Sheerwater vs VR3 for an EVO 4th cell?

**Gill Envy** · 15th February 2007, 18:25

Mdemon, thanks for your in depth reply...nice and comprehensive, very helpful.

Quote: (Originally Posted by Mdemon)

I found, on my Classic, that the 4th cell VR£ didn't track particularly accurately what the Inspo handsets were doing. Not wildly out, but I didn't fancy basing my deco on it. This was using both DeltaP adapters and also mounting the cell in the head with the others. So, I set the VR£ to a fixed setpoint of 1.25 and accept the slightly longer deco as conservatism.

Yeah, the VR3 is pretty much off the list now mostly in terms of vision compatability...

Quote: (Originally Posted by Mdemon)

However, the biggest reason for keeping the 4th cell was so that in the event of a bad flood, or total battery failure or total handset failure or handsets locking me out (which happened to a mate), the independent cell would still give me PO2 info. I think this is more valuable than the realtime deco to be honest.

Agreed. If I had a back up deco computer already, I'd probably be more interested in a streight po2 display. I'm sticking to mostly rec limits with little to no deco at this point. My hope is to "Keep It Simple-er" by adding only one more screen to the mix with the emphasis on real time po2 and deco as a bonus.

Quote: (Originally Posted by Mdemon)

I've got a rEvodream and that is better still. It's redundancy you can actually use as a primary if you wanted to - and it comes with a HUD as well as a handset. Don't worry about the tapping - it is a total PITA and my knuckles are still sore but actually it is very simple and safe. Turn it on. Dive. Turn it off. Battery life is two years IIRC? Varies with backlight usage etc. Very nice redundancy package + HUD, but no realtime deco or O2 control.

Looks like a nice set up, but again i'm looking to add one screen to the mix, i'd have three with the rEvo since i prefer a back up deco computer.

Quote: (Originally Posted by Mdemon)

The Shearwater seems to be in a different league again. Everyone with one seems delighted with it. And it does what you want. On the downside, you have no redundancy against duff cells and it's more expensive. However, that needs to be weighed up against how often you think you'd need redundant cells and I can't see it being that often. So it comes down to the cost and whether the extra functionality is what you want to pay for IMHO.

More expensive than the rEvo, but closely matched in cost to the VR3 and has deco. I'm impressed also with the added bail out gas options, as I am contemplating and feeling ready for mod2 and deeper diving.

My intent from the beginning has been to take baby steps, take a year diving whatever system I chose without modification, the way it was designed, and to fully understanding it's quirks before going deeper, doing more complex diving. I have been very cautious about adding any complexity to this already complex system. The planned modifications: some sort of stand/travel frame, a 4th cell and back up deco computer will help me achieve my goals, sticking a careful balance between the risks of added complexity and the value of redundancy. I feel that i have a pretty solid grasp of the strengths and weeknesses of the vision and am looking forward to getting back to the level of diving I used to do on OC...at a gradual and steady pace.

JonnyB · 15th February 2007, 19:04

Hi Dave, thank for the response, i will try to explain further how i think.
1. The fourth cell would be used for calculating deco, therefor i would want to have it as close as possible to AVppO2 on C1-C3.
2. Yes all cells are exposed to 100% humidity, but the placement of the censor will have a huge role in showing the correct value or not, right?
3. Yes i have looked at this option, talked to many people diving/teaching the Meg and other units and none of then thinks it is a good sollution, read reason 2.

/Jonny

Quote: (Originally Posted by Dave Sutton)

In order :

(1): A 4th cell is *mainly* of value for independant deco calcs with a tertiary responsiblity as a last ditch PP02 monitor used to survive a pod-fry. In the unlikely event that you need the 4th cell for life support maintenance, it means that your main elesctonics are fried, not that its cells are bad per-se. Use of one cell to ascend and deco out is not an issue, it's easy to do and is as reliable as is required in that situation. Bottom line: If it worked before, it'll work now. You can do a dil flush to validate if you are worried.

(2): *All* cells are exposed to 100% humidity in every rebreather as that's the humidity of circulating gas bolus in every rig. Location from this standoint is not critical. Yes, downstream of the scrubber is "better". It's easy to do (see below).

(3): You can add a 4th cell with the greatest of ease into any rig by simply using a "tee" in the inhale hose, and on any OTS counterlung rig by simply adding a P-Connector into the fabic. Adding a P-Connector to a Meg is a piece of cake.

