Conductivity channel advantages presented by RBR at Ocean's 2010 MTS/IEEE

At the Ocean's 2010 MTS/IEEE 2010 Seattle meeting Frank Johnson Chairman of RBR presented a paper entitled "Advantages in performance of the RBR conductivity channel with Delrin ™/ceramic inductive cell."

Please download the full paper, the abstract and the conclusions are presented below.

Abstract

This paper demonstrates several key advantages of the inductive conductivity sensor. In calibration the sensor has a linear response and may be calibrated with direct traceability to primary standards without assumptions about the salinity scale; one calibration can be used for a wide range of salinities and temperature compensation can be directly measured independently. In the field it has demonstrably superior passive exchange of measurand within the sensor and this is confirmed by the comparative TS plots when used simultaneously with an electrode based sensor.

CONCLUSIONS

1. The conductivity channel with Delrin/ceramic inductive cell as developed by RBR satisfies UNESCO IOC requirements. Durability of the mechanical properties of the inductive cell together with good metrological characteristics of the conductivity channel makes it possible to provide oceanographers with a reliable accurate CTD system for oceanographic observatories.

2. A two-point calibration procedure performed with Micro-salinometer MS-310 using conductivity ratio principle and set at T=15°C, makes RBR conductivity channel calibration independent from the PSS-78 converted conductivity. Metrological traceability of the conductivity measurements relate only to the measurement uncertainty of the determination of the value C(35,15,0). Evaluation of the stability of the RBR conductivity channel at these 2 points allows an estimate of typical drift to be less then 0.01mS/cm per year.

3. Conductivity to temperature correction algorithm works well as compensation of the error of calibrated at S35T15 point conductivity channel in the dynamic temperature range. Typical conductivity to temperature non-compensated error is 0.001mSm/cm per °C, and after temperature correction, uncompensated residuals lie within uncertainties of the method of the conductivity determination and typically do not exceed ±0.005mS/cm.

4. The mechanical design of the cell allows surrounding seawater to flush freely through the cell without the need for pumping of the sample. This is a big advantage in the conditions of the limited power deployments. Comparison of the flushing ability of the RBR inductive cell with the SBE-37 in the laboratory controlled conditions and on the mooring deployment in dynamic environment demonstrates a significant advantage of the RBR CTD system to measure dynamic changes in salinity of water masses without pumping.