VR3 Manual Errors - High PPO2 Alarm and CNS Calculations [Archive]

Mark F L Davison

05-05-2004, 20:36

VR3 Manual Errors

I see that we have some VR3 users on this forum. So I will repeat here my original post that I have on Delta P's forum. All VR3 users should know about the following errors. Both these errors relate to how the manual states the VR3 will function and what it does in practice.

High PPO2 Alarm

The first and potentially more serious error is the High PPO2 alarm. The manual indicates that the High PPO2 alarm activates at 1.6, whereas it only operates at 1.8. I will refrain from a long argument about what is a safe PPO2 level. What I will remind you all that most mainstream diver training organisations (including BSAC) suggest that 1.4 should be the limit and a few technical agencies will extend the maximum to 1.6. I will also point out that changing the MOD / PPO2 limit relevant for each gas only changes the depth at which you are advised to make a switch, it does not change the High PPO2 alarm level. This is a common misunderstanding by VR3 users.

CNS Calculation

The manual indicates that the VR3 degrades the CNS in accordance with NOAA?s system of 90 minute half life time. This is the standard that most diving training agencies use, although BSAC, who like to be different, use a half life time of 2 hours. However the actual degrade is 0.5% per minute which equates to 30% per hour. This can have a serious effect on your residual CNS, for example if you collect 60% CNS at the end of a dive and dive 2 hours later, the NOAA?s calculation would give you a starting CNS of 30%, whereas the VR3 would give you 0%.

Delta P?s View

Delta P are aware of these issues and have stated that they will correct the manual, rather than make any changes to the software as they are content with the calculations.

My View

My view is that firstly I want to know what my dive computer is telling me and what safety related information it?ll give me. I am concerned that the manual is wrong; it indicates a lack of quality control, which is great shame on such an innovative product. A lack of adequate quality control on a product used as a mixed gas dive computer must be of some concern. Regardless of any of these issues I feel that divers, like you, who use the VR3 should be fully aware of these issues.

These errors were discovered by me conducting a number of dives over 2 weeks and extensive reading of the manual and use of the simulator mode.

Keith Lawrence(BSAC)

05-05-2004, 22:29

Dear All

Posts such as Mark?s always create a dilemma for forum moderators. Whilst not wishing to suppress what could be important information to divers I have to be aware for the potential of incorrect information being posted to our forums.

On this occasion I have taken the view that Mark?s post should remain, but I have informed the makers of the VR3 computer of its presence and invited them to reply publicly to the comments.

The presence of Mark?s post on a BSAC forum must not be taken as official endorsement of the comments by the BSAC. All posts by individuals to our forums are the personal opinion of the contributors and may not necessarily represent the policy and views of the BSAC.

Keith Lawrence
BSAC Council Member
IT Team Leader

nick kay

06-05-2004, 08:56

Unless I'm mistaken, the VR3 and ProPlanner are "similar"???

Do the issues relating to CNS calculations also therefore refer to ProPlanner???

Philip Smith

06-05-2004, 21:47

CNS Calculation

The manual indicates that the VR3 degrades the CNS in accordance with NOAA?s system of 90 minute half life time. This is the standard that most diving training agencies use, although BSAC, who like to be different, use a half life time of 2 hours. However the actual degrade is 0.5% per minute which equates to 30% per hour. This can have a serious effect on your residual CNS, for example if you collect 60% CNS at the end of a dive and dive 2 hours later, the NOAA?s calculation would give you a starting CNS of 30%, whereas the VR3 would give you 0%.

I am not familiar with the VR3, but there could be a misunderstanding about exponential decay here. A decay with a half-time of 90 min is equivalent to a decrease of approximately 0.77% per minute applied cumulatively (like compound interest in reverse). At that rate, in 2 hours, 60% would decline to 24% (not 30% -- since that is half the original value, it would take the half-time, i.e. 1.5 hours). It is not clear where the figure of 0.5% per minute comes from, but if it represents an exponential decay rather than a linear decline, it is equivalent to a half-time of 138 minutes (i.e. slower than the recommendation of NOAA and BSAC).

On the other hand, if the VR3 really does have a CNS% half-time of 90 minutes, the rate of decline calculated (incorrectly) on a linear basis over 2 hours would appear to be 0.5% per minute.

