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Ref. No. [UMCES] CBL 2016-011
ACT VS16-02
26
Individual response slopes and intercepts of instrument measurement versus reference DO
for each of the laboratory trials at a fixed temperature and salinity level are summarized in Table 4.
Slope responses are somewhat variable across temperature with no uniform trend. The response
slopes did decrease slightly across salinity levels, averaging 1.22, 1.11, and 1.01 for salinity trials
of 0, 10, and 35, respectively.
Table 4.
Summary of regression statistics for the PME miniDOT versus reference sample response curves
for each of the nine laboratory trials.
Test ID
R2
y Intercept
Slope
LT15S00
0.921
-2.203
1.660
LT15S10
0.913
-1.470
1.312
LT15S35
0.996
-0.426
1.062
LT04S00
1.000
-0.110
0.991
LT04S10
0.999
-0.021
0.983
LT04S35
1.000
-0.042
0.960
LT30S00
1.000
0.053
1.018
LT30S10
0.997
-0.125
1.042
LT30S35
1.000
0.089
1.005
Results of the 56 day long-term stability and thermal stress challenge for the PME
miniDOT are shown in figure K. The instrument was maintained in a well circulated tank and
oxygen content manipulated by alternately varying water temperature set point between 15 and
25
o
C several times per week of deployment. The data completion result for the stability test was
100%. The time series of instrument readings at 15min intervals is plotted against discrete values
for Winkler reference samples (
top panel
) along with the time series of the difference between
instrument and reference measurements (
bottom panel
).
The overall mean difference between
measurements was
0.034 (s.d. = 0.107) mg/L for 77 comparisons (out of a potential total of 77).
There was a small but statistically significant trend in accuracy over time (slope = -0.002 mg/L/d;
r2 = 0.11; p=0.003) indicating very modest performance drift over the 56 days.
Results for a sensor response time assessment of the PME miniDOT are shown in figure L.
The top panel depicts the time series of 5s instrument reads during transfers between adjacent high
(9.6 mg/L) and low (2.0 mg/L) DO water baths, maintained commonly at 15
o
C. The bottom panel
(
lower left
) depicts results fit with a 3 parameter exponential decay function: DO
rel
= DO
relMin
+ a
e
-
bt
and indicated τ calculated from fit. Data for low DO to high DO transitions (
lower right
) were
treated similarly but normalized to steady state value in subsequent high DO tank and subsequently
fit with an analogous 3 parameter exponential rise function: DO
rel
= DO
relMin
+ a(1-
e
-bt
) with
indicated τ being directly calculated from fit.
The calculated τ
90
was 90 s during high to low
transitions and 63 s for low to high transitions covering a DO range of approximately 8 mg/L at a
constant 15
o
C.