As I have mentioned previously, I am designing a temperature and
humidity control system for my university lab that I am working in.
Several dsPIC controlled remote terminal units (RTUs) will be placed
in self contained chambers. These RTUs will provide a means to log and
control temperature and humidity. Within the chambers are special
fungi that require a high relative humidity (RH) level to grow
effectively - sometimes even close to 100% RH.
I am concerned that water from the air may condense on the PCBs and
cause problems (such as undesirably conducting electricity, and so
on). Should I be worried about this? If so, what can I do about it?
Also, are there any other potential problems that I should be aware of
for running home-made electronic equipment in a high humidity
environment?
Will a crystal/crystal oscillator deviate enough from it's desirable
frequency in a high humidity environment to cause serial communication
issues
> Hi all,
>
> As I have mentioned previously, I am designing a temperature and
> humidity control system for my university lab that I am working in.
> Several dsPIC controlled remote terminal units (RTUs) will be placed
> in self contained chambers. These RTUs will provide a means to log and
> control temperature and humidity. Within the chambers are special
> fungi that require a high relative humidity (RH) level to grow
> effectively - sometimes even close to 100% RH.
>
> I am concerned that water from the air may condense on the PCBs and
> cause problems (such as undesirably conducting electricity, and so
> on). Should I be worried about this? If so, what can I do about it?
>
> Also, are there any other potential problems that I should be aware of
> for running home-made electronic equipment in a high humidity
> environment?
>
> Will a crystal/crystal oscillator deviate enough from it's desirable
> frequency in a high humidity environment to cause serial communication
> issues?
V G wrote:
> I am concerned that water from the air may condense on the PCBs and
> cause problems (such as undesirably conducting electricity, and so
> on). Should I be worried about this?
Yes.
> If so, what can I do about it?
Put only the sensors in the chamber with the electronics in the normal room
environment. That's what wires are for.
On Sat, Jul 24, 2010 at 8:39 AM, Olin Lathrop <spam_OUTolin_piclistTakeThisOuTembedinc.com> wrote:
> V G wrote:
>> I am concerned that water from the air may condense on the PCBs and
>> cause problems (such as undesirably conducting electricity, and so
>> on). Should I be worried about this?
>
> Yes.
>
>> If so, what can I do about it?
>
> Put only the sensors in the chamber with the electronics in the normal room
> environment. That's what wires are for.
That would not be practical. The chambers themselves are quite large,
and the room that the chambers are stored in is itself quite humid. It
would not be practical to run long wires into the chambers (especially
those for SPI, I2C, and 1-wire communications intended for short
distances).
Would coating the PCB and electronics with some sort of spray help to
prevent problems caused by water? Any other ideas?
> Why do the PCB's need to be exposed to the high humidity?
>
> On 7/24/2010 8:14 AM, V G wrote:
>> Hi all,
>>
>> As I have mentioned previously, I am designing a temperature and
>> humidity control system for my university lab that I am working in.
>> Several dsPIC controlled remote terminal units (RTUs) will be placed
>> in self contained chambers. These RTUs will provide a means to log and
>> control temperature and humidity. Within the chambers are special
>> fungi that require a high relative humidity (RH) level to grow
>> effectively - sometimes even close to 100% RH.
>>
>> I am concerned that water from the air may condense on the PCBs and
>> cause problems (such as undesirably conducting electricity, and so
>> on). Should I be worried about this? If so, what can I do about it?
>>
>> Also, are there any other potential problems that I should be aware of
>> for running home-made electronic equipment in a high humidity
>> environment?
>>
>> Will a crystal/crystal oscillator deviate enough from it's desirable
>> frequency in a high humidity environment to cause serial communication
>> issues?
>>
Varnish/seal everything. What the army in WWII called "tropicalised".
Also only have probes and moisture/heat source in the high RH environment. Put the electronics elsewhere. Some components don't like fungi. Some fungi may secrete liquids that attack wiring or even insulation?
Crystal is more concerned about temperature. But unless you are doing very accurate timing and the crystal has a trimming capacitor to fine tune frequency, it's unlikely to matter.
On Sat, Jul 24, 2010 at 8:49 AM, Michael Watterson <.....mikeKILLspam@spam@radioway.org> wrote:
> Varnish/seal everything. What the army in WWII called "tropicalised".
I like this idea.