Dave

**Dave Sutton** · 16th February 2007, 00:59

Quote: (Originally Posted by JonnyB)

Hi Dave, thank for the response, i will try to explain further how i think.
1. The fourth cell would be used for calculating deco, therefor i would want to have it as close as possible to AVppO2 on C1-C3.
2. Yes all cells are exposed to 100% humidity, but the placement of the censor will have a huge role in showing the correct value or not, right?
3. Yes i have looked at this option, talked to many people diving/teaching the Meg and other units and none of then thinks it is a good sollution, read reason 2./Jonny

(1): No matter what, the 4th cell will read plenty close enough for deco calculations, *surely* better than just a simple prediction of a fixed setpoint into a computer. If all 4 cells are not tracking, investigate the *problem* as they ought to track within, say 0.1 or so. That's PLENTY close enough.

(2): If the cell is anywhere in the inhale bag, it's *reading* what you are *breathing* so I don't know how much better you would want it.

(3): Opinions of those with emotional investments into hardware are not opinions I take all that seriously. Simply ask *yourself* "what's the possible downside of adding this?". Since there is no downside at all, and only upside, what is there to object to? 4th cell, giving complete validation of the existing system accuracy? No downside there.

The "Not Invented Here" syndrome is the likely reason for lack of enthusiasm from the guys you are talking to. Not sure what else to say.

Dave

sensor330 · 16th February 2007, 01:16

I've just finished installing my 4th cell so I'll see how it works out this weekend. Make things a little more cluttered as far as cables go but I'll have to sort it out.

divetheworld · 16th February 2007, 07:17

[quote=JonnyB;96282][quote=divetheworld;96154]The Shearwater connects in parallel with your existing three to give on-line PO2 and (GF)deco.

Quote:

sorry for the hijack guys...
this is something i have been thinking about doing with my meg, anyone knows if it is possible?

/Jonny

It was made for a Meg Bro'

Shearwater Research Inc. - Computers for Diving

JonnyB · 16th February 2007, 07:35

[quote=divetheworld;96723][quote=JonnyB;96282]

Quote: (Originally Posted by divetheworld)

The Shearwater connects in parallel with your existing three to give on-line PO2 and (GF)deco.

It was made for a Meg Bro'

Shearwater Research Inc. - Computers for Diving

So you mean that i can add the Shearwater parallel to the apecs?

/Jonny

divetheworld · 16th February 2007, 07:41

[quote=JonnyB;96724][quote=divetheworld;96723]

Quote: (Originally Posted by JonnyB)

So you mean that i can add the Shearwater parallel to the apecs?

/Jonny

Yup, the Shearwater will parallel with any unit that I have encountered because it has a very high internal resistance.
It will not affect the APECS, and the APECS will not affect it.

The software routine for calibration is matched for the Meg perfectly too.

Mdemon · 16th February 2007, 09:47

Quote: (Originally Posted by Dave Sutton)

(1): No matter what, the 4th cell will read plenty close enough for deco calculations, *surely* better than just a simple prediction of a fixed setpoint into a computer. If all 4 cells are not tracking, investigate the *problem* as they ought to track within, say 0.1 or so. That's PLENTY close enough.

(2): If the cell is anywhere in the inhale bag, it's *reading* what you are *breathing* so I don't know how much better you would want it.

(3): Opinions of those with emotional investments into hardware are not opinions I take all that seriously. Simply ask *yourself* "what's the possible downside of adding this?". Since there is no downside at all, and only upside, what is there to object to? 4th cell, giving complete validation of the existing system accuracy? No downside there.

The "Not Invented Here" syndrome is the likely reason for lack of enthusiasm from the guys you are talking to. Not sure what else to say.

Dave

Hi Dave,

I agree, there are no big downsides, other than cost, to adding a 4th cell. The questions here are more about what you are going to use it for and what extra functionality comes with the hardware you're thinking of buying.

I'm not sure actual deco is better than a fixed setpoint to be honest. On the assumption that your setpoint is lower than the actual will ever be (and granted, we all know what assumptions lead too...), you will be padding, slightly, your deco. So, if there is a difference between the main cells and 4th cells it becomes irrelevant from a deco perspective.

