problem with the depth reading

[Maxime]

Hi everyone,

SorenB, I have exactly the same problem, diving in Nemo33 (actually 35m) my ostc mk2 shows 33m.
I compared my mk2 with A LOT of other divecomputers and my mk2 always shows the shallowest depth.

[Bardass]

in french
http://www.nemo33.com/fr/plongee/briefi ... -connaitre
"La plongée dans la zone entre -20m et le fond (-35m) NE PEUT DEPASSER 10minutes cumulées par heure de plongée."

in english
http://www.nemo33.com/en/dive/briefing- ... ed-to-know
"The dive time between -20m and -34m CAN NOT EXCEED 10 minutes."
"The maximum depth for students of a DEEP DIVER SPECIALTY is 35m if he/she has minimum 20 Dives."

in german
http://www.nemo33.com/de/plongee/tauche ... tsgruenden
"Taucher dürfen sich MAXIMAL 10 Minuten am Stück im Bereich zwischen -20m und dem Boden (-35m) aufhalten."

[dmainou]

So the pool owners can't agree on the depth?

May wish to check this link:

http://www.si-micro.com/applications/consumer/

It is for the link for the Pelagic supplier... not much info though (at least when compared to the info provided by intersema.)


Found a reference that the same sensor (mk2) is used by the Vr3 and other technical pc's.

Jan, how different is the reading between your three pc's?

D

[SorenB]

Hi dmainou,
I guess you were so busy laughing that you forgot to actually go the the web-site of Nemo 33 (http://www.nemo33.com/en/dive/briefing- ... ed-to-know)

Trusting a 5 line intro in wikipedia seems to be the norm today, instead of trusting the people that runs the place. In any case my old dive computer that I used to check the OSTC again in Nemo was checket against a Sherwater Predator less that 14 days ago and was accurate to 0.1 m at 45 m. Not to talk about the three other dive computers in the water at the same time which all showed 35 m. I think this is what counts and not some speculations about other manufacturers "tuning" their dive computer.
Also, when I check the current pressure displayed on the OSTC it is off 1-1,5 % (too low) in comparison to the realtime on-line atmosphaeric pressure of the metrological institute.
As such, it does indeed seem a problem with the calibration of the OSTC despite your attempts to "prove" the contrary. I guess neighter fatiger, patrick nor I am lauching very much about this as we seem to be ones that have a problem trusting our newly acquired dive computer (and probably have to send the computer back to Henrichs Weikamp for re-calibration). I think that trust in our instruments is something we can all relate to.
best regards
Soren

[Solodiver]

dmainou Wrote:
> Jan, how different is the reading between your
> three pc's?

Find attached a pofile of the same dive logged with each of the units.

The predator shows 65m, the MK2 shows 63,37m in jdivelog. The Gekko shows 64,01 in jdivelog but this is different to the values shown on the display in the water (Sorry, don't know the exact value for this dive, sample rate for the Gekko is set to 10sec). I'm not really sure, but I remember it showed less than the MK2 in the past, but seing this profile and checking the history it might be the other way round.

Has someone checked the readings with different/older version of the MK2 firmware? I've the feeling that I had a bigger difference to my Gekko in the past.

BTW, this is my raw data right now (running 1.83):
C1: 2483
C2: 5062
C3: 392
C4: 224
C5: 2029
C6: 60
D1: 15038..41
D2: 26637+ (raising quite fast)
OFF: 15059
SENS: 4269+
xdT: 407++
xdT2: 403++
amb: 977..80
temp: 232
ADO: 431
BATT: 4163

The pressure around here should be 1024hPa regarding to different and current informations on the internet, the unit shows 976..980mbar which seems quite a difference.

Hope this helps

[Heiko]

My barometer is showing 966mbar, my OSTC MK2 is showing 969-971 at amb.

Cheers

Heiko

[Regthing]

I wouldn't use the local weather report to tell me what the air pressure is, this is averaged over a number of baromoeters in the area used by the the weather folk, local variations are to be expected.

And again your barometer would need to be calibrated to be any good as a comparison.

[Solodiver]

I don't belive that the local weather stations are so wrong. I've several nearby which I can check, including an official one at the airport, a school and a private guy - all of them are showing 1024 to 1025hpa for the last couple of minutes (and hours too).

Please check the attachment: My MK2 is showing 977..979mbar right now so I checked my shearwater predator which is showing 970/971 which is very near to the MK2 readings. So what is wrong here?

[nakatomi]

The weather station 3m from here (same altitude) is currently showing 1014mbar (10 minutes ago)
My Mk.2 is bouncing around between 1006 and 1014 right now.
That seems as accurate to me as such a handheld device can possibly get.

[sailor]

Hello,

these pressure-sensor used in DCs are not designed to measure very exactly a pressure of around 1 bar.
They are designed to measure a pressure from less then 1 bar to a max. of 14 bars ( OSTC MK2 ).

I believe the altimeter function was not a good idea because it makes some people believe it can measure very exactly around 1 bar.

The DR5 uses two sensors, guess why?
Because it is not possible to design a pressure sensor with a reasonable tolerance from 1 bar to 30 bars.
So one sensor is good from the surface up to 100 meters, the other one from @ 100 meters up to the maximum depth.
The sensor for depths below @ 100 meters will not give acceptable tolerances from the surface to 100 meters and the other sensor will die below 150 meters.

A sensor of a weather-station will die at 3 bars so it can be much more acurate at 1 bar, a DC sensor has to withstand at least @ 10 bars, so it will not be able to have a very small tolerance @ 1 bar.

Just my two cents, Reiner

[Bardass]

right now
my MK2 is showing between 992 and 995mbar
my citizen Promaster is showing 995
my suunto s6 is showing 994

nothing wrong, except maybe the pressure value for the MK2 changing too fast : between 992 and 995 in a few seconds

[dmainou]

Hi Soren,

I did check their website. There is no section outlining the pool facts such as the maximum depth, the number of liters their filtration, etc. It will actually be quite cool if they did as it is a unique pool.

There is a section where they offer SSI training. Within that section they offer a "deep" course that qualifies a diver to go up to 35m. That does not mean that the pool is 35m deep as instructors do not need to take you to the maximum depth of a certification. They just need to take you within the range.

Most OW courses are around 10m although they roughly qualify the diver to 2ata and so on.

So a deep cert, which may well be anything less than 35m and more than the deph of the previous SSI certification is within the range of the pool.

Other sections of the website refer both to 34 and 35m. So, Do we know if it is 35, 34.5 or 35.5 or 33 as the name implies?

The best way for you to get comfort is to go into the pool with a 30m spool that has knots every 5 meters, tie the mk2 to it and get one of your buddy's to hold the spool whilst you check the depth recorded by the mk2 at all those depths.

Or, post the output of your Mk2.

The only actual test was posted by Fatiger and it came very close.

D

[dmainou]

BTW,

This spanish part of the website sets it at 33m

http://www.nemo33.com/es/gm/foro-preguntas-respuestas

Google comes out with the following results to searches within the nemo33.com website:

33m 38 references
34m 3 references
35m 69 references
"33 meters" 1 reference
"34 meters" 0 references
"35 meters" 0 references

Up to you if you do the testing or not but you need to make sure that the instrument you are using to measure is accurate before using it to measure anything at all.

[Solodiver]

sailor Wrote:
> these pressure-sensor used in DCs are not designed
> to measure very exactly a pressure of around 1
> bar.

Sure? At least when it comes to units controlling a ccr (which is the MK2 not doing what is really, really sad!) I expect them to be _very_ accurate (think about calibration and ppo2 f.i.).

So I expect my (hardwired) shearwater predator is correct as is the MK2, but still the weather stations around shows 5% plus!?

[SorenB]

Hi Dmainou,
If you cannot come up with something sensible to say perhaps it would be better not to say anything once in a while. You are actually telling everyone here in the forum that the people that run NEMO 33 do not know how beep their pool is. You have never been there and you have never talked to the people there and still you have a very strong opinion on the issue and is very good at coming up with fantastic theories. Amazing ego. Before you make statistics on the internet, perhaps you should consider just how much junk information that is on the web. I have no intention about discussing this any further whith someone who obviously doesn't know what he is talking about. Soren

[dmainou]

Dude,

I'm just going by their website. If the people that constructs the nemo33.com website can't put their act together and the depth of the pool changes depending on the language that you navigate is a different q.

You have stated over and over again that your computer is off by comparing your computer with something that someone TOLD you measured ABC.

The only thing I have encouraged you to do ,more than once, is to grab a piece of string, measure it and then proceed to compare it to your computer's reading.

It is not unreasonable.

Up to you if you do it or not.

I may have an "Amazing ego" dont worry brother you can continue to think that the earth is flat and that you will fall if you navigate long enough. You won't know if that is true until you test it.

D

BTW. I wouldn't give a rat's ass if it is 33, 34 or 35m. We are discussing if your sensor & other's are accurate or not. To be able to measure that you need a measure tape not an anecdotal quote from the staff of a pool or a website that continues to vary depending where you read it.


SorenB Wrote:
-------------------------------------------------------
> Hi Dmainou,
> If you cannot come up with something sensible to
> say perhaps it would be better not to say anything
> once in a while. You are actually telling everyone
> here in the forum that the people that run NEMO 33
> do not know how beep their pool is. You have never
> been there and you have never talked to the people
> there and still you have a very strong opinion on
> the issue and is very good at coming up with
> fantastic theories. Amazing ego. Before you make
> statistics on the internet, perhaps you should
> consider just how much junk information that is on
> the web. I have no intention about discussing this
> any further whith someone who obviously doesn't
> know what he is talking about. Soren

[dmainou]

Hi guys,

I have been reading a couple of manuals for everyone's comfort:

Suunto HelO2

Depth gauge:
• Temperature compensated pressure sensor
• Fresh water calibrated (calibrated in compliance with EN 13319)
• Maximum depth of operation: 120 m/393 ft (complying with EN 13319)
• Accuracy: ± 1% of full scale or better from 0 to 120m /394ft at 20°C/68°F (complying with EN 13319)

No Salinity adjustment available

Dive Rite Nitek Trio (Seiko)

Depth sensor
Sea or fresh water calibration
Measuring range: 0 to 328 feet (0 to 100 m) measured every second
Accuracy: +/- 3% + 2 feet (0.5 m)

Hollis DG01 bottom timer

Fresh for dives over 3000ft (no disclosure of salinity setting)

OPERATIONAL PERFORMANCE
Function: Accuracy:
Depth: ±1% of full scale


Conclusion

• Assuming your diving in a liquid that has the exact characteristics for which your sensor was calibrated, don't hold your breath for 50cm as the sensor can be off by that much.
• Those computers that have no fresh water/salt water setting are likely to be set at 1.015 salinity. (and still can vary for as much as the previous point). If you want to know why buy a copy of the standard.
• If your are diving in a liquid different to the salinity settings, again it could be wrong for a couple of meters. 50m of fresh water with a salinity setting of 1.04 are displayed on the screen as 48m +-50cm. However deco and PPO2 calculations are NOT affected as the whole calculation is based on pressure.
• Also, I believe that all of the computers above use the same sensor as it is one of the few specifically designed for scuba.

Therefore your mileage may vary

PS. Jan, I know why you can remember that one computer was different to the other underwater and you have a different result on JDiveLog. There is a small, easily fixable, bug in JDiveLog. It's taking raw data without adjusting for salinity. I have reported it to both Pascal and Matthias. Should be fixed soon in JDiveLog.(nothing wrong with the Mk2.)

Best regards,

D

[nakatomi]

This discussion is sort of funny in a strange way.

The Nemo33 pool was 33 meters deep, back when it opened in 2004. At the time it was supposedly the deepest pool in the world.
You can find tons of press releases mentioning the 33 meters.

How the pool would grow deeper by 2 meters over the following 6 years is indeed very mysterious.
As is the fact why anyone would be stupid enough to name a 35m deep pool "Nemo 33" in the first place.

So maybe we should face the fact that it´s 33 meters deep (maybe 25cm more if they fill it to the rim) and that Soren´s OSTC is spot-on.

[nakatomi]

By the way, here is an article from timesonline.co.uk that has more details than most other press mentions:

http://www.timesonline.co.uk/tol/travel ... 479662.ece

[Regthing]

OK, I did some testing today...

I set the salinity at 1.00 an put in a small pressure vessel. Unfortunately I didn't have a clear one large enough to view the actual reading but took maximum depth from the log.
[img]http://i197.photobucket.com/albums/aa14 ... 011223.jpg[/img]

I increased the pressure to 8 bar as measured in a recently calibrated gauge
[IMG]http://i197.photobucket.com/albums/aa14 ... 011225.jpg[/IMG]

Allowed the pressure to disipate and noted the maximum depth 80.28m
[IMG]http://i197.photobucket.com/albums/aa14 ... /OSTC2.jpg[/IMG]



I also found a website that gives regular updates from the weather station at Glasgow Airport, which I am right next to.
[IMG]http://i197.photobucket.com/albums/aa14 ... g/OSTC.jpg[/IMG]


Overall I think I'd be quite happy with that!

I'm going to see about getting a clear endcap for the pressure vessel so futue test will alow me to monitor the OSTC during the "dive".

[Solodiver]

Come on guys, lets not dispute in here. We have people around having strong opinions in different ways - but in the end we're discussing about one of the finest dive computers around. Would be great to concentrate together to make it even better, so please, please take a deep breath, stay calm and lets stay cooperative. If I could, I would all of you pay a beer and have some nice talks together, face to face!

I know I brought it up - but please lets stops now the discussion about this Belgian pool. I think we've gathered some interesting information in this thread and in the end I'm still very curious what the actual issue is. For me it is still not clear where exactly the noted differences are coming from and which unit is right and which is even more right or just wrong.

Many Thanks to all of you for your support and collaboration in the past, looking forward to see all of you around in the next years also,
Jan

[dmainou]

Hi Jan,

Realistically, no one gives a rat's ass about the pool. I am happy to report that I have scuba dived twice in a pool in 10 years (for my OW and for deco procedures)

So, not a pool diver. I would do that pool once just to say I've been there but that's it.

The only reason to want to know the EXACT depth is to help a fellow diver to gain comfort with his pc. I have suggested him to go down with a measure tape (or a spool) whilst someone holds the other end at the surface. Then compare it to the reading. This is regardless of the depth of the pool. Conduct the test at 20m for the love of God! (I really don't care if it is 33 or 35)

This has not been welcome. The diver seems reluctant to do any testing even to post the dump of his computer. He simply wants the OSTC to match other computers that match the E13319 standard AND that are likely to have little to no adjustment in their salinity settings. This is regardless of whether his sensor is showing the correct reading or not.

Well, my answer to that is that the important thing is that the sensor is accurate as that will drive deco calcs and gas changes. Who cares if a bloody mares nemo (which I initially thought was being used to compre) or a suunto helio2 says it is a different depth because their salinity levels can't be adjusted.

The Mk2 is not that kind of computer as the Mk2 can be adjusted depending on the conditions. If you miss adjust the salinity don't worry as all calculations are done based on pressure. The salinity adjustments only adjust the display you read.

If you can't handle that reality ebay is your friend, you have purchased the wrong product.

Now back on track. (so we can stop speaking a bout the bloody pool)

I believe that there are two sources of variation

* If you happen to have a good sensor like fatiger's then you are spot on. If your sensor is a bit off then the factory that produced the sensor will give it the OK for sale if the error is less than +/-1%
* As mentioned before the salinity settings of each computer. If I divide the reading from my bottom timer by 1.015 the outome matches the Mk2's raw data. Same thing if I divide the display of the Mk2 by my salinity setting (1.03) or the output of my old N2ition 3.

The sensor is used by almost every dive computer manufacturer and it is calibrated at the sensor's manufacturer's plant.

I hope this helps to explain the differences between readings.

If you are still in doubt find a pressure pot or find a lake, a buoy and a piece of string.

Best regards,

D

[Regthing]

If I get time tomorrow I'll pot test my OSTC, UWATEC bottom timer and Apeks Quantum (Seiko, same as the Dive Rite) together and see what variance I get.

The uwatec is set for fresh water (well the old ones where, I'm assuming the 330m are too) and the Apeks can be set for fresh or sea water.

[size=x-small]P.S. I'm in the "Not really caring about the depth reading" camp, it's just that I can so I will do tests if it helps others[/size]

[Patrick75]

Hello,
dmainou you do not consider what the others have to say, you are only continuously interested by the normal operating characteristics of the sensor.
In my own opinion it is not the problem : we are speaking on anormal readings, not on standard ones.
I think that MY Mk2 does not measure the pressure with a sufficient accuracy : for example I dove twice in pools with paint marks "5M", "10M", "20M" and MY Mk2 displayed "9.5M" instead of "10M". That means -5% and -3M at an actual depth of 60M. I had also an Uwatec bottom timer which display well "10M" at the same depth (salinity setted at 1.00).
This is only an example, at sea the same drift occured also by comparison with others divers instrument.
Considering "border line" the -5% depth accuracy, I proposed that HW implement a correction factor function which could allow me, and also the others in the same case to adjust the display (linear corrective factor 1/0.95).
Again, I have also compared the displayed surface pressure with official meteo services information : MY Mk2 display 1035 or 1040 mBar when the official information is around 1015 or 1020 mBar.
Thanks every one for your information.
My goal to inform HW is achieved even with no answer received from them : the 1.82 beta method was not properly stated in details in my own opinion.
I very much appeciate my Mk2 but definitively not the depth accuracy of MY set.
Best Regards Everyone,
Patrick OSTC 464

[Solodiver]

Regthing Wrote:
-------------------------------------------------------
> If I get time tomorrow I'll pot test my OSTC,
> UWATEC bottom timer and Apeks Quantum (Seiko, same
> as the Dive Rite) together and see what variance I
> get.

Thx Scott! If possible could you keep the pressure at a constant level please? We also have to consider the sample rates of the different units (which could also be a source of the different readings/profiles) and maybe the sensors behave differently after some time. Also the temperature might be a factor, but I guess you have no chance to change it?

And if you do pics afterwards please do one with the raw data, just for any case and HW (and maybe other users) to be able to compare it to others.

For the rope/string thing: One have to consider a stretching of the rope whilst being wet and quite long having some weight pulling down.

Thx,
Jan (who just came out of a 4 degree cold fresh water water having different readings of 60m+ on his predator and 59,34m on the MK2 which could be covered my the 1,015 difference mentioned by dmainou)