> Also only have probes and moisture/heat source in the high RH
> environment. Put the electronics elsewhere. Some components don't like
> fungi. Some fungi may secrete liquids that attack wiring or even insulation?
For this project, it would be impractical to separate the PCB and
sensory equipment. Also, I don't need to worry about fungal invasion.
These fungi play nicely. Humidity is the only thing I'm worried about.
> Crystal is more concerned about temperature. But unless you are doing
> very accurate timing and the crystal has a trimming capacitor to fine
> tune frequency, it's unlikely to matter.
> I am concerned that water from the air may condense on the PCBs and
> cause problems (such as undesirably conducting electricity, and so
> on). Should I be worried about this? If so, what can I do about it?
If you *ABSOLUTELY* must put the controller inside the high humidity shell:
- Seal the controller in its own dry air environment.
- In situations where an item MUST share the high humidity air,
consider the possibility of maintaining the controller at a suitably
higher temperature. This will lower the *effective* RH of air which
comes in contact with it.
- If electronics MUST be exposed to moist air, corrosive atmospheres
etc there are 'conformal coatings available which form a barrir twixt
them and their world. The best ones are very good indeed at doing
this.
Russell
>
> Also, are there any other potential problems that I should be aware of
> for running home-made electronic equipment in a high humidity
> environment?
>
> Will a crystal/crystal oscillator deviate enough from it's desirable
> frequency in a high humidity environment to cause serial communication
> issues?
>
In the concrete testing laboratory, they take day or 2 since casting 6" x 12" concrete cylinders, and cure them generally 7 or 28 days in a 100% humidity room. There are no controls, just some misting nozzles spraying a small amount of water near the ceiling. Check with a local concrete contractor for laboratory contacts.
On 7/24/2010 8:39 AM, Olin Lathrop wrote:
> V G wrote:
>
>> I am concerned that water from the air may condense on the PCBs and
>> cause problems (such as undesirably conducting electricity, and so
>> on). Should I be worried about this?
>>
> Yes.
>
>
>> If so, what can I do about it?
>>
> Put only the sensors in the chamber with the electronics in the normal room
> environment. That's what wires are for.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014. Gold level PIC consultants since 2000.
>
Wireless, or power line modems. Bare minimum electronics in humid area. I have to assume the water would not be distilled quality, but contain all sorts of ions, make it conductive, corrosive, and make deposits when evaporation occurs. None of these are good for electronics, or even high voltage power lines. Cleveland has a length of high voltage (11kv ??) feeder lines near an interstate highway at a higher level. The road salt spray has shorted these lines, taking them out of service with some major important (airport) customers. It is now routine, several times a year to have linemen wipe the insulators with damp rags.
> On Sat, Jul 24, 2010 at 8:39 AM, Olin Lathrop<olin_piclistKILLspamembedinc.com> wrote:
>
>> V G wrote:
>>
>>> I am concerned that water from the air may condense on the PCBs and
>>> cause problems (such as undesirably conducting electricity, and so
>>> on). Should I be worried about this?
>>>
>> Yes.
>>
>>
>>> If so, what can I do about it?
>>>
>> Put only the sensors in the chamber with the electronics in the normal room
>> environment. That's what wires are for.
>>
> That would not be practical. The chambers themselves are quite large,
> and the room that the chambers are stored in is itself quite humid. It
> would not be practical to run long wires into the chambers (especially
> those for SPI, I2C, and 1-wire communications intended for short
> distances).
>
> Would coating the PCB and electronics with some sort of spray help to
> prevent problems caused by water? Any other ideas?
>
> Varnish/seal everything. What the army in WWII called "tropicalised".
1. About the best conformal coating is "Parylene" which is partially
a state of mind and partially a range of products. Application is
annoying so usually done by specialists. Works very well. I only
mention it in case your university uses it . If not then suggestion 2.
is probably the most practical.
2. The following will do what you want very well indeed:
Exceptionally good and suitable for DIY use is eg Dow Corning 1-2577.
This can be applied by dipping, spraying or brushing.
eg you CAN dip a pcb in the liquid, pull the board out at the rate
they recommend, dry it as recommened and get a VERY thin (100 micron)
coating that makes your boards about RH proof in most cases.*
A 0.1mm coating is enough to allow a board to operate dripping wet, if
one insists. It gets better - the material is UV fluorescent so you
can check for coverage with a UV lamp AND it can be soldered through
AND you can spot touch it up after soldering.
