Rudimentry sensor mV monitoring

Gilles · 4th June 2006, 09:57

Quote: (Originally Posted by UWSojourner)

Hey Gilles,

Can you give us an idea of your calibration routine before you went with this "wet sensor calibration." Are your sensors stored in hot humid conditions? Or are you calibrating in an air conditioned building where humidity is kept much lower? I assume you are on Apecs? How do you perform the steps for calibration of that system?

Anything you can pass on with regard to temperature and humidity of calibration location and location where your meg is stored might be helpful.

Thanks.

Hi UWS (Couldn't find your name);

I'm glad someone finally asked for some detail.

I reside in Miri, Sarawak (Tropical jungle). The Meg is stored in a non-air-conditioned room adjascent to a moderately air-coned house . Cooling in my 2-story house is done by runnning air-cons upstairs, and sometimes 1 (of 3 available downstairs) air-con is on for the kids playroom. Meg is stored in 25-27 degC temp with plenty of ventilation (via a fan).

I've just arrived from a dive outing. I will detail the procedure I used on the boat after the days diving. This is the same procedure I used to practise in the above described room before I made this post.

Slide 1 in the attached .ppt photos my Head and calibration coupling that fits into the bottom nipple (that fits inside the scrubber cartridge). Following the air calibration, I plug in my cal-kit and I crack open the OMS flow meter to its minimum (some 0.5 L/m) of 99% O2 (slide 2). I also like to keep the head upright whilst flowing the O2 as this avoids gravity segregation of O2 and prevents the apparent slow response of an otherwise perfectly fine sensor 2. If 1 of the sensors is a bit slow, I hit cal when 2 of the sensors are at or above their theoretical mV (in this case however, all 3 have an equivalent response time).

Note also that the breathing hose port is open (no cap) when doing this to avoid any chance of building pressure.

Slide 3 details new data acquired today, and slides 4 and 5 chart it.

I also went out today to determine how long during the 1st dive it takes for the sensors to change their state. Note that I'm using a 9-hr old calibration performed some 6 days ago after a days diving.

After stopping briefly @6m with an O2 flushed loop (to readings of 1.7-1.8), I flushed and went down quickly to 40m with EAN30 dil. Flushed and started off at about 1.7, flushed every 5 minutes or so, and at 15 minutes all 3 sensors @1.5. On way up, stopped @6m and switched to bail-out. Opened the OPV, pinched the loop hose with left hand and hit the manual O2 button for a few seconds. Got readings of 1.55-1.65.

I could never achieve this before and always felt insecure (and thus dived at 1.0 all the time). I'm much more comfy now with the 1.2-1.3's!

I hope I got the right amount of detail

. Don't hesitate to ask for more.

Gilles

**UWSojourner** · 4th June 2006, 22:45

Quote: (Originally Posted by sabgia)

Hi UWS (Couldn't find your name);

Hi, I'm Kevin.

Quote: (Originally Posted by sabgia)

I reside in Miri, Sarawak (Tropical jungle). The Meg is stored in a non-air-conditioned room

I guess I'd suggest one more test (if you're not tested out at this point). Try a dil flush on the loop before you store it for the night before a dive. Cal on Dil (not atmospheric air) and O2 then close the head and flush the loop with dil. Then do your dives and measurements.

I guess I'm wondering whether the near saturated air inside the sensors before the dive is reaching a quick dew point and causing your problems. Maybe starting with dry gas inside the sensors will help. Might be worth a try.

Good luck and let us know how your tests go.

Jordan · 5th June 2006, 02:29

Quote: (Originally Posted by MikeH)

That's just because your a very dry(pun intended) person....

