Panel meter display

Packhorse

Im just playing around with a 3.5 digit panel meter for use as a PPO analizer.
the max it can display is 1999.
As a O2 analizer for nitrox (eg 1 bar) it is prefferable for it to read .209 PPO for air. This will give the greatest acuracy. But once under more pressure (eg for a Rebreather PPO display) the greatest PPO it will display will be 1.999.
I can imagine that there may be certain situations(none of them good) that the PPO may get higher so the display can be calibrated to read a PPO of up to 19.99. But setup this way air would only read as 0.21 not .209
So which would be better for a Rebreather PPO meter? If your PPO is above 2 do you really need to know how much over 2 it is?
As far as I can figure this is the only real diffrence between a nitrox analizer and a Rebreather PPO display. (except the water proofing).


For the record I am working on a analizer that will give a warning if the EAN mix is above or below the preset value so it can be used with a continuing blending system. But this could easily be used for Rebreather PPO display with a hi and low warning system of LEDs buzzers or even a vibrator.
Do any warning systems use vibrators?

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Dsix36

IMHO - YES!!!

I had been experimenting and had hit 2.0 on a couple of situations and merely ascended to "save the day".
I had an instance where my PO2 was 3.18 and bailed out instantly. If I was reading 1.999 and tried to ascend to lower PO2,,,,,,who knows?

But, you must remember that I was an idiot
Now, I am just a better trained idiot

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nicka

ive got both of my home builds set with decimal reading of 0.21
they stay reasonable stable when diving and not constantly jumping numbers, with tiny changes in ppo2.
I guess it allows me to potentially see a 2.00 reading !! but so far 1.90 the hottest ive ever run , and a o2 shut down and dil purge came one breath later.
good luck with your gauge.

Muddweller

When building mine I considered this also but then when you take into account that the tolerance of the sensors themselves can be 2% accross the range, it becomes pointless to have such resolution in the dispaly.

And as already pointed out the fluctuations in the display for the least significant digit can be distracting.

Regards
Karl

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teomannaskali

those fluctuations in the display can also mean that the display has not crashed and is still measuring...


teoman

paulraymaekers

but in influences the 'readability' of the display: if you see a variing digit all the time, it takes far longer to read and interprete the display 'in a flash' than if the digits do not move
a bit like reading analog and digital displays: the last one demands an extra 'conversion' time to interprete the value, and with moving digits this time increases

on the very very first rEvodreams I had 3 digits after the dot, I ended up by masking them!
paul

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lizardland

KISS displays (certainly the older ones, don't know about the new ones) only go to 1.999.

I don't think it matters whether you see 1.999 or 3.whatever, the horse has already bolted by that point.

I've just moved to a Shearwater and one of the things that makes me uncomfortable in using it as a primary display (that I hadn't thought about when I bought it) is that two decimal places don't move much. I have a natural distrust of any display that is doing any major processing to the raw data so I find the lack of movement a bit off-putting.

I'd disagree with Paul's comment, though it's probably subjective and depends on each diver, but I don't find three decimals harder to read. When I glance at my display I look at the first figure (hopefully "1") and the second figure (and that's just a quick check for a "1" or "2", anything else means do something) then something in my brain acknowledges whether or not the displays are moving. I have no idea what the last two digits are reading.

My girlfriend is a lecturer in dyslexia and one thing I've learned from her is that people are either distinctly visual in the way the process data (i.e. they see a picture of the whole data set in their mind) or sequential (i.e. they get the numeric data and process each element step by step). I don't think system designers take this into account when they design displays that need to be processed fast by the user, you usually get a graphic or numeric display, rarely both. In tests I'm right up on the extreme of visual processing, for example I find cars with a numeric speedo really hard to drive.

Anyway... I guess it comes down to how your brain works as to how you want to design your displays.

Cheers,

Stuart

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Packhorse

Thanks for your input guys. You raised some issues I wouldnt have thought of. I have built my analizer with it dispalying 0.209 (with+/-0.003)
I am now starting on a PPO as well and have settled on 00.21 display.
My main reason for choosing this was more to do with the fact I used a panel meter with REF pins and I didnt need a opamp and also that I think I would find the small fluctuations annoying.

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teomannaskali

"My main reason for choosing this was more to do with the fact I used a panel meter with REF pins and I didnt need a opamp and also that I think I would find the small fluctuations annoying."

You do not need an op amp to do that. My lascars show 0.209 and dont have opamps. Just a trimpot.

You are probably right about the fluctuations. But you are a home builder and your systems can crash at any moment. So I find that information very valuable. If it starts really anoying you put some tape on it. The white semi transparent type so that you see it changing only if you look at it.

Teoman

WD8CDH

Hi Packhorse,I think the reduction in active parts will outweigh the loss of a digit as far as safety goes.With multiple meters, you could have some as X.XXX and some as XX.XX but you should shift them so the decimal points line up.On my last P02 display, I even went to the point of using two different brands of panel meters to reduce the chances of simultanuous failures.Ron