Underwater video connector

[Jinx-4]

Trying to help a friend out with a problem. He's got 50m of this cable

http://www.canare.com/ProductItemDisplay.aspx?productItemID=82

going to the SDI output of a camera in an underwater housing. He
gets a very good picture with the cable connected unbroken directly
to the camera, but he really wants this cumbersome cable removable

The previous set-up was analogue video and picture quailty didn't
suffer going through an 8-pin connector (a kind of sealable DIN)
and short lengths of hook-up wire to the camera. The picture with
SDI is badly torn and unstable though

So we're looking for either submersible AV connectors or a way to
use the existing connection that will either not affect the SDI or will
buffer it. He's looked at an SDI-analogue convertor. Expensive

TIA

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[Bob Axtell-3]

The best way to do it is to make up the connectors as needed. Then
enclose the cable connector ends in a neoprene bag, and seal the ends
using hose clamps. But before you actually tighten the hose clamps,
fill the neoprene with kerosene (or mineral oil). Then tighten the
clamps over the bag ends.

The kerosene will prevent water from penetrating the bag, because
kerosene can't be easily compressed, even at 100' or more.

This is the method used by underwater seismic detectors, and they
operate in tough environments being dragged behind a boat.

On 6/24/09, Jinx <joecolquitt@...> wrote:

> Trying to help a friend out with a problem. He's got 50m of this cable
>
> http://www.canare.com/ProductItemDisplay.aspx?productItemID=82
>
> going to the SDI output of a camera in an underwater housing. He
> gets a very good picture with the cable connected unbroken directly
> to the camera, but he really wants this cumbersome cable removable
>
> The previous set-up was analogue video and picture quailty didn't
> suffer going through an 8-pin connector (a kind of sealable DIN)
> and short lengths of hook-up wire to the camera. The picture with
> SDI is badly torn and unstable though
>
> So we're looking for either submersible AV connectors or a way to
> use the existing connection that will either not affect the SDI or will
> buffer it. He's looked at an SDI-analogue convertor. Expensive
>
> TIA
>
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[Jinx-4]

Hi Bob, thanks

> fill the neoprene with kerosene (or mineral oil). Then tighten the
> clamps over the bag ends.

That's something along the lines of what I was thinking. I'll be seeing
him tomorrow and we can work out what's practical. He does ads,
feature films, music vids etc, so this isn't a long-term installation and
may be in use for anything from an hour to a week before being
broken down. The video line is the most important. The camera is
doing the good quality recording, and the feed to the surface is for
his director and needs to be of at least reasonable quality. Other
lines in the cable are used for controls (LANC or whatever this
camera has) so their connectors are not so critical. He's a pretty
pragmatic person and would probably accept a 'messy' solution
if it meant a good result

I'll report back anyway


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[solarwind]

On Thu, Jun 25, 2009 at 5:29 PM, Bob Axtell<bob.axtell@...> wrote:
> The kerosene will prevent water from penetrating the bag, because
> kerosene can't be easily compressed, even at 100' or more.

What happens if there is a few sparks? Will it be a fire hazard?
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[Herbert Graf-5]

On Fri, 2009-06-26 at 17:20 +0100, solarwind wrote:
> On Thu, Jun 25, 2009 at 5:29 PM, Bob Axtell<bob.axtell@...> wrote:
> > The kerosene will prevent water from penetrating the bag, because
> > kerosene can't be easily compressed, even at 100' or more.
>
> What happens if there is a few sparks? Will it be a fire hazard?

Remember the fire triangle: Heat, Air(oxygen), Fuel. You need all three
to have fire.

In the case of a bag of kerosene submerged in the water you definitely
have fuel, you barely have heat, and you don't have air.

That said, I would personally try to choose a medium less flammable then
kerosene, that stuff burns WAY to easily.

TTYL

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[Tamas Rudnai]

I am not a chemist nor a fire/explosive expert but as far as I know
kerosene, petrol and diesel are not flammable till is in liquid form. They
need to have a certain amount of air-fuel mixture to be able to lit it up.

BTW not sure if that could happen but if there is any open electrode of both
anode and cathode then it can break down the water to oxygen and hydrogen
gas which is highly flammable if mixed that even the smallest spark can
cause a fire. Not sure if a microelectronic device could do this thing.

