calibrating on multiple days diving

[tbone1004]

It's one button on most units (the 2.7meg being a notable exception). I dont get the months at a time avoidance.

My cells move back and forth between 2 units and I always recalibrate if they move.

the risk of miscalibrating is very real, so calibrating for the sake of calibrating is an unnecessary risk. You aren't saving any time by not calibrating since you are still validating, but I have found that it forces you to pay more attention if you go into it thinking you shouldn't have to calibrate and then find out you do. It also forces you to start tracking the mV output in air and in O2 to start predicting what the output should be.
If you move cells back and forth then it shouldn't change the calibration, but it does definitely increase the odds that something went wrong and you won't be able to use the same calibration.

 

[broncobowsher]

Also need to question your source of O2. If doing something like Truk, I calibrate at home on a known O2 source. Because I know the O2 I will be getting on the islands isn't 100%.

As stated, no calibrate, only verify on a multi day use.

 

[Jack Hammer]

Or you could just calibrate in air and match it to O2. (JJ-CCR, calibration is super fast and simple)

NEVER calibrate a rebreather in air unless it has multi-point calibration like the old megs. If you calibrate in air you run a serious risk of oxtox due to linear deviation.



You validate calibration, but you only calibrate when it no longer matches a known source. If I O2 flush and it's between 0.98 and 1.02 I consider it "good enough" and don't bother calibrating

Yeah, that came out wrong on my part. What I was poorly attempting to say was to check MVs in air and verify what you are expecting to see with O2 via calibration. (Air MV x 4.76)

I mark my air MV on an assembly sticker on unit and with what O2 is expected to show so it can be rechecked easily.

With something so quick and simple to do I have no idea why anyone would suggest doing it only a few times a year. (Again, I'm on a JJ)

 

[rddvet]

I calibrate every time I build my unit. I thought that was pretty standard, but apparently not.

 

[_Ralph]

I'm on the fence with calibrating every time .... and with differing mentalities from training on several different units..



On one hand, unless you proactively do something to record and look at cell readings over time (each calibration), you may not see a problem.

With the JJ, I was taught to calibrate every time..... What I do, is verify the cells are within .1mV in air from the previous calibration, and that they are within <2mV in O2.... If they aren't, I don't hit the confirm option and source out the issue. If they are within that tolerance, then what is the harm on hitting the confirm button?

On my sidekick... I verify that the mV line up with the contents of the loop (if I'm 11.0mV in air, I want to see at least 50.5mV after a few O2 flushes)....

These are all for "current/old" cells, not newly installed cells of course.


_R

 

[rjack321]

the risk of miscalibrating is very real, so calibrating for the sake of calibrating is an unnecessary risk. You aren't saving any time by not calibrating since you are still validating, but I have found that it forces you to pay more attention if you go into it thinking you shouldn't have to calibrate and then find out you do. It also forces you to start tracking the mV output in air and in O2 to start predicting what the output should be.
If you move cells back and forth then it shouldn't change the calibration, but it does definitely increase the odds that something went wrong and you won't be able to use the same calibration.

You do what you want.

This pretty much goes against every CCR manufacturer's recommended practice and also against how nearly every scientific instrument is used to measure pH, DO, chlorine, TSS, temperature, or anything else. You don't avoid calibrating (for months) because of a risk of screwing it up. You follow procedures and verify against known standards.

 

[wedivebc]

When in training you calibrate every day for the practice. In real life I calibrate when there is a change in my O2 reading in air and in pure O2. I used to calibrate my pathfinder in air all the time because it was easy to do that. I would verify my calibration in O2 once in a while as well. With high quality cells there is very little linear drift or offeset so calibrating in air was not an issue. On my Tiburon I calibrate in O2 and then only when my air point mv readings have changed from a previous calibration. With Vandergraph cells that change can take months.

 

[Jack Hammer]

I'm kinda confused, maybe some one can clarify. What's the big hassle and downside to calibrating daily? Is this a unit specific thing? What am I missing or misunderstanding?