The actual half-time could be calculated from two observations of CNS%, x0 and x1, taken at times t0 and t1, respectively, from the following formula:
half-time = LN(0.5)*(t1 - t0)/LN(x1/x0)

Philip Smith

Keith Lawrence(BSAC)

06-05-2004, 22:15

Dear All

I have received the following from Simon Pridmore of Delta P Technology which he has asked me to post ?

?
CNS degradation on the VR3 now follows the NOAA 90 minute half-time protocol. Some versions of the software have featured a more complex protocol but we have now returned to the comparatively straightforward NOAA protocol referred to in the manual.

A high PO2 warning comes up on the VR3's screen when the PO2 of the selected gas reaches dangerous levels and you have no gas with a lower O2 content in your gaslist to switch to. This level is presently set to 1.8. Our view is that it is the diver's responsibility to analyse the gas in his cylinders and keep to his desired MOD.

VR3 users will be happy to hear that a brand new manual will be released later this month and should be available shortly afterwards as a downloadable pdf from our website www.vr3.co.uk
?

Thank you Mark and Delta P, I feel that a balance has been struck on our forums. I will not comment further on this, I?ll leave it to you all to sort out.

Kind regards

Keith Lawrence

mark f l davison

06-05-2004, 22:26

Philip

I'll try to be clear, '0.5% per minute' is exactly what it states, every 2 minutes the value drops by 1%, So afer 10 minutes it drops by 5%. My point is that the VR3 does not do a half life time calculation of any sort. I'll do a different example. Using the NOAA example, dive results in a CNS of 60%, 90 minutes later NOAA value = 30%, VR3 calulates this as 15% (0.5%per minute = 45% - 60-45=15). BSAC and IANTD manual calulations only drop the residual value after every 2 hours or in IANTD (NOAA) case 90 minutes.

My point is the VR3 does not do what the manual states. Delta P have acknowledged this point, but they have yet to 'correct' the manual.

:=CNS Calculation
:=
:=The manual indicates that the VR3 degrades the CNS in accordance with NOAA?s system of 90 minute half life time. This is the standard that most diving training agencies use, although BSAC, who like to be different, use a half life time of 2 hours. However the actual degrade is 0.5% per minute which equates to 30% per hour. This can have a serious effect on your residual CNS, for example if you collect 60% CNS at the end of a dive and dive 2 hours later, the NOAA?s calculation would give you a starting CNS of 30%, whereas the VR3 would give you 0%.

I am not familiar with the VR3, but there could be a misunderstanding about exponential decay here. A decay with a half-time of 90 min is equivalent to a decrease of approximately 0.77% per minute applied cumulatively (like compound interest in reverse). At that rate, in 2 hours, 60% would decline to 24% (not 30% -- since that is half the original value, it would take the half-time, i.e. 1.5 hours). It is not clear where the figure of 0.5% per minute comes from, but if it represents an exponential decay rather than a linear decline, it is equivalent to a half-time of 138 minutes (i.e. slower than the recommendation of NOAA and BSAC).

On the other hand, if the VR3 really does have a CNS% half-time of 90 minutes, the rate of decline calculated (incorrectly) on a linear basis over 2 hours would appear to be 0.5% per minute.

The actual half-time could be calculated from two observations of CNS%, x0 and x1, taken at times t0 and t1, respectively, from the following formula:
half-time = LN(0.5)*(t1 - t0)/LN(x1/x0)

Philip Smith

Nigel Hewitt

07-05-2004, 07:50

> My point is the VR3 does not do what the manual states. Delta P have acknowledged this point, but they have yet to 'correct' the manual.

Oh get real. Whinging about the VR3 manual is like whinging that the sky is blue, it is still blue, no body cares that it is blue, nobody is doing anything about it. Blue! Any description of what the users think of the VR3 manual will have poor old Keith going 'please moderate you language gentlemen' at us.

Aside from the manual it's not a bad computer... Just don't use it on deep air. You need all your brain on line to work your way through its 'features'.

OK the deep stops stuff annoys me. I want a computer to plan me shortest time to surface when I set it to 0% conservatism not get bent because its idea of a deep stop is different from that of the software I planned my slate with. "USE TABLES" is not a helpful message when you know you are well inside a Bulhman profile. Yes I have bent it three times.

nigelH

mark f l davison

08-05-2004, 14:53

Nigel

It looks like we might get a new VR3 manual, so perhaps it does pay to provide feedback rather than accepting the status quo.

