Fwd: Re: [PATCH] Fix up SAC calculations for ATM/bar confusion
Dirk Hohndel
dirk at hohndel.org
Mon Feb 25 17:10:47 PST 2013
Jukka <jukka.lind at kolumbus.fi> writes:
> On 25.02.2013 23:04, Dirk Hohndel wrote:
>> Chris Lewis <chrislewis915 at gmail.com> writes:
>>
>>>> As an example one real dive: Double7/300, pressure from 260 to 10 bar.
>>>> Subsurface says I used 3500 litres but Suunto Dive Manager 3176,4 litres.
>>>> It's a 9 % error.
>> But that assumes that the Suunto DM number is correct.
>> And I have absolutely no reason to believe that it is any better than
>> ours...
> Actually Suunto's model is far from perfect ! After each full 50 bar
> theres a flat. The bigger pressure, clearer flat. See 300 and 310 bar.
>
> 140 139.581
> 150 149.551
> 160 155.642
> 170 165.37
> 180 175.097
> 190 184.825
> 200 194.553
> 210 198.113
> 220 207.547
> 230 216.981
> 240 226.415
> 250 235.849
> 260 237.01
> 270 246.126
> 280 255.242
> 290 264.357
> 300 273.473
> 310 273.369
> 320 282.187
> 330 291.005
> 340 299.824
> 350 308.642
> This information collected via testing DM3.1.0 each point at a time.
Just for kicks and giggles, here is the comparison with our numbers -
simply calculating gas_volume(1_L_Tank, pressure) for the given values.
Second column is Suunto, third colum is Linus' function
140 139.581 138.203
150 149.551 148.075
160 155.642 157.946
170 165.37 167.818
180 175.097 177.690
190 184.825 187.561
200 194.553 197.433
210 198.113 204.068
220 207.547 210.777
230 216.981 217.562
240 226.415 224.422
250 235.849 231.356
260 237.01 238.366
270 246.126 245.451
280 255.242 252.611
290 264.357 259.846
300 273.473 267.155
310 273.369 274.540
320 282.187 282.000
330 291.005 289.535
340 299.824 297.145
350 308.642 304.830
>> So let's assume we take whatever temperature reading we have at the time
>> during the dive into account, plus the non-linearity of compression. And
>> the mixture of gas in the tank. Is that all it takes to get the correct
>> volume of gas inside the tank?
> Even a simple correction factor would give a better result.
I certainly think that this is way better than what we had...
/D
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