Question What is your tolerance for error in your SPG?

[Wibble]

My tolerance toward fools is greater than my tolerance for SPGs. Zero tolerance for back gas; last stage: 50 bar or less since I've already calculated my Respiratory Minute Volume.

What does this mean? Did Yoda say this?

 

[DiveGearExpress]

SPG manufacturers all seem to reference the EN250 SCUBA equipment standards from the European Union for their accuracy specification of these devices. Here is our tektip on what the EN250 standard says you should expect from your SPG....

Inside Submersible Pressure Gauges | Dive Gear Express®

Inside Submersible Pressure Gauges As divers, we often make important decisions based on the cylinder pressures indicated by these very simple mechanical devices. We had our SPG ...

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[Belzelbub]

Swapped my daughter’s transmitter to my reg and checked pressure. Her transmitter is one I bought in 2013 or so, and read by the VT4.1. My transmitter was refurbished last year. Batteries in both should be equal. Just did annual battery swap last week, so zero dives on either.

11 psi difference. 2045 on hers, 2056 on mine.

 

[Seaweed Doc]

Not sure about Okinawa, but I always have lower pressure in the water than what it read in the shop. The shop is 18-20 degrees C, the water could be 5 degrees C. And the air on the beach could be colder.

Diving in the tropics, I've had tanks read more when I hit the water on an early AM dive than they read in the air. The water was warmer than the air.

 

[bradlw]

Swapped my daughter’s transmitter to my reg and checked pressure. Her transmitter is one I bought in 2013 or so, and read by the VT4.1. My transmitter was refurbished last year. Batteries in both should be equal. Just did annual battery swap last week, so zero dives on either.

11 psi difference. 2045 on hers, 2056 on mine.

One of several reasons I don't like digital gauges for most applications....not just SCUBA. The engineer in me gets too caught up in the digits....can't stand when things are "off" or when they don't work correctly.

that said, 11/2050 = approx 0.5% error
what are the spec'd tolerances of the transmitters? probably more than that

 

[Robert H. Diver]

One of several reasons I don't like digital gauges for most applications....not just SCUBA. The engineer in me gets too caught up in the digits....can't stand when things are "off" or when they don't work correctly.

that said, 11/2050 = approx 0.5% error
what are the spec'd tolerances of the transmitters? probably more than that

So you’d rather have a big @$$ Needle that could be off by 50-100 psi? Doesn’t make sense.

 

[MacDuyver]

How did the tank feel? If it was warm or hot, then that 3000 psi will drop as the tank cools, and it can be a significant jump.

That will work as well. At least you'll then know that there is a difference or not. If your gauge matches, then the problem is either at the shop that filled, or due to the temperature at the time of checking. The owner of the shop I use instructs his employees to overfill a bit to allow for the pressure drop as the tank cools. Generally, I drop off and pick up later, so they are at room temp. Only on one or two occasions has he had to top off.

Follow up:
I'm really glad i checked here and brought my gear in for an actual calibration check before I dropped cash on new gauges!

My gauge was 10-20ishlbs low at 500PSI, and reading about 100lbs low at 3000psi, which is about 3% error which is fine by me. My depth gauge was spot on.

Lesson for the day I took away from talking to this guy was to check all tanks against my gauges now that I know they're very much within tolerances, and check them cold. Refuse or get them to top off tanks that are outside of my acceptable limits.... which I consider 500lbs light to be outside of my acceptable limits.

All for the cost of a coffee and shooting the **** with an old timer over my lunch break. win, win in my book.

 

[napDiver]

@MacDuyver I almost never take a hot fill because of this. Leave the tank and come back the next day or atleast a few hours later.
Typically they will fill it twice. (1) fill it and hits 3000 PSI HOT/warm, once it cools down (2) fill it again to 3000 PSI and not hot.

 

[bradlw]

So you’d rather have a big @$$ Needle that could be off by 50-100 psi? Doesn’t make sense.

yep..... especially when compared with a digital gauge that might be off by 50-100 psig.
I don't really care if my tank is 2,003 psig or if it's 2,033 psig
knowing that it is really 2,012.5 psig is really way more info that I need to be cluttering my brain with

Add to that the advantages of being able to see at a glance that the relative angle of the needle is where I expect it to be without even registering what the number is
+ being able to see if it's trending up or down without doing math
yeah, I'd rather have analog

For doing partial pressure blending.... yeah I might rather a digital gauge....

Another example..... I have a digital tire pressure sensor system for my camper. Indicates to the tenth of a psig. Drives me nuts when I can't get all six tires to match. It's a psychological thing I guess.

 

[MacDuyver]

yep..... especially when compared with a digital gauge that might be off by 50-100 psig.
I don't really care if my tank is 2,003 psig or if it's 2,033 psig
knowing that it is really 2,012.5 psig is really way more info that I need to be cluttering my brain with

Add to that the advantages of being able to see at a glance that the relative angle of the needle is where I expect it to be without even registering what the number is
+ being able to see if it's trending up or down without doing math
yeah, I'd rather have analog

For doing partial pressure blending.... yeah I might rather a digital gauge....

Another example..... I have a digital tire pressure sensor system for my camper. Indicates to the tenth of a psig. Drives me nuts when I can't get all six tires to match. It's a psychological thing I guess.

I'm in this boat. There are things I want better precision on. Like I want to know my depth down to +/- a couple feet. The amount of air in my tank, I like being able to quick-glance like a speedometer. That said i want to know that it is indeed giving me a correct reading during that quick glance.