:=> My point is the VR3 does not do what the manual states. Delta P have acknowledged this point, but they have yet to 'correct' the manual.

Oh get real. Whinging about the VR3 manual is like whinging that the sky is blue, it is still blue, no body cares that it is blue, nobody is doing anything about it. Blue! Any description of what the users think of the VR3 manual will have poor old Keith going 'please moderate you language gentlemen' at us.

Aside from the manual it's not a bad computer... Just don't use it on deep air. You need all your brain on line to work your way through its 'features'.

OK the deep stops stuff annoys me. I want a computer to plan me shortest time to surface when I set it to 0% conservatism not get bent because its idea of a deep stop is different from that of the software I planned my slate with. "USE TABLES" is not a helpful message when you know you are well inside a Bulhman profile. Yes I have bent it three times.

nigelH

Nigel Hewitt

08-05-2004, 15:06

> It looks like we might get a new VR3 manual, so perhaps it does pay to provide feedback rather than accepting the status quo.

But that's been *going to happen* for some time so don't hold your breath that your new items will be in it. I suspect that we'll all download it, read it, and go *Gosh! I didn't know it could do that!* at least once. eg: the profiles: I'm sure they must be some use for something.

nigelH

Matt

10-05-2004, 15:51

:=> It looks like we might get a new VR3 manual, so perhaps it does pay to provide feedback rather than accepting the status quo.

But that's been *going to happen* for some time so don't hold your breath that your new items will be in it.

One reason the manual has been delayed is that the VR3 software has evolved regularly since it was originally launched. I guess there is a balance to strike between developing new features and writting manuals.

eg: the profiles: I'm sure they must be some use for something.

IIRC The Profiles feature was added after feedback from users (mainly technical instructors), who variously dived Nitrox / Trimix / Rebreather with standard mixes. The Profile feature allows 3 seperate gas sets to be maintained for 3 different activities.

BTW The deep stop algorithm was made mandatory after real world trials of the current model.

Nigel Hewitt

10-05-2004, 16:24

> One reason the manual has been delayed is that the VR3 software has evolved regularly since it was originally launched. I guess there is a balance to strike between developing new features and writting manuals.

In my part of the computer business undocumented features are called bugs. Life support equipment, like the death support stuff I've worked on, really does need to have accurate instructions. Manuals should track with software revisions.

> BTW The deep stop algorithm was made mandatory after real world trials of the current model.

I'm sure it's wonderful if you are diving the computer's plan but if you're diving the same slate as everybody else in the group it just gets bent. I guess I have to live with it. At least it carries on giving me the time and depth and doesn't go into sulk mode like some.

nigelH

Firestorm

10-05-2004, 16:36

:=> One reason the manual has been delayed is that the VR3 software has evolved regularly since it was originally launched. I guess there is a balance to strike between developing new features and writting manuals.

In my part of the computer business undocumented features are called bugs. Life support equipment, like the death support stuff I've worked on, really does need to have accurate instructions. Manuals should track with software revisions.

:=> BTW The deep stop algorithm was made mandatory after real world trials of the current model.

I'm sure it's wonderful if you are diving the computer's plan but if you're diving the same slate as everybody else in the group it just gets bent. I guess I have to live with it. At least it carries on giving me the time and depth and doesn't go into sulk mode like some.

nigelH

It seems the way you dive the VR3 is a bit pointless really if all you're using it for is an expensive dive timer & possibly ppo2 monitor.
If you want to use a runtime alongside it then why not just do a diveplan and make a runtime from that. At least the VR3 will base the plan on your past/recent dive history.

F.

Nigel Hewitt

10-05-2004, 19:25

>> I'm sure it's wonderful if you are diving the computer's plan but if you're diving the same slate as everybody else in the group it just gets bent. I guess I have to live with it. At least it carries on giving me the time and depth and doesn't go into sulk mode like some.

>It seems the way you dive the VR3 is a bit pointless really if all you're using it for is an expensive dive timer & possibly ppo2 monitor.

>If you want to use a runtime alongside it then why not just do a diveplan and make a runtime from that. At least the VR3 will base the plan on your past/recent dive history.

Oh come on. I do dive other profiles than that. Up to 40 meters I'll just jump in the water with a computer, timer and tables in my pocket in case it all clangs up. It's just that it inserts what are effectively arbitrary stops that I can't turn off so it does not provide a useful backup on a planned dive.
There may be heroes that go 60m that way but I'm not brave enough yet. I want to know my buddy is on the same schedule and we have the backup gas as the deco rises. I may well change but I'm a newbie when it comes to deep (in my terms) CCR diving.

