VR3 question

[Kristen]

I was reading a diver article on the VR2 a while back which seemed to suggest that the VR2 and VR3 would lock out and just refer you back to the tables if you miss a stop and do not get back to it within 1 minute (rather than recalculating ascent/deco time etc) ? Is this the case with the VR3 ? Whilst far from ideal to miss a stop (even a non-mandatory one) I would hope that the comp would re-calc stops etc.

Thanks in advance,



Kristen

[Phil Ennis]

It doesn't lock you out, it keeps calculating for you but it does tell you to refer to tables, probably a legal thing.

If you go to the Delta P website, you can download the manual which is now a lot better than the old one.

[Padowan]

Originally Posted by KCR

I was reading a diver article on the VR2 a while back which seemed to suggest that the VR2 and VR3 would lock out and just refer you back to the tables if you miss a stop and do not get back to it within 1 minute (rather than recalculating ascent/deco time etc) ? Is this the case with the VR3 ? Whilst far from ideal to miss a stop (even a non-mandatory one) I would hope that the comp would re-calc stops etc.

If you violate a stop level, for example the deep micro bubble stops (I've missed these before) a counter starts counting down from 60, with an arrow telling you to go back down. When you arrive back below the stop depth, the counter starts counting BACK UP - so if you violated the stop for 15 seconds, it would take 30 seconds for the violation to completely clear.

If you completely miss a stop by the 60 seconds, the icon in the corner changes, and it says "Use Tables" but the deco schedule is still active, and calclating whta DeltaP call a "Best Guess" schedule, which seems to closely resemble what ever remaining stops you had before you violated things. On the Log of a dive, there are 2 messages which are noted, one if you, for example, miss a deep stop but clear the remaining duration, and a second message if you surface with deco outstanding - I can't remember the exact wording of each message, something like "Missed Decompression" and something else.

[Mark Chase]

As above and its the same for the VR2. I have done this when I was inside a wreck and it asked for a stop that I couldn’t get back down for. It asks you to refer to tables but continues best guess deco. I continued to dive the unit two or three times a day for the next few days and the warning staid there but it worked fine. Surprisingly the warning gave up after a while despite the repeated diving.

I have no idea what happened to JBs computer but he either didn’t read the instructions (he is male after all ) or he had a faulty unit.

ATB


Mark Chase

[MattS]

I have no idea what happened to JBs computer but he either didn’t read the instructions (he is male after all ) or he had a faulty unit.

I don't think that Bantin has quite got his head around the fact that the VRs deep stops are integral to the algorithm it uses. He was ascending up a wall and did not bother to do the deep stops, so the computer told him he had missed stops.

Whether you break a deep stop or shallow stop the VR reacts the same. You get the 'use tables' caution and the unit continues to compute the profile the same as it did before the violation.

If they had room on the display the caution would probably read "You ignored my advice once. Here is the information but you are on your own."

[Kristen]

Thanks for the replies. Are you saying that the VRs don't recalculate the deco profile if you miss one stop and just tell you what the remaining stops are assuming that you did not miss the stop or does it recalc. the deco required on the further stops to take account of the missed stop ?

Thanks in advance,



Kristen

[bang-on]

kristen,
as stated the vr3 will advise 'use slates' but will recalculate the deco based on the new circumstances ie 'missed 43 mtr microbubble stop' due to problems with ascent,at 30 mtrs diver stops.....the vr3 will now calculate a decompression shedule from that point to the surface.it will however continue to show 'use tables' and 'missed stops' will also be shown.
it will always give a decompression shedule irrespective of what the diver has presented it with and i think thats why its popular with cave divers who do very long in-water times and varrying depth profiles.
if you check www.vr3.co.uk you will find a good Q/A section on the vr3/vr2.

cheers
barrie

[MattS]

AIUI

You need to think in terms of the Buhlmann model inside the VRs.

Every 10 seconds the computer samples depth and looks at the gas you have told it you are breathing and applies that to 16 compartments. When one of those compartments exceeds it's surfacing M-Value you have a ceiling below the water line which is displayed as a standard stop depth. The VRs implement deep stops, so they look at your max depth and the current standard stop depth and insert a series of intermediate stops.

Now you start to ascend. The cieling is roughly ascending, but much slower than you are ascending. Lets say you ascend 1m above the 17m deep stop. The Vr continues to sample depth and the gas you told it you are breathing and it continues to load and unload the 16 compartments accordingly. As you are at 16m it will use that depth in calculations, well about 2.6bar pressure as far as the VR3 is concerned. The shallow stops would be reduced the same as they would on a non-deep stop computer, like an Aladin for instance. After 60 seconds the VR displays a 'use tables' caution and recalculates the remaining deep stops.

Now lets say you ascend early from a shallow stop. What happens to the model is that the hypothetical gas pressures in one or more compartments will exceed the surface M-Values, this is a theoretical bend. However the computer is a machine and does not need evacuating to a chamber. It just sees the compartment loading values have exceeded a significant threshold (the M-Value) and continues to load and unload hypothetical inert into and out of the compartments. Although you happen to be on the surface the display will be showing that you still have several minutes to complete at whatever stop depth you ascended from. The stop time will reduce based on your current depth of roughly 1000 milli bar pressure. I suspect that once on the surface the VR assumes you are breathing air. After (IIRC) 5 minutes it stops displaying the last stop but continues to calculate the hypothetical inert in the compartments.

So whatever you happen to do, the VR just doggedly carries on calculating the loadings in it's compartments, based on sampled pressure and breathing gas selected. If you are still walking you could dive it and it would still tell you the deco requirements of the model it implements.

HTH

[BJ]

I am told that the computer is meant to display best-guess deco info at the same time as Missed Stops - Use Tables. That makes sense. Unfortunately the VR2 I was loaned by Kevin did not show the crucial information at this time. (I was diving with a lawyer who witnessed what it displayed each time.)

I assume that either 1) the computer was faulty or 2) there was a bug in the software that was exposed when diving in fierce up/down currents that you find in the Maldives in January. It was not that I intentionally missed stops. It was that if you are being sent about from (say) 25m to 18m and back again, and the computer wants a deep stop at 20m you can do little about it. Looking through the viewfinder of an SLR doesn't help either. It only gives you 60 seconds to get down to the stop depth and that's not long if you are busy doing something else like taking a photograph when the deep-stop display appears.

If I had still continued to receive other info such as depth time and stop/depth and duration it would not have been a problem. Kevin denies the example I had was faulty but we witnessed the effect on a series of dives and I found it very frustrating...

It is difficult to imagine the effect of diving in an ocean current that is affected by topography and goes both up and down at times. Hence my comment that it would have been OK for square profile diving and an ascent up a line.

[MattS]

If I had still continued to receive other info such as depth time and stop/depth and duration it would not have been a problem.

As a matter of interest John, what was displayed on the left half of the screen?