Needless to say, anything this good (let alone being made by Dow) is
not very cheap but a little goes a VERY long way.
Here it is with its cousins. ALL these use the same basic material but
it is "borne" differently.
Low VOC (volatile organic) is ozone safer, less regulatory issues,
kills fewer brain cells and so probably less fun to sniff.
ie use these ventilated.
2577 The boss
2577 low VOC - more environmentally friendly
2620 - less viscous version
2620 low VOC - ....
The "Conformal coatings family datasheet" mentioned on the above page
is excelllent - needs free registration.
* BUT add a sealed container with its own dry air and a dessicant bag
to keep it that way under all conditions. eg air at a given
temperature with only modest RH will have water condense out if cooled
far enough.
3. You can get some gain by just spraying with readily available
dometic clear "varnish" eg polyurethane 'plastic'** BUT 2577 is about
3 zillion times better.
** Polyurethane is *NOT* a plastic.
Not many people know that :-).
Even though Wikipedia calls it one and many many many other sites do as well.
It's actually an "elastomer" fwiw.
Ignore the indignant yelling that will now start and eg read this
which gives a small clue that the statement may be correct :-). http://www.mearthane.com/urethane_plastic.html
V G wrote:
> That would not be practical. The chambers themselves are quite large,
> and the room that the chambers are stored in is itself quite humid.
As bad as the inside of the chambers though?
> It
> would not be practical to run long wires into the chambers (especially
> those for SPI, I2C, and 1-wire communications intended for short
> distances).
Not necessarily, although you may have to reduce the bit rate. The things
you are measuring are very slow compared to even a "slow" bit rate in
microcontroller terms, so this should not be a issue.
Also, there must be a wall somewhere that separates the inside and outside
of the chamber, and I doubt that wall is so thick as to make wires from one
side to the other "long".
> Would coating the PCB and electronics with some sort of spray help to
> prevent problems caused by water? Any other ideas?
I think you'll need more than just spray, probably real potting. Again, I
would try to minimize the circuitry in the harsh environment. If you really
really need some electronics near the sensors (you still haven't provided
convincing evidence that you do), then make it a minimal PIC system that
reads the sensors on the board and passes the aggregated data back over a
single serial stream that can handle the run to outside the box. You send
in 5.7V and ground, and the board returns a UART output at some slow baud
rate, like 1200. The purpose of 5.7V is that you can put a LDO on the board
to make locally clean 5V power. If you are really worried about noise, the
UART output can be differential, but I expect that's a complication not
needed in this case.
Now you can make multiple of these small sensor boards, each being carefully
potted and sealed. You can even spread around several per chamber, with the
aggregating and control logic happening outside where the environment is a
bit more benign and where it's possible to do maintainence and debugging
while the chamber is running.
> Low VOC (volatile organic) is ozone safer, less regulatory issues,
> kills fewer brain cells and so probably less fun to sniff.
> ie use these ventilated.
> 2577 The boss
> 2577 low VOC - more environmentally friendly
> 2620 - less viscous version
> 2620 low VOC - ....
>
> 1-2577 data sheet http://www.bkelectric.com/linked/dowcorning%201-2577.pdf
Quoting V G <.....x.solarwind.xKILLspam.....gmail.com>:
>
> Would coating the PCB and electronics with some sort of spray help to
> prevent problems caused by water? Any other ideas?
On Sat, Jul 24, 2010 at 5:14 AM, V G <EraseMEx.solarwind.xspam_OUTTakeThisOuTgmail.com> wrote:
> Hi all,
>
> As I have mentioned previously, I am designing a temperature and
> humidity control system for my university lab that I am working in.
> Several dsPIC controlled remote terminal units (RTUs) will be placed
> in self contained chambers. These RTUs will provide a means to log and
> control temperature and humidity. Within the chambers are special
> fungi that require a high relative humidity (RH) level to grow
> effectively - sometimes even close to 100% RH.
Hi VG, one question please: how do you will control accurately both
temperature and humidity in the same time? There is an interdependence
between temperature and humidity in a closed chamber, two sensors that
are kept at different temperatures will show different RH values, but
the same dew point can be calculated.Before taking a measurement, you
always need to wait long enough for the conditions to stabilize. Not
only RH levels need to stabilize but also temperature. That's clear,
why it is not possible to make extremely accurate relative humidity
measurements.
