Vision: 4th cell or 3 cell monitor?

**aainslie** · 21st July 2008, 22:48

Greetings all,

If you were to get a deco computer independent of your Vision electronics with live PO2 monitoring, which would you prefer and why:

1) A system that monitored a 4th, independent cell, or

2) A system that monitored the three cells already monitored by the Vision electronics?

I'm trying to make up my mind between Narced@90's two offerings and can't make up my mind. Thsoe of you with experience in the field, I'd love to hear your feedback about what's good and bad about the two philosophies.

**Gill Envy** · 22nd July 2008, 00:15

I've thought this over quite a bit back when we owned evo's. In fact I had quite a bit of time to think it over when I got locked out of the vision on two trips. I concluded that getting the adapter for three cell monitoring was the way to go, even if you used a 4th cell most of the time. I at least wanted to be able to hook up the secondary to all three cells and run the unit manually (using a shearwater, vr3 etc) if the vision "went blind" on a remote trip. If we had had this capacity the two times the sh*t hit the fan we might very well still be vision owners as we would have been happy to run the units manually if it meant we could still keep diving on our two big annual trips.

The value of a 4th cell never quite caught on for me because of the added logistics and the fact that if something really goes wrong with the electronics, it's best to bail out and return to the surface so it didn't seem to have much advanage. it's what you can do from that point forward that really counts, IMHO. As for the configuration for when things are running normally, you will have to balance how much you value having a truly independent monitoring system on one cell vs the value of having a true back up, but which shares cells. I really like being able to cross check all three cells on a separate screen to see if an errant reading can be verified. a 4th cell might give more piece of mind in an acute meltdown of the vision, in terms of getting you back to the surface, which is of course priority number one but for the rest of the trip, having all three cells will allow you to keep diving, and the value of that can not be underestimated.

there has been talk that sharing cells, particularly with an eCCR, which runs on more juice, runs the risk of cross current pollution. I have yet to hear of a real case of this though, and have not had such a problem so far using the shearwater Pursuit and HUD, which are independent computers with separate batteries, sharing all three cells.

my 02 cents.

g

Quote: (Originally Posted by aainslie)

Greetings all,

If you were to get a deco computer independent of your Vision electronics with live PO2 monitoring, which would you prefer and why:

1) A system that monitored a 4th, independent cell, or

2) A system that monitored the three cells already monitored by the Vision electronics?

I'm trying to make up my mind between Narced@90's two offerings and can't make up my mind. Thsoe of you with experience in the field, I'd love to hear your feedback about what's good and bad about the two philosophies.

cramerdn · 22nd July 2008, 13:22

You coud even put 4 cells in and then monitor 1,2, and 3 with the vision and 2,3,4 with the shearwater.

**sfldiver** · 22nd July 2008, 14:48

Quote: (Originally Posted by cramerdn)

You coud even put 4 cells in and then monitor 1,2, and 3 with the vision and 2,3,4 with the shearwater.

With this scenario, if the #2 sensor failed, it would fail on both computers, so are each of the computers actually independent of each other? Doesn't appear to be the case.

Personally, I have a VR3 on my Optima connected to a 4th cell and running a separate deco calculation, based on different software, which I feel gives me an increased safety factor, because if I always ensure that I complete the lengthiest deco obligation, then theoretically, I have a higher probablility of being clean at the end of the dive.

There are advantages to both scenarios, but my vote goes towards setting up the separate computer linked to the 4th cell, as it allows me to have a truly independent backup, and I consequently sleep very well at night.

**aainslie** · 22nd July 2008, 15:52

I agree that a 4th cell gives true independence, but the question is, does it give the best ouctome under failures of different types?

There are two failures that worry me:

a) A total failure of 1 or more sensors. I suppose that 2+ sensors is the most worrying. Until 3 die, one could still use the Vision electronics, albeit with some concern. Still, here a 4th independent sensor might be nice.

b) A total failure of the Vision. Here, it seems to me the parallel monitoring of the 3 cells would be nice.

