CCD chip in mineral oil...

You likely have an optical/focus problem. Mineral oil is an excellent, transparent liquid dielectric, but it does have a different refractive index than air, so your optical system may require some tweaks to bring things back into focus.

Bert

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Bert Hickman 
Stoneridge Engineering 
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The refractive index of oil is different from air's one, so if the lens' outside is not flat you will be severely out of focus.

--
Saludos

To test this, try making a simple shadow box: aim the CCD toward some light, then lay something opaque and insulating (like an insulated wire) against the surface of the CCD's image plane (_not_ the lens -- the chip itself). If a honkin' big black thing shows up in your erstwhile gray image, you know it's an optical problem.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

I wouldn't be surprised if the refractive index of mineral oil isn't a lot closer to that a lot of clear plastics than air is. Plastics like, for instance, the stuff they make cheap camera lenses out of.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

As part of an experiment (which I'm not ready to describe until I've done it, then there will be video and a detailed description on my web site), I'm running a small computer, submerged in mineral oil. That part is a well known technique and works fine with cheap materials.

What would be very useful for my experiment would be to have a CCD camera, also submerged. Since I can't have any air pockets in this system, it would be helpful/simplify things if the mineral oil could be in direct contact with the CCD chip surface. This does not seem to work so far. I get a uniform, gray image. The camera works again once it "dries" out. What I'm trying to figure out is why (and what to do about it,of course).

I'm using pharmacy-bought mineral oil that has "d-alpha tocopherol as a stabilizer because it was handy. I haven't had much luck finding information on whether this substance is electrically conductive. Apparently the question doesn't come up much. :) I see a few references from reliable sources (not putting much stock in the hair-brained claims from supplement mongers) that it is an important Vitamin for "nerve conductivity", but none specify whether they mean "electrical" or "chemical" conductivity. My, el cheap-o mutitester shows the mineral oil as infinite resistance (it goes at least into the megaohms), but I assume the tiniest bit of conductivity would be enough to foul such a sensitive chip? Or is there some other factor at play that I'm not considering? At first I was thinking maybe a thermal problem but after several days soaking at room temperature, it still behaves the same...

I've ordered some "100% pure" mineral oil, marketed specifically for submersion of electronics, but while I'm waiting, I though I'd pick some brains...

If the problem is actually a function of the mineral oil, I've been considering coating the chip with epoxy, under the lens, but as this will be irreversible, I was hoping to get some input on whether this has a chance of working before I sacrifice my (admittedly cheap) camera chip. Some distortion from the epoxy is acceptable, but I think I can mostly overcome that by sandwiching the epoxy between the chip and a portion of a microscope slide (it's not for anything critical and failure would only cost me a few hundred dollars and a week to order new parts).

I would appreciate any input on conductivity of d-alpha tocopherol, other reasons why mineral oil might affect a CCD chip, or other chip coatings if epoxy sounds like it might be a problem. Thanks.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++=

It sounds like the mineral oil changes the dielectric constant hence increasing the capacitance in and around the chip. Mineral oil is used to increase the high voltage breakdown voltage in air for many applications though I don't know what the additives in drug store product does.

tm

Is this a packaged CCD sensor with a glass window? Are you doing this to make it capable of being subjected to a lot of pressure, like a submersible vehicle or sensor package? If so, the glass window may break under pressure.

I'm just guessing, as you give few details. Yes, as others mention, the lens may have to be replaced or at least refocused to work in the oil. The lens relies on the difference in refractive index between air and the lens material to bend light. if the surrounding medium is oil instead of air, the lens needs to be different.

Jon

I'm guessing he won't be able to tweak it. according to this,

mineral oil is n =~1.33 and other oils are even higher. Since glass is 1.4 to 1.5, well the lens is just not doing much.

George H.

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Are you using the same oil to immerse the rest of the computer? If so, I concur with others that it's an optical problem. If it were electrical I'm pretty sure you'd have seen other electrical issues. Granted you aren't exp osing processor chips etc. directly to the oil, but all those interconnects etc. should have seen some adverse effects.

Mark L. Fergerson

FWIW,

These compounds are nonionic*, so there should be very little conductivity indeed. Perhaps some adsorbed moisture could screw with that, but that would be true of any oil I think.

*At least, in the absence of a base. The phenol group could be saponified in the same way as phenol (historically, carbolic acid) or regular fatty acids (which makes regular soap). The result probably wouldn't remain in solution, but would precipitate as a white solid. Not that it's very easy to get NaOH to dissolve in oil in the first place to try that. :)

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

As part of an experiment (which I'm not ready to describe until I've done it, then there will be video and a detailed description on my web site), I'm running a small computer, submerged in mineral oil. That part is a well known technique and works fine with cheap materials.

