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Thread: Review of Narked@90’s Mini Cell Checker

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    Mar 2006
    Inspiration Vision

    Inspo Classic, Dolphin, Ray

    Review of Narked@90’s Mini Cell Checker

    O.K., so I finally got myself a cell checker: Narked@90’s new Mini Cell Checker, the sort-ofportable, mechanical and above all quite affordable little brother of their older bigger all singing & dancing self-contained cell checker.
    With "self contained" I mean that the bigger one can do all the work by itself: it has its own electronic displays for showing the cell values, where the mini-checker relies on either your CCR or a good old voltmeter to display the results. It has no electric or electronic components, other than the cables to attach it to your CCR.

    I actually prefer that passive setup: no worries about batteries, displays, pumps, switches, etc: just a well-designed mechanical box that piggybacks on the electronics you already have in your CCR.
    Why double up if you had it already, eh..? It also makes it capable of taking quite a beating.

    Brent & John asked me to write a review, so here it is!

    Let’s first look at what it is. Essentially, the minichecker (which lazy me will abbreviate to MCC in this article) is a round pressure container in which you can place up to three oxygen cells, and expose them to pressures up to 2 bar (i.e. a PO2 of 2 bar) without having to get wet in the process.
    It weights just over 1 kilo, and its size is best described as a little bigger than a can of beer (or coke, for the non-drinkers amongst you..).

    It is fitted with:
    • a mechanical push-button oxygen inlet that conveniently hooks up to your MP oxygen hose
      from CCR to raise the pressure inside,
    • a similar push-button for deflation and flushing (replacing the air inside with oxygen),
    • an overpressure valve (OPV), set at around 2 bar, for those idiots who think they should need
      to test their cells at 10 bar or so,
    • a screw-on lid that has three numbered positions for attaching up to three cells to be tested.
      This is available in three versions: with molex, coax of banana plug attachments;
    • a mechanical precision gauge with a range of 0-2 bar to indicate the pressure inside the test
    • an attachment cable that you hook up to either your rebreather or a good old (milli)volt meter.
      Like the lids, there are 4 types of cable available: molex, coax, banana plug of crocodile
      clamps for a volt meter hookup.

    See picture on next page for a graphical explanation of the various components.

    The principle of the whole system is simple:
    1. Temporarily remove the cells from your CCR and attach them to the plugs in the lid of the
      Alternatively, in case of testing new (replacement) cells, you can leave the old cells in the
      CCR, put the new cells in the MCC, but swap the cables over from the old cells to the cable
      “boom” of the MCC. This way you can test your new cells before actually putting them in
      your CCR. Sort of "try before you buy";
    2. Attach the cable boom coming from the MCC to the cell plugs in your CCR scrubber had (the
      plugs normally attached to your inboard cells);
    3. Flush the MCC by keeping both the oxygen inlet and deflate button pressed, as such
      replacing the air inside with oxygen;
    4. Switch on CCR, calibrate cells to 100% O2 at 1 bar, as you would normally do when they
      were still inside your Inspo;
    5. Now raise the pressure in the MCC by pushing the O2 inlet button;
    6. Compare the pressure shown on the mechanical gauge on the front of the MCC to the PO2
      shown on the handset(s) of your favorite CCR.
      This allows you to verify the linearity of the cells in the whole 1.0-2.0 bar PO2 range.
    7. Leave the cells at a high PO2 value (e.g. 1.8 bar or so) for a while, to check if they do not
      “die” after an extended period of exposure, as such indicating a spent or rogue cell.

    There are also other methods of measuring (the supplied manual is quite complete in this respect), but for the review here I’ll stick to the simplest method available in combination with my Inspo Vision. It would also work likewise on a Classic.

    So: how are my practical operational experiences?

    Here is what I did to test the little beast:
    • As a baseline reference, I started with testing my brand-new cells with my good old digital voltmeter, directly attached to the cells. IMPORTANT TIP: make sure you use the little adapter supplied by APD that comes with every coax Inspo, otherwise you ruin the little centerpin of the coax connection in the cell!