So, what's more likely - 3 cells failing, but not the 4th , or a total failure of the Vision? I suspect the latter. In which case having the parallel monitor would be best, it seems to me.

That's where I am right now. Am I missing something? It seems 3 in parallel mildly dominates an independent 4th for redundancy, but I may be missing a key failure mode or scenario.

***Beanie*** · 22nd July 2008, 16:01

I've tried both
VR3 as 4th cell and shearwater HUD and 3 cell monitor
I prefer the 3 cell HUD

It shows me what the Vision is seeing
It's perminently connected (vr3 is a bit of a pain)

**sfldiver** · 22nd July 2008, 17:06

Quote: (Originally Posted by aainslie)

I agree that a 4th cell gives true independence, but the question is, does it give the best ouctome under failures of different types?

There are two failures that worry me:

a) A total failure of 1 or more sensors. I suppose that 2+ sensors is the most worrying. Until 3 die, one could still use the Vision electronics, albeit with some concern. Still, here a 4th independent sensor might be nice.

b) A total failure of the Vision. Here, it seems to me the parallel monitoring of the 3 cells would be nice.

So, what's more likely - 3 cells failing, but not the 4th , or a total failure of the Vision? I suspect the latter. In which case having the parallel monitor would be best, it seems to me.

That's where I am right now. Am I missing something? It seems 3 in parallel mildly dominates an independent 4th for redundancy, but I may be missing a key failure mode or scenario.

My Optima does come with two idependent handsets, each monitoring all three cells, plus I have a HUD, which is controlled by the second handset, and I also have the VR3 monitoring the 4th cell. Therefore, here's how I deal with each of the failures:

Failure a)

If one cell dies, the voting logic still averages the two remaining cells and my primary controls my selanoid, plus I can verify the #'s w/ the 4th cell on the VR3.

If two cells die, I would either bailout to oc or use the combination of the remaining cell and the 4th on my VR3 to monitor my PO2 and fly my O2 manually as I ascended.

If three cells fail, I would most likely bailout, but if I was in a tricky situation, I could use the 4th cell on the VR3 to continue monitoring my PO2 and fly the Rebreather manually as I ascended, until I got to a point where bailout was more practical.

Failure b)

If my primary handset failed, which has happened to me, I would fly the Rebreather manually and monitor my PO2 via the HUD and the 4th cell on the VR3.

If both my primary and secondary handset failed, then I would bailout, but if I was in a tricky situation, I could use the 4th cell on the VR3 to continue monitoring my PO2 and fly the Rebreather manually as I ascended, until I got to a point where bailout was more practical.

As you can see, the combination of dual handsets, a HUD and the 4th cell on a VR3 certainly gives you many options to deal with just about any likely scenario.

And that's why I went with the 4th cell VR3 option.

Tienuts · 22nd July 2008, 18:50

I know where Andrew is going with his question, and I have been kicking the same question around myself.

Adrian, as you know we have discussed this at length, and I agree with all of your points, however here is some food for thought - your VR3 is monitored by only one cell. What if this cell is the one that fails? Now obviously, you have the secondary, the HUD, and the VR3 can just be adjusted to a setpoint, but the point is your $500 live PO2 redundancy has just gone out the window.

With preventative measures on cells (regular testing for linear Mv readings, proper storage, and regular replacement,) it's probably far more likely to have 1 cell fail, then 2 during the course of the dive. (Although not impossible.) The argument could be made that if your independent computer is monitoring multiple cells, a failure of 1 cell would not kill your live PO2 monitoring.

Of course with Adrian's setup, you have more cells, and thus added redundancy for O2 monitoring.

**sfldiver** · 22nd July 2008, 21:02

Quote: (Originally Posted by Tienuts)

I know where Andrew is going with his question, and I have been kicking the same question around myself.