Mike

A'ight punk... you must still be mad at you for snubbing you on the Pott Springs dive. Your small tanks would've worked just fine. Speaking of which, I did just dive it today. Blue water and of course a lot of flow. Say, I did see some line arrows that may have been somewhat new. You been in there yet? The initials were MHL

I did actually get turned around at one point (I was swimming what I thought was out and came across a line arrow pointing rearward). 'Twas the first time that happened to me. I ended up turning on a Y that I wasn't aware of due to all of the silt I stirred up. I was solo.. shit I can't imagine what it would've looked like if my buddy could've made his way in (he couldn't make it through the entrance restriction that had some tenacious flow). Anyways, on the dive I just ended up turning around and found my way in no time...this cave is pretty small and it would be kind of hard to get lost... every tunnel ends in some kind of breakdown or just stops. Some of the ends of the breakdown are actually pretty freaky 'cause they end in a slide. The line oftentimes obviously keeps going right through the breakdown indicating a collapse after the line had been lain. It's not a dive for the faint of heart... I just put my sidemount rig back together and this was my 3rd OC dive since January. I will have to get the Otooptima fired back up soon (looking forward to seeing the kewl parts of Madison Blue and of course Rose). My OC SAC rate on my 1st dive after the OC hiatus was prolly 'bout 1.0 and dive #2 prolly .8 and dive 3 prolly .7 so it's not taking too long. The buoyance shift took 1.5 dives to get back to normal. Rambling.. Good night y'all

Gilles · 5th June 2006, 12:55

Quote: (Originally Posted by UWSojourner)

Hi, I'm Kevin.

I guess I'd suggest one more test (if you're not tested out at this point). Try a dil flush on the loop before you store it for the night before a dive. Cal on Dil (not atmospheric air) and O2 then close the head and flush the loop with dil. Then do your dives and measurements.

I guess I'm wondering whether the near saturated air inside the sensors before the dive is reaching a quick dew point and causing your problems. Maybe starting with dry gas inside the sensors will help. Might be worth a try.

Good luck and let us know how your tests go.

I agree its worth a try

. If that is the case, dryer air is acting as a cushion protecting the sensors from the humidity. Einstein wouldn't be happy (as their wouldn't be any diffusion of H2O molecules), but we can find out. Must wait until Wednesday night though (Tuesday midday your time).

Note that there really isn't a problem, providing calibration is performed whilst the cells are in a representative state (the "wet" cells still have a near perfect linear response). That "representative state" appears to be more likely following a dive, rather than before the beginning of a dive day.

Nice pair of Megs by the way. Would you happen to have any pre and post dive mV's?

G

**UWSojourner** · 5th June 2006, 17:49

Quote: (Originally Posted by sabgia)

If that is the case, dryer air is acting as a cushion protecting the sensors from the humidity. Einstein wouldn't be happy (as their wouldn't be any diffusion of H2O molecules), but we can find out.

The "thought" wasn't that the dry air prevents diffusion or acts as a cushion. I was just wondering whether the near-staturated warm air already inside the sensor was condensing when cooled slightly upon entry to the water. I hadn't heard of condensation problems of this magnitude (only 1.3 PPO2 at 20fsw and that after relatively short dives) so thought ruling out other factors was worth a shot.

Quote: (Originally Posted by sabgia)

Would you happen to have any pre and post dive mV's?

No mV's yet, but I'll be diving for 5 days starting toward the end of the week and will try and get some data.

Gilles · 8th June 2006, 12:45

Quote: (Originally Posted by UWSojourner)

Hi, I'm Kevin.

I guess I'd suggest one more test (if you're not tested out at this point). Try a dil flush on the loop before you store it for the night before a dive. Cal on Dil (not atmospheric air) and O2 then close the head and flush the loop with dil. Then do your dives and measurements.

I guess I'm wondering whether the near saturated air inside the sensors before the dive is reaching a quick dew point and causing your problems. Maybe starting with dry gas inside the sensors will help. Might be worth a try.

Good luck and let us know how your tests go.

Kevin;

I performed your test. Yesterday morning, cal'd on dil (air) using the cal-kit, closed the lid and left everything on for the day, and went on a great night dive that unfortuneately lasted only 1 hour (can't wait to get a Rebreather buddy

). Dived to 30m with EAN30 as dil and started off with 1.2's as expected. 10-15 minutes later, could only get 1.0's on dil flushes and 1.3-1.4's with O2 @6m (while buddy was deco'ing).

Getting very consistent behaviour of the sensors. They seem to undergo a change of state. I have recieved two PM's from others experiencing similiar (Meg & KISS so far). I don't see how this can be Meg specific.

I wish I could get more interest (and data) on this string.