What would be very useful for my experiment would be to have a CCD camera, also submerged. Since I can't have any air pockets in this system, it would be helpful/simplify things if the mineral oil could be in direct contact with the CCD chip surface. This does not seem to work so far. I get a uniform, gray image. The camera works again once it "dries" out. What I'm trying to figure out is why (and what to do about it,of course).

I'm using pharmacy-bought mineral oil that has "d-alpha tocopherol as a stabilizer because it was handy. I haven't had much luck finding information on whether this substance is electrically conductive. Apparently the question doesn't come up much. :) I see a few references from reliable sources (not putting much stock in the hair-brained claims from supplement mongers) that it is an important Vitamin for "nerve conductivity", but none specify whether they mean "electrical" or "chemical" conductivity. My, el cheap-o mutitester shows the mineral oil as infinite resistance (it goes at least into the megaohms), but I assume the tiniest bit of conductivity would be enough to foul such a sensitive chip? Or is there some other factor at play that I'm not considering? At first I was thinking maybe a thermal problem but after several days soaking at room temperature, it still behaves the same...

I've ordered some "100% pure" mineral oil, marketed specifically for submersion of electronics, but while I'm waiting, I though I'd pick some brains...

If the problem is actually a function of the mineral oil, I've been considering coating the chip with epoxy, under the lens, but as this will be irreversible, I was hoping to get some input on whether this has a chance of working before I sacrifice my (admittedly cheap) camera chip. Some distortion from the epoxy is acceptable, but I think I can mostly overcome that by sandwiching the epoxy between the chip and a portion of a microscope slide (it's not for anything critical and failure would only cost me a few hundred dollars and a week to order new parts).

I would appreciate any input on conductivity of d-alpha tocopherol, other reasons why mineral oil might affect a CCD chip, or other chip coatings if epoxy sounds like it might be a problem. Thanks.

Good guess Joe. Yes, it is for a submersible sensor, under VERY high pressu re. I specifically got the IR camera (not "thermal") so that it does not ha ve any cover over the chip. And the space behind the lens (plastic lens I a ssume) will be filled with oil before before pressure is applied. I did thi nk about needing to refocus the lens for the oil (and for the water outside the probe, but I'm pretty sure that's not the only issue. If the RI of the oil happens to be very close to that of the plastic (which I currently hav e RI info on), then I have another problem I didn't anticipate, the lens mi ght not be adjustable far enough to make up for it.

The main reason I say that's not the only problem is that I'm pretty sure I got the same uniform gray whether the camera was in darkness, full sunligh t, or shining a light into the lens. I hadn't bothered to check the RI of t he oil, so I wasn't considering that possibility (other than assuming the p ics would be a bit blurry until I adjusted the lens), so I'll rerun those t ests to try and rule that out.

I also cant rule out that some moisture got into the oil, but (I haven't ex actly been doing this in a clean-room. It's a personal project. I'm actuall y a programmer, not a chemist or physicist), but I doubt it would be more t han the summer humidity here in Miami, which doesn't seem to bother digital cameras noticeably.

Thanks for the ideas everyone, I'll let you know how things go.

sure. I specifically got the IR camera (not "thermal") so that it does not have any cover over the chip. And the space behind the lens (plastic lens I assume) will be filled with oil before before pressure is applied. I did t hink about needing to refocus the lens for the oil (and for the water outsi de the probe, but I'm pretty sure that's not the only issue. If the RI of t he oil happens to be very close to that of the plastic (which I currently h ave RI info on), then I have another problem I didn't anticipate, the lens might not be adjustable far enough to make up for it.

I got the same uniform gray whether the camera was in darkness, full sunli ght, or shining a light into the lens. I hadn't bothered to check the RI of the oil, so I wasn't considering that possibility (other than assuming the pics would be a bit blurry until I adjusted the lens), so I'll rerun those tests to try and rule that out.

exactly been doing this in a clean-room. It's a personal project. I'm actua lly a programmer, not a chemist or physicist), but I doubt it would be more than the summer humidity here in Miami, which doesn't seem to bother digit al cameras noticeably.

tried taking of the lens and covering parts of the sensor with something li ke a piece of paper?

if it works you should be able to see dark and light areas

-Lasse

It could well be more than this, but if the camera has auto level, in the absence of any input signal it may adjust things to the same neutral gray. You could tell this by waving your hand in front of the thing or otherwise switching the light on and off: most auto leveling algorithms would respond by "bouncing" down to dark then recovering to gray, "bouncing" up to white then recovering to gray, etc.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

tabilizer because it was handy. I haven't had much luck finding information on whether this substance is electrically conductive. Apparently the quest ion doesn't come up much. :) I see a few references from reliable sources ( not putting much stock in the hair-brained claims from supplement mongers) that it is an important Vitamin for "nerve conductivity", but none specify whether they mean "electrical" or "chemical" conductivity. My, el cheap-o m utitester shows the mineral oil as infinite resistance (it goes at least in to the megaohms), but I assume the tiniest bit of conductivity would be eno ugh to foul such a sensitive chip?

