Pressure Flow,

This is totally confused..

One minute you say port B is at 'ambient' e.g. atmospheric...

next thing you tell us it is at some other pressure 0.0304 psi.

This seems odd, are the pressures at both ports varying????

KISS ... keep it simple.... keep one port at real genuine ambient e.g the pressure that is outside your office window.

Then vary your flow and see how the pressure on the other port varies....

It also seems to be a rather high pressure setup if the high port is going up by 1bar...

Draw a picture and give us more info'

Del

Ok,

What I was trying to relate was one set of parameters. The Pressure sensor manufacturer has these set of spec's

When port "B" is at ambient, (outside the window pressure) ~14 psi,, and the "HIGH" pressure port "A" is at a pressure that is 1 ATM higher (~14psi) with these pressures applied there is a 120 cubic centimeter amount of flow through the sensor using "AIR" per minute. from port "A" to port "B"

What I am trying to learn is what the amount of flow this sensor would have when attached to a research balloon at 100,000 feet and is measuring the pressure differential between inside the balloon and the outside atmosphere.

The designed pressure differential we are shooting for is 210 Pa ( 0.03045 PSI) between the inside and outside of the balloon. we are trying to monitor this very low pressure.

The "Ambient" air pressure at 100,000 feet is 0.1582 PSI,,

and the inside of the ballon is 0.03045 PSI higher than that.

what is the flow from "A" to "B" how much?

"AIR" would be a good start,

and not too sure at these pressures if the air densisity is all that different than Hydrogen or not.

But this is what we are trying to get the answer to, how much H2 is going to leak out of the balloon per minute at these pressures.

Joe

Forget all about the ambient port and the change in ambient pressure, that's the whole point of it being differential.

E.G. The change in ambient effects both ports equally and always cancels out..

(unless your mechanical arrangement somehow prevents this)

Therefore, in theory, any tests you do at ground level will apply exactly the same at any altitude/pressure.

Agin your reply is somewhat confusing...one minute you are talking about the high pressure port being at 1atm higher than the low... then a little further on you are talking about measuring 'this very low pressure.'

Is this a hot air ballon? Or is it a helium balloon with some sort of pressure relief valve?

Are you trying to measure the differential pressure between the inside and outside of the ballon,or the flow of gas through some sort of orifice?

I am sorry if this is confusing, i'll answer your questions here,

Agin your reply is somewhat confusing...one minute you are talking about the high pressure port being at 1atm higher than the low... then a little further on you are talking about measuring 'this very low pressure.'

I'm trying to give out some parameters of the sensor, ok,

going with your statement in another answer that they cancel each other out,

at ~14 psi differential we have a 120 cubic centimeters of flow, per minute.

what is the flow at 0.03045 PSI?

That's keeping it simple,

then add densiity into it, and I would think it would b a lot different too, air at sea level is like molasses compared to air at 100,000 feet.

Is this a hot air ballon? Or is it a helium balloon with some sort of pressure relief valve?

You could call it a helium balloon,, except we use Hydrogen,, same difference tho,

and yes on the valve, the set point of the valve will be 210 Pa

we we want to monitor the pressures to verify if the valve works at the right pressures, or if we have a failure of the balloon envelope system also.

Are you trying to measure the differential pressure between the inside and outside of the ballon,or the flow of gas through some sort of orifice?

The pressure differential between inside and outside of the balloon.

Joe

Right ... that's better.

I can see how you are confusing yourself, I'll make a few suggestions.

1. Forget about flow, just measure the pressure between inside and outside, this will tell you if the valve is working.

2 The question of flow is entirely different....if your valve doesn't have a sufficiently lage orifice to allow for sufficient flow this will show up as a change in pressure reading (#1)....

3. Your point about the air being denser etc, is confused thinking... (I believe) If you just conside flow as number of molecules per second then the question of density dissapears.... e.g at low densities it's just low flow. They are inextricably linked.

4. Trying to measure flow through a fixed orifice in not a linear relationship with pressure... this is why I have made point #1.

I hope this clarifies things a bit?

To sumarise, it seems there are two questions...

1, does the vlave open and close correctly and

2, Does the valve allow a sufficient flow to do it's job?

Regards

Del

Hi Del,

Thanks for all the replies.

Right ... that's better.

I can see how you are confusing yourself, I'll make a few suggestions.

