Puzzle for the components "Gurus" out there...failure in a vacuum enviroment?

[David Harper]

I'm engaged in a high altitude project incorporating an automatic
camera. In order to ensure that the potential cameras selected were
capable of operating in a near-vacuum, two were tested in a vacuum
chamber. One was a Kodak Ke60, and the other was a Samsung 80Ti.
Both had leads soldered to the shutter contacts, which were controlled
by solid state relays via a microcontroller. The 80Ti's only other
modification was removal of the large flash cap, as we were not
planning on using a flash (not that a flash at 100k ft would do any
good anyway). The 80Ti operated throughout the test, while the Ke60
failed at around 1 PSI. The standard "burned electronics smell" was
present after opening the chamber.

After opening the case to the Ke60 to determine what cause the Ke60
failure, it looks like there was heating near the flash circuitry.
Specifically, there is some discoloration near the contacts to a
silver, eliptical-shaped capacitor (looks wrapped) with "333KS" on the
side. Is this a pressure sensitive component? (the chamber went from
14.7 PSI to about .05 PSI in about a minute, so it was rapid
depressurization). The large flash cap was still good, so I don't
believe this was the point of failure.

Could it have been this 333KS component? If not, what potential
components may have failed due to decreased ambient pressure?

Thanks in advance for any advice!
Dave

 

[Ken Finney]

I'm engaged in a high altitude project incorporating an automatic
camera. In order to ensure that the potential cameras selected were
capable of operating in a near-vacuum, two were tested in a vacuum
chamber. One was a Kodak Ke60, and the other was a Samsung 80Ti.
Both had leads soldered to the shutter contacts, which were controlled
by solid state relays via a microcontroller. The 80Ti's only other
modification was removal of the large flash cap, as we were not
planning on using a flash (not that a flash at 100k ft would do any
good anyway). The 80Ti operated throughout the test, while the Ke60
failed at around 1 PSI. The standard "burned electronics smell" was
present after opening the chamber.

After opening the case to the Ke60 to determine what cause the Ke60
failure, it looks like there was heating near the flash circuitry.
Specifically, there is some discoloration near the contacts to a
silver, eliptical-shaped capacitor (looks wrapped) with "333KS" on the
side. Is this a pressure sensitive component? (the chamber went from
14.7 PSI to about .05 PSI in about a minute, so it was rapid
depressurization). The large flash cap was still good, so I don't
believe this was the point of failure.

Could it have been this 333KS component? If not, what potential
components may have failed due to decreased ambient pressure?

Thanks in advance for any advice!
Dave

Just off the top of my head, high altitude involves low pressure, low
humidity,
radiation, and cold temperatures. Since this was in a pressure chamber,
radiation
and temperature doens't apply, but don't be surprized is it works in a
pressure
chamber but not at altitude due to these factors. Low humidity probably
isn't
a factor, but some equipment will stop working at low humidity. If the
failed
part has any sort of cavity that couldn't vent, it likely was the source of
the
problem. Another issue is corona, arcing will occur that would't at normal
pressure, both inside and outside the parts.

 

[default]

I'm engaged in a high altitude project incorporating an automatic
camera. In order to ensure that the potential cameras selected were
capable of operating in a near-vacuum, two were tested in a vacuum
chamber. One was a Kodak Ke60, and the other was a Samsung 80Ti.
Both had leads soldered to the shutter contacts, which were controlled
by solid state relays via a microcontroller. The 80Ti's only other
modification was removal of the large flash cap, as we were not
planning on using a flash (not that a flash at 100k ft would do any
good anyway). The 80Ti operated throughout the test, while the Ke60
failed at around 1 PSI. The standard "burned electronics smell" was
present after opening the chamber.

After opening the case to the Ke60 to determine what cause the Ke60
failure, it looks like there was heating near the flash circuitry.
Specifically, there is some discoloration near the contacts to a
silver, eliptical-shaped capacitor (looks wrapped) with "333KS" on the
side. Is this a pressure sensitive component? (the chamber went from
14.7 PSI to about .05 PSI in about a minute, so it was rapid
depressurization). The large flash cap was still good, so I don't
believe this was the point of failure.

