Computer vs Gauge Failures

[RPanick]

Reading through a few of the posts I got to thinking about what are the chances that a computer would fail on a dive. The more I thought about it, the question really became what are the chances of any piece of instrumentation failing. So are gauges more dependable than a computer. Here is the statement I'm looking for a survey on:

Have you had a computer or guage fail on a dive. Please exclude cases of physical damage, I'm talking about simple failure. Also, please indicate if it was infant mortality in the computer (i.e. if a computer will fail, its likely in the first few hours of operation). Battery failures simply should not happen if they are checked prior to a dive and/or changed regularly, so please don't count them either).

If you want to clarify please describe what happened.

 

[DA Aquamaster]

I have had one computer failure during a dive. This was due to a defective computer that was replaced under warranty. It occurred with about 80 dives on it so I would not call it infant mortality. It was also air integrated but despite loss of N2 loading info, it continued to display tank pressure until the end of the dive.

I had another non dive failure after the computer's third diving day. The computer would not initialize at the start of the next diving day so it was not a failure during a dive but was none the less a pain.

I have also had one battery failure with a computer. Your assumption that battery failure should not happen is not quite correct. In my case, the voltage prior to the dive was sufficient to preclude the low battery indicator display. However the voltage was not adequate to prevent the computer from dying 120 ft down in 39 degree water once it cold soaked. I also had a similar battery failure on an electronic SPG. The normal low voltage warning parameters on some units are just not adequate to ensure adequate warning in very cold water diving situations and extra care is required.

In contrast, a mechanical SPG is very reliable as it is very simple with a bourdon tube and a very simple mechanisim to move the needle. An SPG will even function even if leaky or flooded and the condensation in the guage will warn you of this long before corrosion kills the guage.

A mechanical depth gauge is also very simple and reliable with either a standard bourdon tube or a bourdon "C" tube in the gauge with a simple mechanisim to move the needle.

A capillary depth gauge is super simple with no mechanical parts to fail.

If you are using a computer, you should always have a contingency plan that is sufficient to get you to the surface and through any required deco obligations safely. So the use of a computer does not alleviate the need for thorough pre dive planning. A backup gauge of some sort is also a requirement.

This can be a simple and very thin capillary depth gauge (which is very accurate at depths above 60 ft and great for deco) that will fit easily in a pocket or a standard depth gauge in a pocket or wrist mounted. In my case I also carry a lift bag and a reel with the line marked in 10 ft increments to 40'. A buddy's depth gauge or computer also works but is less convenient and requires the buddy to be present.

But in short, 1 computer failure and 1 unannounced battery failure in about 600 computer dives is still not bad with a combined failure rate of only .3 %.

 

[Uncle Pug]

Never have had a computer failure.

Haven't had a gauge failure either.

 

[Snowbear]

Have you had a computer or guage fail on a dive.

I had a computer fail to stay in my pocket :eek5:

I was using it to basically back up what I thought I was doing wink. At what I was figuring was the end of particularly aggressive multi-level dive I pulled it out at about 17' to see what it said. It had long since cleared and I stuck it back in the pocket and zipped it. Well, when I was rinsing gear, it wasn't in the pocket. Crap! When I went back 2 days later I knew about where I was when I lost it, so searched around and found it within 2 minutes - WooHoo! It was right where I dropped it, but now was in 23' of water and had racked up 38 min of ascent time with a 10' ceiling. I put it in the pocket (for real this time!) and took it with me to 107'. It was so severely bent by the time I finished that dive and the 76' second dive that it stayed in freakout mode for 56 hours!

Next DIY project is to get the bungie loop installed in my dry suit pocket so I don't keep dropping stuff in the ocean.

 

[RPanick]

I tend to agree most mechanical guages tend to be pretty reliable.

But this got me to thinking a bit. Has anyone taken apart their computers to see what they are using to measure depth and tank pressure? Or simply know what kind of sensors they are using.

Oh, and my comment about battery failure, that's personal bias, I check my indicator before every dive, but I also change the battery once a year, or before extensive (expensive) dive trips. They really don't cost all that much, and the old battery makes a nice backup.

 

[DA Aquamaster]

With around 130 dives per year, I normally change my computer battery around the 4th of July at about the same time I haul the boat for some mid season preventive maintenance. They are under $4.00 each so why not.

I have noticed that over a period of several years some computers can develop significant depth errors. (3-5 ft at 100 ft) I have seen this most often with the pelagic made "hockey puck" style computers but then I have also seen far more of them than others in this area. In my experience it is a good idea to compare your computer to other computers or depth gauges at depth from time to time to see if one of them has a possible calibration issue developing.

A 1 to 2 ft difference is pretty normal as nearly all computers leave the factory with +/- 1% accuracy and two computers at opposite ends of the scale will produce a 2 ft difference at 100 ft. Anything more than that could denote a problem.

 

[5615mike]

Never had a guage failure only a computer failure. Replaced under warranty. Had a battery go bad also which was weird since it showed 5 bars before the dive and then locked up. Replaced the battery and has been fine since.

IMO guages are your life line. Computers ARE NOT. Exactly why I don't use AI computer. You should always use an SPG with it which really defeats the purpose anyway. Dive Safe

 

[diver_paula]

There was a man in our club that would test any club member's depth guage in an automotive lab. He's retired now or he'd still do it. It was amazing how many gauges did not record the same depth as the calibrated lab chamber. He'd provide charts showing how far off a gauge was at each 5 or 10' interval of depth. He tested each gauge multiple times and provide the average and worst charts.

My Sherwood depth gauge was off a full 10' at 100'. NOT GOOD. However, given I knew that, I was able to take that into consideration when planning a dive. I then made the mechanical gauge my backup and a Suunto computer my primary. It was very interesting watching the differences. For the past 8 years I've been diving with two Suunto's and the most they've been 'off' is 1 foot. Which is easily understood given the two different locations of the gauges.

Paula

 

[diver_paula]

p.s. I did have one of the computers fail. The depth stopped reading correctly. (I'd be at depth and it would still show I was on the surface at times.) This was replaced with no questions asked.

 

[miesemer]

My Cobra's cylinder pressure tranducer failed last week. Pressure would bounce from actual tank pressure to 0 and sometimes back to something in between. Mostly it now just sits on 0. I used a backup mechanical SPG to complete my vacation dives. The computer continued to run it's depth sensor and other functions accurately.