Keeping condensation from blocking camera view


#1

Hey all!

So Brian Adams, Erika Bergman, and I went on an OpenROV adventure in Monterey this weekend using my inflatable boat. Our goal was to test some new concepts for the next revision of the ROV design as well as get some practice with ocean dives. Here's a video recorded using Screencastify:

http://youtu.be/VRahE47Zyes

The whole deployment went great, except after sealing the tube in the humid coastal air, a large amount of condensation started to accumulate inside the tube and block our view. That, on top of the glare from the white batteries (I'm working on that as well) made it a lot harder to see what was going on later in the dive. If we had a perfectly clear view, I think we would have seen a lot more.

I'm going to start experimenting with different ways to keep condensation from getting in the way of the camera, and I was hoping to get some help with ideas as well as testing.

To start out, here are the methods for reducing visibility problems from condensation that I've accumulated so far (organized into two mitigation categories):

Keeping moisture out of the air in the first place:
1. Placing desiccant packs in tube prior to dive to dry out air
2. Placing other water-absorbing material (such as rice) in tube prior to dive
3. Filling tube with helium
4. Filling tube with air from "canned air" cannister
5. Filling trash bag with desiccant powder and assembling tube inside trashbag

Keeping condensation away from camera area:
1. Placing cloth above and below camera so it can wipe off condensation as it moves up and down
2. Using a small computer fan to blow on the inside of the tube in front of the camera
3. Placing a heater around the area the camera looks through
4. Using a peltier cooler to attract moisture that would otherwise accumulate on the tube

Can anyone think of other (preferably simple and low cost) ways to prevent condensation issues? Would anyone be willing to do some experimentation with any of these methods to see how well they work?

I'll post more about my own experimentation as it happens.

Happy diving!

Eric


#2

Among the options you've posted .........

ALWAYS FROM MY POINT OF VIEW ONLY.

Group one:

Dessicant.

May work fine. Silica-Gel woks quite well for electronics in very wet environments (used for electronics protection onboard). It absorbs quite a big ammount of moist (specific absortion surface= 800m²/gram), is cheap and has no chemical activity.

Other absortion materials do not have the same specific surface or are more expensive.

Options 3,4 and 5, are more complex or expensive.

CressiSub makes "Cressi Anti-Fog Spray" for diving equipment. A few years ago, I was involved in a diving team. As we used Full masks for being able to speak while underwater, we were not able to "flood and blow" the mask for cleaning. That spray worked fine.

As for CressiSub specifications it is suitable for glass and polycarbonate.

Group two:

"Windshield wipers" inside the tube are not very trustfull. Its easy to get "lines" and blurred areas.

Im not for setting more parts inside the tube. The more weights on the ROV, the less payload capacity and ........ less battery time.

Regards


#3

Eric,

GoPro has been using these inserts for their cameras to prevent condensation: GoPro Inserts

I've used the anti-fog gel on my mask for scuba diving, but it does leave a film.

Honestly, in my opinion, the long term solution to this is to get as many heat generating sources outside the electronics tube as possible, lights, ESC's, etc... Or the camera needs to be stand-alone.


#4

http://www.sepa-europe.com/en/fan/axial/mf_10a03a

Not a cheap fan, but tiny, 3.3v, and *silent* which helps with future audio applications.


#5

Have tried with a combination of getting vacuum inside the housing and silica. It do helps a lot, but there is still some fog inside. My homemade tool can be seen on this link: http://openrov.com/forum/topics/leaking-electronic-housing?commentId=6365107%3AComment%3A99735


#6

Basically you are correct there are only 2 real ways to prevent condensation either drop the level of moisture in the gas or prevent the temperature dropping below the dew point (due to the heat conductance of water this would be difficult) have a look at Psychrometrics

As you indicate pressurised gas (Helium $$$$, air or CO2) will have considerably lower moisture content so no condensation will be able to occur

Therefore, by removing both syringe plungers you can pass gas through the E-tube and this should eliminate the issue (note you cannot vacuum test the unit after doing this or you will just suck in the air from around the vacuum tester)

This can be done by Scuba gear


Canned Air

or Bike CO2 pumps

Alternately

Or you can also drop the moisture levels in the air during the vacuum testing of the ROV by placing the ROV in the fridge (whist still under vacuum) for a while (say 30 minutes?) and then depressurise the vacuum so that it pulls in the cool air from the fridge (which will be quite low moisture) and then place the syringe plunger back in whist still in the fridge


#7

Hi
I have also been thinking of these solutions and especially dry gas. I was also considerung co2, but if there ist still some moisture inside, this could form acid, that might be corrosive and damage the electronics. A better alternative would be nitrous oxide (laughing gas), as it is used in devices to make whipped cream. This is also heavier then air, so it can be poured into the rov, when one side is still open.
Hub


#8

I would think that the silica dessicant should work fine if given a time to reduce the RH inside the E-tube prior to diving, so long as the water temperature is not more than say 10-15degC below ambient air temperature.

If diving in colder waters you could put the E-tube in the fridge (as Scott W notes) or freezer for very cold water for a while with one or both ports open, before sealing, so the internal air is below the water temp. That way the air trapped in the E-tube will have a lower water content than what is required for condensation to occur when the surface of the E-tube drops back down to water temp. You may need to insulate the E-tube when chilling to stop the moisture from condensing before it has a chance to normalise with the air in the fridge.

Another Option would be a condenser (say a bucket of ice and some copper tube) which could be used with ambient air to flush through the E-tube prior to diving, this way you could fairly quickly drop the water content of the air in the E-tube immediately prior to the dive.


#9

In addition to the silica gel bags, I use canned air (be sure to use a non-flammable product) to replace the warm and humid air in the tube by cold and dry air. Works fine and can be handled well on-site. Scott's suggestion to use CO2 bike spray may work as well.

-Stefan


#10

I’m using Moisture Munchers - desiccant capsules made for SeaLife underwater cameras. They are blue and turn pink when they need replacing. What I did is zip tie the capsule between the bend in the camera cable. Works great and doesn’t take up much space!


#11

There are some other pre-packaged silica gels of the indicating variety, too. Here’s one I’ve been using lately:

Like the “Moisture Munchers”, these are one-shot only- they’re in a plastic bag that is difficult (though not impossible) to get hot enough to recharge the silica gel without melting the plastic). Note that these are 10g bags, much more desiccant than the moisture munchers.

If you want a smaller bag, here’s a 3g variety:

-W