Could it have been this 333KS component? If not, what potential
components may have failed due to decreased ambient pressure?

Thanks in advance for any advice!
Dave

Air becomes ionized at lower voltages when pressure is reduced. That
is how fluorescent lamps, neon tubes, plasma globes work. The gas
lends the characteristic color to the discharge but the discharge
takes place at/because of a reduced pressure.

You probably still had the high voltages present when the pressure
went down. You would have to disable/disconnect the oscillator so it
won't produce high voltage before you test. Beyond that, the
proximity and potential difference of the discharge point etc can
explain one camera working and the other failing.

Once a gas ionizes it conducts electricity - the discharge probably
heated part of the circuit or some component and caused it to burn,
the carbon present also conducts and may cause the discharge to
continue when pressure is restored or reduced.

Or there may be some other thing that is contributing, like out
gassing of some component, circuit board material, leakage of
electrolyte from electrolytic caps (a more conductive vapor produced
when electrolyte boils, or out gasses).

Were the circuit boards and components coated with anything like clear
thick varnish? That is one of the techniques used with equipment
intended to work at high altitude. Usually the whole circuit is
dipped in something called "conformal coating" if it is made for the
military. Even if it is sealed in a hermetic container.

Parts should also be derated for operation in a vacuum since heat
won't be transferred by convection and only conduction or radiation.
I'm guessing that probably isn't your problem, but one never knows.

 

[Al]

I'm engaged in a high altitude project incorporating an automatic
camera. In order to ensure that the potential cameras selected were
capable of operating in a near-vacuum, two were tested in a vacuum
chamber. One was a Kodak Ke60, and the other was a Samsung 80Ti.
Both had leads soldered to the shutter contacts, which were controlled
by solid state relays via a microcontroller. The 80Ti's only other
modification was removal of the large flash cap, as we were not
planning on using a flash (not that a flash at 100k ft would do any
good anyway). The 80Ti operated throughout the test, while the Ke60
failed at around 1 PSI. The standard "burned electronics smell" was
present after opening the chamber.

After opening the case to the Ke60 to determine what cause the Ke60
failure, it looks like there was heating near the flash circuitry.
Specifically, there is some discoloration near the contacts to a
silver, eliptical-shaped capacitor (looks wrapped) with "333KS" on the
side. Is this a pressure sensitive component? (the chamber went from
14.7 PSI to about .05 PSI in about a minute, so it was rapid
depressurization). The large flash cap was still good, so I don't
believe this was the point of failure.

Could it have been this 333KS component? If not, what potential
components may have failed due to decreased ambient pressure?

Thanks in advance for any advice!
Dave

I see why you are trying to save some money, but COTS (commerical off
the shelf) is not reliable in harsh environments. If you want COTS
equipment to work at high altitudes, seal it in a container which will
provide it with a standard pressure/temperature/humidty.

Al

 

[Watson A.Name - Watt Sun]

I'm engaged in a high altitude project incorporating an automatic
camera. In order to ensure that the potential cameras selected were
capable of operating in a near-vacuum, two were tested in a vacuum
chamber. One was a Kodak Ke60, and the other was a Samsung 80Ti.
Both had leads soldered to the shutter contacts, which were controlled
by solid state relays via a microcontroller. The 80Ti's only other
modification was removal of the large flash cap, as we were not
planning on using a flash (not that a flash at 100k ft would do any
good anyway). The 80Ti operated throughout the test, while the Ke60
failed at around 1 PSI. The standard "burned electronics smell" was
present after opening the chamber.

After opening the case to the Ke60 to determine what cause the Ke60
failure, it looks like there was heating near the flash circuitry.
Specifically, there is some discoloration near the contacts to a
silver, eliptical-shaped capacitor (looks wrapped) with "333KS" on the
side. Is this a pressure sensitive component? (the chamber went from
14.7 PSI to about .05 PSI in about a minute, so it was rapid
depressurization). The large flash cap was still good, so I don't
believe this was the point of failure.