Adrian, as you know we have discussed this at length, and I agree with all of your points, however here is some food for thought - your VR3 is monitored by only one cell. What if this cell is the one that fails? Now obviously, you have the secondary, the HUD, and the VR3 can just be adjusted to a setpoint, but the point is your $500 live PO2 redundancy has just gone out the window.

Tony, if my 4th cell goes, then I still have two ways to monitor my PO2, my secondary handset and the HUD; however, at that point I would probably terminate the dive, because I don't like relying on a fixed PO2 settings for deco calculations on the VR3, so I view it as if I lost my backup decompression calculating ability, because I don't have the deco activated on my secondary handset yet and I don't usually carry tables on me.

The real quesion is, how many levels of redundancy is enough or too much, because remember, as you add more components to increase the level of redundancy, you also increase the probability of a failure due to the shear number of components in your setup.

cramerdn · 22nd July 2008, 23:33

Quote: (Originally Posted by sfldiver)

With this scenario, if the #2 sensor failed, it would fail on both computers, so are each of the computers actually independent of each other? Doesn't appear to be the case.

Actually that's the advantage. Now you have a control and you can see that the failure is definately that one cell. Vision is fine, you finish the dive with a cell warning alarm but it still has two cells running. The Shearwater is fine, since it does'nt contol anything.

Quote: (Originally Posted by sfldiver)

Personally, I have a VR3 on my Optima connected to a 4th cell and running a separate deco calculation, based on different software, which I feel gives me an increased safety factor, because if I always ensure that I complete the lengthiest deco obligation, then theoretically, I have a higher probablility of being clean at the end of the dive.

That logic only works for the shallowest of stops which basicly means you are using Buhlman, and also means you will have the largest O2 exposere. Adding length to deep stops could incur more obligation depending on the model. I can't see the benifit in competing deco models. The thing I like about the Shearwater is that it comes very close to the Vision's numbers. Its a back-up not more noise in the decision cycle. If I could change either the Visison or teh Shearwater so they both had the same model, that would be even better.

To me the plumbed in Shearwater is the second back up anyway since the Vision has two independant controllers already. Its main utility for me is I can take my dive history with me if I strap on OC between Rebreather dives so I have running totals of deco and O2.