I like the VR3 as a computer. It does a lot of things I want. It just has some very unnecessary quirks that don't seem to fit its target audience.

Maybe it's just me. Too many years in the computer business mean that I do not trust computers enough to let them be 'in charge'.

nigelH

Firestorm

10-05-2004, 20:21

:=>> I'm sure it's wonderful if you are diving the computer's plan but if you're diving the same slate as everybody else in the group it just gets bent. I guess I have to live with it. At least it carries on giving me the time and depth and doesn't go into sulk mode like some.

:=>It seems the way you dive the VR3 is a bit pointless really if all you're using it for is an expensive dive timer & possibly ppo2 monitor.

:=>If you want to use a runtime alongside it then why not just do a diveplan and make a runtime from that. At least the VR3 will base the plan on your past/recent dive history.

Oh come on.

Now, now Nigel keep your hair on!

I do dive other profiles than that. Up to 40 meters I'll just jump in the water with a computer, timer and tables in my pocket in case it all clangs up. It's just that it inserts what are effectively arbitrary stops that I can't turn off so it does not provide a useful backup on a planned dive.

But you know that the unit inserts these stops so you can plan for them with your buddy. Like I said take a runtime from your VR3 diveplan then both you & your buddy can dive to that. So yes you can use it as a useful backup.

There may be heroes that go 60m that way but I'm not brave enough yet. I want to know my buddy is on the same schedule and we have the backup gas as the deco rises. I may well change but I'm a newbie when it comes to deep (in my terms) CCR diving.

I wasn't aware that we were talking about 60m "hero" diving. But yet again if you've planned the dive as I've said above there isn't a problem.

I like the VR3 as a computer. It does a lot of things I want. It just has some very unnecessary quirks that don't seem to fit its target audience.

Maybe it's just me. Too many years in the computer business mean that I do not trust computers enough to let them be 'in charge'.

nigelH

Personaly I don't mind the deep stops, however it would be useful to be able to disable the feature for when I'm diving with someone who hasn't got a VR3 so as to ascend together or not load a buddy's computer while he/she is waiting for me to do the deep stops.

F.

Nigel Hewitt

11-05-2004, 07:41

> Now, now Nigel keep your hair on!

Too late. Too late for me. (weeps theatrically)

>I wasn't aware that we were talking about 60m "hero" diving.

Sorry. I rather assumed it rather than saying it. I can't see anybody shelling out for a VR3 if all they do is 30m stuff so I guessed.

> Personaly I don't mind the deep stops, however it would be useful to be able to disable the feature for when I'm diving with someone who hasn't got a VR3 so as to ascend together or not load a buddy's computer while he/she is waiting for me to do the deep stops.

I agree about deep stops, they are clearly a good idea, but if the software that wrote the slate we all carry (up to 7 divers) had different deep stops (eg: Pyle) then me suddenly wanting to break and do a little extra hang that junks all our run times isn't going to happen. Conversely if we have a fault early in the dive being able to bail out on the computer is a big bonus as is the 'wreck? what wreck?' bottom of shot line scenario.

I quite like the thing but I wanted a tool and it wants to be nanny. I put the conservatism on the slate and I want the computer to be on the edge. It is easy to pad a stop to get more safety margin. If I have the time and gas I normally overrun my shallowest stop where possible. Bending the computer on something trivial like exactly what depth do you do the deep stop at when there is no agreement on this is annoying. If I blow the Buhlmann algorithm then yes, it has every right to give up on me, it can no longer do sensible maths but this isn't what I'm talking about.

*sigh*

nigelH

Matt

11-05-2004, 14:55

In my part of the computer business undocumented features are called bugs. Life support equipment, like the death support stuff I've worked on, really does need to have accurate instructions. Manuals should track with software revisions.

Personally I think you are overstateing the case. I don't class the VR3 as life support equipment. It provides a decompression forecast, that's all. The life support equipment is the grey stuff between your ears. The core functions of the VR3 are and always have been documented.

I guess DeltaP have struggled at times to communicate how the unit works in a manner which the user understands. I can sympathise as I spend a great deal of my time attempting to translate what is written in a developers notes or a help file into something comprehendable to a user. Personally I don't see much point in paying for manuals unless they are usable by the users.