Tamas



On Fri, Jun 26, 2009 at 5:48 PM, Herbert Graf <hkgraf@...> wrote:

> On Fri, 2009-06-26 at 17:20 +0100, solarwind wrote:
> > On Thu, Jun 25, 2009 at 5:29 PM, Bob Axtell<bob.axtell@...> wrote:
> > > The kerosene will prevent water from penetrating the bag, because
> > > kerosene can't be easily compressed, even at 100' or more.
> >
> > What happens if there is a few sparks? Will it be a fire hazard?
>
> Remember the fire triangle: Heat, Air(oxygen), Fuel. You need all three
> to have fire.
>
> In the case of a bag of kerosene submerged in the water you definitely
> have fuel, you barely have heat, and you don't have air.
>
> That said, I would personally try to choose a medium less flammable then
> kerosene, that stuff burns WAY to easily.
>
> TTYL
>
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[Bob Blick-4]

On Fri, 26 Jun 2009 18:55:23 +0100, "Tamas Rudnai"
<tamas.rudnai@...> said:

> I am not a chemist nor a fire/explosive expert but as far as I know
> kerosene, petrol and diesel are not flammable till is in liquid form.
> They
> need to have a certain amount of air-fuel mixture to be able to lit it
> up.
>
> BTW not sure if that could happen but if there is any open electrode of
> both
> anode and cathode then it can break down the water to oxygen and hydrogen
> gas which is highly flammable if mixed that even the smallest spark can
> cause a fire. Not sure if a microelectronic device could do this thing.

Automotive in-tank fuel pumps use gasoline for lubricant. At least it
sure looked that way when I disassembled one. Even more exciting, the
brushes/commutator area is flooded with fuel. Apparently not a problem
even when you run out of fuel and start sucking air.

I also always wondered about the fuel level sensor, like a big wirewound
potentiometer up in the air area of the tank.

It appears to be quite safe.

But I would certainly want a second opinion before implementing my own
version!

Cheerful regards,

Bob

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[Picbits Sales]

Funny you should mention this Bob but I've come across exactly the same on
my travels. I've seen current regulated feeds of 200mA going to the fuel
sender (wirewound as well). 200mA is enough to heat the element up and cause
sparking across the rheostat type winding. I assume there is no sparking due
to at least one part of the wiper being in touch with a couple of parts of
the winding but its still enough to make you ponder .....

Dom
----- Original Message -----
From: "Bob Blick" <bobblick@...>
To: "Microcontroller discussion list - Public." <piclist@...>
Sent: Friday, June 26, 2009 7:19 PM
Subject: Re: [EE] Underwater video connector

>
> On Fri, 26 Jun 2009 18:55:23 +0100, "Tamas Rudnai"
> <tamas.rudnai@...> said:
>> I am not a chemist nor a fire/explosive expert but as far as I know
>> kerosene, petrol and diesel are not flammable till is in liquid form.
>> They
>> need to have a certain amount of air-fuel mixture to be able to lit it
>> up.
>>
>> BTW not sure if that could happen but if there is any open electrode of
>> both
>> anode and cathode then it can break down the water to oxygen and hydrogen
>> gas which is highly flammable if mixed that even the smallest spark can
>> cause a fire. Not sure if a microelectronic device could do this thing.
>
> Automotive in-tank fuel pumps use gasoline for lubricant. At least it
> sure looked that way when I disassembled one. Even more exciting, the
> brushes/commutator area is flooded with fuel. Apparently not a problem
> even when you run out of fuel and start sucking air.
>
> I also always wondered about the fuel level sensor, like a big wirewound
> potentiometer up in the air area of the tank.
>
> It appears to be quite safe.
>
> But I would certainly want a second opinion before implementing my own
> version!
>
> Cheerful regards,
>
> Bob
>
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>
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[Olin Lathrop]

solarwind wrote:
> What happens if there is a few sparks? Will it be a fire hazard?

Not without oxygen.


