How to make a digital ppo2 display?

paulraymaekers · 10th August 2007, 16:35

Quote: (Originally Posted by Rebreathing Red)

you can make your own conclusions

eeuuh, and that is.....???

sorry, I'm missing something...

paul

DanFountain · 10th August 2007, 17:30

Quote: (Originally Posted by Rebreathing Red)

I have nothing to gain or loss in this. I'm just sharing what I know.
So let's ignore my prevoius graph and do a little math.

A straight line can be defined by the equation y=mx+b
So if po2 0.0 = 0 millivolts and sensor A has the following po2 0.21 = 12 mv (newer sensor)
Sensor B p02 0.21 = 9 mv (older sensor)
since po2 0=0 then b=0 (no linear offset)

therefore y=mx

A
13=0.21m
m= 61.905

B
9=0.21m
m=42.857
The slope is different on sensor A and B

so looking at a po2 of 1.6 we get the following
Sensor A =61.905*1.6 = 99.048 mv
sensor B = 42.857*1.6= 68.571 mv

you can make your own conclusions

Red,

What you wrote is right on. Cells will exhibit somewhat different response slopes, as you showed. That's why each (panel meter, microcontroller, whatever) needs to be calibrated to a particular sensor. If one were to switch one PO2 indicator between different cells, the readings certainly wouldn't be the same. The adjustment pot simply adjusts the gain or slope of the PO2 indicator to the slope of the sensor. The two response "curves" you illustrate are perfectly suited for a single-point calibration, since they are essentially straight lines in the area of interest and have a Y-intercept of zero. Just sharing what I know.

-Dan

whoizrob · 11th August 2007, 16:44

I can't seem to find Dave, is he on this site?

Rob

lof · 14th August 2007, 03:43

Quote: (Originally Posted by Drmike)

HI guys,

I want to make some ppo2 displays. Housing is a piece of cake but what I know sod all about is the electronics side.

I pressume Ill need 3 displays and 3 pots a battery and......

Is there an idiots guide on the net anywhere?

anyone advise with part numbers (RS or otherwise?)

wiring diagrams or even complete boards?

Cheers
m

Mike

I have bunch of leftover clear tube, some machined endpoints and even one or two Mark Munro PCBs buried in my boxes of abandoned dive gear.
You can have them when you stop by.

dan140465 · 21st December 2007, 18:11

Does anyone have any contact details for dave mager ?
Is he still making displays ?

Cheers
Danny

decoweenie · 21st December 2007, 18:21

Quote: (Originally Posted by dan140465)

Does anyone have any contact details for dave mager ?

Email: dave AT dmager.freeserve.co.uk

dan140465 · 21st December 2007, 18:44

many thanks

10th August 2007, 16:35	#31 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,510	Re: How to make a digital ppo2 display? Quote: (Originally Posted by Rebreathing Red) you can make your own conclusions eeuuh, and that is.....??? sorry, I'm missing something... paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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10th August 2007, 17:30	#32 (permalink)
DanFountain This is my custom title! Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Dec 2005 Location: Lake Superior Posts: 103	Re: How to make a digital ppo2 display? Quote: (Originally Posted by Rebreathing Red) I have nothing to gain or loss in this. I'm just sharing what I know. So let's ignore my prevoius graph and do a little math. A straight line can be defined by the equation y=mx+b So if po2 0.0 = 0 millivolts and sensor A has the following po2 0.21 = 12 mv (newer sensor) Sensor B p02 0.21 = 9 mv (older sensor) since po2 0=0 then b=0 (no linear offset) therefore y=mx A 13=0.21m m= 61.905 B 9=0.21m m=42.857 The slope is different on sensor A and B so looking at a po2 of 1.6 we get the following Sensor A =61.9051.6 = 99.048 mv sensor B = 42.8571.6= 68.571 mv you can make your own conclusions Red, What you wrote is right on. Cells will exhibit somewhat different response slopes, as you showed. That's why each (panel meter, microcontroller, whatever) needs to be calibrated to a particular sensor. If one were to switch one PO2 indicator between different cells, the readings certainly wouldn't be the same. The adjustment pot simply adjusts the gain or slope of the PO2 indicator to the slope of the sensor. The two response "curves" you illustrate are perfectly suited for a single-point calibration, since they are essentially straight lines in the area of interest and have a Y-intercept of zero. Just sharing what I know. -Dan __________________ Try not. Do - or do not. There is no try. -Yoda
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11th August 2007, 16:44	#33 (permalink)
whoizrob New Member Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Apr 2006 Location: Sacramento Posts: 72	Re: How to make a digital ppo2 display? I can't seem to find Dave, is he on this site? Rob
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14th August 2007, 03:43	#34 (permalink)
lof RebreatherWorld Sponsor Current Rebreather/s: Megalodon Prism Topaz Sport Kiss Classic Kiss MK 15.X Other CCR RB80 / Clone Other SCR Home Build Other Rebreather/s: Other CCR RB80 / Clone Other SCR Home Build Join Date: Jun 2005 Location: USA Posts: 482	Re: How to make a digital ppo2 display? Quote: (Originally Posted by Drmike) HI guys, I want to make some ppo2 displays. Housing is a piece of cake but what I know sod all about is the electronics side. I pressume Ill need 3 displays and 3 pots a battery and...... Is there an idiots guide on the net anywhere? anyone advise with part numbers (RS or otherwise?) wiring diagrams or even complete boards? Cheers m Mike I have bunch of leftover clear tube, some machined endpoints and even one or two Mark Munro PCBs buried in my boxes of abandoned dive gear. You can have them when you stop by. __________________ Jakub Golem Gear ShopKeeper www.golemgear.com
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21st December 2007, 18:11	#35 (permalink)
dan140465 Custom Title Allowed! Current Rebreather/s: Sport Kiss Classic Kiss Other CCR Other Rebreather/s: Inspiration Classic Classic Kiss Other CCR Join Date: Dec 2005 Location: Portsmouth, UK Posts: 115	Re: How to make a digital ppo2 display? Does anyone have any contact details for dave mager ? Is he still making displays ? Cheers Danny __________________ Same S**t different Day !
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21st December 2007, 18:21	#36 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: How to make a digital ppo2 display? Quote: (Originally Posted by dan140465) Does anyone have any contact details for dave mager ? Email: dave AT dmager.freeserve.co.uk
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21st December 2007, 18:44	#37 (permalink)
dan140465 Custom Title Allowed! Current Rebreather/s: Sport Kiss Classic Kiss Other CCR Other Rebreather/s: Inspiration Classic Classic Kiss Other CCR Join Date: Dec 2005 Location: Portsmouth, UK Posts: 115	Re: How to make a digital ppo2 display? many thanks __________________ Same S**t different Day !
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