AST sensors

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kensuf

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I'd like to open up a discussion on AST sensors.

Attached is a graph of the mv output of 3 cells from a dive I did a couple of weeks ago. All three cells calibrated before the dive, with C1 having the greatest offset, C2 the second and C3 the lowest offset. At approximately 30 minutes into the dive, C3 started to drift, registering a lower mv output than it did at calibration, but it was still responding. Around 45 minutes into the dive, C1 also started to have an offset drift, with the off-set appearing to lower to close to the same level of C2.

The impact to me was that at this point, my Shearwater displayed three completely different PO2s. I used a DIL flush to confirm which cell was good and proceeded to abort the dive, while flying the unit on C2. On the way up, I performed an O2 flush and at this point, C2 was voted out by the Shearwater; the offsets of C1 and C3 had drifted to a point where the Shearwater thought their PO2 was close enough to each other, and it assumed C2 was the bad egg. PO2 readings were roughly 1.1, 1.7 and 1.0; the O2 flush was deep enough that 1.7 would have been the correct reading.

What is interesting is these don't seem to be acting "current limited" like we traditionally think because they are still responsive and reactive throughout the range, but rather they appear to have a drop in off-set which is used at calibration.

I'm not sure what else to think / say, I'll leave it to you to decide, but I'd probably be pretty cautious when diving these cells and be sure to confirm them with a DIL flush periodically throughout the dive and an O2 flush on the way up.

 
I have also seen some pretty anomalous behavior. I suspect, based on my experience, that if you pull them for a couple of days and let them “rest” that you’ll get a good calibration again and furthermore that those cells would pass a current limit check at the beginning of a subsequent dive.
 
There is another thread on here about the AST cells. I actually bought two from CCDS at the height of not being able to find any. I had one sensor starting to go so I needed a backup. I was lucky enough to get two full sets of my regular cells and have not used the AST. Based on the other thread, it seems the AST cells are meh. They seem hit or miss. People aren't happy with them, but they don't hate them either. It's honestly the most negative reviews I've seen for an oxygen cell in a while. I personally am just holding onto them as backups that will only be used in a pinch if I'm out of the regular ones and there's still problems finding them due to COVID spikes.

More importantly when the hell did you get a JJ?

Whoops, edit: I see you saw the other thread.
 
A friend of mine got divorced a year ago, he asked me to buy his JJ. I've done all of a dozen dives on it, most of which were a few days ago when I had to loan a student my counterlungs from my fathom. It's a neat unit, but there are some things I don't like, the head attachment being top of that list.
 
A friend of mine got divorced a year ago, he asked me to buy his JJ. I've done all of a dozen dives on it, most of which were a few days ago when I had to loan a student my counterlungs from my fathom. It's a neat unit, but there are some things I don't like, the head attachment being top of that list.

Curious to hear more of your thoughts if it's not too off topic. Do you mean head attachment to scrubber or head/scrubber attachment to canister? Because I agree about the latter. You end up with a ton of grit trapped in the head o rings after a single dive.
 
If anyone has a couple of cells to donate, I'll throw them in a Temp&Humidity Chamber and see how the current produced various with T&H. Be curious to see if temperature and/or humidity is causing the reduction in current output.
 
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A friend of mine got divorced a year ago, he asked me to buy his JJ. I've done all of a dozen dives on it, most of which were a few days ago when I had to loan a student my counterlungs from my fathom. It's a neat unit, but there are some things I don't like, the head attachment being top of that list.

I heard you were having a interesting class experience. Makes the job fun.
You should post a JJ review one day when you’re bored in corona hell. JJ was on my list until I found the fathom.
 
If anyone has a couple of cells to donate, I'll throw them in a Temp&Humidity Chamber and see how the current produced various with T&H. Be curious to see if temperature and/or humidity is causing the reduction in current output.

if there come an end in sight for the difficulty in getting cells and I no longer have a need for these cells as backups I will send them to you
 
Sounds good. Do you have the molex or coax (JJ) version?
 
https://www.shearwater.com/products/perdix-ai/

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