analog vs digital gauge (SPG vs Air Integrated Dive Computer)

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I've had my Oceanic VT3 hoseless AI for more than 5 years, more than 600 dives, perfect performance. I've had my backup Oceanic Geo2 and SPG for more than 4 years, more than 500 dives, perfect performance.

---------- Post added December 7th, 2015 at 08:31 AM ----------

Hi

Thanks everyone for the tips and experiences.

I guess I will go with digital as I have never read a case of digital failure before.

(I read like 5 cases of SPG needle being stuck and the case that, 'Colliam7' mentioned about, the cover popping off twice)

Hopefully modern digital gauge is somewhat less prone to malfunction : )

Ps, Is there any highly regarded digital console that I should look into? (Currently, I like the idea of Proplus3 but its hard to find a review online)

Are you sure you want a console?
 
that is the issue. Currently there are no AI computers really worth buying because they're all horrifically expensive and many lack some very important features and don't really provide anything that is that important. SPG's are cheap, carry a spare in your save a dive kit. 99.999% of all the big technical dives are being done without digital gauges, for a reason.
 
Hi, tbone1004

May I ask why wired AI computers would be inferior to wrist dive com? I thought it use similar electronics and algorithm inside?

Seabear HUDC looks very cool but it double the price of Oceanic proplus3. Is it that much better?

Ps, I don't have a wrist dive com yet and I don't plan to get it. Dive console or HUD seems like a better idea to me.

---------- Post added December 7th, 2015 at 08:44 PM ----------

I've had my Oceanic VT3 hoseless AI for more than 5 years, more than 600 dives, perfect performance. I've had my backup Oceanic Geo2 and SPG for more than 4 years, more than 500 dives, perfect performance.

---------- Post added December 7th, 2015 at 08:31 AM ----------



Are you sure you want a console?

Thanks for the review on Oceanic wrist dive com.

Well, I don't normally wear a watch so I like the idea of having just one unit (console vs dive com+spg) and that unit connected to first stage so less thing to carry or worry about.

People seems to advise against it though lol
 
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A few observations:

1. In the past the advice was to face the SPG away from you when pressurizing the regulator, in the event the face blew out of the SPG. That's ancient advice as modern SPGs won't fail that way.

2. In the even more distant past before the earth cooled, the high pressure port and HP hose did not always have a very small restriction in them so it was possible to slam the SPG with high pressure gas. Now however, both the HP port and the HP hose have very tiny orifices that won't allow enough gas through to either slam the SPG with sudden high pressure, or cause significant gas loss in the event of an HP hose failure.

3. As noted in the above post, the reason for leaving the purge button slightly depressed when turning on the tank valve is to prevent the knife edge seat on a piston reg from slamming into the seat, accelerating wear. That's semi-old advice as seat materials are much better now and true knife edge seating surfaces are much less common.

4. On the other hand, the practice came back into fashion with high percentage nitrox mixes and O2 mixes. There have been several instances of first stage fires and even a couple that catastrophically failed when O2 was used and the valve was turned on quickly without the purge being depressed.

In this case, the problem is adiabatic heating of the oxygen as it enters the reg and then is suddenly compressed. High flow rates around sharp edges as the gas floods into the regulator can also result in hot spots. In both cases, if you get enough heat to ignite the O-rings, you'll have a first stage fire. EPDM and Viton are used as they have higher ignition temps than nitrile O-rings, but they can both still be burnt if the temperature is high enough. Viton has a higher ignition temp than EPDM, but when it burns it produces phosgene gas, which was used in gas attacks in WWI and isn't something you really want to breathe.

Most are brief and usually not even noticed other than the first stage suddenly leaking. I've had few first stages over the years come in with charred O-rings and that's essentially what happened. However There have been some more spectacular failures.

So for air and recreational nitrox mixes, I wouldn't worry about it, but for O2, it's prudent to turn the tank valve on slowly.

5. As for reliability of SPGs versus air integrated gauges there are some significant downsides to air integrated gauges and electronic SPGs:

a) they require batteries where an SPG does not. Beyond the obvious issue of limited battery life, there are other potential issues. A long time ago, electronic SPGs made an appearance and I tried one for awhile. At the time I was doing deep, cold water dives and I found that with bottom temps of 35 degrees F it was not uncommon for the SPG to quit when it cold soaked and the battery voltage dropped. It's not pleasant to look at your SPG and see a blank display because it got cold and decided to pack it in.

