Question What is your tolerance for error in your SPG?

[mcohen1021]

This would be a great way to compare between AI and your analog gauge

 

[Wibble]

How do you know if your AI (digital) gauge is more accurate than your SPG analogue gauge?

Accuracy; the deviation from the absolute pressure in Bar (kilos per square centimetre) or pounds per square inch. Just because a digital gauge says 1234 doesn't mean to say that it's 1234.

However, a digital gauge can show a much smaller decrease in pressure than an analogue gauge, simply because the needle on the analogue gauge is relatively large. Analogue mixing gauges are much larger, 10cm/4inches or more so that you can see the needle move.



I had a leak on my rebreather which was bubbling from behind my head. I use AI transmitters and can see this in my Nerd display. It was hard to determine where those bubbles were emanating from, so had to go through a diagnosis. I stopped, waited and monitored the oxygen and diluent pressures for a minute to see what was going on, as in to give me a clue if it's one or the other. Nothing moved, but the bubbles kept pouring out. Didn't seem to be either oxygen nor diluent. Then turned off the bailout. Still bubbling. Purged the bailout and the bubbles stopped coming out from behind my head. Turned it on and more bubbles; rolled around to see if they were coming out somewhere... Then found it: the connection to the bailout valve (mouthpiece) had become undone. Tightened the hose connector by hand; bubbles stopped. The bubbles were coming out of the mouthpiece and travelling up the loop hose covers to exit behind my head! Carried on with the dive.

The AI digital readout was really helpful in this incident as it should show a small change in pressure and being a number, is unambiguous.

 

[scubadada]

Is this a good time for the discussion about the accuracy of analogue vs. digital gauges?...

I was just looking at the user's manual for the new Mares Sirius AI computer yesterday and saw this. I may have seen something like it before but don't remember it

My Oceanic VT3 and Shearwater Teric run off a single PPS transmitter, they read the same pressure, I assume that sent by the transmitter. My SPG reads 75-100 psi higher. I have a tank checker gauge that reads in between the AI computers and the SPG. a bit closer to the AI computers.

It's kind of like having three watches, displaying different times, who knows which, if any, is actually correct? They are close enough for me.

 

[Belzelbub]

How do you know if your AI (digital) gauge is more accurate than your SPG analogue gauge?

Most people wouldn't know. Really the only way would be to compare it to a gauge traceable to NIST (or equivalent) standards.

For the purposes of this thread, and our use. Two or more gauges more or less agreeing, with another as an outlier, is a good enough indicator. Theoretically possible that the outlier is the correct one, but definitely less likely.

 

[Belzelbub]

My Oceanic VT3 and Shearwater Teric run off a single PPS transmitter, they read the same pressure, I assume sent by the transmitter.

Yes, it is. Transmitter just sends a string of information that contains the serial number, pressure reading, battery status, and, IIRC, a checksum to make sure the data is not corrupt.

The computer just receives the signal, makes sure the SN matches, then puts the rest of the information in the appropriate buckets. Something would be very wrong if you VT3 and Teric read different values.

 

[scubadada]

I know some folks run two AI computers and two transmitters. For those who do, do your two computers display the same tank pressure or different values? If different, what kind of differences to you see?

 

[Wibble]

I know some folks run two AI computers and two transmitters. For those who do, do your two computers display the same tank pressure or different values? If different, what kind of differences to you see?

Both computers need to be configured for both transmitters.

Then the only difference would be if one computer didn't receive the data packet, possibly due to the signal being too weak.

 

[scubadada]

Both computers need to be configured for both transmitters.

Then the only difference would be if one computer didn't receive the data packet, possibly due to the signal being too weak.

One tank, two transmitters, two computers. Do the two transmitters send the same pressure value or not?

I have 3 transmitters but 2 are in Florida, if I get no responses, I will try this sometime. I dive a single transmitter and a SPG

 

[Belzelbub]

One tank, two transmitters, two computers. Do the two transmitters send the same pressure value or not?

I have 3 transmitters but 2 are in Florida, if I get no responses, I will try this sometime. I dive a single transmitter and a SPG

I have 3 transmitters. All three are in Florida. The good news is so am I. I don't think I'll be able to try this today, but can probably do it tomorrow.

 

[Wibble]

One tank, two transmitters, two computers. Do the two transmitters send the same pressure value or not?

Extra info. Had ass-u-me d that you meant two transmitters on two cylinders.

Would put money on the two transmitters sending different pressures due to accuracy differences.