Technical Question about Digital SPG - How does it measure? Does it measure absolute or gauge pressure?

[scottgrizzard]

So, I am wondering about the technical side of how the digital gauge works in a transmitter.

My understanding is that a traditional analog bourdon tube spg actually measures gauge pressure... the spg would read 44psi lower at 100 feet than at the surface (4ATA - 1ATA). Is this correct?

How does a transmitter's gauge work? Is it measuring absolute pressure or gauge pressure?

 

[mr_v]

To add to @rjack321's comment - gauges are approximators. Use them to figure out whether your tank is full and if you're close to 1/3. Don't use them for precise gas estimation. Read the bottom part of the following page:

Pressure Gauges (SPG)

Submersible Pressure Gauges (SPGs) and Instrument Consoles

www.divegearexpress.com

You should also read the disclaimers about "thin SPG." From DGX Thin SPG, Naked:

Termo specifications for their gauges only reference the European Union recreational EN250 standard, which essentially means all their gauges are officially rated by the manufacturer to the {164 fsw | 50 msw} depth of the standard.

Termo Industria also makes a compact SPG model they call the "2K" and we sell it as our "DGX Thin SPG". The Thin SPG has a polycarbonate face cover held in place with a large O-ring seal. The thin gauge has an issue with depths significantly below {164 fsw | 50 msw}; it doesn't flood but you can't trust the indication either. What happens is water pressure causes the plastic face cover to depress slightly into the cavity of the gauge eventually touching and holding the needle against the dial so that it cannot move. When that is happening, the gauge reading as indicated by the needle is unreliable. Once you ascend, the cover returns to normal and the needle returns to normal indication as well. We don't recommend our "Thin SPG" for use significantly below {164 fsw | 50 msw}."