Two displays connected to one cell?

lizardland · 18th January 2008, 11:40

Are there any problems connecting two displays to one cell other than the practical aspect of actually making the connection?

I've just bought a Shearwater. The plan is that it will replace the Jetsam displays on my KISS as the primary pO2 display. I'd like to add a secondary at some point but I don't necessarily want a HUD. I have three kidneys with different connection combos so the various options could be:

1. Kidney A is a blank kidney with two cable glands. The Shearwater is wired into one gland leaving the possibility of a HUD, Subsea or Sartek monitor added to the other which could read all three cells.

2. Kidney B is a modified Jetsam kidney with a cable gland for the Shearwater and the two spare display ports. I could cut down a Jetsam triple display to make a double display reading 2 cells... so still having 3 independant displays (albeit one of them reads all three cells) and both a primary and secondary system.

3. Kidney C which is a stock Jetsam kidney. Leave the triple display and dive the Shearwater just as a computer.

I'm still deciding which of the three systems I'm going with (option 3 seems unlikely) but I'm not sure if I'll just be making a rod for my own back by hooking 2 displays to each cell. Will I get weird readings? If one of the displays fails then will I get problems with the reading on the other?

Or am I, as the great Anglo Saxon phrase goes, gilding a turd? Should I be happy with one primary display?

This weather better change soon as boredom is putting my dive kit at risk of permanent damage.

Cheers,

Stuart

Ben Field · 18th January 2008, 12:19

I have Shearwater Kidney with Shearwater GF and HUD connected via two seperate cable glands, the HUD is essentially another display in terms of cable connections, the only point the GF and HUD meet is where the wires and connected to the Molex plugs (the Shearwater HUD is completely independant to the Computer, unlike some HUD's) I've had no funny readings or issues... I would go for Option 1 if I where you. My follow on question is how would I go about adding a Third display as all the space in the Molex is gone?

aquaholic · 18th January 2008, 12:30

Stuart,

Quote: (Originally Posted by lizardland)

1. Kidney A is a blank kidney with two cable glands. The Shearwater is wired into one gland leaving the possibility of a HUD, Subsea or Sartek monitor added to the other which could read all three cells.

I am not sure if the DS1 will directly read cells via a standard KISS kidney..

Mine came complete with a replacement kidney that has some sort of electronics build in and three separate ports - all reading the three cells.

Port C would take the Subsea HUD - very simple HIGH/OK/LOW signals and much cheaper than the shearwater one.

Port B can be connected to the DS1 or a computer, but the DS1 can only control the HUD from this port.

Port A can have either computer or DS1 without HUD, but the cable angle is a bit pants to get past the QC turret...

You also have another option to connect the shearwater..
Keep the tripple KISS displays and connect the shearwater via the 2nd O2 port on the KISS and a 4th cell in the counterlung.Have fun fettling.

Sutty · 18th January 2008, 12:59

This is the thing that has always bothered me about dual displays. If for example a Kiss display floods then there is saltwater across the cable ends from the cell, electrically this is the same as saltwater across the cell pins (ignoring the tiny resistance of the cable), a second system attached to the same cell is unlikely to be unaffected. Uri's HUD system has some protective circuitry in the head to solve the problem if the HUD cable floods (so it doesn't affect the original dislay), but the problem on the Kiss display side remains.
I did look at the Shearwater but this is one of the things that put me off. All 3 cells are connected by a single fischer which is protected by a single O-ring seal, and I'm concerned they might all be shorted at once should this fail. I asked Bruce about this at the NEC dive show and he reckoned this O-ring doesn't fail, but it is potentially a single failure point which could compromise all your PO2 monitoring on both displays. The hard-wired version goes some way to removing this of course, but then you can't use it OC.
In the end its all down to risk-benefit analysis I guess.

Neil

Ben Field · 18th January 2008, 13:03

I had my Shearwater hardwired to the kidney because I wouldn't trust Fischers to keep the water out. The GF has a single easy to check o0ring so any leaks will/should be my fault from the loop end!

