PRECISION MEASUREMENT ENGINEERING, INC
1487 Poinsettia Ave., Suite 129
Vista, CA 92081
TEL - (760)727-0300
FAX - (760)727-0333www.pme.com
This report represents a comprehensive examination of miniDOT performance, testing both
miniDOT's accuracy and its ability for use in coastal environments. We are very pleased
with all the observations and test results.
The laboratory testing generally went well. However Figure A and Figure B show gross
errors. We believe that there was something about the test that caused these errors,
especially since errors of this magnitude are not present in later field testing results.
The figure captions suggest the presence of bubbles. This makes sense since we have
seen this effect ourselves. Our manual describes a similar "bubbled bucket" test where we
specifically instruct the customer to position miniDOT with the sensing end upwards to avoid
More generally, there are other test points in Figures A, B and there are also separate
laboratory tests presented in Figures C through I. These other points and other figures
present good agreement in most cases. However we believe all experiments were
conducted in the same way as Figures A and B and so could possibly be contaminated in
the same way although perhaps not to the same degree. We encourage the reader to
consider this when examining the laboratory results especially in those cases where there
are small disagreements.
Field testing also went very well. In every test ACT operators were able to correctly
program and use miniDOT. miniDOT always recorded very good measurements at first,
although sometimes there were fouling effects as time passed.
Figure 5 shows an especially dramatic lapse of good measurement beginning at about
7/16/15. We believe this lapse results from some condition that was external to the
miniDOT and is not an instrument error. The pictures of Figure 4 show that the test was
conducted in a very actively fouled environment. Careful inspection of the lower left
picture shows what other pictures (not presented in the report) clearly identify as a acorn
barnacle covering about 1/3 of the oxygen sensing foil. There is possibly calcareous growth
across much of the remaining area. We believe that these or similar organisms are
responsible for the lapse of good measurement. We can not explain why better
measurement returns about 7/20/15 but the wiper was active during this time and could
have had an effect. We view results of this test as more indicative of wiper performance
than that of the miniDOT oxygen sensor.
The wiper used in this trial was a preliminary version. We've improved it by adding a 'scrub'
motion intended to better contact the sensing foil with the brush.
Taken all together the testing came out very well for our inexpensive miniDOT sensor. We
thank ACT for their diligence and for our opportunity to participate.