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Richard Taylor asks
I have been looking at diferent O2 analysers available here in Oz and am in
a bit unclear on what specifications I should be guided by. It seems that
the MSA MiniOx I O2 analyser in accurate to +/- 1%, graded in increments of
.1% and with a helium variation on the O2 reading of .2%. (these figures
are taken from MSA spec sheet). My question quite simply is..."Is this
specification suitable for O2 analysis in Enriched Air/Nitrox & Mixed Gas
diving?" It is feasable with this unit to be reading say 37.5% O2 when in
fact the EANx O2 content could in effect be 36.5%.; the same variation
could be compounded by analysing a mix tank & reading 16.6% O2 when the mix
contained 15.4%. I am fully aware that safe diving practices should ensure
that you do not dive to the limit of the tables for the particular
breathing mix and that you should allow a reasonable J-factor when
customising your own tables. This does not though take away the apparent
problem that a filling station (or an instructor) may be supplyng a mix
which has a 2% varience.
We are a little isolated down here in Oz, so your comments would be of
interest ( in particular, any filling station or instructor who has
practical advice/experience in operating the MiniOx I O2 anaylser to supply
fills).
This is the norm for all the meters I've read the specs on. BTW the
sensor on the MiniOx is made by Teledyne. I sent a msg out earlier this
mouth, it explained the constructions of these little beasts. The meter
itself can be high accuracy. It's the sensor thats the limiting
factor.
One feature you might want to consider is a meter that has a temperature
compensating probe. I have a meter that does not have this feature. I've
observer when I hold the probe in the palm of my hand you can see the
reading if the meter change (3-4%). I tried the same with a meter that had a
temperature compensating probe and observed it did change but not near
as much.
With the above in mind I've found to get the most out of your meter.
First let the probe come to ambient temperature. Never hold the probe by
the body. When you measure the gas keep the flow a low as possible. You
don't want to change the temp. of the probe or increase the partial
pressure in the flow tube. I know some people who have even put an
Oxygen welding reg with a flow control adjustment on there systems in
order to keep the flow and temp. as low as possible.
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