Dutchy · 18th January 2008, 14:49

Quote: (Originally Posted by Sutty)

This is the thing that has always bothered me about dual displays. If for example a Kiss display floods then there is saltwater across the cable ends from the cell, electrically this is the same as saltwater across the cell pins (ignoring the tiny resistance of the cable), a second system attached to the same cell is unlikely to be unaffected. Uri's HUD system has some protective circuitry in the head to solve the problem if the HUD cable floods (so it doesn't affect the original dislay), but the problem on the Kiss display side remains.
I did look at the Shearwater but this is one of the things that put me off. All 3 cells are connected by a single fischer which is protected by a single O-ring seal, and I'm concerned they might all be shorted at once should this fail. I asked Bruce about this at the NEC dive show and he reckoned this O-ring doesn't fail, but it is potentially a single failure point which could compromise all your PO2 monitoring on both displays. The hard-wired version goes some way to removing this of course, but then you can't use it OC.
In the end its all down to risk-benefit analysis I guess.

Neil

In all honesty I think it depends on your dive profile. I can loose displays and simply abort my dive. What worries me more in this config is "a little bit" of short-circuiting. A completely short circuited circuit should be obvious. But what if its only a partial short circuit (e.g. brakish water ingres) ? In the best case displayed values are different or change quickly (once more obvious) but what if they all more or less deviate by the same offset?

**Gill Envy** · 18th January 2008, 19:02

I've got both po2 meters piggy backed on my copis . never had a problem, well, so far anyway. Was very concerned about this in the beginning and almost went for a fourth cell. I'm monitoring my HUD as the primary, and use the handset to cross check po2 and track NDL/DL. While it's theoretically conceivable that current pollution could cross over at the molex I have yet to hear a good explanation of how that would happen. Most importantly, I have not heard of that actually happening. Questioning weather pollution from ingress or other shorts or malfunctions could subtly effect readings in a way that is not obvious is a good thing to think about. Certainly molex connectors are prone to leaking as a matter of course and food grade mineral oil seems imperative as a safeguard. Until I see otherwise, i'm confident that the chances of a charge effecting all three cell readings on both handsets in consistent ways such that I do not notice and bail out is so remote that it does not outway the value of such a configuration. Well, to say that i'm confident may be a bit misleading, i'm monitor my set up as if i'm expecting to catch it malfunctioning. Confidence and electronics don't tend to go too well together.

IMHO

g

Quote: (Originally Posted by Dutchy)

In all honesty I think it depends on your dive profile. I can loose displays and simply abort my dive. What worries me more in this config is "a little bit" of short-circuiting. A completely short circuited circuit should be obvious. But what if its only a partial short circuit (e.g. brakish water ingres) ? In the best case displayed values are different or change quickly (once more obvious) but what if they all more or less deviate by the same offset?

Mark Chase · 18th January 2008, 20:41

I had a Fischer cable fail on my Classic. It fell out of the VR3

End result... Nothing.

Uri HUD caried on working fine as did the Classic.

ATB

Mark

Sutty · 19th January 2008, 12:58

Quote: (Originally Posted by Mark Chase)

I had a Fischer cable fail on my Classic. It fell out of the VR3

End result... Nothing.

Uri HUD caried on working fine as did the Classic.

ATB

Mark

That's interesting Mark. What was the VR3 cable wired to? direct to a cell, or to Uri's HUD, which provides a buffered output of cell 1 to the VR3. If the latter I wouldn't expect a problem.

Neil

Dutchy · 19th January 2008, 15:12

Hmmm with different observations it will just be me (bench) testing the different scenarios to know what to expect when (not if) it happens for real.... It will take some time though with the display still

preordered.

