VEO 180 NX Algorithms

[belairbrian]

Can anyone confirm if Oceanic changed the formula for NDLs at some point.

The reason I ask is I own 3, 2 are used by my kids, other is a spare.

I was replacing batteries tonite and my son noticed they display different NDLs in Dive plan mode.

Computer 1 (spare) was manufactured in 05/06

Computer 2 was manufactured in 05/05 Refurbished in 12/08

Computer 3 was manufactured in 02/10

Computers 2 and 3 show same NDLs. Computer 1 shows between 15 to 25 % time less at each depth.

Make me think somewhere after 05/06 and 12/08 the software was updated.

 

[GrumpyOldGuy]

Have you dived the spare computer along side the newer ones to verify the pressure (depth) sensors are calibrated the same?

Someone else pointed out to me the same sensor is also used to sense altitude and depth, and if the old one has drifted it might be calculating the NDL based on a false altitude rather than seal level.

 

[DiveNav]

Are all computers in Air mode?

 

[belairbrian]

Are all computers in Air mode?

All 3 were in identical settings. As I mentioned I was changing out batteries, and let all 3 sit long enough to reset. Then verified all settings were the same. Initially the only difference was one was showing the H20 activate as on other two were off.

As for the altitude question that crossed my mind but the 180Nx doesn't activate for altitude mode until 2000 ft MSL. Since I'm at about 200 ft MSL it would take a fairly substantial error to cause that.

 

[GrumpyOldGuy]

All 3 were in identical settings. As I mentioned I was changing out batteries, and let all 3 sit long enough to reset. Then verified all settings were the same. Initially the only difference was one was showing the H20 activate as on other two were off.

As for the altitude question that crossed my mind but the 180Nx doesn't activate for altitude mode until 2000 ft MSL. Since I'm at about 200 ft MSL it would take a fairly substantial error to cause that.

The accuracy of the altitude sensor was a subject of another thread. The issue is the same pressure sensor is used for both altitude and depth. The problem is the pressure involved in depth of water is large (147psi at full scale), yet altitude is sense only in the the bottom 10% of the range (0-14.7psi). Sensors are less accurate the the extreme ends of the scale, which is were altitude is measured, so even a small error (a few psi) could trigger altitude mode. The additive problem is there is no indication on the computer that it is in altitude mode, so you are flying blind to some extent. That's why I suggested diving both computers together, it the depths vary by more than 2 feet then it might indicate the source of the problem.