HydroC underwater CO2 (Contros Systems and Solutions GmbH)

Instrument

The instrument measures the CO₂ mole fraction in a headspace behind a membrane equilibrator with a two-wavelength non-dispersive infra-red detector (NDIR). The equilibrator is composed of a flat silicone composite membrane, the NDIR unit and additional sensors for pressure, temperature and relative humidity used to correct the NDIR signal and calculate the partial pressure. A small internal pump insures the continuous circulation of air in the equilibrator. To correct the drifting of the instrument with time, regular zeroings are automatically performed by scrubbing the CO₂ from the internal gas stream. The zeroings are accounted during post processing of the data. The instrument is calibrated by the manufacturer. In order to achieve a constant and sufficiently short response time of the instrument, the HydroCTM is equipped with a water pump (Sea-Bird Electronics, USA) that provides a continuous water flow of approx. 35 ml sec21 to the membrane, leading to a response time T63% of 3 min and a T99% of approximately 15 min. However, good accuracy has been demonstrated without the use of the pump. The need for deconvolution of the signal is therefore important.

Technical Data

See manufacturer data www.contros.eu

Performance

Accuracy in test tanks at varying salinity, temperature and pCO₂ (bubbling in the tank of CO₂ modified air): using as base Baltic Sea water.

Large discrepancy is visible between pCO₂ calculated from discrete samples (pCO₂=f(TA, DIC) at high pCO₂. This appears to be a problem coming from the discrete samples analysis and / or calculations and not from the sensor.

Applications

Long and short term measurement of pCO₂ in aqueous environments. Autonomous deployment requires a battery pack.

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