KISS cell monitoring - passive 2/3-cell & computer

[digital_steve]

i don't have a RB, so take this with a grain of salt... but an aussie company has some monitoring options for the KISS
Subsea Systems KISS Display System

[weazelz]

Originally Posted by David Pye

(Oh, and people, please stop using the word passive, unless you're talking about a true passive - ie non-powered secondary, like the 'proper' one the MK15 had).

I was meaning passive in the sense of just doing ppO2 monitoring - ie no hi/lo alarming, deco calculation, etc. not, obviously, in the electrical sense

[NotDeadYet]

Originally Posted by David Pye

Sure, you can buy an analogue secondary, but then your two primary sources of reference (HUD + VR3) aren't independent at all, so you end up having the check all three, which defeats the point imho...

I don't agree. The HUD is a remote display for the main computer. HUD flashing in front of you is a primary display, the other display is your cross check, there is no need to check the computer as well as the HUD is just a repeater unit for what it is doing. The HUD and computer are not your main systems, the HUD and secondary are.

My Mk15 is set up like this. The Hammerhead drives a HUD unit and there is a Sartek digital display as well, I never look at the HH handset except at deco.

"Secondary" display implies nothing other than it is a second display. It isn't a back-up, it is a cross-check and is as much a primary system as the VR£, or in my case the HH.

(Oh, and people, please stop using the word passive, unless you're talking about a true passive - ie non-powered secondary, like the 'proper' one the MK15 had).

The Mk15 secondary used the cells as batteries so still technically "powered". Passive means that the signal has little or no processing, it's just an analogue voltmeter with gain adjustment, the KISS is similar in that it is just a digital voltmeter. OK there is an A/D convertor and a gain adjustment but it is still a raw signal. Clip the piggybacked resistor off the back and you have a direct mV display. The Mk16's used a digital display which is similar in principle, still a passive display.

Cheers,

Stuart

[turbanator]

Originally Posted by David Pye

(Oh, and people, please stop using the word passive, unless you're talking about a true passive - ie non-powered secondary, like the 'proper' one the MK15 had).

David

Originally Posted by NotDeadYet

The Mk16's used a digital display which is similar in principle, still a passive display.

Cheers,

Stuart

I understand the definition (it was me that mentioned it in the 1st place )

Stuart, just to clear things up, are you saying that the Mk 16 no batteries, other than the cell itself, in the circuit. I can see that the Mk15 could be a millivolt meter reading the voltage the cell (to be technical, since that's how this has gone, it's actually measuring current ), but surely the mk16 would need a battery to power the LCD.

r
P

[NotDeadYet]

Originally Posted by turbanator

Stuart, just to clear things up, are you saying that the Mk 16 no batteries, other than the cell itself, in the circuit. I can see that the Mk15 could be a millivolt meter reading the voltage the cell (to be technical, since that's how this has gone, it's actually measuring current ), but surely the mk16 would need a battery to power the LCD.

r
P

Nope, the Mk16 is a powered display. What I meant was that what makes the display "passive" is that all it is doing is reading and displaying raw voltage. It still needs some power to make the display light up but I still see that as being "passive". OK, it will have some processing in that the cell signal has to go through an analogue/digital convertor but other than that all it is doing is displaying the voltage with a gain correction to make it meaningful.

The KISS displays are just straight voltmeters too, if you buy an un-mod'ed meter from Farnell and plug it into the board then it displays mV. Dave Dillabough pigybacks resistors onto the back of the meters for Jetsam which alters the display. It is a bit of an optical illusion, a KISS display is not showing the pO2, it is displaying the mV reading of the cell multiplied by (approx) 2. It just happens that twice the average output of a R22D is roughly the same as the pO2. If you used R22DHO cells then the mV output would be more or less the same as the pO2 and you could get away with a simple voltmeter circuit. It could be digital or it could be analogue, either way a fairly unprocessed signal is going to ~ equate to the pO2... hope that makes sense (I'm not entirely sure it does to me ).

Things like HUD's and computers have fairly sophisticated processing to get the number on the screen or make the lights light up in the right sequence. A stock Mk15/16 has an "active" light display and a "passive" number display in that the light display is the cell signal processed into something fancy, the number display just takes the cell voltage and displays it (high output cells so they approximate the pO2 close enough that it doesn't take much fiddling to slide the scale on to the right numbers).

Cheers,

Stuart

[weazelz]

there have been a few references to various generations of displays - could anyone comment on the differences? pictures would be great too

btw - thanks to everyone who has contributed to this thread, I have found it very helpful

[Dave Crampton]

Try these,

1/2nd gen have the single peice of perspex with the displays screwed to the read face with an o-ring forming the seal

3rd gen, three separate transparent plastic covers,

4th gen (I think) the newer VR type RBM display.

Dave C

[gwilson]

Originally Posted by weazelz

there have been a few references to various generations of displays - could anyone comment on the differences? pictures would be great too

btw - thanks to everyone who has contributed to this thread, I have found it very helpful

The very first ones do not have backlighting they are illuminous also take a slightly differant battery to the newer ones.

Front



Back, behind the plug is a small screw for calibration, the 3 rusty magnets are the on/off sliders.



I think the last photo in Dave's post is an alternative "pendant" style display available from Jetsam

[NotDeadYet]

Originally Posted by gwilson

The very first ones do not have backlighting they are illuminous also take a slightly differant battery to the newer ones.

Yep, the 1st gens take a 12V battery (same battery as the old Cockring computer), the 2nd gens have a 6V battery. IIRC Kim said they didn't have any faceplates left for the 1st/2nd gens.

How do you like the CK, Gareth?

[gwilson]

Originally Posted by NotDeadYet

Yep, the 1st gens take a 12V battery (same battery as the old Cockring computer), the 2nd gens have a 6V battery. IIRC Kim said they didn't have any faceplates left for the 1st/2nd gens.

How do you like the CK, Gareth?

Bizarre as its only a piece of cut perspex?

Lots. Just looking forward to getting back home again in 6 weeks to try and get out more.