Some air integrated computers have similar issues, and again way back in the day in very cold water I've seen them fail at depth despite not having any low battery indicator before the dive.

b) You're also dealing with greater complexity and set yourself up for a single failed electrical connection failing both the SPG and the computer. The shop I worked with also broke a boat load of Sherwood Wisdom computers starting from a 100 degree boat deck and going to 35 degree bottom temps in a matter of a couple minutes. Apparently the expansion and contraction involved inside the computer broke connections in them. Sherwood actually called and asked what we were doing to them since we'd had so many failures. I hope they improved the later iterations, but who knows?

c) Mechanical SPGs may be a couple hundred psi off in one end of the range or the other. However if they are in error, they almost always read low on the low end of the scale, as an SPG that reads high at the low end of the scale will have a needle that won't go all the way to the zero stop, and thus people notice the problem as it's reading something higher than zero when there is no pressure on it.

Electronic SPGs will fail the same way. I've seen electronic SPGs and air integrated computers read between 200 and 300 psi when not connected to anything. If you're lucky it'll still be under warranty and/or will be supported by the factory. I've also seen the transducers fail low and reach zero psi well before the regulator stops delivering gas.

The difference then is that mechanical SPGs tend to be what they are in terms of accuracy over the scale from 0-4000 psi and are very constant. For example, I have one SPG that will read 3800 psi while it's twin will read 3600 on tanks filled on the same manifold to the same pressure. They are both accurate and consistent with each other at 2400-2600 psi where I normally turn a dive, so it's not an issue, and that SPG has been that way for years - it's very stable.

Electronic transducers on the other hand seem to just decide to go bad and you won't always catch it when it occurs.

6. "Accuracy" differences. It's harder to extrapolate pressures between the 100 psi hash marks on most SPGs, while air integrated computers and electronic SPGs will often display pressure in 10 or 20 psi increments. The thing is that the more granular display isn't the same as "accuracy". If it's 100 psi off, it's still wrong even in the number is more precise.

On the other hand the trend information is more useable, and it has to be if the computer is also figuring gas consumption.

However, if you have a regulator issue (obstructed filter, partially opened valve, etc) you'll notice it with the needle swing on the mechanical SPG, where an electronic SPG will either average it out and display a constant value, or it will sample at fixed intervals where the pressure may or may not be accurate depending on the pressure at the HP port at the time, potentially producing fluctuating pressures that you'll have to compare against each other.

----

In short, with all thing considered, I see zero value in an air integrated computer or an electronic SPG. Mechanical SPGs are simple, reliable, affordable, are quick and easy to replace if they break, don't require batteries, don't mind cold water,and will quickly clue you into problems such as a partially open valve where an electronic SPG won't. A mechanical SPG will also continue to function if it floods, where an air integrated computer or electronic SPG won't.
 
it's not wireless vs. wired that's the issue. Consoles are big and bulky and largely unnecessary. You have to unclip them to look at them vs. just looking at your wrist, if there isn't a good quick disconnect on them, you have to carry the whole reg set inside to download the dive logs, etc etc.

Now, the Pro Plus 3 isn't a bad computer, it's just way too expensive for what it is. It has 3 gasses which is good for any light technical diving, has gauge mode so it can grow with you, blah blah, so it's fine. But it does have the casio style screen which means a backlight so you may have issues reading it at certain times of the day, have to hit a button to see it at night etc etc, and it's $880 usd if you want to be able to download your dive logs to the computer which is hideously expensive.
The Petrel 2 adds a bunch of stuff you don't need at this point, but has a digital compass, a very nice LED screen, and the ability to upload your dives to an iPhone for $150 less. The only thing it doesn't have is a digital pressure gauge.

Now, here is another issue with digital pressure gauges. You have to make sure the batteries are fresh, and if it fails for whatever reason you have now lost both your tank pressure, and your depth/time tracking in one fell swoop. Not a good day.

You also lose the ability to use that computer on other regulator sets, so if you travel and want to dive but aren't taking your reg, or your reg is in the shop and you have a last minute opportunity to go diving, you lose your AI ability because it is tied to the first stage. Most operators won't let you swap hoses around either.

