Page 19 - Customer Needs and Use Assessments (CNUA) of pH Sensors

ACT In Situ pH Sensors Customer Needs and Use Assessment............................................................................ 18
26. How much are you willing to pay for a new sensor?
Prices among the 26 who answered this question ranged from $200 to $20,000, spanning three orders of
magnitude. This broad data pattern reveals the many levels of in situ pH sensor users. Note that a $1.30/Euro
exchange rate (as of 12/31/11) was applied to the international responses to normalize all results to US dollars.
Breaking down responses according to order of magnitude, 23.1 % wanted to spend no more than $1000 for an
in situ pH sensor ($500 ± $253), 50.0% were willing to pay between $1000 but no more than $10,000 ($2731 ±
$1943), and 26.9 % were willing to pay $10,000 or more ($13,643 ± $4130). This latter group was most likely
to add conditionals to a higher price, such as the requirement that the sensors possess superb performance
characteristics, or that they have the funding in place to afford the gain in performance.
27. Based on your experience with in situ pH sensors, are there any modifications or design additions that
you would recommend?
Comments from 21 respondents on in situ pH sensor user recommendations were captured as narratives and are
summarized below. Note that references to specific makes and models of in situ pH sensors were not mentioned,
so some of the recommendations may not apply to all sensors.
Modification and design modifications fell into several broad categories of areas for improvement. Users
typically cited more than one area, and most of these areas are somewhat inter-related. Improvements in
calibration, for instance, was the largest category, and recommendations here overlapped with biofouling and
design recommendations. Users want to be able to perform in situ calibrations and to be able to cover a broad
range of oceanic salinities, temperatures, and pressures. Most would at least like to be able to do easy reliable
calibrations out in the field if not in situ. Calibration functions should be built into the units and calibration
procedures available to the users. Selectable pH scales would be a desirable feature.
Adding biofouling control was a chief design recommendation. Sensors could be encased in copper as standard
practice in biofouling environments. The aforementioned improvements in active biofouling control are linked
to improved calibration in the sense of extending calibration life. Long life expectancy in a sensor includes a
slow loss in calibration.
Design recommendations include more durable construction for field use and sensors designed for deep water
use. Divers have complained about positively buoyant in situ sensors. Perhaps these sensors could be housed in
packages that are neutrally buoyant or slightly negatively buoyant underwater to prevent the units from floating
away from divers. Pumps could be added to units to provide flow-through measurements. More data offload
options like real-time data transmission or telemetry are needed.
Better protection of the reference electrode from seawater intrusion to avoid significant drift. One respondent
recommends that a sensor have a more straightforward way to be grounded (if necessary) during calibration.
In this instance, during calibration the user was advised to ground the sensor with a wire. However, the output
voltage changed depending on how the wire was grounded (fully in solution versus only the end of the wire in
solution).
General recommendations to improve accuracy/repeatability in pH sensors rounded out the comment section,
often tied in with the aforementioned design modifications and steps to improve overall longevity. Finally,
performance recommendations of accuracy include increased consistency of measurements between sensors.