I doubt if it is electrical conductivity. But you could easily extend the range of your cheap multimeter by using a dc supply of moderate voltage and monitoring the current.

Dan

I'll have to go along wiht th eothers about the refractive index being the problem. Now a solution ? HA.

The problem is that in general a denser material will have a higher refract ive index. You need the light bent a certain way. Now, if you can come up w irth something with a higher refractive index than oil, well you just make a lens out of that right ? Problem is that such a material might just be op aque lol.

This is beyond me also, but I have an idea. the math involved nmight be doa ble by someone here, but I suggest an air lens. I know you do not want an a ir pocket but it might be inavoidable.

Now to focus in air, you use a convex lens which has a higher refractive in dex than aiur, correct ? Now you are in oil, and use a lens with a much low er refractive index than the "medium" I guess you would call it. In that ca se, I suppose the lens will have to be concave.

An intersting problem really, to which I would like to see a solution.

I'm betting you need an added lens to get things into focus. Being totally unfocused will also bamboozle the brightness compensation logic, so the gray isn't a surprise. As others have mentioned, try covering half of the chip with something opaque.

While an air lens in oil can also work, the glass around it must be hermetically sealed and very strong, and the focal length will vary with depth.

There are some very dense glasses available. Google for an "Abbe Diagram" to see the options. People do make lenses for use in water, and mineral oil isn't that far off.

You might want to ask around in sci.optics.

Joe Gwinn

Hard problem.

One possible method is to use the lightest possible oil and C-axis normal sapphire lenses.

The power of a lens (i.e. the reciprocal of its focal length) is given approximately by the "lensmaker's equation",

P ~= (n2/n1 -1) (1/r1 -1/r2)

where r1 and r2 are the surface radii, n2 is the lens index, n1 is the medium index (air = 1, oil ~= 1.33 to 1.6, depending on composition).

In lens design, rays start from the left, and the radii are positive if they're convex towards the left. Thus in a biconvex lens, which has r1 > 0 and r2 < 0, the powers contributed by the two surfaces add.

If you take a normal crown glass single-element lens (n~1.52) with a focal length f in air, and dunk it into oil with an index of 1.35, the new focal length is

f' = f (1.52-1) /(1.52/1.35 - 1) ~ 4.13 f .

High index plastic used for eyeglasses has an index of about 1.68. With that, the focal length ratio would improve to 2.7x.

Out past about 1.2 microns, you can use silicon lenses, which would help a lot, but your webcam won't see anything. There are also materials such as silicon nitride, with N = 2.0, but you won't find that at K-Mart.

Assuming your package has a window, you have to consider that as well, and of course the refraction at the water/window surface, which will shorten the apparent focal length on the water side.

You can probably make this work at VGAish resolution and smallish aperture (f/8 or so), but going any further will require a real optical design.

You might want to order a set of eyeglasses from Zenni with high-index lenses and a nice circular outline. Don't bother getting them coated, because the coating will be wrong for the medium and the reflections won't be too bad anyway.

Eyeglasses are specified in dioptres, which are reciprocal metres of focal length, i.e. a 2.5 dioptre lens has a focal length of 40 cm in air and probably a bit over a metre in oil. So you want to get the highest power they make, and stack both lenses together.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

What would be very useful for my experiment would be to have a CCD camera, also submerged. secret, can't tell, etc...

=================

Is this some kind of joke? Why in the world would you want to submerge the imaging chip in mineral oil? In any case, the analyses about index of refraction are certainly correct. j

, also submerged. secret, can't tell, etc...

e imaging chip in mineral oil?

I'm guessing it will see very high pressure

-Lasse

On Saturday, May 10, 2014 2:27:41 PM UTC-4, Lasse Langwadt Christensen wrot e:

ra, also submerged. secret, can't tell, etc...

the imaging chip in mineral oil?

Good guess. Then the solution is to just make a window from .5 - 1 inch acr ylic. at .5 i. dia, that should take 3000 psi, don't you think?