unique solution for the dual measurement of trace and ultra-trace moisture

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Designed for industry-leading quality control measurements in UHP bulk gases, the compact DF-760E ULTRA is a unique dual-analysis solution for trace and ultra-trace moisture and oxygen.

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MonoExact DF150E


The MonoExact DF150E combines the reliability of Servomex’s tried and tested Coulometric oxygen sensor with a more user-friendly package.

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MonoExact DF310E


Designed specifically for accurate measurements of oxygen in industrial gas (IG) applications.

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