SERVOPRO AquaXact 1688

Aluminum Oxide - The key solution for moisture and dew point measurements

Aluminum Oxide is a sensing technology that provides dew point and parts-per-million measurements of moisture, with results that are free of drift and insensitive to temperature changes. Used in a range of industrial and UHP gas applications, it is at the heart of our AquaXact 1688 moisture transmitter.

Aluminum Oxide (Al2O3) sensors work by measuring the capacitance between the aluminum core and a gold film deposited on the oxide layer. The capacitance varies according to the water vapor content in the pores of the oxide layer.

The ultra-thin Al2O3 sensors have three innovative structural improvements that offer better performance than traditional Al2O3 sensors, with advantages for sensitivity and stability.

1. A much thinner oxide layer: This results in higher capacitance, since this is inversely proportional to the distance of the capacitor’s plates from each other. Higher capacitance results in a more sensitive measurement. The thinner layer also allows water molecules to travel in and out of the pores more quickly, ensuring a faster response.

2. A better-defined barrier layer: The sharply defined barrier means that the sensor’s wet to dry capacitance ratio is very high, reducing the effects of any drift due to undesirable factors. It also reduces metal migration, one of the major causes of drift in conventional Al2O3 sensors.

3. Unique pore geometry: Holding more water than conventional sensors, the ordered pore geometry increases the change in capacitance for a given change in dew point. This means greater accuracy and a quicker response. It is also more stable, so only annual calibration checks are needed when the sensor is used in clean, non-corrosive gases.

Related and alternative technologies

In some analyzers, Aluminum Oxide sensors work alongside Paramagnetic and Coulometric sensors to provide a dual measurement for oxygen and moisture. However, Aluminum Oxide sensing does not reach the ultra-trace levels of detection required for all UHP gases. Laser Moisture technology is often a better fit for this application.

Key applications

Air separation units

Medical gases


Key benefits

Fast response

Highly accurate

Free of drift

Ideal for:

Dew point and parts per million moisture measurements in a wide range of industrial gas applications.

Explore the Aluminum Oxide analyzers we have for your process

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

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AquaXact 1688


A rugged ultra-thin film Aluminum Oxide moisture sensor which measures moisture in a wide variety of gas phase process applications.

SERVOPRO AquaXact 1688
  • Fast and accurate moisture measurements
  • Rugged ultra-thin film Aluminium Oxide sensor
  • Functions as a standalone 4-20mA transmitter
  • Remotely interfaces with compatible controller or analyser
  • Sensor element is NIST-traceable and field-replaceable
  • IP65-rated connector

AquaXact Controller


Built specifically to work in harmony with the AquaXact 1688 ultra-thin film Aluminum Oxide moisture transmitter.

  • Specifically designed to operate AquaXact 1688
  • High-clarity colour touchscreen display
  • Alarms, relays, and advanced communications
  • Allows easy sensor tip replacement in the field
  • Powerful, intuitive software control
  • Compact and easy to integrate into your system

MonoExact DF310E


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

  • Accurate measurements of oxygen and moisture
  • Designed for industrial gas applications
  • Tried and tested digital Coulometric oxygen sensor
  • Non-depleting Paramagnetic sensor option
  • Plug-and-play moisture sensor support
  • Analogue and digital communication options
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MultiExact 4100


A high-performance multi-gas analyzer designed to provide up to four simultaneous gas stream measurements.

SERVOPRO MultiExact 4100
  • Highly adaptable multi-gas analyzer
  • Provides up to four simultaneous measurements
  • Wide range of sensing technology options
  • Versatile solution for industrial and medical gases
  • Built-in support for moisture sensor
  • Optional advanced digital protocols

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