What I found with the shoulder-mounted and scrubber mounted 4th cell was that the cells didn't track particularly well, or fast. I noticed that in the scrubber one the cell was always wetter. I guess this interfered with the cell reading. The shoulder-mounted one just didn't seem to get enough of the gas path to react quickly. Either way, it would have got me out of Dodge should the handsets stop working, but left me uneasy enough not to trust it for realtime deco. Not because the figures were that far out, but because I preferred the padding of a fixed set point. Using an extension and placing the cell next to the others gave a much closer track, but by that point I was happy with the fixed setpoint thing.

I have a PPort in the inhale counterlung and until recently I had both VR£ 4th cell and the rEvodream cells hanging in that. As you say, very easy to do. Do you think the PO2 fluctuates more where there is a greater distance between O2 injection and cells? I ask because the cells are very close on the Inspo but further away when you have the cells in the Inhale CL.

Not being negative about 4th cell - just listing my experiences with some of them. It's the second mod, after the BOV that I think all Rebreather users should make.

**Dave Sutton** · 16th February 2007, 12:12

Quote: (Originally Posted by Mdemon)

I agree, there are no big downsides, other than cost, to adding a 4th cell. I'm not sure actual deco is better than a fixed setpoint So, if there is a difference between the main cells and 4th cells it becomes irrelevant from a deco perspective.

What I found with the shoulder-mounted and scrubber mounted 4th cell was that the cells didn't track particularly well, or fast. I noticed that in the scrubber one the cell was always wetter. I guess this interfered with the cell reading. The shoulder-mounted one just didn't seem to get enough of the gas path to react quickly. I have a PPort in the inhale counterlung and until recently I had both VR£ 4th cell and the rEvodream cells hanging in that. As you say, very easy to do. Do you think the PO2 fluctuates more where there is a greater distance between O2 injection and cells? I ask because the cells are very close on the Inspo but further away when you have the cells in the Inhale CL. Not being negative about 4th cell - just listing my experiences with some of them. It's the second mod, after the BOV that I think all Rebreather users should make.

Deco computations work fine off of predicted PP02 *as long as you are able to hold setpoint*. But when the feces hits the rotating ventalator things change. I plan SCC diluent only as one of my main survival modes, and trust me: If I go into that mode, I'm going to be *very* grateful for the PP02 cell talking to my deco computer. Yes, I *can* do without it, but I'm all for workload reduction at that point. Ditto for my 02 only deco modes... and to re-beat an old horse, I take advantage of the PP02 spike on descent too. So meausured PP02 deco is part and parcel of my entire "package" of desires in my rig.

The best place to measure PP02 is at the DSV.... the gas you are inhaling is the gas to measure. I made up a DSV once that had a 4th cell mounted *right there* and had a dedicated Juergensen HUD board and battery mounted under the DSV in a small delrin box with a HUD indicating PP02 in front of my face. Worked a charm... what better place to measure PP02? The only reason I went away from that system was due to the desire to use a BOV and I never engineered a BOV/DSV/Cell "Trifecta". But the idea still exists in my mind to make one when I have time. With that said, the inhale hose is the obvious next best spot followed by the top of the inhale counterlung. All you need is gas passage over the face. It'll measure just fine. And frankly I am not all that concerned about "tracking".... as long as things are within 0.1 or 0.2 that's clse enough. And I'm not worried about response time either... as long as I get some sort of reading in 5 seconds or so that's cool too. I am not a microprocessor, so I buffer the response in my head...

If you measure the gas at the point of 02 injection, or closer to it, you may end up with unmixed gas flowing for a second or two over the cells, but again, with a "human" computer looking at the result, who cares? On my 3 cell probes I inject my gas (manual dil and 02) right thru the sensor probe so all three sensors see the gas flowing over the cells every time I do a manual injection. Dancing cells = happy Dave. I know they are responsive and that makes me happy! The computer does not respond with deco for these short period spikes, and all is well.

Maybe I ought to get back to completing the DSV/BOV/HUD/4th cell "all in one" design. I actually had it semi-built, I think the prototype is still under my bnch someplace in a fish tub. Be a nice plug and play device for the thinking CCR diver. *When* someone else offers one for sale, remember that you saw it here first.... I don't have enough fingers to count the commercial products that are now offered by various guys who have copied my stuff, which is fine with me, except it would be nice if they sent me one as a present when doing so!

