Vision Cell Warning Question

Dave Faye

During my last 3 dives I have had 3 back to back cell warnings (not cell failures) immediately after I surface from each dive. In each case, cell 1 reads high ppo2 only at the exact moment I surface after the dive. Sometimes it reads 2.25 (which is not possible). I have been using the new version of the software and have about 10 dives on the new software without incident. This did not happen with the prior version of software. Air and 02 flushes at 20' show all is well with the cell. The cell is only 6 months old and is fine under all other circumstances. I wonder if this is a software issue or maybe just a faulty cell. As I said above, the cell is fine at all other times. I will switch the cell out tonight and see what happens. Anyone else have a similar issue?

Dave

01RMB

Does not sound good. I have had a cell react slowly and give cell warnings if I don't dry the head overnight when doing mutliple consecutive dive days but not the problem you describe.

It will be interesting to see what changing the cell does and if the problem persists send Nicki an email. I have found her to be very responsive in the past if I have had a problem.

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Rod

Genesis

It is almost certainly NOT the cell, and I bet its not the software either.

Without having a detailed schematic of the APD units I would tend to point my finger at the hardware - specifically, current leakage between the V+ feed and the sensor input for that sensor's conditioning/amplification channel.

A reading of 2.25 is likely "pegged", if APD is following common practice among the designs I've seen. For the software to see a "all bits 1" value is unlikely if it was referencing a bad value - it likely would see a junk number instead. All 1s on ONE channel is likely real - all 1s on ALL channels could be a communication problem between the processor and ADC (if the processor either doesn't check or doesn't have a means of testing communication integrity), but if the other two channels are ok this is very unlikely.

This is a very dangerous situation as the causes of current leakage tend not to go away - instead, they tend to spread. For example, if somehow salt water (a very small amount) or other contamination got into that part of the circuitry then it may spread between the channels. Typically we're talking millimeters of separation (if that) between the various channels within the circuitry of the unit - so expecting this to remain localized to channel #1 is unrealistic.

The possibility exists that all of the channels could "peg" on you during a dive, leaving you with little option but an immediate bail.

I would not dive the unit with it exhibiting this fault - even momentarily and upon surfacing.

I also noted this on the other thread where you posted the occurrance of the fault...... Get the unit looked at before using it again.

I may be being overcautious here, but from the work I've done on the K1 and all the testing and fault tree analysis I've done for it, this sort of fault just jumps out at me as one you DO NOT want to ignore.

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