I've did some experiments quite long time:
adsabs.harvard.edu/abs/2009JPhCS.182a2018S
but my goal was to keep the same in two different chambers.
On Sun, Jul 25, 2010 at 10:39 AM, Vasile Surducan <piclist9spam_OUTgmail.com> wrote:
> Hi VG, one question please: how do you will control accurately both
> temperature and humidity in the same time?
I have algorithms that can manage that pretty well. Also, tolerance is
wide enough.
> There is an interdependence
> between temperature and humidity in a closed chamber, two sensors that
> are kept at different temperatures will show different RH values, but
> the same dew point can be calculated. Before taking a measurement, you
> always need to wait long enough for the conditions to stabilize. Not
> only RH levels need to stabilize but also temperature. That's clear,
> why it is not possible to make extremely accurate relative humidity
> measurements.
Thanks, but keeping the RH value within 10% is reasonable for my
purposes. Temperature should be kept within 3 Kelvin of the desired
temperature.
> I've did some experiments quite long time:
> adsabs.harvard.edu/abs/2009JPhCS.182a2018S
> but my goal was to keep the same in two different chambers.
> On Sun, Jul 25, 2010 at 10:39 AM, Vasile Surducan <@spam@piclist9KILLspamgmail.com> wrote:
> > Hi VG, one question please: how do you will control accurately both
> > temperature and humidity in the same time?
VG said
> I have algorithms that can manage that pretty well. Also, tolerance is
> wide enough.
What Vasile is saying is "Y' canna break the laws of Physics" (as
Scotty noted from time to time).
In a completely closed system you CANNOT control both temperature and
RH at once.
Read on for what you can do, and how.
For practical purposes, in a closed system there is a completely
constrained relationship in a closed system between temperature,
pressure, volume and Relative Humidity for a given chamber size,
amount of air, and amount of water.
Assuming that your other contents do not alter (and what eg plants do
MAY or may not violate that constraint) then messuring eg just mean
temperature will give you mean RH and controlling just temperature
will control RH - not necessarioly in a manner that is desired.
IF the system under consideration is not closed then you CAN control
both temperature and RH.
If it IS closed then you cannot.
eg you may have a growing space in a semi sealed container inside a
larger lab. The space can be ventilated with a fan from the lab and
can be heated. Air circulation is provided by an internal fan. If the
test box is too be held warmer than the outside lab then it can be
heated and controlled. Heating the air will reduce the RH. If the RH
in the box is to be lower than the lab then you can probably juggle in
blown air and heating to achieve a desired RH and temperature mix
(don't take that as Gospel.)
You can reduce RH in the box with eg a Peltier cooler that reduces air
below its dew point so that it loses water content. If you reintroduce
the coiled dier air directly into the box then net temperature and RH
will fall. If you reheat the air before reintroduction you can reduce
box RH and lower or raise temperature depending on degree of reheat.
If there IS no box and the lab is your whole environment then the
above method works if you drain the condensed water to outside the
lab. If instead you want to increase RH you can use steam or eg an
ultrasonic fogger and water supply. Overall the heater, cooler, water
drain and fogger will give you complete control. The system is not
closed as you allow water to enter and leave and energy for heating
and cooling. For a true otherwise sealed system you will need to vent
your Peltier hot side to outside the system in some cases or at all
times + more heating.
BUT if you do not have these cross boundary linkages OR a system
within a system (eg box inside lab) you cannot control both
temperature and RH at once. But you can have years of harmless fun
trying.
_________
Have you found a source of 1-2577 in small quantity yet ? :-)
(I have a 1 litre bottle thereof but am 'a bit far away').
> VG said
>> I have algorithms that can manage that pretty well. Also, tolerance is
>> wide enough.
>
> What Vasile is saying is "Y' canna break the laws of Physics" (as
> Scotty noted from time to time).
>
> In a completely closed system you CANNOT control both temperature and
> RH at once.
> Read on for what you can do, and how.
>
> For practical purposes, in a closed system there is a completely
> constrained relationship in a closed system between temperature,
> pressure, volume and Relative Humidity for a given chamber size,
> amount of air, and amount of water.