Dave

Mdemon · 16th February 2007, 12:42

Quote: (Originally Posted by Dave Sutton)

D

Maybe I ought to get back to completing the DSV/BOV/HUD/4th cell "all in one" design. I actually had it semi-built, I think the prototype is still under my bnch someplace in a fish tub. Be a nice plug and play device for the thinking CCR diver. *When* someone else offers one for sale, remember that you saw it here first.... I don't have enough fingers to count the commercial products that are now offered by various guys who have copied my stuff, which is fine with me, except it would be nice if they sent me one as a present when doing so!

Dave

If poo hits the air conditioning, you can turn the VR£ onto reading the external PO2 (4th cell) quite easily. More easily than turning on the OC gases IMHO! I wish DeltaP would sort that. So you have the option, and semi closed would be an occasion where 4th cell would be very useful for deco info.

I have a Bob Howell ADV and it's HUGE! I looked at installing a cell in it, since it was nearer to the DSV and I could use the ADV to blow the cell face clear. Never got round to it though.

As for your DSV/BOV/HUD/4th cell, you need to complete the job and add the ADV to it. Quite easily done - we've scribbled a few ideas down and when I've saved up my pocket money I'll buy a CNC machine and make the damned thing.

There was some debate about HUDS on The List recently. It got me thinking. The two things I'd like to be able to see all the time are my PO2 and my depth. Can you add a simple gauge to your list please? Many thanks. Deposit in the post. Pick it up Tuesday?