1. Forget about flow, just measure the pressure between inside and outside, this will tell you if the valve is working.

That would be ideal. And we can get sensors that indeed will measure pressures that LOW, 210 Pa is incredibly low amount of pressure.

Problem is, COST,, while we can get sensors that measure pressures as low as 1/2 PSI full scale for as little as 20 bucks, sensors that have capabilities to measure pressures this low are extremely costly.

<>The one we are getting, costs $100 bucks OEM price, but it works in a different way than a standard type of sensor. It uses "Flow" to determine the pressure, A Regular pressure sensor like you can get anyplace, like,,this one here,

http://tinyurl.com/2y5e92

This style would be prerferrable, but by the time you get down to the 210 Pa level, or we are getting a 0 to 500 Pa scale one, By the time you get down to those pressures, the absolute cheapest one we can find worldwide is well over 800 bucks! YES $800.00 EACH!! This is NOT an option for us, At the end of this message i'll add to who we are and what we do.

Anyway, this sensor we are hopeing to use measures on a different way other than a strain guage, it measures the flow somehow by using a as they say "Small Flow" And they give you the spec's of the flow that i have been quoteing here.

What we are trying to determine is how much the flow will be at those incredible low pressures. so we do not "Vent' out too much lifting gas during the mission and loose lift.

2 The question of flow is entirely different....if your valve doesn't have a sufficiently lage orifice to allow for sufficient flow this will show up as a change in pressure reading (#1)....
not sure what the internal orifice is, they do not spec that. the connection tubing is .125' id.

3. Your point about the air being denser etc, is confused thinking... (I believe) If you just conside flow as number of molecules per second then the question of density dissapears.... e.g at low densities it's just low flow. They are inextricably linked.

4. Trying to measure flow through a fixed orifice in not a linear relationship with pressure... this is why I have made point #1.

Exactly, thats why I'm here to see if anyone has any idea as to how to calculate the flow. if it was linear, this would be simple, it'd be a percentage right? if it's 120 cm/min at 14 psi, and we apply .03045 psi to it, that a 0.002175% of the pressure so tyhat would be what,, 0.002175 * 120 cubic cm / min = .261 cubic cm/mn? but i know it's not this simple.

I hope this clarifies things a bit?
We are making progress he he he.

To sumarise, it seems there are two questions...

1, does the vlave open and close correctly and

2, Does the valve allow a sufficient flow to do it's job?

Regards

Del

Ok Del and any others readg along this is who we are and what we do,

Please read on below. yes I know it's a somewhat long letter, but please do. It explains what we are attempting to do.

I am the founder and program director of something called Near Space Sciences. We are a totally non-profit group of people that offer to students of all ages the chance to do actual "Space Exploration"

Non-Profit is putting it mildly, most of our flights to the "Edge Of Space" actually send to the "Edge Of Space", several hundreds of dollars of electronic equipment, and we do it all at no cost to the school or it's students.

Please take a visit to our web site to see some of the fantastic imagery and programs we offer to the Schools and Students. It's at. http://www.qsl.net/wb9sbd/educators.html
The above link is our preferred site to view, but sometimes that server is flaky,, if it doesn't work check out a stripped down mirror site at http://www.mwt.net/~mayen1/educators.html

Our last Mission to the edge of space happened just a few months ago, on May 21st.

We had a launch for several hundred boy & girl scouts at the Sauk County Wisconsin fair grounds.

This was our 43rd flight to the "Edge Of Space" This flight made it all the way up to

102,528 feet! Yes One hundred two thousand, five hundred and twenty eight feet UP!

A short video of the launch can be seen at,, http://www.youtube.com/watch?v=NoUkgWOUbNQ


Ok, we have been asked many times by many groups to do a LONG duration flight. Most of our flights last three to four hours. But to do a LONG duration flight is way past our budget. It requires NASA type of funding, for the balloon itself will cost several thousands of dollars. So sadly we have had to tell the students that it is beyond our possibilities. But recently we have been doing research on methods of a long duration flight.

One of the long term goals of Near Space Sciences is to achieve the ability to stay airborne for days-enough time to cross the Atlantic Ocean. Right now, we launch balloons that self destruct after 3 hours and rarely travel more than 300 miles from launch site to touch down.

We think we have figured out a system to do this for some students. But it involves closely monitoring the pressure differential between the inside of the balloon to the outside atmosphere. Of course that's where the sensor comes in. I won't go into the exacting details right now. WAY too technical for this e mail.. we will be actually control the floating height of the payload. so to make it stop rising and keep it from eventually popping. But we need to be able to monitor how much actual differential pressure is in the balloon system.