>
> Assuming that your other contents do not alter (and what eg plants do
> MAY or may not violate that constraint) then messuring eg just mean
> temperature will give you mean RH and controlling just temperature
> will control RH - not necessarioly in a manner that is desired.
>
> IF the system under consideration is not closed then you CAN control
> both temperature and RH.
> If it IS closed then you cannot.
>
> eg you may have a growing space in a semi sealed container inside a
> larger lab. The space can be ventilated with a fan from the lab and
> can be heated. Air circulation is provided by an internal fan. If the
> test box is too be held warmer than the outside lab then it can be
> heated and controlled. Heating the air will reduce the RH. If the RH
> in the box is to be lower than the lab then you can probably juggle in
> blown air and heating to achieve a desired RH and temperature mix
> (don't take that as Gospel.)
>
> You can reduce RH in the box with eg a Peltier cooler that reduces air
> below its dew point so that it loses water content. If you reintroduce
> the coiled dier air directly into the box then net temperature and RH
> will fall. If you reheat the air before reintroduction you can reduce
> box RH and lower or raise temperature depending on degree of reheat.
>
> If there IS no box and the lab is your whole environment then the
> above method works if you drain the condensed water to outside the
> lab. If instead you want to increase RH you can use steam or eg an
> ultrasonic fogger and water supply. Overall the heater, cooler, water
> drain and fogger will give you complete control. The system is not
> closed as you allow water to enter and leave and energy for heating
> and cooling. For a true otherwise sealed system you will need to vent
> your Peltier hot side to outside the system in some cases or at all
> times + more heating.
>
> BUT if you do not have these cross boundary linkages OR a system
> within a system (eg box inside lab) you cannot control both
> temperature and RH at once. But you can have years of harmless fun
> trying.
Haha, thanks. But I've already thought of all that!
> Have you found a source of 1-2577 in small quantity yet ? :-)
> (I have a 1 litre bottle thereof but am 'a bit far away').
I have not found the exact product, but there seems to be some sort of
lacquer coating at my university electronics store. I'll go take a
closer look.
RussellMc wrote:
> In a completely closed system you CANNOT control both temperature and
> RH at once.
Right, but where did you get the idea these were closed systems? The OP
said they were environmental chambers for the purpose of growing molds. I
wouldn't call something a "environmental chamber" that didn't have a way of
adding water or removing water, in addition to adding and possibly removing
heat.
On Mon, Jul 26, 2010 at 7:26 AM, Olin Lathrop <RemoveMEolin_piclistTakeThisOuTembedinc.com> wrote:
> Right, but where did you get the idea these were closed systems? The OP
> said they were environmental chambers for the purpose of growing molds. I
> wouldn't call something a "environmental chamber" that didn't have a way of
> adding water or removing water, in addition to adding and possibly removing
> heat.
That is mostly correct. But they're not molds. They're fungi. All
oranges are fruits, but not all fruits are oranges.
>> What Vasile is saying is "Y' canna break the laws of Physics" (as
>> Scotty noted from time to time).
>>
>> In a completely closed system you CANNOT control both temperature and
>> RH at once.
>> Read on for what you can do, and how.
> Haha, thanks. But I've already thought of all that!
Thinking is an excellent first step.
Some of it will have to be implemented for success.
'
>> Have you found a source of 1-2577 in small quantity yet ? :-)
>> (I have a 1 litre bottle thereof but am 'a bit far away').
>
> I have not found the exact product, but there seems to be some sort of
> lacquer coating at my university electronics store. I'll go take a
> closer look.
There are many many many conformal coating products available.
Some work better than others.
Few are utterly superb.
1-2577 is.
DC products are often enough among the best available and always worth a look.
In this case 1-2577 is available, affordable if you can get a small
enough quantity (expensive but very little needed) and works far far
better than typical lacquers, varnishes, resins.
1-2577 was reported by Sandia laboratories as being used to coat
concentrator solar cells in outdoor use. A more demanding application
would be hard to find. They changed back to it after having tried
another product that did not work as well.
Poor university student, ... research ... lab ... if its as good as
they say ... widerr use .. when I finish here I'll remember ...:-)
RM
The 1-2577 Low VOC Coating manufactured by Dow Corning Solar Solutions
is a silicone solvent based moisture cure that can be accelerated with
mild heat to provide faster curing times. Ideal for use as a
Photovoltaic cell and module coating due to it’s resistance to
humidity and other harsh environments. This solar panel coating also
offers excellent abrasion resistance and has good dielectric
properties. The clear, Dow Corning 1-2577 cures with a hard slick
surface, is mil spec and UL approved. The one part RTV also contains a
UV indicator and adheres to metal, aluminum, ceramic and plastic.