18th January 2008, 11:40	#1 (permalink)
lizardland Yak Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Classic Kiss Home Build Join Date: Mar 2005 Location: North... Posts: 1,186	Two displays connected to one cell? Are there any problems connecting two displays to one cell other than the practical aspect of actually making the connection? I've just bought a Shearwater. The plan is that it will replace the Jetsam displays on my KISS as the primary pO2 display. I'd like to add a secondary at some point but I don't necessarily want a HUD. I have three kidneys with different connection combos so the various options could be: 1. Kidney A is a blank kidney with two cable glands. The Shearwater is wired into one gland leaving the possibility of a HUD, Subsea or Sartek monitor added to the other which could read all three cells. 2. Kidney B is a modified Jetsam kidney with a cable gland for the Shearwater and the two spare display ports. I could cut down a Jetsam triple display to make a double display reading 2 cells... so still having 3 independant displays (albeit one of them reads all three cells) and both a primary and secondary system. 3. Kidney C which is a stock Jetsam kidney. Leave the triple display and dive the Shearwater just as a computer. I'm still deciding which of the three systems I'm going with (option 3 seems unlikely) but I'm not sure if I'll just be making a rod for my own back by hooking 2 displays to each cell. Will I get weird readings? If one of the displays fails then will I get problems with the reading on the other? Or am I, as the great Anglo Saxon phrase goes, gilding a turd? Should I be happy with one primary display? This weather better change soon as boredom is putting my dive kit at risk of permanent damage. Cheers, Stuart __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
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18th January 2008, 12:19	#2 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,482	Re: Two displays connected to one cell? I have Shearwater Kidney with Shearwater GF and HUD connected via two seperate cable glands, the HUD is essentially another display in terms of cable connections, the only point the GF and HUD meet is where the wires and connected to the Molex plugs (the Shearwater HUD is completely independant to the Computer, unlike some HUD's) I've had no funny readings or issues... I would go for Option 1 if I where you. My follow on question is how would I go about adding a Third display as all the space in the Molex is gone? __________________ www.hugsac.org.uk Beware Fridge Suck
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18th January 2008, 12:30	#3 (permalink)
aquaholic hohum Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Feb 2005 Location: UK Posts: 100	Re: Two displays connected to one cell? Stuart, Quote: (Originally Posted by lizardland) 1. Kidney A is a blank kidney with two cable glands. The Shearwater is wired into one gland leaving the possibility of a HUD, Subsea or Sartek monitor added to the other which could read all three cells. I am not sure if the DS1 will directly read cells via a standard KISS kidney.. Mine came complete with a replacement kidney that has some sort of electronics build in and three separate ports - all reading the three cells. Port C would take the Subsea HUD - very simple HIGH/OK/LOW signals and much cheaper than the shearwater one. Port B can be connected to the DS1 or a computer, but the DS1 can only control the HUD from this port. Port A can have either computer or DS1 without HUD, but the cable angle is a bit pants to get past the QC turret... You also have another option to connect the shearwater.. Keep the tripple KISS displays and connect the shearwater via the 2nd O2 port on the KISS and a 4th cell in the counterlung.Have fun fettling. __________________ Trying things different to the norm is the route to a new norm....
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18th January 2008, 12:59	#4 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 775	Re: Two displays connected to one cell? This is the thing that has always bothered me about dual displays. If for example a Kiss display floods then there is saltwater across the cable ends from the cell, electrically this is the same as saltwater across the cell pins (ignoring the tiny resistance of the cable), a second system attached to the same cell is unlikely to be unaffected. Uri's HUD system has some protective circuitry in the head to solve the problem if the HUD cable floods (so it doesn't affect the original dislay), but the problem on the Kiss display side remains. I did look at the Shearwater but this is one of the things that put me off. All 3 cells are connected by a single fischer which is protected by a single O-ring seal, and I'm concerned they might all be shorted at once should this fail. I asked Bruce about this at the NEC dive show and he reckoned this O-ring doesn't fail, but it is potentially a single failure point which could compromise all your PO2 monitoring on both displays. The hard-wired version goes some way to removing this of course, but then you can't use it OC. In the end its all down to risk-benefit analysis I guess. Neil __________________ Never forget that life is a finite resource.
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18th January 2008, 13:03	#5 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,482	Re: Two displays connected to one cell? I had my Shearwater hardwired to the kidney because I wouldn't trust Fischers to keep the water out. The GF has a single easy to check o0ring so any leaks will/should be my fault from the loop end! __________________ www.hugsac.org.uk Beware Fridge Suck
