Vintage-Modern non-compatibility issue

[ScubaLawyer]

Had a beautiful dive yesterday here off Laguna Beach. Used my trusty 1958 Mistral single stage (modified with a long yoke). Rather than put an analog pressure gauge on via a banjo like I usually do, I decided to try a wireless transmitter for my Galileo Luna. Very interesting results. Worked fine on initially turning on the air. During the dive I would loose telemetry after a few quick breaths in rapid succession or during a long drawn out inhale. After about 20 seconds I would regain telemetry but my air pressure would read either zero or about 400 pounds less than what it did just before I lost telemetry. After another breath it would read the correct pressure. Then the whole process would start over again. I assume it was just the rapid drop in pressure at the valve caused by the one-stage mechanism as I have never experience that on a two-stage reg. Something tells me the designers of wireless pressure transmitters didn’t bother to use single stage regs in their testing protocols. No big deal save for the initial shock when I looked at my pressure for the first time a few minutes into the dive and saw it read zero (hence the few quick breaths ). Mark

Wireless '58.jpg

[Avanwyk1]

Was the j-valve in the reserve position?

[couv]

Sounds like the rookie couldn't keep up with the veteran.

[ScubaLawyer]

Was the j-valve in the reserve position?

J-valve was initially in up (reserve) position. I then tried it the other way. Didn't seem to notice much difference. Happened at 2250 psi and at 500 psi, and everywhere in between. I reset the reserve to the up position. At 300 psi I pulled the reserve and the guage went to 500 psi, then promptly registered zero again on my next breath. Go figure.

[ScubaLawyer]

Sounds like the rookie couldn't keep up with the veteran.

Isn't that always the case.

[Bryan]

Could the flow through the valve diminish that quickly as to throw off the transmitter? I didnt think the pressure drop on a single stage would be enough to cause it to act that way. Would the sampling rate of the transmitter have anything to do with it?

[ScubaLawyer]

Would the sampling rate of the transmitter have anything to do with it?

You might be on to something. The Luna manual says there is a 4 second sampling rate so if it samples at a pressure drop that might be enough. Plus, the computer calculates remaining air time based on depth and remaining tank pressure (and I think your air consumption rate averaged as the dive progresses but i'm not sure). If it gets random pressure readings it might throw a wrench into its calculations and cause it to reset. Dunno, just a guess. I'm sure there are folks here that know much more about it than I do.

[SurfLung]

- I seem to remember some discussion about the hole from the banjo being small enough to rob pressure from the gauge when you inhale... Causing the needle on the SPG to move. If this is true, I can see where your modern sensor might not be able to settle on a consistent reading.

[Ron]

Would the sampling rate of the transmitter have anything to do with it?

You might be on to something. The Luna manual says there is a 4 second sampling rate so if it samples at a pressure drop that might be enough. Plus, the computer calculates remaining air time based on depth and remaining tank pressure (and I think your air consumption rate averaged as the dive progresses but i'm not sure). If it gets random pressure readings it might throw a wrench into its calculations and cause it to reset. Dunno, just a guess. I'm sure there are folks here that know much more about it than I do.

You could probably mitigate this, at least from a software perspective, if you could modify the sample rate and set it higher. Example: every .5 seconds instead of 4. I'm not sure if that is end user configurable, but you can at least check. At some point, it becomes a mechanical issue which would be Luis' wheelhouse.

Either that or just run a SPG and stop trying to be so fancy like a millennial.

[ScubaLawyer]

Either that or just run a SPG and stop trying to be so fancy like a millennial.

Probably the first, last and only time I'll ever use a wireless transmitter with a single stage reg. Just wanted to see what would happen. As far as adjusting the sampling rate, I have a hard enough time just turning the damn thing on and off and then seeing the display with my old man eyes. I'll leave the 'spirament'n to the younger generation who might possibly care.

But, good idea on adjusting the sampling rate lower (er higher?). You know what I mean.Mark.

[Chris]

Not an insult here, but along with the hole in the banjo being too small, did you remember to turn your air on all the way? Known some good divers who ran low on air with half a tank because of that.

[ScubaLawyer]

Not an insult here, but along with the hole in the banjo being too small, did you remember to turn your air on all the way? Known some good divers who ran low on air with half a tank because of that.

Yes. Air full on. Not even a quarter turn back.