Product is available in bottles, pails and drums.
Krayden, Inc. is an authorized distributor for the Dow Corning
PV-based silicone materials being produced to increase efficiency in
solar manufacturing. With a specialty in technical support for
high-tech based applications and manufacturer trained representatives,
Krayden, Inc. can offer knowledgeable assistance as well as
re-packaging, dispensing and processing solutions for any of your
V G wrote:
> That is mostly correct. But they're not molds. They're fungi. All
> oranges are fruits, but not all fruits are oranges.
So a mold is a particular class of fungus? I didn't know that.
By the way, you say that this fungus is benign. That may be, but the same
warm and moist conditions may grow other fungi on your electronics. I would
design the electronics for arbitrary warm and moist conditions and not
assume only your particular research fungus will be exposed to it.
On Mon, Jul 26, 2010 at 8:04 AM, Olin Lathrop <spamBeGoneolin_piclistspamBeGoneembedinc.com> wrote:
> So a mold is a particular class of fungus? I didn't know that.
>
> By the way, you say that this fungus is benign. That may be, but the same
> warm and moist conditions may grow other fungi on your electronics. I would
> design the electronics for arbitrary warm and moist conditions and not
> assume only your particular research fungus will be exposed to it.
The environment is kept as sterile as possible (so as to prevent other
fungi/bacteria from invading the growth plates). However, it is a good
idea to assume it is not sterile. Good call.
If a fixed source of electric power is available, a simple solution is to slightly warm the inside of the enclosure with the controller (not the temp/humidity sensor).
A cheap IP55 plastic container may be ok if a small lamp (0,2-0,3W?) is inserted into the case because this lowers the internal RH and avoids condensation on the electronics. I seen this some years ago in an underground laboratory for biological studies: there were some dataloggers with this arrangement. The site was into a show cave, where humidity was always near 100%RH.
The simplest way is using a small thermos, put inside all your
electronics and close it hermetically.
It assumes your PCB is dissipate very small temperature
In that way your fungus will be happy and will stay outside the PCB.
BTW, what is used for that fungus?
>
>
> If a fixed source of electric power is available, a simple solution is to
> slightly warm the inside of the enclosure with the controller (not the
> temp/humidity sensor).
> A cheap IP55 plastic container may be ok if a small lamp (0,2-0,3W?) is
> inserted into the case because this lowers the internal RH and avoids
> condensation on the electronics. I seen this some years ago in an
> underground laboratory for biological studies: there were some dataloggers
> with this arrangement. The site was into a show cave, where humidity was
> always near 100%RH.
>
> regards,
> Marco
>
>
>
On Wed, Jul 28, 2010 at 8:33 AM, Vasile Surducan <RemoveMEpiclist9TakeThisOuTgmail.com> wrote:
> The simplest way is using a small thermos, put inside all your
> electronics and close it hermetically.
Thanks. That's a really good idea. Even an airtight lunch box should
do. Never thought of that.
> It assumes your PCB is dissipate very small temperature
Yes, it shouldn't dissipate much heat.
> In that way your fungus will be happy and will stay outside the PCB.
I'm not worried about the fungus, the PCB wont do anything to the
fungus. And this fungus wont do anything to the PCB or the electronics
either.
By use, I'm assuming, the usage of the product. i.e. I just finished applying 'milky Spore" to my lawn to combat Japanese Beetles (Grub). And then there is BT (Bacillus Tueng.. (sp)) to control the cabbage butterfly larva on the cabbage plants. THe answer might be it's proprietary, but maybe a very broad hint might be nice.
> On Wed, Jul 28, 2010 at 8:33 AM, Vasile Surducan<piclist9EraseME.....gmail.com> wrote:
>
>> The simplest way is using a small thermos, put inside all your
>> electronics and close it hermetically.
>>
> Thanks. That's a really good idea. Even an airtight lunch box should
> do. Never thought of that.
>
>
>> It assumes your PCB is dissipate very small temperature
>>
> Yes, it shouldn't dissipate much heat.