21st July 2008, 22:48	#1 (permalink)
aainslie So Cal Tech Diver Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Apr 2006 Location: LA Posts: 262	Vision: 4th cell or 3 cell monitor? Greetings all, If you were to get a deco computer independent of your Vision electronics with live PO2 monitoring, which would you prefer and why: 1) A system that monitored a 4th, independent cell, or 2) A system that monitored the three cells already monitored by the Vision electronics? I'm trying to make up my mind between Narced@90's two offerings and can't make up my mind. Thsoe of you with experience in the field, I'd love to hear your feedback about what's good and bad about the two philosophies. __________________ Andrew Ainslie
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22nd July 2008, 00:15	#2 (permalink)
Gill Envy Shearwater Copis Divers Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,348	Re: Vision: 4th cell or 3 cell monitor? I've thought this over quite a bit back when we owned evo's. In fact I had quite a bit of time to think it over when I got locked out of the vision on two trips. I concluded that getting the adapter for three cell monitoring was the way to go, even if you used a 4th cell most of the time. I at least wanted to be able to hook up the secondary to all three cells and run the unit manually (using a shearwater, vr3 etc) if the vision "went blind" on a remote trip. If we had had this capacity the two times the sht hit the fan we might very well still be vision owners as we would have been happy to run the units manually if it meant we could still keep diving on our two big annual trips. The value of a 4th cell never quite caught on for me because of the added logistics and the fact that if something really goes wrong with the electronics, it's best to bail out and return to the surface so it didn't seem to have much advanage. it's what you can do from that point forward that really counts, IMHO. As for the configuration for when things are running normally, you will have to balance how much you value having a truly independent monitoring system on one cell vs the value of having a true back up, but which shares cells. I really like being able to cross check all three cells on a separate screen to see if an errant reading can be verified. a 4th cell might give more piece of mind in an acute meltdown of the vision, in terms of getting you back to the surface, which is of course priority number one but for the rest of the trip, having all three cells will allow you to keep diving, and the value of that can not be underestimated. there has been talk that sharing cells, particularly with an eCCR, which runs on more juice, runs the risk of cross current pollution. I have yet to hear of a real case of this though, and have not had such a problem so far using the shearwater Pursuit and HUD, which are independent computers with separate batteries, sharing all three cells. my 02 cents. g Quote:* (Originally Posted by aainslie) Greetings all, If you were to get a deco computer independent of your Vision electronics with live PO2 monitoring, which would you prefer and why: 1) A system that monitored a 4th, independent cell, or 2) A system that monitored the three cells already monitored by the Vision electronics? I'm trying to make up my mind between Narced@90's two offerings and can't make up my mind. Thsoe of you with experience in the field, I'd love to hear your feedback about what's good and bad about the two philosophies. __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
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22nd July 2008, 13:22	#3 (permalink)
cramerdn Obey my dog! Current Rebreather/s: Evolution Dolphin Other Rebreather/s: Dolphin Join Date: Dec 2006 Location: Townsville QLD Posts: 738	Re: Vision: 4th cell or 3 cell monitor? You coud even put 4 cells in and then monitor 1,2, and 3 with the vision and 2,3,4 with the shearwater. __________________ "Its better to live one day as a tiger than an entire life as a worm." "But who's ever heard of a worm skin rug?"
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22nd July 2008, 14:48	#4 (permalink)
sfldiver S.C.R.U.B.'S Photographer Current Rebreather/s: Optima Other Rebreather/s: Join Date: Jul 2007 Location: Pompano Beach, FL Posts: 819	Re: Vision: 4th cell or 3 cell monitor? Quote: (Originally Posted by cramerdn) You coud even put 4 cells in and then monitor 1,2, and 3 with the vision and 2,3,4 with the shearwater. With this scenario, if the #2 sensor failed, it would fail on both computers, so are each of the computers actually independent of each other? Doesn't appear to be the case. Personally, I have a VR3 on my Optima connected to a 4th cell and running a separate deco calculation, based on different software, which I feel gives me an increased safety factor, because if I always ensure that I complete the lengthiest deco obligation, then theoretically, I have a higher probablility of being clean at the end of the dive. There are advantages to both scenarios, but my vote goes towards setting up the separate computer linked to the 4th cell, as it allows me to have a truly independent backup, and I consequently sleep very well at night. __________________ *Currently piloting & shooting...* Dive Rite O2ptima FX Rigged w/ a Dsix Custom Aluminum Frame, Nomad Wing, Transpac Harness and VR3 Computer w/ VPM-B/E & a 4th Cell Sensor Link.* Canon PowerShot G9 Digital Camera *Rigged in a Patima-PDCH 2008 G9 Aluminum Housing w/ an Inon UWL-100 Achromat Wide Conversion Lens, 2 Inon UCL-165M67 Close-Up Lenses and 2 Inon Z-240 Strobes.