G

Micko · 8th June 2006, 13:04

Interesting must try this makes sence to cal on moist sensors considering after 20 or so min they will be wet with condensation.
There must be a crappy batch of sensors getting around since the start of this thread i have heard of people with the same probs.

Gibbon · 8th June 2006, 23:41

Quote: (Originally Posted by UWSojourner)

The "thought" wasn't that the dry air prevents diffusion or acts as a cushion. I was just wondering whether the near-staturated warm air already inside the sensor was condensing when cooled slightly upon entry to the water. I hadn't heard of condensation problems of this magnitude (only 1.3 PPO2 at 20fsw and that after relatively short dives) so thought ruling out other factors was worth a shot.

No mV's yet, but I'll be diving for 5 days starting toward the end of the week and will try and get some data.

We get the same effect as Giles.

If anything, in this region we probably have the least difference between air and water temperatures. Air 27-33 water 28-29.

Giles your night dive would have been a good example of this.

IMHO the difference between loop temperature and water temperature is the key - we produce far more humidty whilst diving than enters the loop from natural humidity pre dive.

For you guys with a large difference between water and loop temperatures - where does the majority of your condensation occur? either in the lungs or in the canister I presume - for us perhaps there is another factor causing the condensation to occur in the head?

We have a new rulling this season 1 weekend in 4 will not be diving - so as it is the weekend nearest spring tides - this weekend is the one we are not diving, but next weekend along with mV I will log temperatures - pre dive, and then from the meg, loop and water temp, I suppose if I record what the computer says for water temp as well then we will have 2 points to calibrate that over as well

Gilles · 9th June 2006, 13:11

Quote: (Originally Posted by Micko)

Interesting must try this makes sence to cal on moist sensors considering after 20 or so min they will be wet with condensation.
There must be a crappy batch of sensors getting around since the start of this thread i have heard of people with the same probs.

I don't think that there's a bad batch of sensors. They seem to work fine (remain linear). Its only a problem if your diving them on a dry calibration.

Is there anyone who can say that the sensors are outputting the same mV in Air and O2 pre and post dive? Is the Meg the only make that provides these measurements?

I have my doubts that this is Meg specific!

I consistently observe a change of state that takes about 15 minutes from the start of loop breathing. The effect (voltage attenuation) seems to remain the same (magnitude is not random), but I have yet to do a dive longer than 70 minutes. On 2nd and 3rd dives, the attenuation observed at the end of the 1st dive doesn't change.

Test your readings in water!

G

seafox · 27th June 2006, 00:54

Quote: (Originally Posted by Jordan)

We did our 2nd dive at Cow and afterwards, he was amazed to see my optima sensors bone dry. I sure am glad I can leave my unit together for a few days in between dives and not have to let the sensors dry out.

Jordon, I find the same thing. In warm water, the head is almost always dry, as are the cells.
I wonder if this is because of the design, placement of the cannister and the inclusion of the water trap?
PS: This not the case in very cold water as condensation is produced as a byproduct of the chemical reaction.