Could it have been this 333KS component? If not, what potential
components may have failed due to decreased ambient pressure?

The value would probably be 33 nanofarads and the K stands for 10
percent tolerance. This might be the cap that discharges thru the
trigger coil to make the high voltage pulse across the flash tube. It
does charge up to several hundred volts, so that might be the reason
why it failed.

If you don't need the flash circuitry, remove it, because it generates
high voltage, which could be an even bigger problem if your equipment
is subjected to temperatures that cause condensation.

Thanks in advance for any advice!
Dave

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[David Harper]

Just off the top of my head, high altitude involves low pressure, low
humidity,
radiation, and cold temperatures. Since this was in a pressure chamber,
radiation
and temperature doens't apply, but don't be surprized is it works in a
pressure
chamber but not at altitude due to these factors. Low humidity probably
isn't
a factor, but some equipment will stop working at low humidity. If the
failed
part has any sort of cavity that couldn't vent, it likely was the source of
the
problem. Another issue is corona, arcing will occur that would't at normal
pressure, both inside and outside the parts.

Yes, the enclosure will be insulated and exposed to high altitudes for
no longer than 2 hours. Being as adiabatic as it is, I expect to see
minimal heat loss from the equipment inside. Radiation won't be a
problem either, as 100k ft is still WELL inside the Van Allen
radiation belts.

I wasn't aware of what you call corona (I'm assuming you aren't
refering to effects from the sun's corona). Can you give me a summary
of what this is and what you mean?

Thanks,
Dave

 

[David Harper]

Air becomes ionized at lower voltages when pressure is reduced. That
is how fluorescent lamps, neon tubes, plasma globes work. The gas
lends the characteristic color to the discharge but the discharge
takes place at/because of a reduced pressure.

You probably still had the high voltages present when the pressure
went down. You would have to disable/disconnect the oscillator so it
won't produce high voltage before you test. Beyond that, the
proximity and potential difference of the discharge point etc can
explain one camera working and the other failing.

Once a gas ionizes it conducts electricity - the discharge probably
heated part of the circuit or some component and caused it to burn,
the carbon present also conducts and may cause the discharge to
continue when pressure is restored or reduced.

Or there may be some other thing that is contributing, like out
gassing of some component, circuit board material, leakage of
electrolyte from electrolytic caps (a more conductive vapor produced
when electrolyte boils, or out gasses).

Were the circuit boards and components coated with anything like clear
thick varnish? That is one of the techniques used with equipment
intended to work at high altitude. Usually the whole circuit is
dipped in something called "conformal coating" if it is made for the
military. Even if it is sealed in a hermetic container.

Parts should also be derated for operation in a vacuum since heat
won't be transferred by convection and only conduction or radiation.
I'm guessing that probably isn't your problem, but one never knows.

That post was highly helpful. I imagine that is very likely the cause
of the problem. Conformal coating sounds ideal. Do you know any
available sources or substitutes for this?

Thanks!
Dave

 

[Al]

Yes, the enclosure will be insulated and exposed to high altitudes for
no longer than 2 hours. Being as adiabatic as it is, I expect to see
minimal heat loss from the equipment inside. Radiation won't be a
problem either, as 100k ft is still WELL inside the Van Allen
radiation belts.

I wasn't aware of what you call corona (I'm assuming you aren't
refering to effects from the sun's corona). Can you give me a summary
of what this is and what you mean?

Thanks,
Dave

Go to your local electonics parts supplier and I am sure you will find a
bottle of "corona dope." It has been used for decades to prevent arcing
in the high voltage sections of TVs.

Al

 

[Lewin A.R.W. Edwards]

I'm engaged in a high altitude project incorporating an automatic

That post was highly helpful. I imagine that is very likely the cause
of the problem. Conformal coating sounds ideal. Do you know any
available sources or substitutes for this?

