Homemade PO2 meter

Corallaro

Hi Paul

nice to read you

for the moment i use a like DPM's: triple homemade display

but an analog display without a battery maybe minus point of failure....

when i have more time i will make an lm3914 led display and an analog display if i found the components...

the probem is the correct microamperometer...i need an 1 microamperes fs witn an more high possible internal resistance...

i will test either solutions.....

curiosity...game...toy....?

for the moment i am making a simple system to test my cells at 1.6 o2 ata...

Giovanni

marekm

Hi Paul,

Firstly, I'm amazed that someone of your standing was attracted to post in this thread by a lowly homebuilder .

Anyway, the reason I am looking at building analogue displays, is because I have built 6 different DPM based PO2 meters, and they all need batteries. Making a device that needs no batteries is an elegant solution. Kind of like the mechanical wrist watch that does not need batteries or winding up. As long as you wear it, it works. Same with the PO2 meter, if you plug in the O2 cells, it works. Ideally there will be no situation where the PO2 meter fails due to the battery going flat.

Cheers.
-Marek

undrh2o

Have a look here not just samples - regular price is $35

paulraymaekers

hello marek, the chance of failure in an analog MECHANICAL system with moving coil etc is always far bigger than the risc of flat battery :-)

normal DPM consume 100-300 micro-amps (no backlight, as there is no backlight in analog systems eighter)
means it runs multiple 1000 of hours on a lithium batt

regards
paul

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jmhardingjr

Yup,

I've spoken to Kevin Jurgensen and he said that the MK-15/Prism secondaries are pretty fragile. The jeweled movement, springs, needles, etc add up to whole other set of protential problems. It makes sense. Essentially, trading a DPM for an analog guage is just moving over to another set of potential failure points. They just happen to be mechanical instead of electronic failure points.

Just my two cents.

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plazma

Did the Cis Lunar have some kind of analog PO2 meter with out moving coil?

-Pasi

marekm

Based on the photos of the Cis Lunar, the alternate PO2 display is an array of LED's ranging from the red zone (low PO2) to green (ok PO2) then back to red (high PO2). Also, they need a battery to work.

Tom Rose

Hi Paul,

Why do people dive historical dive gear?

Why do people try to experiment?

Sometimes it is for fun....sometimes it leads somewhere....

I never discourage people trying things...I may point out some approaches that have been tried....but...gosh knows....something could come out of his inquires....

No matter what we know...its what we don't know that is the future....

And yes, I only use electronic displays now...but if i could find a mechanical display that was as rugged, damned right I would use it.

And yes, you are right, Op Amps are actually easier to use than transistors for gain, buffering, and bias compensation.

Tom

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Dave Sutton

Paul's dead right here. The meters are (sadly) obsolete.

The old Mark-15 system works fine, it is a simple MV meter directly wired to the cells with a potentiometer set up so you can calibrate the thing. The meter is just a simple MV meter with a custom face. Good thing? Simple. Bad thing? They break. You can use single jewel movements, You can use dual jewel movements. In the end they *all* break.

Mark-16 went to a digital meter, the battery simply powers the LCD display. It's been very reliable, more so than the mechanical meters. The first moment that a digital display was available for the Mark-15 as a retrofit, I simply sent my check.


Simple = Good. With that said, mechanically durable is a requirement. Meters are not as durable as digital displays and the displays are "simple enough" to be fully reliable. Yes they fail if flooded.... so do the meters (although it's tru that the meters "may" work when flooded.... for a little while anyhow.. as the actual meter on a Mark-15 display is soldered closed).


With that all said, Tom is right too: Experimentation is fun. Making up this stuff is neat. Mechanical systems are interesting to build. Just be aware that it's simply an excercse in vintage technology, not what will probably end up being as robust as a more modern system.


I'd love to see the LED array PP02 meter, tranistors and all. The nold Rev-G Analog Mark-15 control pod I have here is made that way.. and always works (so far anyhow!)


Dave


(Oh, do I offend you with my "tone"... ?? If so, don't read what I write).....

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marekm

This is what I was aiming at with the analogue LED based PO2 meter. And also the fact that it removes the 'black box' component out of the PO2 meter, since I know what each transistor does, rather than have a unknown IC on a DPM.

As for the mechanical analogue mV gauges, I did not realize they were so fragile, I simply assumed they were not used because they were retro and uncool. In terms of how fragile they are, does anyone know if they are more or less delicate than a HID bulb?