Why are two different DSAT-based computers providing different NDL times?

[scubaozy]

i don't see how a 'low' battery would affect the readings of any computer! in my 26yrs of using dcs, they operate pretty binary...either on or off based on the battery. so i'd be careful about making it a blanket statement vs *that particular* dc was acting strange. if it were me - and i had bought it new and noticed that abnormal behavior - i'd immediately return it for a replacement. that's a pretty strong indication of a defect (most likely with the sensor...which is, ime, what fails most often with dcs).

i mean, if dcs were that glitchy based on battery level, we'd hear about it far far more often. a 4mtrs diff is a significant error and would surely be causing DCS hits. get a new computer man.

Most of the pressure sensors are piezoelectric and they are voltage sensitive. Modern dc normally are designed not to switch to dive mode when battery level is not sufficient. In my case it was a suunto stinger that I replaced the battery the day before diving. During the dive I noticed that depth readings were off, I actually thought I damaged the sensor during battery replacement. At the surface I noticed that battery level was shown low. Problem was, the battery had been waiting too long in the shelf. I picked up a new battery that day and put it in and all was resolved.
This all happened in freezing temperatures, so, if you have not been diving in those conditions, it is unlikely you can reproduce this, but does not mean it does not happen. I wrote it here so that others are not surprised when experiencing similar situation.

As I wrote earlier, algorithm chosen for 2 DC might be same in terms of compartments and half times but each manufacturer would have to implement a multilevel logic. They might choose 1hz resolution or 1minute, 0.1 resolution for depth vs full meters, differences in rounding etc. There is enough playroom there to make a difference in your ndl.

 

[Jim Lapenta]

Interesting, I do not change any of my Oceanic computer batteries until the low battery icon is displayed. The NDLs have never been off. My family is currently diving 2 Pro Plus 2s, a VT4 and a Geo 2, and a VT3

I have discovered that different brands of batteries will cause the Oceanic Veos to act funky. I have a Veo 200, 180, and 100 for students to use since I sold both of my Perdixes as I'm getting away from deep dives and teaching tech classes.
For my own tech dives the Predator and an OMS bottom timer are all I need for anything up to 200 feet with tables cut on Multi Deco.
In the Oceanic computers I get the most consistent performance and readings as well as battery life with Panasonic and Energizers. Panasonic being the best. Duracell's are absolute garbage batteries and give wonky results in computers. They also suck at and are good for destroying dive lights. Sony's are hit and miss.
I was told years ago by an Oceanic/Aeris rep that the battery brand can make a pretty significant difference and I have seen that over the 18 years I've been using Oceanic computers. Something to do with the actual voltage/current and rate of discharge.

 

[scubadada]

Hi @Jim Lapenta

I've been diving a variety of Oceanic computers for 20 years, Pro Plus 2, VT3, Geo2, VT4. Your post prompted me to go take a look at the batteries in my save a dive kit. All my CR2s, 2430s, and 2450s are Duracell. That's most likely what is in all the computers also. Funny thing, I've never had a problem with any of the computers, battery life, or strange behavior

I nearly only change the computer batteries when the low battery indicator comes up. What kind of problems have you noticed with your Veos and Duracell batteries?

 

[scubadada]

Hi @divedrewsf

I hope this mystery is solved at some point, I would love to know the answer

You have many computers running DSAT, perhaps you could briefly run each through planning to make sure they all display the same NDLS and match those in the owner's manuals. I have never seen or heard of a faulty pressure sensor giving longer NDLs, only shorter, but you never know.

Assuming the pressure sensors seem OK, dive them again. Though I am skeptical of a battery cause, particularly in 2, you could always try replacing at least one to check (assuming the Atmos 2 seems correct). If you happen to have the download software, you can examine the profiles and tables. I believe Oceanic and Aeris use different apps and that older and newer computers might require different versions of their brands app. These may not be currently available.

Best of luck, let us know