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22nd July 2008, 15:52	#5 (permalink)
aainslie So Cal Tech Diver Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Apr 2006 Location: LA Posts: 262	Re: Vision: 4th cell or 3 cell monitor? I agree that a 4th cell gives true independence, but the question is, does it give the best ouctome under failures of different types? There are two failures that worry me: a) A total failure of 1 or more sensors. I suppose that 2+ sensors is the most worrying. Until 3 die, one could still use the Vision electronics, albeit with some concern. Still, here a 4th independent sensor might be nice. b) A total failure of the Vision. Here, it seems to me the parallel monitoring of the 3 cells would be nice. So, what's more likely - 3 cells failing, but not the 4th , or a total failure of the Vision? I suspect the latter. In which case having the parallel monitor would be best, it seems to me. That's where I am right now. Am I missing something? It seems 3 in parallel mildly dominates an independent 4th for redundancy, but I may be missing a key failure mode or scenario. __________________ Andrew Ainslie Last edited by aainslie : 22nd July 2008 at 15:55.
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22nd July 2008, 16:01	#6 (permalink)
*Beanie* Gallery Administrator Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,312	Re: Vision: 4th cell or 3 cell monitor? I've tried both VR3 as 4th cell and shearwater HUD and 3 cell monitor I prefer the 3 cell HUD It shows me what the Vision is seeing It's perminently connected (vr3 is a bit of a pain) __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk
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22nd July 2008, 17:06	#7 (permalink)
sfldiver S.C.R.U.B.'S Photographer Current Rebreather/s: Optima Other Rebreather/s: Join Date: Jul 2007 Location: Pompano Beach, FL Posts: 819	Re: Vision: 4th cell or 3 cell monitor? Quote: (Originally Posted by aainslie) I agree that a 4th cell gives true independence, but the question is, does it give the best ouctome under failures of different types? There are two failures that worry me: a) A total failure of 1 or more sensors. I suppose that 2+ sensors is the most worrying. Until 3 die, one could still use the Vision electronics, albeit with some concern. Still, here a 4th independent sensor might be nice. b) A total failure of the Vision. Here, it seems to me the parallel monitoring of the 3 cells would be nice. So, what's more likely - 3 cells failing, but not the 4th , or a total failure of the Vision? I suspect the latter. In which case having the parallel monitor would be best, it seems to me. That's where I am right now. Am I missing something? It seems 3 in parallel mildly dominates an independent 4th for redundancy, but I may be missing a key failure mode or scenario. My Optima does come with two idependent handsets, each monitoring all three cells, plus I have a HUD, which is controlled by the second handset, and I also have the VR3 monitoring the 4th cell. Therefore, here's how I deal with each of the failures: Failure a) If one cell dies, the voting logic still averages the two remaining cells and my primary controls my selanoid, plus I can verify the #'s w/ the 4th cell on the VR3. If two cells die, I would either bailout to oc or use the combination of the remaining cell and the 4th on my VR3 to monitor my PO2 and fly my O2 manually as I ascended. If three cells fail, I would most likely bailout, but if I was in a tricky situation, I could use the 4th cell on the VR3 to continue monitoring my PO2 and fly the Rebreather manually as I ascended, until I got to a point where bailout was more practical. Failure b) If my primary handset failed, which has happened to me, I would fly the Rebreather manually and monitor my PO2 via the HUD and the 4th cell on the VR3. If both my primary and secondary handset failed, then I would bailout, but if I was in a tricky situation, I could use the 4th cell on the VR3 to continue monitoring my PO2 and fly the Rebreather manually as I ascended, until I got to a point where bailout was more practical. As you can see, the combination of dual handsets, a HUD and the 4th cell on a VR3 certainly gives you many options to deal with just about any likely scenario. And that's why I went with the 4th cell VR3 option. __________________ *Currently piloting & shooting...* Dive Rite O2ptima FX Rigged w/ a Dsix Custom Aluminum Frame, Nomad Wing, Transpac Harness and VR3 Computer w/ VPM-B/E & a 4th Cell Sensor Link.* Canon PowerShot G9 Digital Camera *Rigged in a Patima-PDCH 2008 G9 Aluminum Housing w/ an Inon UWL-100 Achromat Wide Conversion Lens, 2 Inon UCL-165M67 Close-Up Lenses and 2 Inon Z-240 Strobes.
