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Ref. No. [UMCES] CBL 2016-014
ACT VS16-05
13
RESULTS of LABORATORY TESTING
Instrument accuracy for the Hach HL4 LDO sensor was tested under nine combinations of
temperature and salinity over a range of DO concentrations from 10% to 120% of saturation.
Specific test conditions are summarized in Table 1. Results are plotted as a time series of
instrument readings against the time series of comparative Winkler reference samples (Figures A-
I). The bottom panel of each figure shows the time series of the difference in instrument
measurement versus corresponding reference sample (denoted as Delta’s). Comparisons of tank
duplicates taken at opposite sides of the tank from between 9-18 of the timepoints during each trial
showed a mean difference of 0.017 mg/L, with a range over the nine trials of 0.006 – 0.038 mg/L.
Those values are within the analytical precision of the reference method and indicate conditions
throughout the tank were very homogeneous. However, small changes in measured DO
concentrations did occur during some of the sampling phases indicating the tank was slightly
moderating after sparging was stopped. Those small drifts in DO concentrations were clearly
captured by both instrument and reference sample measurements.
Table 1.
Dissolved oxygen temperature and salinity challenge trial conditions. For each trial pre and post
measurements of tank temperature (
o
C) and salinity (S) were made with a calibrated SBE26+4M CTD,
equilibrated in well mixed tank for 20 min until stable readings obtained.
Trial ID
Mean
Temperature
o
C
S.D.
Temperature
o
C
Mean
Salinity
PSU
S.D.
Salinity
PSU
Levels of
DO tested
mg/L
Figure
for
HL4
L_T15_S00
15.44
0.03
0.00
0.000
0, 2, 5,9,10,14
A
L_T15_S10
15.47
0.01
8.82
0.003
0, 2, 8, 9, 13
B
L_T15_S35
15.39
0.03
34.20
0.009
0,2,6,8,12
C
L_T04_S00
5.40
0.08
0.00
0.000
0,4, 12, 17
D
L_T04_S10
5.30
0.03
8.98
0.009
0, 5, 12, 16
E
L_T04_S35
5.23
0.07
34.77
0.073
0, 4, 10, 14
F
L_T30_S00
30.22
0.03
0.00
0.000
0, 3, 5, 9
G
L_T30_S10
30.51
0.12
9.28
0.036
0, 3, 7, 10
H
L_T30_S35
30.61
0.07
34.43
0.050
0, 2, 6, 9
I
The mean and standard deviation of the differences between the Hach HL4 and reference
measurements for each trial (n = 19 – 51 comparative observations) are presented in Table 2.
Explanations for the difference between observed and possible comparative observations for the
Lab trials are noted in the respective figure legends. The mean of the differences among trials
ranged from -0.315 to 0.304 mg/L over eight of the nine trials. N
o data was recorded during one of
the trials due to an apparent internal power failure.
There was an apparent temperature effect on
instrument response with mean offsets varying from 0.084, 0.001, and -0.217 mg/L across
temperature trials of 5, 15, and 30
o
C, respectively. Similarly there was an apparent salinity effect
on instrument response with the mean offsets varying from 0.058, -0.103, and -0.115 mg/L across
salinity trials of 0, 10, and 35, respectively.