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

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.