>
>
>> In that way your fungus will be happy and will stay outside the PCB.
>>
> I'm not worried about the fungus, the PCB wont do anything to the
> fungus. And this fungus wont do anything to the PCB or the electronics
> either.
>
>
>> BTW, what is used for that fungus?
>>
> What do you mean?
> > The simplest way is using a small thermos, put inside all your
> > electronics and close it hermetically.
> Thanks. That's a really good idea. Even an airtight lunch box should
> do. Never thought of that.
Yes - a sealed container is a good idea
But several people have suggested similar already.
If the idea of using a sealed plastic box seems like a suddenly good
suggestion then perhaps you are not receiving all posts, or not
reading all that you receive on the subject.
eg from a prior post:
If you *ABSOLUTELY* must put the controller inside the high humidity shell:
- Seal the controller in its own dry air environment.
- In situations where an item MUST share the high humidity air,
consider the possibility of maintaining the controller at a suitably
higher temperature. This will lower the *effective* RH of air which
comes in contact with it.
On Wed, Jul 28, 2010 at 5:15 PM, RussellMc <EraseMEapptechnzgmail.com> wrote:
>> > The simplest way is using a small thermos, put inside all your
>> > electronics and close it hermetically.
>> Thanks. That's a really good idea. Even an airtight lunch box should
>> do. Never thought of that.
>
> Yes - a sealed container is a good idea
> But several people have suggested similar already.
> If the idea of using a sealed plastic box seems like a suddenly good
> suggestion then perhaps you are not receiving all posts, or not
> reading all that you receive on the subject.
Russel, a sealed plastic box is not a thermos. A thermos is a glass
with double walls and vacuum between walls.
An 100%RH at 8C in the outside atmosphere will not create condensed
water in the inside except maybe at the cork
(with a proper cork will be avoided there too).
Now maybe you can understand better.
>
> eg from a prior post:
>
> If you *ABSOLUTELY* must put the controller inside the high humidity shell:
>
> - Seal the controller in its own dry air environment.
>
> - In situations where an item MUST share the high humidity air,
> consider the possibility of maintaining the controller at a suitably
> higher temperature. This will lower the *effective* RH of air which
> comes in contact with it.
>
> _______
>
> There have been a few other similar suggestions.
>
>
>
> R
Vitaliy said:
>>> > The simplest way is using a small thermos, put inside all your
>>> > electronics and close it hermetically.
SolarWind said
>>> Thanks. That's a really good idea. Even an airtight lunch box should
>>> do. Never thought of that.
Russell said
>> Yes - a sealed container is a good idea
>> But several people have suggested similar already.
>> If the idea of using a sealed plastic box seems like a suddenly good
>> suggestion then perhaps you are not receiving all posts, or not
>> reading all that you receive on the subject.
Vitaliy said:
> Russel, a sealed plastic box is not a thermos. A thermos is a glass
> with double walls and vacuum between walls.
> An 100%RH at 8C in the outside atmosphere will not create condensed
> water in the inside except maybe at the cork
> (with a proper cork will be avoided there too).
> Now maybe you can understand better.
No, no entropy change between us, we are pretty much of the same
understanding I imagine. - but you may or may not be altering
SolarWind's :-).
I noted that you said "thermos" BUT that he said "EVEN an airtight
lunchbox should do ..."
So I addressed where he had got to and was going.
You are of course correct about the thermos technically being a
technically superior solution.It also has limitations which may or may
not outweigh the gains compared to other alternatives.
As I and others had noted, if you place the board in a sealed sub
container you can then (probably) more easily control the RH of this
smaller container. Both heating the container and/or dehumidifying it
with eg a Peltier cooler were suggested as alternatives.
> No, no entropy change between us, we are pretty much of the same
> understanding I imagine. - but you may or may not be altering
> SolarWind's :-).
> I noted that you said "thermos" BUT that he said "EVEN an airtight
> lunchbox should do ..."
>
> So I addressed where he had got to and was going.
>
> You are of course correct about the thermos technically being a
> technically superior solution.It also has limitations which may or may
> not outweigh the gains compared to other alternatives.
>
> As I and others had noted, if you place the board in a sealed sub
> container you can then (probably) more easily control the RH of this
> smaller container. Both heating the container and/or dehumidifying it
> with eg a Peltier cooler were suggested as alternatives.
