DIY Oxygen Analyser
So far, I've made 2 analysers. They both utilise the Omni
Components supplied International Technologies M-03F oxygen sensor.
The 1st analyser was as described on Dave Cordes
site. Accuracy, when compared
with commercial analysers, was within 0.2% with excellent repeatability.
The finished article basically consisted of a multimeter (it had a 200mv
range and only cost a tenner) with a bolt on module containing the circuit.
The multimeter was hacked so that when the central dial is turned (switching
the unit on), it always ends up on the 200mv DC range.
During the calibration process, the bolt on module
was uncased, giving my friendly dive shop owner one or two reservations
as to letting me play with 'it' and pure O2. After calibration, it was
tested against a 50% mix lying in the shop. The shop analyser said 50.1%,
mine said 50.2%.
The finished prototype is here
A few modifications were made to Dave's design. Firstly,
I didn't need the timing circuitry as the unit would derive it's power
from the multimeter. Next, the multi-turn pot was unavailable from Maplin's
and rather than purchase an expensive alternative, I decided an 18 turn
trimmer pot (79p) would do the trick. The downside to this is that you
need to fabricate a spindle and knob to adjust it. This was achieved by
filing the end of a rivet until it fit securely into the adjustment screw.
The knob was then glued into place at the other end.
The finished article looks pants, but hey, it works,
and who's going to 'borrow' it if left unattended?
The next job was to construct an adaptor to actually sample
the mix. Once again, a prototype design and a more functional design were
created. Both began life as a plastic overflow 'T' piece. The prototype
basically consisted of the T, a reducer insert and Epoxy resin. I won't
go into details about this one, suffice to say it was adequate (see the
above photo) but far from ideal. From this, Mk2
and Mk3 were born.
The following photo shows sampling
of nitrox using the Mk2 adaptor
and the first prototype analyser:-
Not being happy with only owning 1 analyser, I decided
to make another (well 2 if the truth be known).
Analyser Number 2