The Pro Plus 3 is also big....


Lots of things to think about, but keep reading and don't jump the gun yet.
 
Hi DA Aquamaster

Thanks for the history lesson that is very insightful!


Regarding the battery in electronic SPG, I fully understand what you said but a little confused about the voltage drop.

Do you think the case of failure is due the lithium ion in electronic SPG (or badly design enclosure) and not just any battery in general? Otherwise wouldn't other electronic device such as dive come suffers from the same failure?

If so, I will then have to think twice about using any device with similar battery inside.



Regarding the 5)c) "SPG that reads high at the low end of the scale will have a needle that won't go all the way to the zero stop"

Does it get worse over time or something that can happen instantaneously? Is there anything we can do to prevent this?

---------- Post added December 7th, 2015 at 09:45 PM ----------

Hi tbone1004

Thanks for the tips, I can see now that dive console attaching to first stage can sometimes be a downside.

I actually considered Proplus3 because it is all in one unit and also the price.

Being in Thailand we don't get a lot of choice with gear, Suunto is pretty much has monopoly here and the popular nova4 plus gauge and compass will cost quite similar anyway.

I guess I will have to look into dive com too.

But from reading this forum. Redundancy is another thing to think about.

Losing a dive console meaning lose both information, but even using the wrist dive com with SPG and one malfunction I will lose 1 critical information anyway.

Do diver typically use 2 dive com for redundancy, or 1 dive com 1 dive console, or just a dive com alone?
 
Hi DA Aquamaster

Thanks for the history lesson that is very insightful!


Regarding the battery in electronic SPG, I fully understand what you said but a little confused about the voltage drop.

Do you think the case of failure is due the lithium ion in electronic SPG (or badly design enclosure) and not just any battery in general? Otherwise wouldn't other electronic device such as dive come suffers from the same failure?

If so, I will then have to think twice about using any device with similar battery inside.



Regarding the 5)c) "SPG that reads high at the low end of the scale will have a needle that won't go all the way to the zero stop"

Does it get worse over time or something that can happen instantaneously? Is there anything we can do to prevent this?
 
Hi

After reading many forums it shocked me that there are more than one case where SPG failure occurred.

So I wondered if air integrated dive computer/console would be a better option in reliability and accuracy (when full/low on gas)?

Also, can modern SPG (digital and analog) handles the tank pressure when turned on instantaneously, or do we still need to ease pressure by purging the regulator?

snsb,

I can share my setup and thoughts and reasoning behind it.

I have a brass and glass SPG and depth gauge. I also have a wrist computer with wireless AI.

For me the AI computer has worked flawlessly. I can set two tank pressure alarms (not sure if this is common on all AI computers). The alarm is visual and audible and requires a button clearing.

Pre dive I check both readings match. Obviously during the dive I monitor my gas consumption on my wrist computer. The nice benefit of being able to monitor my gas on my wrist is it's much easier to just glance at my wrist rather than unclipping my SPG each time I want to check gas. Also, because it's on my wrist in front of me I check it more often. It's right there almost like a heads up display. Upon each of the two tank pressure alerts I check my SPG to verify both are the same. Thus far they have always been the same. Right now if my computer were to fail I have my SPG and depth gauge to fall back on. The weak link in this setup is I have no backup for time. My intention is to replace the depth gauge with a puck style computer.

So my final setup will be SPG, AI computer and backup computer.

I don't know if this is common for all transmitters but mine is pressure activated. In other words pressure turns it on. So after a dive I always de-pressurize my regs to save battery life. I was taught to always slowly pressurize your regs and face the SPG in a safe direction, because as mentioned, the face plate could blow out and cause injury.

My only complaint about the wireless AI computers are the transmitters are fragile. Most are made of plastic which I think is a flaw in design. This isn't so much a problem during the dive, but on a rocking boat they could easily be damaged by something hitting them or someone lifting the tank by the transmitter. I keep my first stage plugs in my save a dive kit just in case it were to get damaged. In that case I could still dive, but I would be very conscious to monitor my SPG.

Hope this helps.
 
Hi tbone1004

Thanks for the tips, I can see now that dive console attaching to first stage can sometimes be a downside.