I have to agree with Russell here. A thermos is good for only so long.
Eventually the inside of the thermos will reach the same temperature as
the outside atmosphere. The only way it could be better than a plastic
lunchbox is if it could be filled with dry gas - but then the lunchbox
trick can have the same dry gas fill.
Both could have silica gel or similar moisture absorbents put in them to
help keep the humidity level down.
But in some ways I would lean towards the plastic lunch box as it is
possible to mount the connectors in the walls of the box, and properly
seal around them. It is much harder to do that with a thermos as you
need to put the connectors in the stopper, or have a moisture proof
gland in the stopper. Either of these is going to be difficult for an
off-the-shelf thermos.
Another problem is the size of the thermos opening - it may put
unrealistic constraints on the size and shape of PCB one uses. You can
get suitable plastic boxes up to very large sizes, large enough that you
could have a 12V car battery in there with all sorts of electronics, and
still seal the whole lot up after a dry nitrogen fill, and know that it
is going to have a decent chance of not getting condensation inside the
box.
-- Scanned by iCritical.
>> You are of course correct about the thermos technically being a
>> technically superior solution.It also has limitations which may or may
>> not outweigh the gains compared to other alternatives.
....
> I have to agree with Russell here. A thermos is good for only so long.
> Eventually the inside of the thermos will reach the same temperature as
> the outside atmosphere. The only way it could be better than a plastic
> lunchbox is if it could be filled with dry gas - but then the lunchbox
> trick can have the same dry gas fill.
I wasn't meaning to disagree with Vitaliy - just note that I'd
understood his point and that what I'd mentioned was similar in some
aspects and different in others - both are complementary.
Alan's various other suggestions were interesting as they
unsurprisingly reflect some of the things I've thought about to keep
sealed torches condensation free. If you take a waterproof light, heat
it in the sun until it is nice and toasty hot and then cool it rapidly
- bucket of water, stream, tropical shower etc - under some conditions
you push the RH in the light over 100% and you get short term internal
misting. This makes it hard to assess ongoing waterproofness and no
doubt leads customers to wonder as well.
I've considered dry gas purges and dessicants. More extreme solutions
such as active dehumidification or internal heating would not be
applicable in this context. One thing I've considered is a pressure
relief passage filled with a suitable "grease" which allows pressure
equalisation without breaking the seal. Potential for pumping problems
over time. Bellow./diaphragm not too easy in a small device.
We nominally rate the altitude range "Dead Sea to Base camp" more for
fun than because those are real limits - they'd work OK on the top of
K2. The Mini is pressure tested to 0.5 atmosphere during manufacture -
so every one is known good to 14 feet deep. It's not intended as a
diving light of course - the aim is to be able to service any amount
of rain, river crossings, water trough, puddles and the like.
Impact resistance - well OT now- is phenomenal. We say exceeds Mil Std
810 part xxx but in fact it's vastly superior. eg in actual tests the
Mini typically survives 100 drops onto concrete from 1.5 metre+ random
axis, 10 drops from 3 metres onto concrete and 3+ drops from 5 metres
onto concrete. The 3 and 5 metre tests are "by eye" but could be
formalised. 5 metres involves throwing the light to appropriate height
and having it impact sickeningly and bounce away into the weeds. Great
fun. I'll put up a video some time. After all that the light is still
running but the outer is getting pretty scuffed by then and we've
found a few points that degrade faster than others that will get
addressed in due course, but overall its phenomenally impact resistant
compared to almost any alternative. Unlike most, it can claim to be
"soldier proof".
> Alan's various other suggestions were interesting as they
> unsurprisingly reflect some of the things I've thought about to keep
> sealed torches condensation free. If you take a waterproof light, heat
> it in the sun until it is nice and toasty hot and then cool it rapidly
> - bucket of water, stream, tropical shower etc - under some conditions
> you push the RH in the light over 100% and you get short term internal
> misting. This makes it hard to assess ongoing waterproofness and no
> doubt leads customers to wonder as well.
> I've considered dry gas purges and dessicants.
Yeah, well, I threw that in there as solarwind appears to be doing this
at the university, possibly as part of a research thing the uni is
doing, so they are likely to have nitrogen available somewhere on
campus, even if not in the particular section that he is working in.
-- Scanned by iCritical.
embedinc.com> wrote:
