problem with the depth reading

[fatiger]

Just got my MK2 10 days ago and go for a dive trip to test it!
Everything is very nice, but the depth reading is off compare to my depth gauge and my old dive computer.
A dive I make from the depth gauge and computer show around 54 meter. The MK2 show only 48 meter. I didn't change the salinity setting (still: 1.00kg/l) How can I adjust the depth reading on the MK2 or I need to send it back to the factory to do the adjustment? Can Anyone help to solve my problem?

[heinrichsweikamp]

Hi,

The sensor is fix-calibrated from the sensor manufacturer. Can you install the 1.82beta firmware (You can got back to the 1.80 stable after the test), please? There is a new menu -> Setup Menu -> More -> Raw Data giving some raw data from the sensor. So we can check if this is a sensor problem or not.

regards,
Matthias

[dmainou]

Hi fatiger,

Were you diving in salt water or fresh?

Apart from matthias input you may wish to match the mk2 to the local salinity. Here in Sydney I use 1.03 to more less match my bt.

Google is your friend in that department.

[fatiger]

I'm diving in Subic Philippine for some ship wreck in Sea. Still too shallow even I set it the salinity at 1.00

[dmainou]

Salinity at 1.00 is for fresh water diving.

Try increasing the salinity to 1.o3 (or 4) and see what happens.

Try doing what matthias suggested and install 1.82

In the end don't worry too much. The ostc works on pressure the meter display is only so you can understand it.

D

[fatiger]

If set the salinity to 1.03 the depth will be even shallower! Sea water is more heavy than freash water! How deep I dive is important for me to set my oxygen percentage!!! 48 meter and 54 meter have a very different PPO2 value! If I use a 24% oxygen for my back gas and think I'm in 48 meter but actually is in 54 meter the PPO2 can go up to 1.54. What if I do a deco using 50% at 21 meter but actually in 26 meter? PPO2 will go up to 1.8??

[JeanDo]

As dmainou said, all the computation done by the Mk2 are from the senseo's pressure. So the displayed ppO2 and computed CNS is right, whatever slainity calibration you do.

I have an unfair question: what depth gauge are you using , How did you calibrate the salinity for that device ?

Thanks,

[ujacek]

Difference between 1.00 and 1.03 salinity settings is 3%, difference between 48m and 54m is around 12%. I think that salinity calibration is not a main cause of this effect.

[Patrick 75]

Hello,
I have the same problem with my Mk2 (Nr 464) (v1.80 but it was the samething with previous versions):
the depth is always 5% less than the real one (9.5M for 10M and thus 57M for 60M)
compared with paint marks or Uwatec deepmeter or others sets.
note : the salinity is correctly setted at 1.00 in fresh water
at the sea level the ambient pressure displayed is also roughly +5% than the current weather information shown by officials, at various locations.
I am aware that the deco is properly calculated on the pressure gradient basis and not on the absolute pressure.
but :
the +5% (and may be -5% for another one) are quite acceptable for the sensor but please, could you implement a correstion factor function which allows the user to adjust the depth like the clock-correction function.
I am right with the user responsability for properly adjusting the parameters of the set, no problem.
Wonderful set, very easy to use, super-Oled display.
Best Regards
Patrick

[SorenB]

Just got the OSTC mk2 1763 and have the same problem as discussed above.

Diving in freshwater to 35 m meter and the OSTC shows 33 m with the salinity set for 1.00 kg/l. It may be that it does not matter much, but it is still a mistake that should be corrected as I would like to be able to trust the computer. That was the reason I bought it. It would be nice if Henrichs Weikamp would devise a solution and not just suggest that we try to upgrade the firmware to a new version to see if it works. To me it looks as a calibration problem.
best regards
Soren

[nakatomi]

As far as I can tell from my (limited) experience, the depth sensor on the Mk.2 is usually very much spot-on and well-calibrated, as is the temperature sensor.
We have around 6 units in use in our diving group, and they are very much identical regarding both measurements.
The readings also correspond to other (trusted) readings.

[dmainou]

Hi guys,

The question has been posted before and has gone unanswered.

What are you using to compare? i.e. another computer or did you actually dropped a lead and measured the length of the rope?

If it is another computer how do you known that the other computer is accurate?

Some computers adhere to an AGREED pressure reading and display the same depth regardless of whether the depth is accurate or not and regardles of the salinity or other dissolved solids in the liquid.