N
What do you think?

These flights are exciting and fun for all. I hope we can work out something to be able to make this a reality.



Thank you For your time.



Joe Mayenschein

Near Space Sciences

Ithink there has to be a cheap simple way of doing it...

Measure the tension in the envelope some way e.g. a long thin section of conductive elasomeric material incorporated into it.

After all that's presumably why you want to measure the pressure ( so you don't burst the envelope? )

It also begs the question... Why do you doubt the valve? Maybe you are just embarking on a 'problem creation excercise ' ! (Isn't that what Mothers in Law are for ? !)

I'll have a breather and let someone else have a think!

Ithink there has to be a cheap simple way of doing it...
If there is, We are open for any ideas out there.

Measure the tension in the envelope some way e.g. a long thin section of conductive elasomeric material incorporated into it.

The tension of the envelope is already been modified by the rest of the balloon design. These envelopes would normally burst with a un measureable differential pressure. As it is right now with the 210 Pa only of internal pressure, the skin (envelope) surface tension is already 125 PSI,,

After all that's presumably why you want to measure the pressure ( so you don't burst the envelope? )
That is yes one reason, but then to monitor the pressure throught the day, the pressure changes with the time of day and grteatly after sundown, to almost zero with the daytime 210 Pa pressure setting,

It also begs the question... Why do you doubt the valve? Maybe you are just embarking on a 'problem creation excercise ' ! (Isn't that what Mothers in Law are for ? !)

Agreed there, we could do the flight with a standard PE (Polyethylene) balloon, with the said valve, but again back to GREAT costs, as PE balloon of the capacity we are using in latex, where the latex costs about 80 bucks, the equivalent in PE is between 1800 and 2400 bucks.

I'll have a breather and let someone else have a think!

I'll be standing by..

One last thaught before my brain explodes.

Han you measure the size of the baloon?

A daft idea... ???

A thread across the internal diameter of the ballon, one end attached to the surface, the thread wrapped around the shaft (or a drum) on a multiturn potentiometer, and then via a spring to the other internal face of the balloon. As the baloon expands and contracts the potentiometer shaft will turn giving you a variable resistance which is really convenient to measure....

Might just work?

Great going Del the Cat. I'm getting dizzy reading all. Does that mean I'm confused?

Suggest you ask him to restart with a new thread and not repeat anything from this thread.

That will keep things going straight to understand better.

Great going.

Can't you actually measure the surface tension of the envelope?

Or possibly a water column & capacitive proximity [it will detect the liquid] switch to measure the differential pressure.

Garth, This is obne method we were thinking about. a somewhat ribe goldberg sensor so to speak, When we were only finding those close to kilobuck sensors,

But when we fount the 100 buck one, but it had that small difference of not being sealed or "Bubble Tight" but has a as they say "Small amount of flow"

to put it simply, in their spec's they say ar "Sea Level" if there is a pressure differential of 1 ATM (~14 PSI) there is a flow of 120 cubic centimeters per minute.

all i'm trying to figure out is at 100,000 feet,, with a pressure differential of 0.03045 PSI what is now the flow?

Joe

<Ithink there has to be a cheap simple way of doing it...>

Perhaps the original Poster could use the table for the International Standard Atmosphere, and monitor the temperature and altitude instead, looking for a correlation? That would be a guide to the pressure inside the balloon.

we know the altiude very precicely, via GPS systems, so this is not the problem,

this is a state of the art balloon system, actually a system that has never been flown before. we could do it blind and see what happens. but the ability to monitor the pressure differentials between inside and outside is a Major part of this experiment in designing a better system.

Joe

How bout some info on the sensor

Make

model

specs

You are trying to use this differential sensor to monitor a valve, is that correct?

the tubes leading to the switch are 1/4"?

Are you trying to record the actual differential pressure? or just when the pressure is out of range, which would mean the valve isn't keeping up?

the flow @ 100'000ft through a 1/4 orfice would be very high, considering the very low density

it seems like you are asking several ?'s

can we define each one, to increase the chances of success

Nasa equations for density, lots of talk about the exponential decrease in density.