15th February 2007, 18:25	#21 (permalink)
Gill Envy Shearwater Copis Divers Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,347	Re: Sheerwater vs VR3 for an EVO 4th cell? Mdemon, thanks for your in depth reply...nice and comprehensive, very helpful. Quote: (Originally Posted by Mdemon) I found, on my Classic, that the 4th cell VR£ didn't track particularly accurately what the Inspo handsets were doing. Not wildly out, but I didn't fancy basing my deco on it. This was using both DeltaP adapters and also mounting the cell in the head with the others. So, I set the VR£ to a fixed setpoint of 1.25 and accept the slightly longer deco as conservatism. Yeah, the VR3 is pretty much off the list now mostly in terms of vision compatability... Quote: (Originally Posted by Mdemon) However, the biggest reason for keeping the 4th cell was so that in the event of a bad flood, or total battery failure or total handset failure or handsets locking me out (which happened to a mate), the independent cell would still give me PO2 info. I think this is more valuable than the realtime deco to be honest. Agreed. If I had a back up deco computer already, I'd probably be more interested in a streight po2 display. I'm sticking to mostly rec limits with little to no deco at this point. My hope is to "Keep It Simple-er" by adding only one more screen to the mix with the emphasis on real time po2 and deco as a bonus. Quote: (Originally Posted by Mdemon) I've got a rEvodream and that is better still. It's redundancy you can actually use as a primary if you wanted to - and it comes with a HUD as well as a handset. Don't worry about the tapping - it is a total PITA and my knuckles are still sore but actually it is very simple and safe. Turn it on. Dive. Turn it off. Battery life is two years IIRC? Varies with backlight usage etc. Very nice redundancy package + HUD, but no realtime deco or O2 control. Looks like a nice set up, but again i'm looking to add one screen to the mix, i'd have three with the rEvo since i prefer a back up deco computer. Quote: (Originally Posted by Mdemon) The Shearwater seems to be in a different league again. Everyone with one seems delighted with it. And it does what you want. On the downside, you have no redundancy against duff cells and it's more expensive. However, that needs to be weighed up against how often you think you'd need redundant cells and I can't see it being that often. So it comes down to the cost and whether the extra functionality is what you want to pay for IMHO. More expensive than the rEvo, but closely matched in cost to the VR3 and has deco. I'm impressed also with the added bail out gas options, as I am contemplating and feeling ready for mod2 and deeper diving. My intent from the beginning has been to take baby steps, take a year diving whatever system I chose without modification, the way it was designed, and to fully understanding it's quirks before going deeper, doing more complex diving. I have been very cautious about adding any complexity to this already complex system. The planned modifications: some sort of stand/travel frame, a 4th cell and back up deco computer will help me achieve my goals, sticking a careful balance between the risks of added complexity and the value of redundancy. I feel that i have a pretty solid grasp of the strengths and weeknesses of the vision and am looking forward to getting back to the level of diving I used to do on OC...at a gradual and steady pace. __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°> Last edited by Gill Envy : 15th February 2007 at 18:30.
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15th February 2007, 19:04	#22 (permalink)
JonnyB Johnny The Hatch Current Rebreather/s: MK 15.X Titan Other CCR Other SCR Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Megalodon Sport Kiss Classic Kiss Other CCR Other SCR Home Build Join Date: Jan 2005 Location: Sweden (Stockholm)/Cyprus(Ayia Napa) Posts: 991	Re: Sheerwater vs VR3 for an EVO 4th cell? Hi Dave, thank for the response, i will try to explain further how i think. 1. The fourth cell would be used for calculating deco, therefor i would want to have it as close as possible to AVppO2 on C1-C3. 2. Yes all cells are exposed to 100% humidity, but the placement of the censor will have a huge role in showing the correct value or not, right? 3. Yes i have looked at this option, talked to many people diving/teaching the Meg and other units and none of then thinks it is a good sollution, read reason 2. /Jonny Quote: (Originally Posted by Dave Sutton) In order : (1): A 4th cell is mainly of value for independant deco calcs with a tertiary responsiblity as a last ditch PP02 monitor used to survive a pod-fry. In the unlikely event that you need the 4th cell for life support maintenance, it means that your main elesctonics are fried, not that its cells are bad per-se. Use of one cell to ascend and deco out is not an issue, it's easy to do and is as reliable as is required in that situation. Bottom line: If it worked before, it'll work now. You can do a dil flush to validate if you are worried. (2): All cells are exposed to 100% humidity in every rebreather as that's the humidity of circulating gas bolus in every rig. Location from this standoint is not critical. Yes, downstream of the scrubber is "better". It's easy to do (see below). (3): You can add a 4th cell with the greatest of ease into any rig by simply using a "tee" in the inhale hose, and on any OTS counterlung rig by simply adding a P-Connector into the fabic. Adding a P-Connector to a Meg is a piece of cake. Dave __________________ A quote from Crazyduck - In remembering our own Rob Davies. "Outbound flight 777 heavy you are cleared for flight Due west into that warm red Texas sunset You have angels on your wings and divers memories on your six." Rest In Peace http://www.divetekcyprus.com http://www.diveccr.com
