Presentation for 2017 Argo
Steering Team
David Murphy
Sea-Bird Scientific
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
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
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
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
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
Calibration
before failure
• Screening of all Kistler sensors
Calibration after
failure
Calibration
before failure
Kistler Response at One Atmosphere
55000
54000
A/D Counts
• 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
53000
52000
51000
50000
49000
0
5
10
15
20
Temperature C
25
30
35
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
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
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
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
Stratified tank experiment
for correction of dynamic errors
0.05 m/s
1.
2.
3.
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
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.
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
corrected T interface
aligns with C
Conductivity cell thermal mass
1.
2.
Coefficients
determined by
exploiting expected
shape of diffusive
salinity gradient at
interface
Salinity does not
“overshoot” lower layer
Minimize “rebound”
due to over correction
Conductivity cell thermal mass
-
Correction uses Morison et al. [1994]
method of correcting cell temperature
Conductivity cell thermal mass
For SBE41cp profiling
at 0.10 m/s:
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