For a low-volume hobby/educational project, I suggest you use an
acrylic coating such as
<http://www.mgchemicals.com/products/419b.html>. One of the important
characteristics of acrylic is that it's easy to remove if you need to
modify the circuit. Acrylic has reasonable dielectric properties, and
it's very cheap.

The non plus ultra product is a parylene coating, but this is probably
out of your reach...

 

[default]

That post was highly helpful. I imagine that is very likely the cause
of the problem. Conformal coating sounds ideal. Do you know any
available sources or substitutes for this?

Thanks!
Dave

"Corona" is an electrical discharge in air around a terminal (with
high voltage). Blue light from the source. The voltage ionizes and
lights up the air around the terminal, usually with a moving display.
Tesla coils that don't have a lot of power produce nice coronas, with
a lot of power the discharge looks like lightening (bright white noisy
arcing). UV light and ozone are other byproducts of high voltage
corona.

Corona is Latin for crown.

DOW CORNING CORP. P.O. Box 0994 Midland,Michigan (800) 346-9883 Makes
the stuff used by many military suppliers, describe your application
and see if they recommend something.

Mouser electronics had some spray on stuff they were calling conformal
coating.

There is no hard and fast chemical composition of conformal coating
that I know of. At home for projects that may get wet I use a dip (or
several) in polyurethane varnish. Paraffin wax also works if the item
is heated to about 200F and potted in it (works great for underwater
protection). If your application produces or is subject to heat
paraffin isn't the answer.

The thicker a dielectric coating the better the voltage break-down
resistance. It often helps to heat the circuit before dipping since
heating drives off surface moisture. Heating also thins the first
coat and eliminates some of the air trapped in spaces. Dip in cool
varnish and the contracting air sucks the varnish in. Vacuum oven
coating is another technique if air spaces are a problem.

I jury rigged a pressure cooker, by turning around the vacuum vent and
connecting it to a pump where the pressure relief weight sits, Used my
stove to vacuum impregnate induction coils I was winding with hot
paraffin. It probably wasn't safe, but it worked well enough.

 

[default]

PS if you don't need the flash, like Watson says, remove it.

end of HV problems . . .

There is also the chance that the flash circuitry will interfere
(power supply ripple or EMI) with any telemetry or control signals
your device is receiving. Another thing to test for . . .

 

[Ken Finney]

Yes, the enclosure will be insulated and exposed to high altitudes for
no longer than 2 hours. Being as adiabatic as it is, I expect to see
minimal heat loss from the equipment inside. Radiation won't be a
problem either, as 100k ft is still WELL inside the Van Allen
radiation belts.

I wasn't aware of what you call corona (I'm assuming you aren't
refering to effects from the sun's corona). Can you give me a summary
of what this is and what you mean?

Thanks,
Dave

Radiation may be a big problem. Radiation at 30,000 feet is a problem, it
is a lot bigger problem at 50,000 feet, and an even bigger problem at 70,000
feet. And I assume at even bigger problem at 100,000 feet. The failures
you will see are random, and normally go away when the power is recycled on
the hardware. Because of the randomness of the failures and the inability
to repeat them exactly in a lab environment, many people don't know how bad
the problem is, or that it is getting much worse due to reduced feature
size.

As someone else has already pointed out, corona is the electrical discharge
between points because of the air being ionized. As pressure goes down, the
voltage potentail the air can block goes down also, and at some voltage (I
know it can occur at 70 volts, I don't know how much lower, but there is a
low voltage cutoff below which it doesn't occur) the air will become ionized
and begin to conduct, causing a short. And it is not just a pressure issue,
the component gasses change the equation (i.e. just because it passes corona
testing with the gasses in the air at sea level, doesn't mean it can
withstand the same voltage with the gasses available at 100,000 feet).
Also, if any of the parts have cavities, corona can occur inside the parts,
and conformal coat applied to the circuit board won't help.

NASA has lots of data available on the web, you might be able to find
something that will help you.