I actually considered Proplus3 because it is all in one unit and also the price.

Being in Thailand we don't get a lot of choice with gear, Suunto is pretty much has monopoly here and the popular nova4 plus gauge and compass will cost quite similar anyway.

I guess I will have to look into dive com too.

But from reading this forum. Redundancy is another thing to think about.

Losing a dive console meaning lose both information, but even using the wrist dive com with SPG and one malfunction I will lose 1 critical information anyway.

Do diver typically use 2 dive com for redundancy, or 1 dive com 1 dive console, or just a dive com alone?

---------- Post added December 7th, 2015 at 10:04 PM ----------

Hi CuzzA

It really helps. Your technique sounds like a good way to go.

Depth and Pressure monitored by analog and digital device and redundancy in both areas too.

Regarding the wireless AI is there any downside to it? I remembered reading that wireless AI works well in most situation excepts behind scooter, as its magnetic will interfere with the link. That's about the only downside I know.

Also, any brand/model is appreciated

Thank you
 
lots of downfalls to AI but the big one circles back to price.

Let's evaluate a couple simple options and we'll stay with Oceanic because you mentioned it first and I think Suunto is about the worst bang for your buck in the dive industry.

SPG is approximately $75 from most manufacturers
Pro Plus 3 with QD and USB-$880, $680 without either.
Geo 2.0 is a comparable computer, just in a watch form factor. $400 or $490 with USB
Atom 3.1-basically the same as Geo just with AI. $900 including USB

So, with USB downloads, you can spend $680, $570 *Geo plus SPG*, or $900. They are all functionally similar computers, so is going from a watch form factor to a big console with AI worth $100? Is going from a watch with a SPG up to AI worth $350? Only you can answer that, but most of the industry has determined that the answer is a resounding no. AI is nice to have, no one will argue with it, but the transmitters are big, the reliability is a lot better than it used to be but can still have issues, and it is VERY expensive. For $900 that Atom is still only a 3 gas computer where as the diver you have no ability to control conservatism, requires a proprietary USB cable to download dives, and has the casio style screen. If you want to spend $900 on a computer, look at the Seabear H3 which is about that price, but has a VERY nice screen, you get to control how conservative you want to be with NDL's, has NFC upload, digital compass, etc etc. Has the ability to go AI once they release the transmitters, and can actually be worn as your every day watch if you so choose.

The reality with pressure is this.
Say you're an "average" diver with a sac rate around 0.65cfm. If you're doing a 100ft dive with an AL80 *not recommended, but happens all the time*, then you will be breathing ~2.6 cfm which is about 100psi/minute. This is very convenient because you only have to look at your pressure gauge every 5-10 minutes. You did your rock bottom calculations and know you need 1000psi buffer for your ascent in an emergency, and you have a full tank, so you have 2000psi to burn. You do a quick calculation and say your maximum bottom time is going to be 20 minutes because 2000psi/100psim=20min and this coincides with your NDL's.
You descent, and record depth/time/pressure like you were trained to do. You say ok it took me 5 minutes and 500psi to descent because you were excited whatever whatever. You glance at your watch every few minutes and at 15 minutes you check your pressure gauge and see that it's around 1500psi. You know that you have 5 minutes and 500psi until you have to ascent because of both gas and the dive plan, so at 13 minutes you check your SPG again. It's now reading 1100psi, you were breathing a little more than you expected so you signal "up" to your buddy and start your ascent. Get to your safety stop and check your depth/air/time to start your safety stop and after your predetermined time you ascent. Log yourself out for time and pressure, and you're done. You checked your SPG a total of 8 times, only 4 of which were under water. Once after you assembled your gear, once before you jumped in, and once before you descended. These should all be close enough to the same value. During the dive you checked 4 times, once when you hit your planned depth, once about 10 minutes in, once before your ascent, and once at the safety stop. You logged yourself out for time and pressure for the last one.

This obviously only works for square profiles not sawtooth where you would check at every depth change, and is somewhat simplified for easy math, but it is how we actually conduct technical and cave dives. It is all based on proper dive planning and time to where you should know within 200psi of where your gauge is going to be when you look at it. This comes more easily with time and experience, but that is why digital pressure gauges are still considered nice to have, but not necessary for our world
 

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