Manuals are a very limited method of providing user support, there are far better ways. DeltaP have set up a self help forum at <a href="http://www.vr3.co.uk" >http://www.vr3.co.uk</a> They have also dedicated support staff contactable by e-mail, fax and telephone. Personally I think both of these facilities are both more cost effective and plain more effective than continually republishing a manual which people will still get confused with.

:=> BTW The deep stop algorithm was made mandatory after real world trials of the current model.

I'm sure it's wonderful if you are diving the computer's plan but if you're diving the same slate as everybody else in the group it just gets bent. I guess I have to live with it.

My point was that the decision to make the deep stop algorithm mandatory was the result of actual dives. The deep stops are part of the forecast that the VR3 provides. If you want to use a different deep stop algorithm then the VR3 cautions 'Use Tables' which is effectively what you are doing anyway.

Nigel Hewitt

11-05-2004, 15:14

> Manuals are a very limited method of providing user support, there are far better ways. DeltaP have set up a self help forum at <a href="http://www.vr3.co.uk" >http://www.vr3.co.uk</a> They have also dedicated support staff contactable by e-mail, fax and telephone. Personally I think both of these facilities are both more cost effective and plain more effective than continually republishing a manual which people will still get confused with.

I don't think we are going to agree here. Email, fax and telephone have their place and I'm pleased they are there but when I'm sitting on a boat next weekend, feeling rather queezy but that's me on a boat, I don't want to know I can email my problem off and somebody will deal with it first thing on Monday I need to read the answer now.

I've written manuals and I know it's definitly not a fun job but it needs to be done and not skimped on. We are all looking forward to the new manual and the start of a whole new chapter for the users with DeltaP. As I say I like the computer. If it went south I'd replace it with another C4 but it could so easily offer more solutions to real diving problems.

Now I'd better drop the subject or KeithL will give me a detention or something for monopolising his boards for a personal rant.

nigelH

Matt

11-05-2004, 16:00

:=>I wasn't aware that we were talking about 60m "hero" diving.

Sorry. I rather assumed it rather than saying it. I can't see anybody shelling out for a VR3 if all they do is 30m stuff so I guessed.

The VR3 was originally concieved for divers that consider 60m to be rather tame! It has turned out to be attractive to a far wider audience. No doubt the increase in SCR and CCR diving has played a part in the VR3s acceptance into advanced recreational and mainstream technical diving. Personally I realised the VR3s value after a month diving in Truk and Bikini using an original brick VR3. My other dive computer started talking gibberish on day 4 and my attempts to manually track tissue codes degraded to guestimates.

Interestingly the people that the VR3 was originally intended for are now using it to push the envelope even further. Cave divers like Dr Jerome Meynie are completeing profiles which would be pretty much impossible to plan in advance.

:=> Personaly I don't mind the deep stops, however it would be useful to be able to disable the feature for when I'm diving with someone who hasn't got a VR3 so as to ascend together or not load a buddy's computer while he/she is waiting for me to do the deep stops.

I agree about deep stops, they are clearly a good idea, but if the software that wrote the slate we all carry (up to 7 divers) had different deep stops (eg: Pyle) then me suddenly wanting to break and do a little extra hang that junks all our run times isn't going to happen.

The point has already been made that you can use the Dive Plan function of the VR3 to write up your slate and come up with a mutually aggreeable schedule with your team. The VR3 is pretty close to Pyle anyhow.

I quite like the thing but I wanted a tool and it wants to be nanny. I put the conservatism on the slate and I want the computer to be on the edge. It is easy to pad a stop to get more safety margin.

It appears to me that some VR3 users expect more of it than they would from any other dive computer, mixed gas or otherwise. That is pretty interesting in it's own right. From what I can make out you're looking for an electronic slate which will allow you to put in your own schedule, monitor it and compare to an agressive Buhlmann schedule.

If I have the time and gas I normally overrun my shallowest stop where possible. Bending the computer on something trivial like exactly what depth do you do the deep stop at when there is no agreement on this is annoying. If I blow the Buhlmann algorithm then yes, it has every right to give up on me, it can no longer do sensible maths but this isn't what I'm talking about.