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[cdenk]

And then within a narrow range of mixture ratios. But even then there
could be a big boom I suppose. The variable resistance fuel level
sending units are used by the zillions, but it doesn't seem to be a
problem. It's just chaffed wires in airline fuel tanks. I tend to
believe that a tank is a small confined space, and it doesn't take much
available gasoline, or whatever fuel to create a saturated vapor
atmosphere, which is a ratio well above the explosive limit. And the
time the atmosphere is within the limits of being dangerous is very
limited. When fueling aircraft with gasoline, the concern is with a
spark just outside the fill point. This is also with autos, and someone
that walks up with a static charge, and sets the area off into flame. :(

Olin Lathrop wrote:

> solarwind wrote:
>  
>> What happens if there is a few sparks? Will it be a fire hazard?
>>    
>
> Not without oxygen.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> [phone].  Gold level PIC consultants since 2000.
>  

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[Bob Axtell-3]

Kerosene is VERY difficult to ignite. Kerosene is similar to aviation
jet fuel, and yes this _IS_ what is used in underwater seismic pods.

But if you insist, use mineral oil instead. 'Course, it will burn as well....

On 6/26/09, Carl Denk <cdenk@...> wrote:

> And then within a narrow range of mixture ratios. But even then there
> could be a big boom I suppose. The variable resistance fuel level
> sending units are used by the zillions, but it doesn't seem to be a
> problem. It's just chaffed wires in airline fuel tanks. I tend to
> believe that a tank is a small confined space, and it doesn't take much
> available gasoline, or whatever fuel to create a saturated vapor
> atmosphere, which is a ratio well above the explosive limit. And the
> time the atmosphere is within the limits of being dangerous is very
> limited. When fueling aircraft with gasoline, the concern is with a
> spark just outside the fill point. This is also with autos, and someone
> that walks up with a static charge, and sets the area off into flame. :(
>
> Olin Lathrop wrote:
>> solarwind wrote:
>>
>>> What happens if there is a few sparks? Will it be a fire hazard?
>>>
>>
>> Not without oxygen.
>>
>>
>> ********************************************************************
>> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
>> [phone].  Gold level PIC consultants since 2000.
>>
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[Jinx-4]

> Kerosene is VERY difficult to ignite

My recollection is kerosene has quite a high vapour pressure and
ignition temperature, so there should be no great problem using it.
And frankly, if there's activity on a digital video cable that could
ignite kero, a small pouch of it catching fire is a minute worry
compared with the AV equipment that's just been munted. The
lingering smell of a fuel might be a drawback. Something high-
viscosity like glycerol (even though it's water-miscible, but that
would help with clean-up) might be an alternative

Part of this could be semi-permanent. One end of the pouch could
be permanently attached to the underwater housing. The cable can
go into the pouch, connect, the Jubilee clip (hose clamp) is almost
tightened, quick squirt of whatever from a syringe, and tighten the
clamp completely

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[Jinx-4]

Firstly we replace the soldered splices with proper BNC connections.
Splits in the cable, where the SDI is separated from the control lines,
is now a Y-shaped heatshrink, back-filled with co-polymer sealer

At the underwater housing is a bulkhead connector. This has a BNC
on the outside and a BNC on the inside. A BNC to SDI lead goes
from that to the camera. To seal the outside the plan is to use a length
of 30mm diameter rubber tubing. One end surrounds the bulkhead
connector, fixed to the housing with a flange. The other end goes over
the video lead, with a rubber sleeve filling the space between the tube
and the lead. A vaseliney-type goo and hose clamp will seal that, and
finally strain relief to immobilise the connection

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[Peter Restall]

On Mon, 29 Jun 2009 13:00:25 +1200, Jinx wrote:

> Firstly we replace the soldered splices with proper BNC connections.
> Splits in the cable, where the SDI is separated from the control lines,
> is now a Y-shaped heatshrink, back-filled with co-polymer sealer
>
> [snip]

Morning Jinx.

Any pictures per chance ?

Cheers,

Pete Restall
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[Jinx-4]

> Any pictures per chance ?

Sorry, Peter, not yet. The job isn't quite complete. Here are some
part numbers though (guess whose catalogue was handy)

Heatshrink (Tyco), Radiospares 218-1426
Bulkhead 75 ohm BNC connector, Radiospares 546-4099
Radiospares crimp m & f BNC
Selley's All Clear co-polymer sealer

I've come to prefer the All Clear to silicone for many jobs as it
adheres to materials like acrylic, metal and rubber much better.
All Clear is thinner than silicone, about as viscous as syrup

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