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16th February 2007, 00:59	#23 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Evolution Megalodon rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,907	Re: Sheerwater vs VR3 for an EVO 4th cell? Quote: (Originally Posted by JonnyB) Hi Dave, thank for the response, i will try to explain further how i think. 1. The fourth cell would be used for calculating deco, therefor i would want to have it as close as possible to AVppO2 on C1-C3. 2. Yes all cells are exposed to 100% humidity, but the placement of the censor will have a huge role in showing the correct value or not, right? 3. Yes i have looked at this option, talked to many people diving/teaching the Meg and other units and none of then thinks it is a good sollution, read reason 2./Jonny (1): No matter what, the 4th cell will read plenty close enough for deco calculations, surely better than just a simple prediction of a fixed setpoint into a computer. If all 4 cells are not tracking, investigate the problem as they ought to track within, say 0.1 or so. That's PLENTY close enough. (2): If the cell is anywhere in the inhale bag, it's reading what you are breathing so I don't know how much better you would want it. (3): Opinions of those with emotional investments into hardware are not opinions I take all that seriously. Simply ask yourself "what's the possible downside of adding this?". Since there is no downside at all, and only upside, what is there to object to? 4th cell, giving complete validation of the existing system accuracy? No downside there. The "Not Invented Here" syndrome is the likely reason for lack of enthusiasm from the guys you are talking to. Not sure what else to say. Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com
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16th February 2007, 01:16	#24 (permalink)
sensor330 RBW Member Current Rebreather/s: Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Feb 2005 Location: Victoria, British Columbia, Canada Posts: 594	Re: Sheerwater vs VR3 for an EVO 4th cell? I've just finished installing my 4th cell so I'll see how it works out this weekend. Make things a little more cluttered as far as cables go but I'll have to sort it out.
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16th February 2007, 07:17	#25 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,636	Re: Sheerwater vs VR3 for an EVO 4th cell? [quote=JonnyB;96282][quote=divetheworld;96154]The Shearwater connects in parallel with your existing three to give on-line PO2 and (GF)deco. Quote: sorry for the hijack guys... this is something i have been thinking about doing with my meg, anyone knows if it is possible? /Jonny It was made for a Meg Bro' Shearwater Research Inc. - Computers for Diving __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe
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16th February 2007, 07:35	#26 (permalink)
JonnyB Johnny The Hatch Current Rebreather/s: MK 15.X Titan Other CCR Other SCR Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Megalodon Sport Kiss Classic Kiss Other CCR Other SCR Home Build Join Date: Jan 2005 Location: Sweden (Stockholm)/Cyprus(Ayia Napa) Posts: 991	Re: Sheerwater vs VR3 for an EVO 4th cell? [quote=divetheworld;96723][quote=JonnyB;96282] Quote: (Originally Posted by divetheworld) The Shearwater connects in parallel with your existing three to give on-line PO2 and (GF)deco. It was made for a Meg Bro' Shearwater Research Inc. - Computers for Diving So you mean that i can add the Shearwater parallel to the apecs? /Jonny __________________ A quote from Crazyduck - In remembering our own Rob Davies. "Outbound flight 777 heavy you are cleared for flight Due west into that warm red Texas sunset You have angels on your wings and divers memories on your six." Rest In Peace http://www.divetekcyprus.com http://www.diveccr.com
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16th February 2007, 07:41	#27 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,636	Re: Sheerwater vs VR3 for an EVO 4th cell? [quote=JonnyB;96724][quote=divetheworld;96723] Quote: (Originally Posted by JonnyB) So you mean that i can add the Shearwater parallel to the apecs? /Jonny Yup, the Shearwater will parallel with any unit that I have encountered because it has a very high internal resistance. It will not affect the APECS, and the APECS will not affect it. The software routine for calibration is matched for the Meg perfectly too. __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe
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16th February 2007, 09:47	#28 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,946	Re: Sheerwater vs VR3 for an EVO 4th cell? Quote: (Originally Posted by Dave Sutton) (1): No matter what, the 4th cell will read plenty close enough for deco calculations, surely better than just a simple prediction of a fixed setpoint into a computer. If all 4 cells are not tracking, investigate the problem as they ought to track within, say 0.1 or so. That's PLENTY close enough. (2): If the cell is anywhere in the inhale bag, it's reading what you are breathing so I don't know how much better you would want it. (3): Opinions of those with emotional investments into hardware are not opinions I take all that seriously. Simply ask yourself "what's the possible downside of adding this?". Since there is no downside at all, and only upside, what is there to object to? 4th cell, giving complete validation of the existing system accuracy? No downside there. The "Not Invented Here" syndrome is the likely reason for lack of enthusiasm from the guys you are talking to. Not sure what else to say. Dave Hi Dave, I agree, there are no big downsides, other than cost, to adding a 4th cell. The questions here are more about what you are going to use it for and what extra functionality comes with the hardware you're thinking of buying. I'm not sure actual deco is better than a fixed setpoint to be honest. On the assumption that your setpoint is lower than the actual will ever be (and granted, we all know what assumptions lead too...), you will be padding, slightly, your deco. So, if there is a difference between the main cells and 4th cells it becomes irrelevant from a deco perspective. What I found with the shoulder-mounted and scrubber mounted 4th cell was that the cells didn't track particularly well, or fast. I noticed that in the scrubber one the cell was always wetter. I guess this interfered with the cell reading. The shoulder-mounted one just didn't seem to get enough of the gas path to react quickly. Either way, it would have got me out of Dodge should the handsets stop working, but left me uneasy enough not to trust it for realtime deco. Not because the figures were that far out, but because I preferred the padding of a fixed set point. Using an extension and placing the cell next to the others gave a much closer track, but by that point I was happy with the fixed setpoint thing. I have a PPort in the inhale counterlung and until recently I had both VR£ 4th cell and the rEvodream cells hanging in that. As you say, very easy to do. Do you think the PO2 fluctuates more where there is a greater distance between O2 injection and cells? I ask because the cells are very close on the Inspo but further away when you have the cells in the Inhale CL. Not being negative about 4th cell - just listing my experiences with some of them. It's the second mod, after the BOV that I think all Rebreather users should make. __________________ www.southwestmafia.com "small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!" The WRONG Attitude will get you killed. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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16th February 2007, 12:12	#29 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Evolution Megalodon rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,907	Re: Sheerwater vs VR3 for an EVO 4th cell? Quote: (Originally Posted by Mdemon) I agree, there are no big downsides, other than cost, to adding a 4th cell. I'm not sure actual deco is better than a fixed setpoint So, if there is a difference between the main cells and 4th cells it becomes irrelevant from a deco perspective. What I found with the shoulder-mounted and scrubber mounted 4th cell was that the cells didn't track particularly well, or fast. I noticed that in the scrubber one the cell was always wetter. I guess this interfered with the cell reading. The shoulder-mounted one just didn't seem to get enough of the gas path to react quickly. I have a PPort in the inhale counterlung and until recently I had both VR£ 4th cell and the rEvodream cells hanging in that. As you say, very easy to do. Do you think the PO2 fluctuates more where there is a greater distance between O2 injection and cells? I ask because the cells are very close on the Inspo but further away when you have the cells in the Inhale CL. Not being negative about 4th cell - just listing my experiences with some of them. It's the second mod, after the BOV that I think all Rebreather users should make. Deco computations work fine off of predicted PP02 as long as you are able to hold setpoint. But when the feces hits the rotating ventalator things change. I plan SCC diluent only as one of my main survival modes, and trust me: If I go into that mode, I'm going to be very grateful for the PP02 cell talking to my deco computer. Yes, I can do without it, but I'm all for workload reduction at that point. Ditto for my 02 only deco modes... and to re-beat an old horse, I take advantage of the PP02 spike on descent too. So meausured PP02 deco is part and parcel of my entire "package" of desires in my rig. The best place to measure PP02 is at the DSV.... the gas you are inhaling is the gas to measure. I made up a DSV once that had a 4th cell mounted right there and had a dedicated Juergensen HUD board and battery mounted under the DSV in a small delrin box with a HUD indicating PP02 in front of my face. Worked a charm... what better place to measure PP02? The only reason I went away from that system was due to the desire to use a BOV and I never engineered a BOV/DSV/Cell "Trifecta". But the idea still exists in my mind to make one when I have time. With that said, the inhale hose is the obvious next best spot followed by the top of the inhale counterlung. All you need is gas passage over the face. It'll measure just fine. And frankly I am not all that concerned about "tracking".... as long as things are within 0.1 or 0.2 that's clse enough. And I'm not worried about response time either... as long as I get some sort of reading in 5 seconds or so that's cool too. I am not a microprocessor, so I buffer the response in my head... If you measure the gas at the point of 02 injection, or closer to it, you may end up with unmixed gas flowing for a second or two over the cells, but again, with a "human" computer looking at the result, who cares? On my 3 cell probes I inject my gas (manual dil and 02) right thru the sensor probe so all three sensors see the gas flowing over the cells every time I do a manual injection. Dancing cells = happy Dave. I know they are responsive and that makes me happy! The computer does not respond with deco for these short period spikes, and all is well. Maybe I ought to get back to completing the DSV/BOV/HUD/4th cell "all in one" design. I actually had it semi-built, I think the prototype is still under my bnch someplace in a fish tub. Be a nice plug and play device for the thinking CCR diver. When someone else offers one for sale, remember that you saw it here first.... I don't have enough fingers to count the commercial products that are now offered by various guys who have copied my stuff, which is fine with me, except it would be nice if they sent me one as a present when doing so! Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com
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16th February 2007, 12:42	#30 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,946	Re: Sheerwater vs VR3 for an EVO 4th cell? Quote: (Originally Posted by Dave Sutton) D Maybe I ought to get back to completing the DSV/BOV/HUD/4th cell "all in one" design. I actually had it semi-built, I think the prototype is still under my bnch someplace in a fish tub. Be a nice plug and play device for the thinking CCR diver. When someone else offers one for sale, remember that you saw it here first.... I don't have enough fingers to count the commercial products that are now offered by various guys who have copied my stuff, which is fine with me, except it would be nice if they sent me one as a present when doing so! Dave If poo hits the air conditioning, you can turn the VR£ onto reading the external PO2 (4th cell) quite easily. More easily than turning on the OC gases IMHO! I wish DeltaP would sort that. So you have the option, and semi closed would be an occasion where 4th cell would be very useful for deco info. I have a Bob Howell ADV and it's HUGE! I looked at installing a cell in it, since it was nearer to the DSV and I could use the ADV to blow the cell face clear. Never got round to it though. As for your DSV/BOV/HUD/4th cell, you need to complete the job and add the ADV to it. Quite easily done - we've scribbled a few ideas down and when I've saved up my pocket money I'll buy a CNC machine and make the damned thing. There was some debate about HUDS on The List recently. It got me thinking. The two things I'd like to be able to see all the time are my PO2 and my depth. Can you add a simple gauge to your list please? Many thanks. Deposit in the post. Pick it up Tuesday? __________________ www.southwestmafia.com "small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!" The WRONG Attitude will get you killed. "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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