For reference, on my JJ the process is during assembly read, write down air MV, & calculate expected O2 MV (air MV x 4.76) and write down. Assemble. Once assembled and passes pos/neg, open all valves, hit calibrate on Petrel controller, wait 30 seconds or so, read MV on O2 and hit accept or cancel, compare to what's expected. Repeat next day starting with opening valves and hit calibrate on Petrel then compare to expected, if off investigate further. On my unit this uses a couple bar of O2 and takes about a minute. I don't see a downside to doing it daily.

 

[tbone1004]

I'm kinda confused, maybe some one can clarify. What's the big hassle and downside to calibrating daily? Is this a unit specific thing? What am I missing or misunderstanding?

For reference, on my JJ the process is during assembly read, write down air MV, & calculate expected O2 MV (air MV x 4.76) and write down. Assemble. Once assembled and passes pos/neg, open all valves, hit calibrate on Petrel controller, wait 30 seconds or so, read MV on O2 and hit accept or cancel, compare to what's expected. Repeat next day starting with opening valves and hit calibrate on Petrel then compare to expected, if off investigate further. On my unit this uses a couple bar of O2 and takes about a minute. I don't see a downside to doing it daily.

the risk of a bad O2 flush and miscalibrating. Since very few divers, fewer instructors, and even fewer instructor trainers acknowledge that linear deviation is a thing, they usually don't calculate predicted mV output for calibration. This means you have no actual way of knowing if the system was purged properly and you are getting an accurate calibration on MOST machines *things like the APD, Poseidon, and Divesoft are less prone to a botched calibration*. So you only get a 90% purge on your unit, and because you're an ignorant f*ckhead and don't believe in linear deviation your cells are only 90% linear, so now you have a compounding issue where by the time you hit your 70ft stop and think you're breathing at 1.6, you're actually breathing at 1.6/.9/.9=2.0 and you do the funky chicken and oxtox. I don't care what the manufacturers say, they're trying to CYOA, it isn't because it's best practice, it's just easiest practice to not have to fully teach about how cells works and just tell the diver to calibrate on setup.

@rjack321 in general industry, devices are only calibrated when necessary and against known standards, typically annually. Their calibration is typically validated on a much more frequent period of either hourly, shift, daily, etc. but the calibration is verified, the unit is typically not recalibrated. This at least applies in the plant that I run which has over 1000 devices that are required to be calibrated for our ISO9001, AS9100C, and several customer specific requirements. Most devices are calibrated annually, some biannually, and they are verified at some more frequent interval. With the O2 cells I take this same approach. I calibrate in a known controlled environment, typically directly out of the O2 T-bottle, and then I validate calibration when I assemble. If the validation fails, then I will figure out why and determine proper course of action.

 

[beldridg]

the risk of a bad O2 flush and miscalibrating. Since very few divers, fewer instructors, and even fewer instructor trainers acknowledge that linear deviation is a thing, they usually don't calculate predicted mV output for calibration. This means you have no actual way of knowing if the system was purged properly and you are getting an accurate calibration on MOST machines *things like the APD, Poseidon, and Divesoft are less prone to a botched calibration*. So you only get a 90% purge on your unit, and because you're an ignorant f*ckhead and don't believe in linear deviation your cells are only 90% linear, so now you have a compounding issue where by the time you hit your 70ft stop and think you're breathing at 1.6, you're actually breathing at 1.6/.9/.9=2.0 and you do the funky chicken and oxtox. I don't care what the manufacturers say, they're trying to CYOA, it isn't because it's best practice, it's just easiest practice to not have to fully teach about how cells works and just tell the diver to calibrate on setup.

@rjack321 in general industry, devices are only calibrated when necessary and against known standards, typically annually. Their calibration is typically validated on a much more frequent period of either hourly, shift, daily, etc. but the calibration is verified, the unit is typically not recalibrated. This at least applies in the plant that I run which has over 1000 devices that are required to be calibrated for our ISO9001, AS9100C, and several customer specific requirements. Most devices are calibrated annually, some biannually, and they are verified at some more frequent interval. With the O2 cells I take this same approach. I calibrate in a known controlled environment, typically directly out of the O2 T-bottle, and then I validate calibration when I assemble. If the validation fails, then I will figure out why and determine proper course of action.

I think the important distinction being made here (and in this thread in general) is calibration vs. validation.

I personally very rarely calibrate but I do validate every time I build the unit.

Regards,

- brett