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Underwater carbon dioxide sensor


Contros HydroC CO2 subsea / underwater carbon dioxide sensor

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The CONTROS HydroC® CO2 sensor is a unique and versatile subsea / underwater carbon dioxide sensor for in-situ and online measurements of dissolved CO2. The CONTROS HydroC® CO2 is designed to be used on different platforms following different deployment schemes. Examples are moving platform installations, such as ROV / AUV, long-term deployments on seabed observatories, buoys and moorings as well as profiling applications using water-sampling rosettes.

Individual 'in-situ' calibration

All sensors are individually calibrated in a water tank which simulates the deployment temperature. A sophisticated reference detector is used to verify the p CO2 concentrations in the calibration tank. The reference sensor is recalibrated with secondary standards on a daily basis. This process ensures that the CONTROS HydroC® CO2 sensors achieve unmatched short and long-term accuracy.

Operating principle

Dissolved CO2 molecules diffuse through a custom made thin film composite membrane into the internal gas circuit leading to a detector chamber, where the partial pressure of CO2 is determined by means of IR absorption spectrometry. Concentration dependent IR light intensities are converted into the output signal from calibration coefficients stored in firmware and data from additional sensors within the gas circuit.


  • High accuracy
  • Very robust, depth rating up to 6000 m (profiling)
  • Very fast response time
  • User-friendly
  • Versatile – easy integration into almost every oceanographic measurement system and platform
  • Long-term deployment capability
  • 'Plug & Play' principle; all required cables, connectors and software are included


  • Analog output: 0 V - 5 V
  • Internal data logger
  • External battery packs
  • ROV and AUV installation packages
  • Profiling and mooring frames
  • CO2 flow through sensor for underway (FerryBox) and lab applications
  • External pump (SBE-5T or SBE-5M)
  • Easy deployment together with a CONTROS HydroFlash® O2


A wide range of available accessories ensures that each of the CONTROS HydroC® CO2 sensors can be adapted to meet customers' requirements. The optional pumps with the different flow heads are the most popular options that ensure very fast response times. An anti-fouling head is used under conditions with significant biofouling pressure. The internal data logger can be used in conjunction with the HydroC's flexible power management features and the CONTROS HydroB® battery packs to conduct unattended long-term deployments.

Related publications (PDF)

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