Fresh water means H2O. Do you know how clean (as in disolved anything including chlorine) was in the water you were diving on?

In the end it is about the pressure that is on top of you not the number of meters. The meter display is for us to understand it as the computer has no use for it.

Of course there is the possibility of a failed sensor. However, you can not cry wolf just by comparing it to another computer as that is meaningless.

You are likely to own a spool. Tie it to something relatively static with the water level such as the boat's stern or side handles. Make some knots at certain depths and go down to those depths. Then you can compare and adjust.

If it is really off even after doing full adjustments then you have a case to ask for a replacement pc.

If you are not prepared to do some homework before posting then no one wins and all of us should buy a suunto and get our consistent but inncaurate reading.

Not trying to defend the MK2 just making a point of how statements have been made without anything to back them up.

Best regards

D

[dmainou]

Just for your comfort:

http://www.intersema.ch/index.php?optio ... format=raw

[dmainou]

http://www.intersema.ch/applications/un ... equipment/

Underwater equipment


Water depth is easily determined by measuring the water's pressure. As a first approximation, pressure increase of 1 bar for every 10 meters of depth. Diving computer using the MS5535 or MS5541 can accurately measure depth down to 130 meters (since the MS5535 is a 14 bar sensor).

The MS5535 or MS5541 have a typical resolution of 1.2 mbar representing a water height of 1.2 cm.


Thanks to their digital interface, they can be directly connected to any microcontroller. The internally stored compensation coefficients, increase dramatically the resolution of the device, thus allowing high-precision appliances.

The MS5535 can be ordered with or without protecting gel. This gel will insulate the sensitive part of the sensor from external environment. For more details, follow these links: MS5535/MS5541.

[Patrick 75]

Hello,
Thanks for your comments.
I also appreciate very much the OSTC Mk2 and in no way made a false complaint.
If you read again my previous post you will notice that the depth "measurement" was also performed by means of painted marks on the pool walls, several pools involved.
Thus, the problem on my computer is well documented.
I will try the last version (>1.80) in the near future.
In a constructive way, I suggested that a new function allows to adjust the depth like the clock case : in the +/- 5% range, under the user responsability.
I do not know if the pressure sensor could be exchanged for a new one whith a correct factory setting.
Best Regards,
Patrick

[dmainou]

Hi Patrick,

Jean Do's post asking how was the claimed depth was posted prior to yours so I wasn't referring to you in particular.

I find that mine set at 1.03 is a bit shallower than my BT and a bit deeper if I set it to 1.04.

This tells me that more less it agrees with the BT.

If you google pressure sensors you'll find that they are affected by all sorts of things. For example temperature or the pressure that a current exerts on the sensor which could add or subtract on the reading.

If there is chlorine or other things dissolved in the water the reading will be off.

The colder, deeper and impure the more inaccurate the meter reading will be. However, the concern is around pressure so it is, within reason, irrelevant if 10m are marked a 9.5.

Sorry to get back to the question. On those occasions did you measured the exact depth?

I get comfort that the sensor is built by a leading company and that its sensor is widely used in other computers

Maybe the request should be as follows.

Dear HW,

In addition to the salinity settings would you please be so kind to add a setting that adheres to the CEN European standard for depth display so we can have our inaccurate but consistent reading with other instruments?

Best regards,

D

[fatiger]

I finally find someone to do a dry run test in his lab. He has a pressurize box (I don't know what it exactly call but you know what I mean!) and boots the pressure to 5bar ATM and the computer I set my MK2 salinity on 1.00, the MK2 depth reading is 49.7 meter and compare to other computer in the box show 50 meter. I think the problem maybe from the sensor itself! I find the big different from both my old computer because it had set the safety factor so it show deeper than the real depth.
Is that OK? For a 0.3 meter shallower than the real reading? What should I do?

[dmainou]

Good on you.

Do you know if the computer was dry or inside a liquid? And the temperature.

If possible repeat the test whilst the pc is submerged. A glass of water should do. I think the documents mention 21C. Let the pc be at that temp for some time as well


I'm not an engineer so can't really tell you a lot but there is a lot of info on the links I posted above.

To me, a 0.6% error is quite bearable. I would actually be quite happy with it.

Even at 130m the difference is under a meter.

D

[sailor]

Hi,

i believe you will not find much divecomputers with a smaller difference.
Showing 49,7 mtr for 5 bar overpressure ( 6 bar absolut including ambient ) is most perfect.
There's no problem with the pressure sensor at all.
For sure your old divecomputer and your depth gauge you mentioned in your first post are at fault.
0,3 meter at 50 meter is nothing.

