Thermal Inertia of Conductivity Cells: Observations with a Sea-Bird Cell

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Abstract
We have examined the magnitude and relaxation time of the thermal anomaly of the fluid flowing through the conductivity cell manufactured by Sea-Bird Electronics (SBE) that is induced by the heat stored in the wall of this cell using oceanic data collected in a thermohaline staircase. The relaxation is 9 to 10 s, about twice the value predicted by Lueck, while the initial magnitude of the conductivity error is 2.8%, about 35% smaller than predicted. The error in the measured conductivity is significant and long-lived and results in density errors detectable for 45 s after the sensor enters an isopycnal layer. An efficient numerical algorithm removes the anomaly from the measured conductivity signal and clears the resulting error from the computed salinity and density. Abstract We have examined the magnitude and relaxation time of the thermal anomaly of the fluid flowing through the conductivity cell manufactured by Sea-Bird Electronics (SBE) that is induced by the heat stored in the wall of this cell using oceanic data collected in a thermohaline staircase. The relaxation is 9 to 10 s, about twice the value predicted by Lueck, while the initial magnitude of the conductivity error is 2.8%, about 35% smaller than predicted. The error in the measured conductivity is significant and long-lived and results in density errors detectable for 45 s after the sensor enters an isopycnal layer. An efficient numerical algorithm removes the anomaly from the measured conductivity signal and clears the resulting error from the computed salinity and density.

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