4th June 2006, 22:45	#12 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by sabgia) Hi UWS (Couldn't find your name); Hi, I'm Kevin. Quote: (Originally Posted by sabgia) I reside in Miri, Sarawak (Tropical jungle). The Meg is stored in a non-air-conditioned room I guess I'd suggest one more test (if you're not tested out at this point). Try a dil flush on the loop before you store it for the night before a dive. Cal on Dil (not atmospheric air) and O2 then close the head and flush the loop with dil. Then do your dives and measurements. I guess I'm wondering whether the near saturated air inside the sensors before the dive is reaching a quick dew point and causing your problems. Maybe starting with dry gas inside the sensors will help. Might be worth a try. Good luck and let us know how your tests go.
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5th June 2006, 02:29	#13 (permalink)
Jordan Custom Title Allowed! Current Rebreather/s: Optima Other Rebreather/s: Join Date: May 2005 Location: North Florida Posts: 219	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by MikeH) That's just because your a very dry(pun intended) person.... Mike A'ight punk... you must still be mad at you for snubbing you on the Pott Springs dive. Your small tanks would've worked just fine. Speaking of which, I did just dive it today. Blue water and of course a lot of flow. Say, I did see some line arrows that may have been somewhat new. You been in there yet? The initials were MHL I did actually get turned around at one point (I was swimming what I thought was out and came across a line arrow pointing rearward). 'Twas the first time that happened to me. I ended up turning on a Y that I wasn't aware of due to all of the silt I stirred up. I was solo.. shit I can't imagine what it would've looked like if my buddy could've made his way in (he couldn't make it through the entrance restriction that had some tenacious flow). Anyways, on the dive I just ended up turning around and found my way in no time...this cave is pretty small and it would be kind of hard to get lost... every tunnel ends in some kind of breakdown or just stops. Some of the ends of the breakdown are actually pretty freaky 'cause they end in a slide. The line oftentimes obviously keeps going right through the breakdown indicating a collapse after the line had been lain. It's not a dive for the faint of heart... I just put my sidemount rig back together and this was my 3rd OC dive since January. I will have to get the Otooptima fired back up soon (looking forward to seeing the kewl parts of Madison Blue and of course Rose). My OC SAC rate on my 1st dive after the OC hiatus was prolly 'bout 1.0 and dive #2 prolly .8 and dive 3 prolly .7 so it's not taking too long. The buoyance shift took 1.5 dives to get back to normal. Rambling.. Good night y'all __________________ Is it clear? No. Well, let's go anyways. "Those who would sacrifice a little freedom for a little order, will lose both, and deserve neither." Thomas Jefferson
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5th June 2006, 12:55	#14 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 761	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by UWSojourner) Hi, I'm Kevin. I guess I'd suggest one more test (if you're not tested out at this point). Try a dil flush on the loop before you store it for the night before a dive. Cal on Dil (not atmospheric air) and O2 then close the head and flush the loop with dil. Then do your dives and measurements. I guess I'm wondering whether the near saturated air inside the sensors before the dive is reaching a quick dew point and causing your problems. Maybe starting with dry gas inside the sensors will help. Might be worth a try. Good luck and let us know how your tests go. I agree its worth a try . If that is the case, dryer air is acting as a cushion protecting the sensors from the humidity. Einstein wouldn't be happy (as their wouldn't be any diffusion of H2O molecules), but we can find out. Must wait until Wednesday night though (Tuesday midday your time). Note that there really isn't a problem, providing calibration is performed whilst the cells are in a representative state (the "wet" cells still have a near perfect linear response). That "representative state" appears to be more likely following a dive, rather than before the beginning of a dive day. Nice pair of Megs by the way. Would you happen to have any pre and post dive mV's? G __________________ Gilles http://www.dirrebreather.com Last edited by Gilles : 5th June 2006 at 13:07. Reason: sentence structure
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5th June 2006, 17:49	#15 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by sabgia) If that is the case, dryer air is acting as a cushion protecting the sensors from the humidity. Einstein wouldn't be happy (as their wouldn't be any diffusion of H2O molecules), but we can find out. The "thought" wasn't that the dry air prevents diffusion or acts as a cushion. I was just wondering whether the near-staturated warm air already inside the sensor was condensing when cooled slightly upon entry to the water. I hadn't heard of condensation problems of this magnitude (only 1.3 PPO2 at 20fsw and that after relatively short dives) so thought ruling out other factors was worth a shot. Quote: (Originally Posted by sabgia) Would you happen to have any pre and post dive mV's? No mV's yet, but I'll be diving for 5 days starting toward the end of the week and will try and get some data.