This comes back to the forecast the VR3 considers safe. The deep stops are mandatory because the algorithm judges them to be as essential as the shallow stops. You get the same caution for ignoring deep stops as you do for ignoring shallow stops. Keep in mind that unlike most of the other deco planning algorithms out there, the VR3 algorithm is a direct result of the developers own diving. Maybe next time you are at a dive show you can look up Kevin Gurr and Phil Short. I expect they would be willing to both discuss why VR3 deep stops are mandatory and express an oppinion on other peoples algorithms.

Returning to the point about feedback, I would suggest that if you want to be able to disable deep stops, you let DeltaP know. Much of the VR3 development has been driven by user requests over the years.

Matt

11-05-2004, 16:19

when I'm sitting on a boat next weekend, feeling rather queezy but that's me on a boat, I don't want to know I can email my problem off and somebody will deal with it first thing on Monday I need to read the answer now.

Obviously the first thing is learn to use it before you need it. Having been involved with VR3s since the brick launched, I often get approached on boats by people who want to know what they are doing wrong. 9.9 times out of 10, the answer is in the manual and the user either has not read the manual at all or failed to comprehend it. Admittedly what constitutes a long push and how to fit the strap are not mentioned in the manual ;-)

I've written manuals and I know it's definitly not a fun job but it needs to be done and not skimped on.

I am sure my background in support influences my thinking, but I would rather see my money spent on features than on manuals which get read once and variously thrown away, blown overboard or chundered over ;-))

Now I'd better drop the subject or KeithL will give me a detention or something for monopolising his boards for a personal rant.

Heck we are both BSAC members...at least we are not ranting about BSAC for a change :-)))

Nigel Hewitt

11-05-2004, 17:34

> I am sure my background in support influences my thinking, but I would rather see my money spent on features than on manuals which get read once and variously thrown away, blown overboard or chundered over ;-))

Point.

>> Now I'd better drop the subject or KeithL will give me a detention or something for monopolising his boards for a personal rant.

> Heck we are both BSAC members...at least we are not ranting about BSAC for a change :-)))

I'm sure I could manage a BSAC rant if I tried. *sigh*
Oh well. Catch up with you some time. After that lot I probably owe you a beer.

nigelH

Mike Rowley

12-05-2004, 11:11

:=> I am sure my background in support influences my thinking, but I would rather see my money spent on features than on manuals which get read once and variously thrown away, blown overboard or chundered over ;-))

That has made me feel most inadequate. I have to confess that I found the manual almost unuseable, but then I'm not great at computers. I usually get my son to explain things to me, including the VR3!

I have only two critisisms of the VR3. I would really like a one button OC bailout function. When one needs to bailout there is usually a feeces/fan interface and mental task loading goes sky high. A single (one press) button facility to activate pre-programmed OC bailout gasses would be ideal.

I would also like larger display fonts without loosing information from the main screen in CCR mode. Either that or Delta P to offer arm lengthening proceedures to over 50s as a free extra.

The comfort of the 4th cell is something I would not be without.

:=> Heck we are both BSAC members...at least we are not ranting about BSAC for a change :-)))

I'm sure I could manage a BSAC rant if I tried. *sigh*
Oh well. Catch up with you some time. After that lot I probably owe you a beer.

All change on May 15 chaps. New era again, lets have some optimism! Things can only get better. Now who said that?

Mike

Nigel Hewitt

12-05-2004, 12:19

> I have only two critisisms of the VR3. I would really like a one button OC bailout function. When one needs to bailout there is usually a feeces/fan interface and mental task loading goes sky high. A single (one press) button facility to activate pre-programmed OC bailout gasses would be ideal.

Woo. By the time you get to OC bail out, ie: staying off the loop, you are in so much poo that the computer is not much more. My bail out is usually the same as my DIL so it's what? hold left, squeeze both, hold right from memory. Matt will put me right, he's read the manual and remembers it. 8-)

> I would also like larger display fonts without loosing information from the main screen in CCR mode. Either that or Delta P to offer arm lengthening proceedures to over 50s as a free extra.

LOL! Lenses in a mask are your friend. I'm going from top half distance only to full bifocals soon and the VR3s small print will be part of the reason.

A picture of what the 'large fonts' add-on looks like on the web site would help. At 40 quid do beople buy it unseen?

> The comfort of the 4th cell is something I would not be without.

Not for me. If the other three are starting to disagree what makes the fourth one any better? I certainly don't want my deco planned on just one cell when I know how much the three I have wave about.