Reiner

[SorenB]

Hi Guys,
There is not so much to discuss. The computer was used in NEMO 33 which has a depth rating of 35 m max and it was checked against two other computers (and loads of others before that). So no matter if the sensor is accurate as hell, it is wrong by by more than 5 % in comparison to what it should be. So seems like a problem to me. Any suggestions from Heinrichs Weikamp?
best regards
Soren

[dmainou]

Hi Soren.

Fatiger's test on a pressure pot gave a result of 0.3m error on a 50m (6 ata) exercise.

It is 0.006 off or 0.06% it is nelegible.

To claim that the OSTC is off rather than the gauge on the pressure pot we would need to start by making sure that the pot's gauge is 100% accurate rather than 99.94%.

Remember that his initial post said that it was off by 6m on a 50 odd meter dive?

Dude you are flogging a dead horse.

What I do believe is that other computer manufacturers may choose to err on the deep side (rather than provide an accurate depth measurement) and use this as an opportunity to induce conservatism. i.e. the model requires more deco as you were theoretically deeper. The only thing they need to do is to calibrate their sensors for fresh water use as has been show by testing Fatiger's computer on the pot.

This happens to you every day. Your car has a well known and documented 5% error incorporated into the speedometer.

Car manufacturers do this to avoid legal issues. I wouldn't be surprised if the same happened with dive computers. We won't know about how other computers work cos most computers have a closed algorithm for legal reasons. The OSTC comes with no warranty and therefore the manufacturers can actually afford to tell you the truth.

Think about what you just wrote. You are pointing out the finger at the OSTC by comparing it to an instrument (please read post below about what IS the Nemo 33) which in your own words is only deemed acurate to 35m.

How about if you find a pressure pot or grab some rope, a fresh water lake and do some actual testing.

Best regards.


SorenB Wrote:
-------------------------------------------------------
> Hi Guys,
> There is not so much to discuss. The computer was
> used in NEMO 33 which has a depth rating of 35 m
> max and it was checked against two other computers
> (and loads of others before that). So no matter
> if the sensor is accurate as hell, it is wrong by
> by more than 5 % in comparison to what it should
> be. So seems like a problem to me. Any suggestions
> from Heinrichs Weikamp?
> best regards
> Soren

[dmainou]

BTW

Matthias posted the quote below 3 hours after the inital post.

Have you installed 1.82 and emailed them or posted the information he requested to check if there is a problem with your sensor?

Is that the "sugestion from HW" you were requesting?

I thing that you have received great service from HW.

To be quite honest, you seem to be complaining from your own lack of action.

D




heinrichsweikamp Wrote:
-------------------------------------------------------
> Hi,
>
> The sensor is fix-calibrated from the sensor
> manufacturer. Can you install the 1.82beta
> firmware (You can got back to the 1.80 stable
> after the test), please? There is a new menu ->
> Setup Menu -> More -> Raw Data giving some raw
> data from the sensor. So we can check if this is a
> sensor problem or not.
>
> regards,
> Matthias

[dmainou]

Hurray!

Soren, now I know what you mean by Nemo 33 http://en.wikipedia.org/wiki/Nemo_33

Ok you have stated that the OSTC is showing 33m when all other computers that you have tested show 35m.

Did you know that the Nemo 33 is only 33m deep?

So I think you just verified that other computers are off and the MK2 is not.

Therefore in your own words:

There is not so much to discuss. No matter if the Other computers match as hell, they are wrong by by more than 5 % in comparison to what it should be. So seems like a problem for other computers to me. Any suggestions from Suunto, Seiko and others?

This time you did make me laugh!;)

Best regards,
D

[Solodiver]

The German Version of Wikipedia states its depth is actually 35m:

http://de.wikipedia.org/wiki/Nemo_33

Maybe this is just a marketng trick based on wrong readings of mainstream computers

Jan (who also recognize the MK2 to show noticeable less than his Shearwater Predator but more than his Suunto Gekko)

[dmainou]

I would like to visit it one day to confirm the reading.

However, my mullah is on the 33m as otherwise the pool would be nemo35. (Who wouldn't advertise the last 3 meters)

Anyway, if in doubt:

1.82 -> new menu -> Setup Menu -> More -> Raw Data giving some raw data from the sensor -> email to Matthias.

D