1. Presentation for 2017 Argo Steering Team
David Murphy
Sea-Bird Scientific

2. Topics Kistler Pressure Sensors
Review of problem
Current Status
Status of permission to use anti-foulant in EU
Discussion of response characteristics on Argo CTDs measured in WHOI stratified tank

3. Kistler Pressure Sensor Failures – Summary
Problem detected in Spring of 2016, traced to failure of electronic component
Time of use of lot containing defective components December 2015 – May 2016
Extended burn testing initiated
Screened calibration data looking for defective sensors
Customers notified
To date
305 sensors shipped in suspect time period
14 failures found in factory
8 failures reported from shipped CTDs
25 additional sensors returned to factory for replacement regardless of symptoms

4. Kistler Pressure Sensors Problems – Cause
Failure is in a component with in the temperature compensation portion of the circuit
Causes the Bridge Impedance to change
Pressure Bridge
Temperature Compensation Network
Becomes Electrically Open When Failure Occurs

5. Kistler Pressure Sensors Problems – Cause Cont.
Damage to thermistor causes the part to become open circuit
Temperature cycling provokes the failure shown in X-Ray photomicrograph
GAP

6. Kistler Pressure Sensors – Effect
Calibration after failure
Failure can be shown in calibration as a span shift
Sensor reports higher values than is correct.
Sensors are calibrated once for pressure, many times for temperature
Screening of all Kistler sensors
Built CTDs are temperature calibrated at least 4 times
Temperature cycled from 1 to ~35 C each time
Calibration of pressure temperature reviewed for artifacts
Calibration before failure
Calibration after failure
Calibration before failure

7. Kistler Pressure Sensors – Deep Argo CTD
Acceptance testing for 7K Kistler sensors
Sensors are kept at 40 C and 3500 psia for 1000 – 1500 hours
Cycled to room temperature and one atmosphere twice weekly to measure drift
Screening
Many temperature calibrations done (10 +) cycling 1 – 35 degrees
Results examined for artifact observed in previous slide

8. Update on use of TBTO anti-foulant in the European Union
Sea-Bird has been working with EU regulators in individual countries to allow an exception to regulations prohibiting import and use of TBTO
However, agreement has been reached that Argo is outside of this convention
Because deployment (or “use”) is in the deep ocean
Sea-Bird and our OEM partners (Webb, NKE, etc) can ship floats or CTDs with TBTO to or within the EU because they will be exported for use
Addressed directly by EU law under the following condition: End customers can do normal testing and preparation for deployment in the deep ocean because deployment qualifies as export
Incidentally, this ruling applies to moored equipment as well

9. Alternatives to TBTO
We have been researching alternatives to TBTO in cold and warm water deployments over the past 3 years
To date we have not found a material that matches the efficacy of TBTO
We have had success in UV method through partnering with Danaher sister companies
Enclosed sample path is ideal
Work in progress on optimizing the technology

10. Stratified Tank Results
This analysis was done by Kim Martini
Thanks to Breck Owens and Ray Schmitt for time in the stratified tank
All variants of Argo CTDs were tested, 41,61, STS
Conductivity and temperature data presented here were over sampled at 16 Hz
Paper in preparation for JAOT with results for response times and cell thermal mass coefficients demonstrating results using field and lab data acquired at 1Hz

11. Stratified tank experiment for correction of dynamic errors
0.05 m/s
0.10 m/s
0.15 m/s
Thermistor thermal mass
Time lag between T and C due to sensor separation
Conductivity cell thermal mass

12. Thermistor thermal mass
Temperature profile approximates an ideal diffusive interface.
dT/dt should be a symmetric Gaussian bump. With no corrections applied the first difference of T will be asymmetric because of thermal lag.
Iterate through range of lags and maximize symmetry to find correction coefficient.
Sharper and narrow interface which approaches the temperature in the lower layer faster (i.e. no lag)
This correction is really close to the laboratory values. The correction increases slightly with profiling speed

13. T-C lag due to physical separation of sensors
As in Johnson et al. 2009, once the thermal mass correction is applied no need to apply a T-C lag correction
Thicker temperature interface because the diffusion of heat is two orders of magnitude higher than salinity.
corrected T interface aligns with C

14. Conductivity cell thermal mass
Coefficients determined by exploiting expected shape of diffusive salinity gradient at interface
Salinity does not “overshoot” lower layer
Minimize “rebound” due to over correction
Unable to apply the same symmetry argument to conductivity as changing the cell thermal mass had little effect on salinity.
Should note that here the change in salinity is so great, that it dominates conductivity rather than temperature.

15. Conductivity cell thermal mass
Correction uses Morison et al. [1994] method of correcting cell temperature
This is the correction for the 5 m/s profile which is the slowest, but shows the effect of thermal lag the most.

16. Conductivity cell thermal mass
For SBE41cp profiling at 0.10 m/s:
This is the correction for 0.1 m/s which is about the profiling speed of ARGO floats.
Here alpha is the initial error, while tau_CTM is the response time.
Changing alpha has a much bigger effect on the salinity profile than changing tau_CTM the lag.
We find that alpha increases with increasing velocity, which may explain why the Johnson et al correction seems way off, profiling speeds on the ITPs are 0.3 m/s

17. Improvements to SBE 61 Deep Argo CTD
We have worked towards the development of drift history before deployment
Have purchasing and inventory challenges
Conductivity stability
Experiments have been conducted on the WHOTS mooring. Problem is there is a 1 year interval between fielding an experiment and getting the results
I need an open ocean exposed mooring site at 10 – 20 meters that can be accessed at 3 month intervals.
Pressure
Performance improvements will require trade offs
More mass and higher volume
More processing on board
Or transmit more data back to shore