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8th June 2006, 12:45	#16 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 761	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by UWSojourner) Hi, I'm Kevin. I guess I'd suggest one more test (if you're not tested out at this point). Try a dil flush on the loop before you store it for the night before a dive. Cal on Dil (not atmospheric air) and O2 then close the head and flush the loop with dil. Then do your dives and measurements. I guess I'm wondering whether the near saturated air inside the sensors before the dive is reaching a quick dew point and causing your problems. Maybe starting with dry gas inside the sensors will help. Might be worth a try. Good luck and let us know how your tests go. Kevin; I performed your test. Yesterday morning, cal'd on dil (air) using the cal-kit, closed the lid and left everything on for the day, and went on a great night dive that unfortuneately lasted only 1 hour (can't wait to get a Rebreather buddy ). Dived to 30m with EAN30 as dil and started off with 1.2's as expected. 10-15 minutes later, could only get 1.0's on dil flushes and 1.3-1.4's with O2 @6m (while buddy was deco'ing). Getting very consistent behaviour of the sensors. They seem to undergo a change of state. I have recieved two PM's from others experiencing similiar (Meg & KISS so far). I don't see how this can be Meg specific. I wish I could get more interest (and data) on this string. G __________________ Gilles http://www.dirrebreather.com Last edited by Gilles : 8th June 2006 at 12:47.
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8th June 2006, 13:04	#17 (permalink)
Micko Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Dec 2005 Location: perth Posts: 114	Re: Rudimentry sensor mV monitoring Interesting must try this makes sence to cal on moist sensors considering after 20 or so min they will be wet with condensation. There must be a crappy batch of sensors getting around since the start of this thread i have heard of people with the same probs.
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8th June 2006, 23:41	#18 (permalink)
Gibbon Southern Monkey Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2005 Location: East Devon Posts: 226	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by UWSojourner) The "thought" wasn't that the dry air prevents diffusion or acts as a cushion. I was just wondering whether the near-staturated warm air already inside the sensor was condensing when cooled slightly upon entry to the water. I hadn't heard of condensation problems of this magnitude (only 1.3 PPO2 at 20fsw and that after relatively short dives) so thought ruling out other factors was worth a shot. No mV's yet, but I'll be diving for 5 days starting toward the end of the week and will try and get some data. We get the same effect as Giles. If anything, in this region we probably have the least difference between air and water temperatures. Air 27-33 water 28-29. Giles your night dive would have been a good example of this. IMHO the difference between loop temperature and water temperature is the key - we produce far more humidty whilst diving than enters the loop from natural humidity pre dive. For you guys with a large difference between water and loop temperatures - where does the majority of your condensation occur? either in the lungs or in the canister I presume - for us perhaps there is another factor causing the condensation to occur in the head? We have a new rulling this season 1 weekend in 4 will not be diving - so as it is the weekend nearest spring tides - this weekend is the one we are not diving, but next weekend along with mV I will log temperatures - pre dive, and then from the meg, loop and water temp, I suppose if I record what the computer says for water temp as well then we will have 2 points to calibrate that over as well
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9th June 2006, 13:11	#19 (permalink)
Gilles Worship the feminine Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Den Haag (Netherlands) Posts: 761	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by Micko) Interesting must try this makes sence to cal on moist sensors considering after 20 or so min they will be wet with condensation. There must be a crappy batch of sensors getting around since the start of this thread i have heard of people with the same probs. I don't think that there's a bad batch of sensors. They seem to work fine (remain linear). Its only a problem if your diving them on a dry calibration. Is there anyone who can say that the sensors are outputting the same mV in Air and O2 pre and post dive? Is the Meg the only make that provides these measurements? I have my doubts that this is Meg specific! I consistently observe a change of state that takes about 15 minutes from the start of loop breathing. The effect (voltage attenuation) seems to remain the same (magnitude is not random), but I have yet to do a dive longer than 70 minutes. On 2nd and 3rd dives, the attenuation observed at the end of the 1st dive doesn't change. Test your readings in water! G __________________ Gilles http://www.dirrebreather.com Last edited by Gilles : 9th June 2006 at 13:24.
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27th June 2006, 00:54	#20 (permalink)
seafox 02ptima Instructor Current Rebreather/s: Inspiration Classic Optima Other Rebreather/s: Join Date: Mar 2005 Location: TORONTO, CANADA -Have "02ptima" will travel! Posts: 172	Re: Rudimentry sensor mV monitoring Quote: (Originally Posted by Jordan) We did our 2nd dive at Cow and afterwards, he was amazed to see my optima sensors bone dry. I sure am glad I can leave my unit together for a few days in between dives and not have to let the sensors dry out. Jordon, I find the same thing. In warm water, the head is almost always dry, as are the cells. I wonder if this is because of the design, placement of the cannister and the inclusion of the water trap? PS: This not the case in very cold water as condensation is produced as a byproduct of the chemical reaction. __________________ Protect the SHARKS! Excellence is never an accident; it is always the result of high intention, sincere effort, intelligent direction, skillful execution and the vision to see obstacles as opportunities. Experience is a hard teacher because she gives the test first, the lesson afterwards!
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