Actual Experience with Shearwater AI

[Joneill]

Thanks for the link. I chimed in as well.. Hopefully they will be quick on a minor upgrade like this..

I didn't make it before the beta was closed but I'm looking forward to checking it out.

Good news - Dive Log for iPhone was updated on Jan 6th and now fully supports the Perdix AI. Here is some info I got from them via e-mail:

"Yes, the Perdix AI is fully supported by the current version of Dive Log (2.2.8). It does download the pressure sample data from both possible transmitters and enters the start and end pressure of the “main” tank (the first transmitter) and captures the pressure samples from both transmitters and saves them in the database. Right now Dive Log does not plot the pressure samples on the profile graph (we will add that eventually) however if you sync the data to any of the compatible desktop apps you will see the pressure samples plotted on the graph (not the ability to plot pressure samples is independent of the AI and applies to any dives that have pressure samples store in the database).


Air Consumption Rate is also calculated by Dive Log as long as the required information is entered for the dive. In addition to the start and end pressures, the average depth of the dive (which we calculate from the profile data data or you can manually enter) and the dive time you need to enter the size (and in the case of US and Canadian sized tanks the working pressure) of the tank(s) used.


We have one additional setting available in Dive Log that allows you to ignore “surface samples”. This can be handy for die computers like the Perdix AI that allow you to keep recording samples long after you surface (in case you are planning to go back down again and continue the dive) so that your air consumption calculation does not include those surface samples (this helps you get the same values calculated that you might see in other programs).


Note that Air Consumption Rate can be calculated two ways, one is more appropriate for keeping track of during the dive (this is usually called SAC) and the other is more useful as a “post mortem” so that you can compare one dive to the next (RMV). We calculate RMV and display that in Dive Log currently. Many people use the terms interchangeable (in fact, when I started diving we only calculated RMV and it was called SAC). Here is a blog post that talks about more about this particularly in our Mac application (which can calculate both SAC and RMV):
More Mobile Software - Blog

and here is a general discussion of how to calculate the two values:
NWGratefulDiver.com

and finally a DAN article on the same subject:
Alert Diver | Estimating Your Air Consumption

I hope this is helps. Please let me know if you have any additional questions.

Best Regards,

Greg

Greg McLaughlin
More Mobile Software
www.moremobilesoftware.com"​

 

[KentB]

Thank you - called End Dive.

ah perfect!!
I just got my perdix AI and the transmitter, I only have 2 dives so far on it but no dropped comms at all. in my house it took 10-12 feet or so before it dropped and I had to get back to about 5 feet before it re connected and this was obviously not underwater but I was still happy.

today on dive 2 on the perdix my dive buddy got a new al 80 and couldn't sink he had only dove with steel tanks so he wasn't weighted enough so I went down and grabbed some rocks for him and it counted the 2 min as a dive, then with the rocks he could sink so it reset and went on to dive 2 of the day I read through the manual and missed the "end dive option" so Ive now changed it to 5 min. cheers!!

 

[Joneill]

Have any other Perdix AI users experienced a difference between their SPG pressure reading and the Perdix AI transmitter? I see that my Perdix AI (with new transmitter that came with the unit) is consistently reading 100-150 psi lower than my Dive Rite SPG. This is the case throughout the pressure range (see video below).


At my LDS, we tried 2 other SPG's and they pretty much matched mine. We also tried another new Perdix AI transmitter and it was within 6-8 psi of my transmitter. The tech at the LDS also said that, in his experience, he has seen the PPS/Oceanic transmitters always read lower than SPG's. So the question is: which one is correct?

I also notice that in the few online videos for The Perdix AI, the SPG and Perdix A I readings seem to match better - could there be a batch of transmitters that is not properly calibrated?

See at ~1:38 in here:

See at ~ 0:50 in here:

 

[Texas Torpedo]

I just pulled out my Perdix AI and both the transmitters. One transmitter is currently on one of my recreational reg sets and the other is on one of the 1st stages for my doubles. To see how far off they may be reading I put one on the left post and the other on the right post. With this setup, they'll both experience the same pressure at the same time. The recreational set also has an analog SPG. Prior to testing, I used my handheld pressure gauge to get a reading as well..

The end results are as follows:
Handheld analog pressure gauge: Just slightly under 3,000
Transmitter 1: 2964 (came with Perdix AI new)
Transmitter 2: 2970 (bought used on ebay)
Halcyon analog SPG: Almost 3,100

I didn't take pictures but I went back down with a stage reg w/ analog HOG spg and it read right at 3,000 as well.

So, I'm ranging about the same as you @Joneill with the Halcyon SPG. But, I have two other analog gauges that are pretty darn close to the transmitter numbers. I guess someone would have to have access to a certified pressure gauge to know for sure which ones are most accurate.

 

[KentB]

my transmitter reads just slightly lower than my SPG id say probably 50PSI

 

[clownfishsydney]

Re transmitter reading lower than SPG, could it be that the transmitter pressure is converted to 20C pressure reading? This is what the Uwatec transmitters (at least the first ones) used to do. So on hot days, the SPG will read higher but the transmitter will be lower. Also, SPGs can vary a lot, I know mine do.

 

[Jason]

I used mine last week and my AI transmitter was generally around 50 psi lower than my brand new @Deep Six 2" brass and glass SPG.

 

[ickebins]

What about cross-posting and letting Shearwater know about this thread? Perhaps they are in a position to shed some light....

As I'm also a Perdix AI user an answer would be great.

 

[Oldbear]

I think you guys are comparing apples to oranges...an analog SPG to an electronic device. SPG are notorious for having variances between gauges. I have seen them differ as much as 300 psi plus or minus other gauges...right out of the box.

I get it you want to know your gas pressure to the nth degree. But learn your equipment and factor that into you dive plans. Are you happy with your car's gas guage...a needle. As it approaches the red "E", at sometime you decide to stop driving and refuel. If you plan your dive and then dive it, as oppose to just jumping into the water until your gauge says you are low on gas, you can rely on your diving skills not that gauge.

 

[Alastor]

Although I agree with Oldbear, I would like to report to you my 2c - using transmitters from another brand (I have 3 of them) their difference is in the 5 bar range along the 40-220 bar range (never compared with less than 40). I have only 2 out of 5 SPG that give the same reading into the +/- 5 bar, while other two are one in excess of 10 and the other is -10. The last one is 15 bar more than the transmitter at full scale. Because all the SPG are correctly set to 0 when no pressure is applied I believe that there could be a line from 0 to the max for each SPG and those lines have the same origin but different slope.