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22nd July 2008, 18:50	#8 (permalink)
Tienuts Chief Prankster Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2007 Location: Fort Lauderdale Posts: 299	Re: Vision: 4th cell or 3 cell monitor? I know where Andrew is going with his question, and I have been kicking the same question around myself. Adrian, as you know we have discussed this at length, and I agree with all of your points, however here is some food for thought - your VR3 is monitored by only one cell. What if this cell is the one that fails? Now obviously, you have the secondary, the HUD, and the VR3 can just be adjusted to a setpoint, but the point is your $500 live PO2 redundancy has just gone out the window. With preventative measures on cells (regular testing for linear Mv readings, proper storage, and regular replacement,) it's probably far more likely to have 1 cell fail, then 2 during the course of the dive. (Although not impossible.) The argument could be made that if your independent computer is monitoring multiple cells, a failure of 1 cell would not kill your live PO2 monitoring. Of course with Adrian's setup, you have more cells, and thus added redundancy for O2 monitoring.
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22nd July 2008, 21:02	#9 (permalink)
sfldiver S.C.R.U.B.'S Photographer Current Rebreather/s: Optima Other Rebreather/s: Join Date: Jul 2007 Location: Pompano Beach, FL Posts: 819	Re: Vision: 4th cell or 3 cell monitor? Quote: (Originally Posted by Tienuts) I know where Andrew is going with his question, and I have been kicking the same question around myself. Adrian, as you know we have discussed this at length, and I agree with all of your points, however here is some food for thought - your VR3 is monitored by only one cell. What if this cell is the one that fails? Now obviously, you have the secondary, the HUD, and the VR3 can just be adjusted to a setpoint, but the point is your $500 live PO2 redundancy has just gone out the window. Tony, if my 4th cell goes, then I still have two ways to monitor my PO2, my secondary handset and the HUD; however, at that point I would probably terminate the dive, because I don't like relying on a fixed PO2 settings for deco calculations on the VR3, so I view it as if I lost my backup decompression calculating ability, because I don't have the deco activated on my secondary handset yet and I don't usually carry tables on me. The real quesion is, how many levels of redundancy is enough or too much, because remember, as you add more components to increase the level of redundancy, you also increase the probability of a failure due to the shear number of components in your setup. __________________ *Currently piloting & shooting...* Dive Rite O2ptima FX Rigged w/ a Dsix Custom Aluminum Frame, Nomad Wing, Transpac Harness and VR3 Computer w/ VPM-B/E & a 4th Cell Sensor Link.* Canon PowerShot G9 Digital Camera *Rigged in a Patima-PDCH 2008 G9 Aluminum Housing w/ an Inon UWL-100 Achromat Wide Conversion Lens, 2 Inon UCL-165M67 Close-Up Lenses and 2 Inon Z-240 Strobes.
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22nd July 2008, 23:33	#10 (permalink)
cramerdn Obey my dog! Current Rebreather/s: Evolution Dolphin Other Rebreather/s: Dolphin Join Date: Dec 2006 Location: Townsville QLD Posts: 738	Re: Vision: 4th cell or 3 cell monitor? Quote: (Originally Posted by sfldiver) With this scenario, if the #2 sensor failed, it would fail on both computers, so are each of the computers actually independent of each other? Doesn't appear to be the case. Actually that's the advantage. Now you have a control and you can see that the failure is definately that one cell. Vision is fine, you finish the dive with a cell warning alarm but it still has two cells running. The Shearwater is fine, since it does'nt contol anything. Quote: (Originally Posted by sfldiver) Personally, I have a VR3 on my Optima connected to a 4th cell and running a separate deco calculation, based on different software, which I feel gives me an increased safety factor, because if I always ensure that I complete the lengthiest deco obligation, then theoretically, I have a higher probablility of being clean at the end of the dive. That logic only works for the shallowest of stops which basicly means you are using Buhlman, and also means you will have the largest O2 exposere. Adding length to deep stops could incur more obligation depending on the model. I can't see the benifit in competing deco models. The thing I like about the Shearwater is that it comes very close to the Vision's numbers. Its a back-up not more noise in the decision cycle. If I could change either the Visison or teh Shearwater so they both had the same model, that would be even better. To me the plumbed in Shearwater is the second back up anyway since the Vision has two independant controllers already. Its main utility for me is I can take my dive history with me if I strap on OC between Rebreather dives so I have running totals of deco and O2. __________________ "Its better to live one day as a tiger than an entire life as a worm." "But who's ever heard of a worm skin rug?"
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