> All change on May 15 chaps. New era again, lets have some optimism! Things can only get better. Now who said that?

15 May?
When is the Internet Browser module coming out? That's what we need for a boring deco stop. GPRS from the DSMB. Post the dive report to the web *before* finishing the dive.

nigelH

Mike Rowley

12-05-2004, 17:47

:=> I have only two critisisms of the VR3. I would really like a one button OC bailout function. When one needs to bailout there is usually a feeces/fan interface and mental task loading goes sky high. A single (one press) button facility to activate pre-programmed OC bailout gasses would be ideal.

Woo. By the time you get to OC bail out, ie: staying off the loop, you are in so much poo that the computer is not much more. My bail out is usually the same as my DIL so it's what? hold left, squeeze both, hold right from memory. Matt will put me right, he's read the manual and remembers it. 8-)

:=> I would also like larger display fonts without loosing information from the main screen in CCR mode. Either that or Delta P to offer arm lengthening proceedures to over 50s as a free extra.

LOL! Lenses in a mask are your friend. I'm going from top half distance only to full bifocals soon and the VR3s small print will be part of the reason.

Bin there - done that!

A picture of what the 'large fonts' add-on looks like on the web site would help. At 40 quid do beople buy it unseen?

I have the Blind Gits Mode and dont use it because you loose valuable information from the main screen.

:=> The comfort of the 4th cell is something I would not be without.

Not for me. If the other three are starting to disagree what makes the fourth one any better? I certainly don't want my deco planned on just one cell when I know how much the three I have wave about.
The main value of the 4th cell is confirmation of PO2 readings, not deco. With the VR3 set at 1.3 and no cell there is not a great deal of difference in deco schedules, particularly with square profile dives.
Don't forget, when you dil flush this only tells you that the cells are or are not liear at that PO2. It does not necessarily mean that they will still be linear at a higher PO2 and they usually become non linear at the higher PO2s.
The 4th cell has a lot less to do than the rebreather cells and in my experience is a bit steadier.
:=> All change on May 15 chaps. New era again, lets have some optimism! Things can only get better. Now who said that?

15 May?
When is the Internet Browser module coming out? That's what we need for a boring deco stop. GPRS from the DSMB. Post the dive report to the web *before* finishing the dive.

I have enough trouble working my chart programme on my own! Wish I could remember that password.

Nigel Hewitt

12-05-2004, 18:28

> The 4th cell has a lot less to do than the rebreather cells and in my experience is a bit steadier.

That statement perplexes me. Can you clarify? All the cells are in the same gas flow so they all generate the same internal current of which only a tiny fraction is sampled off.

The thing about the fourth cell holders that worries me is that the front end of the cell and its back end are not likely to be at the same temperature. This is a big NO-NO for galvanic cells with simple thermister temperature compensation.

nigelH

Mike Rowley

12-05-2004, 23:17

Mike Rowley

12-05-2004, 23:34

:=> The 4th cell has a lot less to do than the rebreather cells and in my experience is a bit steadier.

That statement perplexes me. Can you clarify? All the cells are in the same gas flow so they all generate the same internal current of which only a tiny fraction is sampled off.

Tests with an osiloscope have shown that the telydine RB22 BUD cells in the Inspiration experience a maximum current draw in the region of 6 times their rated maximum. As it has been explained to me, this tends to occur when the solenoid fires. I think you can draw your own conclusions as to what is happening here. The 4th cell provides a valuable comparison and verification since it is not subjected to this excess current draw.
For instance, if you have a 1 high - 2 low situation where the one high is actually the correctly functioning cell the 4th cell will help confirm this and you can run manual back to the surface. These malfunctions are rare but have been known to happen.
The thing about the fourth cell holders that worries me is that the front end of the cell and its back end are not likely to be at the same temperature. This is a big NO-NO for galvanic cells with simple thermister temperature compensation.

My experience (Approx 2 years with the 4th cell) has been that the cell tracks the Inspiration cells quite closely. Others I know have a similar experience. Usually it will read approximately 0.01 low which gives a small safety margin in terms of decompression. I don't think there is a significant temperature difference between the two sides of the cell since the gas passes through the ballance holes and the plastic holder with its silicon sealant is a form of insulation from ambient temperature. Some people are now hard wiring the 4th cell into the lid and I understand that APD are about to produce an extended cell holder to facilitate this.