Good Idea,

Lets take this one step at a time

Make

model

specs

here is the page for the sensor,
http://www.sensirion.com/en/02_sensors/04_differential_pressure_sensors/01_analog_differential_pressure_sensors/01_sdp1000.htm

A PDF for it is at,

http://www.sensirion.com/en/pdf/product_information/Datenblatt_SDP1000_SDP2000_Diffenzdrucksensor.pdf

You are trying to use this differential sensor to monitor a valve, is that correct?

The valve is a safety device so to speak, to keep the envelope from going above 210 Pa

the tubes leading to the switch are 1/4"?

Are you trying to record the actual differential pressure? or just when the pressure is out of range, which would mean the valve isn't keeping up?

the flow @ 100'000ft through a 1/4 orfice would be very high, considering the very low density

it seems like you are asking several ?'s

can we define each one, to increase the chances of success

Nasa equations for density, lots of talk about the exponential decrease in density.

Ok good stuff, a proper link for the sensor PDF

Here's the reason for flow

1.2 Altitude Correction

The SDP1000 / SDP2000 differential pressure

transducers achieve their unsurpassed performance

by using a dynamic measurement principle, i.e. an

applied differential pressure forces a small air flow

through the sensor. This results in a dependence of

the indicated differential pressure on the ambient air

density. While the temperature effect is compensated

(see Paragraph 1.1) the altitude above sea level has

an influence on the SDP1000 / SDP2000 output. If

desired, this effect can be compensated by a

correction factor according to the following equation:

Dpeff = Dpsensor * Pcal / Pamb

where Dpeff is the effective differential pressure,

Dpsensor the differential pressure indicated by the

SDP1000 / SDP2000, Pcal the absolute pressure

during calibration (966 mbar) and Pamb the actual

ambient absolute pressure.

Ok that means this sensor won't do what you need it to do, some where inside there's a tiny bleed hole between the 2 chambers. The hydrogen will also become less dense & escape @ ever increasing rates as the altitude increases.

With a sensor that has an orifice, you'll have a constant leak as Garth and I mentioned. Plus the fact that you're looking for a formula to give you the correction factor and, assuming (hoping) that you get a correct figure, is a little too risky for me.

I just checked Dwyer and they've got low pressure devices at costs of <$80. They go down to 0.5 inches of water with ranges of 1 and 2 inches of water available. These correspond to approx. 125 Pa (0.5" water), and 250 Pa (1" water) to 500 Pa (2" water).

We were also dumbfounded to find this sensor also. When one of you guys mentioned Dwyer. We dropped them a note to ask about colder than their "Operating" window.

Yes, great on sending us there, been on all the search engines looking for low pressure differential sensors and Dwyer was never mentioned.

Thanks to all for mentioning them will keep you all advised.

Joe

I'm replying to my own post here,

In addition, if anyomne else knows of other sensors other than the Dwyer one PLEASE let us know. The more we know of the better choice we will make.

Joe

by the way for those that want to contact me off line my e mail address is

nss@mwt.net

I've used sensym parts before..in respiratory measuring instruments (pretty low pressure) they go from cheap n basic to expensive modules. Digi key sell their stuff.

Del

Weren't you the guys with the battery/power supply solar panel question a while back?

How did that turn out?

Weren't you the guys with the battery/power supply solar panel question a while back?

How did that turn out?

yup, that's us, that part hasn't happened as of yet, that will be stage two. After we prove out the balloon envelope system (a flight of 24 to 36 hours in length) then we will start the big project with the solar and all that for the LONG flight.

Joe

I'm confused by what sensor you're using and what you're using it for.

You're actually interested in knowing the pressure difference between the inside and the outside of the balloon, right? So, what you need is a differential pressure sensor.

Yet, you describe your sensor as needing a flow through it to give a pressure reading. This is actually a flow sensor, not a pressure sensor. The pressure difference is read from inside the sensor, not outside of it. The instrument derives flow from the pressure measurement, not the other way around.

Further, I wouldn't want to use this sensor for monitoring the pressure of the inside of the balloon. The way I seem to understand it, you're going to have a constant leak in your balloon just to be able to measure the differential pressure!

Dwyer has a line of pressure sensors, in case you haven't looked at them. Check out their website www.dwyer-inst.com.

Lastly, with hydrogen, you'd probably want to use a gauge and not an electronic transmitter. It takes just one spark. There might also be issues with the effect of hydrogen gas on certain materials. You'll have to contact the sensor manufacturer to see if you can use their product with hydrogen.

There is no need to measure the pressure if the altitude is known. There is a table called the International Standard Atmosphere in Mayhew & Rogers "Thermodynamic and Transport Properties of Fluids", Oxford Basil Blackwell, 1976. It may be available also on the world-wide-wait somewhere. 100,000ft * 12 / 39.37 = 30480m, which is down the bottom of the table. At 30000m, the pressure is 0.01197bara and the temperature is 226.5K At 32000m, the pressure is 0.00889 bar and the ambient temperature is 228.5K. One could interpolate....

A DP cell ought to have a gas-tight seal between the two sides of the operating mechanism, so the question of flow at differential pressures is somewhat confusing, and may be a 'red herring'. Now, if there were to be some sort of bleed valve around the DP cell, that would be another thing.

Does that help?

see message #25

we are fully known all this here,

the pressure we qre measureing is not the ambient, but the differential between the inside and outside of the balloon envelope.

Joe

A failure of the balloon envelope would manifest itself by the balloon coming back to the surface somewhere.

I'm thinking there is something much easier too. The cost..well That is a issue I won't be able to answer straight away but I do have some resources.

I know that on the high pressure systems we use, say a liquid Ar Dewar, we have 300 psi overpressurization valves. Or PRV's (pressure relief [release] valves)

So at different altitudes you are more pressure tolerant/restricted, right?

Hang with me as I am just spittting this out:

If you manifolded a series of PRV's with incrementally different activation points that reflected your pressure limits at variyng altitudes that were controlled by an electronic (low V) [H gas is noted here] the signal could be generated by preset altitudes.

You have PRV's 1-5 manifolded. Each PRV has incremental difference. As altimeter reads corresponding height the corresponding upper limit PRV is actuated, so that if a pressure limit is exceeded for that altitude range the appropriate excess pressure is released.

CR3

does that make any sense?

Something like this:

Pressure transducers could be used for the actuators instead of using the alt. to gen a signal.

yes what you are describing does make sence. but would not work in our design,

see in actuality the "Valve" is a safety device to keep in design the balloon from popping due to over pressure. we could use the balloon as designed, and put exactly the amount of lift to make the mission a success, BUT there is one very touchy area of the flight, the boundary between the troposphere and Stratosphere, it take a bit more of a lifting power to punch through the bouandary.

if we have the lift just right, withinn a few grams of a total 10 pound or so system, AND the air temps aloft are the same as the last sounding, (well withinn 5 degrees or so) the mission will go off as hoped.

But if it's a but cooler,, or we are a few grams too low on our lifting power, when thwe system hits the tropopause it can not punch through, and it gets stuck there.

THEN if we have too much Lift,, or if it's 5 degrees warmer than what we calculated for, it will easily punch through this boandary layer, but the balloon will not have enough strength to keep it from eventually burting at max altitude.

What the valve does is allow us to over fill the balloon to ensure it punches through the tropopause, and yet vent the extra gas, at max altitude to keep it from popping. yet also keep the pressure at or slightl;y above 210 Pa.

More later,,

Haven't done all the science on this idea but it might work. Rather than attempting to control the pressure of the lifting gas, why not just get a balloon that will withstand the maximum pressure differential that you expect to have. Looks like your using vinyl weather balloons from the video which will continue to expand with increasing pressure differential until they 'pop'. This website talks about mylar balloons with reinforcement that can take 45 psi. Mylar doesn't stretch like vinyl. Adding a reinforcing tape around the balloon might keep it from bursting also. You might have to send it up underinflated at ground level so that it becomes full at altitude, but as long as you use the correct mass quantity of lifting gas by doing the ideal gas equation (using the lifting gas constants, not the ideal gas constants) for the lowest expected atmospheric pressure (highest altitude, highest lifting gas temperature, highest differential pressure) and the pressure differential is less than the bursting level pressure, then it might work.

Also, the website also talks about vacuum cells which apparently are capsules that can contain a vacuum and still retain their shape. A vacuum is the absolute best way to achieve lift as, unlike a lifting gas, it has no mass at all (perfect vacuum).

If gas loss is a problem due to leakage or gas permeation through the balloon membrane, then you might could liquify a small amount of a less volatile lifting gas that wouldn't require a refrigeration system, maybe nitrogen. Nitrogen has about the same density as air so you wouldn't gain anything lift wise except it would help keep the balloon inflated to max diameter (Law of Partial Pressures?), which would help lift wise. As long as there was a material amount of a lifting gas in the balloon, I think it would expand to full diameter. A preset pressure regulator might be used to allow the liquified gas to replace the gas lost through leakage or permeation. It would still lose altitude but maybe stay up longer nevertheless. Not sure any of this is valid but you might do the math if you feel inclined.

Anyway, if you just want to stay up there for a few days as opposed to setting an altitude record, then it might not matter what the temperature variations do to the pressure or lift differential as long as the balloon stays below the burst threshold and within an acceptable altitude envelope. Here's some links. Not sure I'm right but maybe right is in or connected to one of the below. Good Luck.

http://www.fuellessflight.com/techno/tech.htm

http://scientificsonline.com/default.asp?sid=edsci&cm_mmc=edsci-_-link-_-na-_-home

http://www.freepatentsonline.com/20060230679.html

Calculating the correct lifting gas mass to be used would be done by finding equilibrium of balloon at desired altitude.

(Displacement of balloon plus displacement of payload)/(mass of balloon plus mass of payload) equals air density at desired altitude.

Then apply pv=nrt using bursting pressure (less a safety factor) as the pressure, balloon displacement as the volume, gas constant for type gas used, and temperature at desired altitude(warmest expected gas temp to be safe against pressure burst from temp increase). n will be the number of moles of lifting gas that that should be used.

Number of moles of gas times atomic weight of gas equals mass of gas to be used.

Set the filling cylinder on a scale and measure the mass(weight) of gas that you put into the balloon when filling it. Only put in the calculated amount.

Once again, don't send the thing up based upon my ideas. It's been 30 years since I had this stuff in school.

i'll try to field a few of the questions.

The envelope is made from latex, cause it's the cheapest possible. The $'s are the driving force behind most of the decisions.

There is a valve in the present design to keep the envelope from exploding, the original post was about how to utilize a cheap differential sensor to monitor the operation of the equlization valve.

I'm sure NSS will correct me if I've got it wrong.

i'll try to field a few of the questions.

The envelope is made from latex, cause it's the cheapest possible.

True

The $'s are the driving force behind most of the decisions.

withinn reason,,

There is a valve in the present design to keep the envelope from exploding,

The valve has always been there, and is a non issue,,

the original post was about how to utilize a cheap differential sensor to monitor the operation of the equlization valve.

Not totally, 99% of the purpoe was to monitor the pressure differentials, of couse this also does in reality end up also monitoring the valve.

I'm sure NSS will correct me if I've got it wrong.

Got it close

but you got a lot of the math right.

Keeping in mind the PRV idea. How about a switch that will activate a valve when the baloon expands to some upper limit. as baloon expands an afixed slide expands with it, when the upper limit is acheived contact is made with switch which in turn actuates vale exhausting excess pressure. Again if varying limits apply, this could be done also using a sereis of points on a slide. Point 1 at altitude X is activated to release pressure, on up the scale.

I am either way off the mark here or is someone scribbling a schematic to implement something along these lines?

It's a bit like my multi turn pot diameter measuring device... nobody wants to play..

Bottom line is...I think cheap low pressure sensors have been located.

I thought I'd seen such things from Sensym, but I made the fatal mistake of believing the poster . (just teasing Guys)

It's fun to have such an exciting project to think about...even if it's just guilt by association!

Del

Thanks for chiming in Del, we really need to put a bell around your neck.

Due to the lack of feedback, I was beginning to fear I had somehow offended the CR4 community as a whole (not undoable for the likes of me). So I shall lay my egocentrism aside and just pat myself on the back while uttering, "It's a damn good idea Charlie. Damn good indeed".

I feel better now.

We could build our own 'virtual balloon'

I'm V good at 'virtual' work ..(just ask my boss) .

BTW "It's a damn good idea Charlie. Damn good indeed".

I hope not, i love this bantering back and forth,

Joe

If you want banter [ most of it abusive ], start a thread about any sort of transportation or power generation that produces more energy than it uses, global warming or anything about cats [nod to Del]

Guilty huh? he he he hey drop us a line and join in on the fun,

i don't know where you are but we have members from all across the country.

Joe & NSS

nss@mwt.net

First, let me say "GOOD FOR YOU"! Exploration, curiosity, and learning is a great thing for anybody; but absolutely critical for young minds.

OK. I have kept silent, mostly because my work computer won't allow your site. It seems to me that C_RUMMEL3 in post 21 had a good idea, but went too far for your application.

If I understand the problem correctly (which is problematical), then what you are looking for is a safety device to keep from over pressuring the balloon correct? If that is the case, then post 21 has it correct, except you only need a single point, not multiple points for control.

I also noted that this is for a future flight. If you are going to have more short range flights in the interim, then take the best ideas that you (and everyone else) have and run an experiment of your own. But call it empirical testing (most people don't know the difference) it sounds better!

"If I understand the problem correctly (which is problematical), then what you are looking for is a safety device to keep from over pressuring the balloon correct? If that is the case, then post 21 has it correct, except you only need a single point, not multiple points for control."

NSS's reply from #41

"There is a valve in the present design to keep the envelope from exploding,

The valve has always been there, and is a non issue,,

the original post was about how to utilize a cheap differential sensor to monitor the operation of the equlization valve.

Not totally, 99% of the purpoe was to monitor the pressure differentials, of couse this also does in reality end up also monitoring the valve."

Since the baloon is susceptible to a different pressure at a different altitude and there are no variable psi PRV's, I have suggested a manifold with actuated valves signaled by preset altitudes which open and close to allow corresponding PRV per given altitude to operate.

Since the balloon is susceptible to a different pressure at a different altitude and there are no variable psi PRV's

The other logical answer is the balloon size measurement as mentioned and assiduously ignored since.

Assuming the payload is dangling beneath the ballon...a thread up to the top of the balloon (ideally inside but not necessarily) could pull nicely onto the spindle of the multi turn pot/optical encode or whatever...this input can go to a small micro controller which can be programmed top open a vent as when required.

If this suggestion doesn't elicit vast praise in short order I shall go and cough up a fur-ball on the kitchen floor in disgust

no, sorry gang,,

the "Size Issue" wasn't really ignored, we alrady know what the size of the balloon will be, see that's the thing on the ground at liftoff it's ohhhh say 6 feet in diameter, maybe less,,

anyway at POP it's close to 30 feet in diameter,

and from liftoff to pop there is a in or un measureable pressure differential all the way to pop and including op, it it rises a pascal or two is about it.

but we are keeping the envelope from expandin beyond the 25 foot mark, and here is where the pressure starts to rise, as the balloon continues rising, the volume can not expand any more to equalie the presures and the differential starts to rise.

eventually there is enough "Pressure" that the total weight densisity wise of the gas inside vs the gas being displced outside actually cancells out the lift and the system parks.

so no pun intended here

"Size doesn't matter"

Joe

Cough....... ping...thud.

Ah that's better!

ahhhhh,,

feels good huh?

is that you stinky Pete?

Mines better.

a manifold & series of switches will work.

The problem is the whole contraption only weighs 10#'s

the grams for switches, tubing, slidewires, encoders & the like

decrease the possible payload or increase the size of the envelope.

Hi everybody.

I dont know if is too late to say something.

But according with the original questions [NSS], I propose to do some energy balance, the ballon is an inestable system, so the internal energy change with temperature and time. But just i wanna know if it is a research project?

Have you heard about the FLUX THEORY?

WHILE YOU HAVE MORE DIFFERENCE BETWEEN TWO POINTS (REFERENCED WITH INTENSIVE VARIABLES LIKE PRESSURE AND TEMPERATURE)YOU CAN GET MORE FLUX, TIL YOU CAN GET THE THERMODYNAMIC EQUILIBRIUM.

If you want we can talk more, but go to www.thermofluids.net

Israel Barron

ibarron@sfmex.com

Sorry folks, had a brain fart on the last post (there may have been a beer or 3 involved as well).

My original intention was to mention a mercury manometer with an optical switch (the route my brain took from C_Rummel3's post) but I got side tracked.

I have since done some of my homework, and that won't work, as I remembers that mercury has a melting point of -35C. I haven't done the math but I am sure that the temperature at "near space" will be well below. I researched other periodic elements, but none of those seemed to be suitable either. They either didn't have a low enough melting point, or they would be in a gaseous state at take-off.

This is where my knowledge of chemical properties dies. If I can't find a website that already has that data, I haven't got a clue.

But I know that there are some bright people on this site. If this sounds like a workable idea, and you have some suggestions, jump in and help.

The problems that I see with this idea (apart from freezing/melting point) is that the medium has to have an opacity that can be detected. Or a density that can be detected by a capacitive probe. Those would both be really cheap ways to go; especially if the equipment is or might be a one way ticket.