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18th January 2008, 14:49	#6 (permalink)
Dutchy SK#007 Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 699	Re: Two displays connected to one cell? Quote: (Originally Posted by Sutty) This is the thing that has always bothered me about dual displays. If for example a Kiss display floods then there is saltwater across the cable ends from the cell, electrically this is the same as saltwater across the cell pins (ignoring the tiny resistance of the cable), a second system attached to the same cell is unlikely to be unaffected. Uri's HUD system has some protective circuitry in the head to solve the problem if the HUD cable floods (so it doesn't affect the original dislay), but the problem on the Kiss display side remains. I did look at the Shearwater but this is one of the things that put me off. All 3 cells are connected by a single fischer which is protected by a single O-ring seal, and I'm concerned they might all be shorted at once should this fail. I asked Bruce about this at the NEC dive show and he reckoned this O-ring doesn't fail, but it is potentially a single failure point which could compromise all your PO2 monitoring on both displays. The hard-wired version goes some way to removing this of course, but then you can't use it OC. In the end its all down to risk-benefit analysis I guess. Neil In all honesty I think it depends on your dive profile. I can loose displays and simply abort my dive. What worries me more in this config is "a little bit" of short-circuiting. A completely short circuited circuit should be obvious. But what if its only a partial short circuit (e.g. brakish water ingres) ? In the best case displayed values are different or change quickly (once more obvious) but what if they all more or less deviate by the same offset? __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. = SK #007
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18th January 2008, 19:02	#7 (permalink)
Gill Envy Shearwater Copis Diver Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,250	Re: Two displays connected to one cell? I've got both po2 meters piggy backed on my copis . never had a problem, well, so far anyway. Was very concerned about this in the beginning and almost went for a fourth cell. I'm monitoring my HUD as the primary, and use the handset to cross check po2 and track NDL/DL. While it's theoretically conceivable that current pollution could cross over at the molex I have yet to hear a good explanation of how that would happen. Most importantly, I have not heard of that actually happening. Questioning weather pollution from ingress or other shorts or malfunctions could subtly effect readings in a way that is not obvious is a good thing to think about. Certainly molex connectors are prone to leaking as a matter of course and food grade mineral oil seems imperative as a safeguard. Until I see otherwise, i'm confident that the chances of a charge effecting all three cell readings on both handsets in consistent ways such that I do not notice and bail out is so remote that it does not outway the value of such a configuration. Well, to say that i'm confident may be a bit misleading, i'm monitor my set up as if i'm expecting to catch it malfunctioning. Confidence and electronics don't tend to go too well together. IMHO g Quote: (Originally Posted by Dutchy) In all honesty I think it depends on your dive profile. I can loose displays and simply abort my dive. What worries me more in this config is "a little bit" of short-circuiting. A completely short circuited circuit should be obvious. But what if its only a partial short circuit (e.g. brakish water ingres) ? In the best case displayed values are different or change quickly (once more obvious) but what if they all more or less deviate by the same offset? __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°> Last edited by Gill Envy : 18th January 2008 at 22:14.
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18th January 2008, 20:41	#8 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,470	Re: Two displays connected to one cell? I had a Fischer cable fail on my Classic. It fell out of the VR3 End result... Nothing. Uri HUD caried on working fine as did the Classic. ATB Mark __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System
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19th January 2008, 12:58	#9 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 775	Re: Two displays connected to one cell? Quote: (Originally Posted by Mark Chase) I had a Fischer cable fail on my Classic. It fell out of the VR3 End result... Nothing. Uri HUD caried on working fine as did the Classic. ATB Mark That's interesting Mark. What was the VR3 cable wired to? direct to a cell, or to Uri's HUD, which provides a buffered output of cell 1 to the VR3. If the latter I wouldn't expect a problem. Neil __________________ Never forget that life is a finite resource.
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19th January 2008, 15:12	#10 (permalink)
Dutchy SK#007 Current Rebreather/s: Sport Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Nieuwegein (The Netherlands) Posts: 699	Re: Two displays connected to one cell? Hmmm with different observations it will just be me (bench) testing the different scenarios to know what to expect when (not if) it happens for real.... It will take some time though with the display still preordered. __________________ = This post is environmentally friendly. It is composed of 100% recycled electrons only. = SK #007
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