    • Next I placed the new cells in the lid of the MCC, locked them up in the pressure pot (at this point obviously still exposed to ordinary air @ 1 bar), and hooked up the supplied (removable) cable set of the MCC.
    • I then measured the millivoltage again, using the little Inspo adapter mentioned above, but this time fitted to the male ends of the MCC cable set, to see if the MCC cable set does a good job in conducting electricity (i.e. does not introduce additional resistance). The mV values were the same as when tested directly on the cells, so a big o.k. for the quality of the cable set. It is well constructed, not flimsy at all.
    • Next the REAL test, where it’s all about! I hooked up the O2 inflator of my Inspo to the inlet of the MCC and flushed the pressure pot by keeping both inlet and outlet button pressed, as instructed by the manual. 10-20 seconds will do the job, as it is only a very small space you have to flush. I watched the pressure gauge settle at around 1.5 bar, indicating a good flush, as the pressure did not rise (which is what you would expect, by keeping both the inlet and outlet button pressed).
    • Next I unhooked the cell cables of my Inspo Vision from their old inboard cells, and hooked them up to the male coax connectors of the MCC cable set. I fired up my Inspo, went through the usual startup and self check screens, and instructed it to calibrate. As the pressure pot was already flushed with oxygen, the solenoid will not inject in order to try to reach 0.7 bar PO2, which is nice (and quiet, and safes oxygen).
      • You MIGHT run the small risk of the Inspo reporting a “cell stuck”, as it may not see the cell mV values move during calibration: after all you are starting already with a PO2 of 1.0 bar due to the previous flushing. This however is easily solved by doing a very short small flush on the MCC: keep both inlet and outlet pressed for a second or so. This will cause a tiny peak up and down again in the PO2, enough for the Inspo to notice the cell not being stuck. In my case I didn’t get the error message: calibration went without any hiccup, in one go.
    • So now on to the final, real unique added value of the MCC: I raised the pressure till 2.0 bar by pressing the white inflator button on the MCC. To make life easy on me, once 2.0 bar inside the MCC was reached I then unhooked the O2 inlet hose, and quickly put my finger on the inlet to keep the O2 in (it does leak out slowly when you do not keep your finger on). Alternatively you can just put back on the little black plastic sealing cap that comes with the MCC to protect the O2 inlet connector. This “trick” is not really necessary, but unhooking it makes it simpler to move the MCC physically around, e.g. close to your CCR handset(s), and in such an angle that you have a good view on both the mechanical pressure gauge and the Vision handset.
    • I was quite impressed by the accuracy: 2.0 bar on the mechanical gauge gave 1.97-1.98 on the Inspo handset. If you keep in mind the MCC’s mechanical gauge has a 2.5% precision (as indicated on its scale: “CL 2.5”), so in theory can be up to 2.5% off, it is hard to determine if that 0.02 error is in reading the mechanical gauge incorrectly (just think of the thickness of the needle itself in combination with my old eyes….), or a remainder of a not 100% perfect calibration, or even a new cell waking up during the whole process. Anyway: a difference of 0.02-0.03 bar at the very high end of the range in my book reads “bloody perfect”!
    • Next I left the cell exposed for a while to 2.0 bar, so see if they stuck there and did not drop off. This was not the case, so o.k. again.
    • I then let the pressure in the pot drop in 0.10 bar intervals, comparing Inspo handset to mechanical gauge on the MCC, to verify linearity across the whole range from 1.0 till 2.0 bar.

    They were spot on in the whole range. So conclusion at this point in the test: MCC works easy and as advertised, and I had bought 3 good new cells. Phew….!

    Just out of curiosity, I next swapped the new cells for the old cells in the Inspo head, but left all MCC cables in place. I placed the old cells in the MCC and repeated the whole process above again, just to see how “bad” my old cells had gotten over time. They had been in the system for 19 months, but were a bit older if calculated from manufacturing: date code was C7, so 22 months old.

    As I am a Lazy Dutch Bastard, I didn’t bother to calibrate the system again with the old cells. I just noted the offset values on the handset when exposed to 1.0 bar O2. Let me explain what I mean here: cell one said 1.04, cell two 0.92 and cell three 0.99. This is not strange, as without doing a new calibration, the Inspo will use its stored calibration values, which were still from the previously tested new cells. I just ignored the "must calibrate!" message.

    I then exposed the old cells up to 2.0 bar again, and just added up the recorded offset at 1.0 bar to what I saw when exposed to 2.0 bar. So e.g. I added 0.08 bar for cell two, as it had indicated 0.92 when exposed to 100% O2 at one bar, and subtracted 0.04 for cell 1 as it had read 1.04 at the start of the test.

    I was pleasantly surprised to see my old cells were still pretty much o.k.: maximum pressure
    differences observed on the whole range were again in the 0.03-0.04 bar range.

    Almost a pity to throw such good cells away; maybe I can sell them on E-bay….? (Warning: this is Sick Dutch humor!).

    So at the end of the day, the little MCC beast lived up to its promises. It is easy, no-nonsense and accurate. It is also very easy to hook up to an Inspo, without having to make any modification whatsoever to the unit, other then temporary hooking up the cell cables from the Inspo to the MCC.

    Overall verdict: useful little beast: well designed and constructed, high build quality, no-nonsense, works as advertised. It is not cheap, but in my book worth the money, as this is typically a device you will be able to use for very many years without deterioration.

    TIP (Typical Dutch - or Scottish): share the use and costs with some of your CCR friends!

    General observation and contemplation: this is a “confidence raising”, “double-check” type of device.

    What I mean is: your cells may pass perfectly during tests, but STILL bite you in the behind on your very next dive. Cells will per definition remain relatively unreliable little monsters, and I doubt you will take out your cells before every diving day in order to go through this whole process: that is just too cumbersome. Hence "condifence raising", not "problem elimination".

    Where I see this thingy being used in practice is:
    • When you swap old cells for new ones, to make double sure your new cells are no DOA’s. Simply a confidence raiser, and an implementation of my famous “trust is good, but control is better” mantra.
    • Before you go on a long and expensive trip to the other side of the world that you do not want to see ruined by something silly as a cell error. TIP: take a spare cell with you, BUT test that one as well upfront!
    • When you observe strange problems with your cells, and want to isolate the problem (“is it cells, or cabling, or connectors?”). Remember that you can also test the cells without your favorite CCR, by just hooking up your good old voltmeter to the cable outlets of the MCC. That way you at least can pin down the quality of the cells as your possible culprit.
    • Instructors and rental stations – if only for legal reasons. You could have the customer observe the quality of the cells, and sign for it, before renting out, or before having your student use your training-CCR. This prevents “you use old sh.t!; you could have known this cell problem!” kind of comments.

    In short: highly recommended.



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    Last edited by Beanie; 10th March 2009 at 10:22.

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