I see a SAC rate on dives downoaded into the Cloud from my Perdix AI. How is this number derived on the Perdix? I’m typically seeing between 13 and 15. I assume lbs/min. What is the latency for the calculation?
SAC rate on Perdix AI
- Thread starter tridacna
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From the AI Manual
7.1. SAC calculations
Surface Air Consumption (SAC) is the rate of change of tank pressure, normalized as if at 1 atmosphere of pressure The units are either PSI/minute or Bar/minute
The Perdix AI calculates SAC averaged over the last two minutes. The data from the first 30 seconds of a dive are discarded to ignore the extra gas that is typically used during this time (inflating BCD, wing, or dry suit).
SAC vs RMV
Since SAC is simply based on rate of tank pressure change, the calculations do not need to know the tank size. However, this means that the SAC is NOT transferable to tanks of a different size.
Contrast this to respiratory minute volume (RMV) which is the volume of gas your lungs experience per minute, measured in Cuft/min or L/min The RMV describes your personal breathing rate, and is therefore independent of tank size
Why SAC instead of RMV? Since RMV has the desirable property of being transferable between tanks of different sizes, it seems to be the better choice on which to base GTR calculations However, the main drawback of using RMV is that it requires setting up tank size correctly for each tank Such setup is easy to forget and is also easy to setup incorrectly
SAC has the great property of not requiring any setup, making it the simplest and most reliable choice The drawback is that it is not transferable between tanks of different sizes.
Cheers - M²
7.1. SAC calculations
Surface Air Consumption (SAC) is the rate of change of tank pressure, normalized as if at 1 atmosphere of pressure The units are either PSI/minute or Bar/minute
The Perdix AI calculates SAC averaged over the last two minutes. The data from the first 30 seconds of a dive are discarded to ignore the extra gas that is typically used during this time (inflating BCD, wing, or dry suit).
SAC vs RMV
Since SAC is simply based on rate of tank pressure change, the calculations do not need to know the tank size. However, this means that the SAC is NOT transferable to tanks of a different size.
Contrast this to respiratory minute volume (RMV) which is the volume of gas your lungs experience per minute, measured in Cuft/min or L/min The RMV describes your personal breathing rate, and is therefore independent of tank size
Why SAC instead of RMV? Since RMV has the desirable property of being transferable between tanks of different sizes, it seems to be the better choice on which to base GTR calculations However, the main drawback of using RMV is that it requires setting up tank size correctly for each tank Such setup is easy to forget and is also easy to setup incorrectly
SAC has the great property of not requiring any setup, making it the simplest and most reliable choice The drawback is that it is not transferable between tanks of different sizes.
Cheers - M²
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