Matt

13-05-2004, 00:18

:=> I have only two critisisms of the VR3. I would really like a one button OC bailout function. When one needs to bailout there is usually a feeces/fan interface and mental task loading goes sky high. A single (one press) button facility to activate pre-programmed OC bailout gasses would be ideal.

Woo. By the time you get to OC bail out, ie: staying off the loop, you are in so much poo that the computer is not much more. My bail out is usually the same as my DIL so it's what? hold left, squeeze both, hold right from memory. Matt will put me right, he's read the manual and remembers it. 8-)

LOL. I Don't do the rebreather thing but that sounds about right. The gas interface is designed to avoid an accidental gas switch, the inconvenience is quite deliberate. A couple people have struggled with the new DVO (Dive Options) menu and found themselves reprogramming the backlight rather than switching gas ;-)

:=> I would also like larger display fonts without loosing information from the main screen in CCR mode. Either that or Delta P to offer arm lengthening proceedures to over 50s as a free extra.

LOL! Lenses in a mask are your friend. I'm going from top half distance only to full bifocals soon and the VR3s small print will be part of the reason.

The Big Graphics (AKA Blind Git) mode, loses the CNS and TTS fields from the display. To have BG and the extra info would require a bigger screen and a bigger, heavier case to house it. The original VR3 was criticised because of it's weight and size, so I guess you can't please everyone :-)

A picture of what the 'large fonts' add-on looks like on the web site would help.

If I get time I will post something up.

At 40 quid do beople buy it unseen?

There's a joke there somewhere 8-)

:=> All change on May 15 chaps. New era again, lets have some optimism! Things can only get better. Now who said that?

I look forward to being able to go diving with the branch I chair without worrying whether I happen to be switching gas at the administratively correct depth, have filled in the correct forms and will not get sued into bankruptcy. Unfortunately I feel that may be a little too optomistic.

Nigel Hewitt

13-05-2004, 09:41

> Tests with an osiloscope have shown that the telydine RB22 BUD cells in the Inspiration experience a maximum current draw in the region of 6 times their rated maximum. As it has been explained to me, this tends to occur when the solenoid fires. I think you can draw your own conclusions as to what is happening here.

Huh? The way the temperature compensation works you can short the output pins out and the cell is effectively unaffected. Virtually all the current the cell produces is dumped through a load resistor to run the thing as a current source. This happens 24 hours a day. A small portion of the voltage from this current is sampled off and more current is dumped through a thermistor to compensate for temperature effects. The external load is to all intents irrelevant to the cell. The nominal 10K published load is about matching the thermistor curve not stressing the cell.

This sort of stuff has been my business for far too long. I had a cell to pieces very rapidly after getting an Inspiration and they are a bit crude but they work within the tolerances published.

> The 4th cell provides a valuable comparison and verification since it is not subjected to this excess current draw.

> For instance, if you have a 1 high - 2 low situation where the one high is actually the correctly functioning cell the 4th cell will help confirm this and you can run manual back to the surface. These malfunctions are rare but have been known to happen.

That puts me in a 2 verses 2 situation. Why should the fourth one be magically right? Yes I have to make a call and four voices may be better than three. If a flush doesn't prove who is telling the truth I suspect I would try to fly numbers that are 'safe' for both votes. Oxygen is one of those things that you just can't afford to get wrong.

>> The thing about the fourth cell holders that worries me is that the front end of the cell and its back end are not likely to be at the same temperature. This is a big NO-NO for galvanic cells with simple thermister temperature compensation.

> My experience (Approx 2 years with the 4th cell) has been that the cell tracks the Inspiration cells quite closely. Others I know have a similar experience. Usually it will read approximately 0.01 low which gives a small safety margin in terms of decompression. I don't think there is a significant temperature difference between the two sides of the cell since the gas passes through the ballance holes and the plastic holder with its silicon sealant is a form of insulation from ambient temperature. Some people are now hard wiring the 4th cell into the lid and I understand that APD are about to produce an extended cell holder to facilitate this.

We must agree to differ here. There is no reason for gas to transfer except when you are changing depth and every reason for a temperature difference to build up. If the cells lasted ten years and were immune to condensation I'd love a cell driving the deco-computer but while I watch three six month old cells only roughly tracking one another by the end of a 90 minute+ dive I'm glad there is a voting system and beeps to warn me if they get too far apart.

Love the ol' turtle. Just don't always trust it.

nigelH