Questions about AI Transmitter

[DanSinks]

I bought a VTX computer and transmitter, the VTX was refurbished the transmitter was new. I assume the transmitter is manufactured by Oceanic but I've heard a lot of the electronics for this type of gear was designed by Hollis, regardless of who manufactured it.

#1. The VTX manual states that the transmitter turns off when the pressure goes below 50PSI, but my transmitter seems to turn off at about 320PSI. The Oceanic/Huish web site states that the transmitter shut off will occur at 300PSI.

#2. The VTX manual states that the transmitter turns off when the pressure is unchanged for 10 minutes. So I sat in my house with my VTX on with tank and transmitter going. The transmitter was still on after an hour of no pressure change, it was occasionally going from 2520 PSI to 2515 then back to 2520 etc. There didn't appear to be any air leaking.

I would have liked it better if the transmitter stayed on longer in #1 and off sooner in #2 but ok if that's how it works I can deal with it.

Just am wondering if other compatible transmitters from different manufacturers work the same.

 

[BoltSnap]

Just am wondering if other compatible transmitters from different manufacturers work the same.

All transmitter that are made by PPS are the same. The only difference maybe the vendor's logo on the box and hardware on the outside so they will work just the same I'd think.

 

[Joneill]

I bought a VTX computer and transmitter, the VTX was refurbished the transmitter was new. I assume the transmitter is manufactured by Oceanic but I've heard a lot of the electronics for this type of gear was designed by Hollis, regardless of who manufactured it.

#1. The VTX manual states that the transmitter turns off when the pressure goes below 50PSI, but my transmitter seems to turn off at about 320PSI. The Oceanic/Huish web site states that the transmitter shut off will occur at 300PSI.

#2. The VTX manual states that the transmitter turns off when the pressure is unchanged for 10 minutes. So I sat in my house with my VTX on with tank and transmitter going. The transmitter was still on after an hour of no pressure change, it was occasionally going from 2520 PSI to 2515 then back to 2520 etc. There didn't appear to be any air leaking.

I would have liked it better if the transmitter stayed on longer in #1 and off sooner in #2 but ok if that's how it works I can deal with it.

Just am wondering if other compatible transmitters from different manufacturers work the same.

• For number 1, I've never breathed my tank down that low, so have no idea if there is a low pressure transmitter shutoff?
• For number 2, I'm pretty sure that the transmitter will stay "on" if it's under pressure regardless of whether the pressure is changing or not? That's why I purge my reg after setting up my gear between dives - no sense wasting battery during surface interval.

EDIT: From page 84 of the Shearwater Teric Manual:

"Applying high pressure > 50 PSI (3.5 Bar) is the only
way to turn on the transmitter. The transmitter will
power off after 2 minutes of no pressure."

 

[tursiops]

my transmitter seems to turn off at about 320PSI

How do you know this? Did you actually run the tank down to find out? Is it possible you have a "low air" alarm set for 300 psi and that is what you are seeing, not a transmitter that turned off?

The Oceanic/Huish web site states that the transmitter shut off will occur at 300PSI.

I can't find that on the website.

The VTX manual states that the transmitter turns off when the pressure is unchanged for 10 minutes.

Where does it say that? I can't find it in the manual.

 

[scubadada]

I have breathed my cylinder down to 170 psi with normal functioning of the transmitter and computer. I have no reason to believe they would not continue to function at a lower pressure. This is with an Oceanic VT3 and a PPS transmitter

 

[DanSinks]

• For number 1, I've never breathed my tank down that low, so have no idea if there is a low pressure transmitter shutoff?
• For number 2, I'm pretty sure that the transmitter will stay "on" if it's under pressure regardless of whether the pressure is changing or not? That's why I purge my reg after setting up my gear between dives - no sense wasting battery during surface interval.

EDIT: From page 84 of the Shearwater Teric Manual:

"Applying high pressure > 50 PSI (3.5 Bar) is the only
way to turn on the transmitter. The transmitter will
power off after 2 minutes of no pressure."

While divers who go below 300 are considered to have stayed too long, one could argue that the transmitter should provide the link and information down to 50 as is stated in the manual. In an emergency situation it could be needed.

 

[Diving Dubai]

In my experience of transmitters from different brands.

None will switch off whilst they're sensing pressure changes during their sampling times. I've deliberately run cylinders dry, underwater (with a redundant gas source) to test different manufacturers transmitters

Transmitters will (MAY) turn off if they don't measure a pressure change over a set time. Sometimes they don't Other times they go "to sleep" - which requires a ventign of the pressure to wake them.

I can't speak for all transmitters but that's my experience of 12 units from 5 "brands"

The only sure (and in my view acceptable way) to shut of a transmitter is to depressurise the 1st stage. In my opinion it's bad practice to leave your system pressurised anyway unless you're putting your kit on immediately . I've done it myself, and seen others do it, where they've turned their tank off put not vented their gear, put their gear on looked at their SPG and thought their valve was on. I always breath and watch my SPG (even with AI) and have seen the problem and turned the valve on before I splashed. I've witnessed on diver not so lucky, but we got to her underwater and fixed the problem before they perished

 

[tursiops]

While divers who go below 300 are considered to have stayed too long, one could argue that the transmitter should provide the link and information down to 50 as is stated in the manual. In an emergency situation it could be needed.

If you can't provide a page number in the manual and a link in the Oceanic website to verify your claims that (a) it shuts off below 300 psi and (b) it shuts off after 10 minutes of no pressure change, then I can only assume your claims are bogus and based on misinformation or misunderstanding.

 

[DanSinks]

How do you know this? Did you actually run the tank down to find out? Is it possible you have a "low air" alarm set for 300 psi and that is what you are seeing, not a transmitter that turned off?

I can't find that on the website.

Where does it say that? I can't find it in the manual.

I tested the turn off pressure by shutting off the tank valve, there still is pressure on the first and second stage, then gradually press the purge with tiny presses to see when the signal from the transmitter is lost, at which time the VTX will flash the pressure amount . There is an SPG on there as well.

I just tried the experiment again, this time it went to about 150 PSI before loosing the signal, but it may be loosing the signal for another reason, maybe I'm holding the VTX at a bad angle. I'm sitting in my chair with the VTX on my knee and the tank/transmitter next to my knee, well within 24" so should not loose the signal. Need to try it again I guess. Sorry about the false alarm.

I miss-stated things a bit, the manual did not have the 10 minute turn off, as I searched around I guess I got both the 300 PSI and the 10 minute turn off from this FAQ:
FAQ - How far will my transmitter transmit air pressure to my wireless computer?

 

[Joneill]

While divers who go below 300 are considered to have stayed too long, one could argue that the transmitter should provide the link and information down to 50 as is stated in the manual. In an emergency situation it could be needed.

If you intentionally go below 300 psi, knowing exactly how far below it you are is not going to help you much! You should already be on a steady ascent to the surface ready to do a CESA if you run dry. Howver, if I get a chance, I'll mount my reg and purge it down to see how low it detects.