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 Author Topic: Arduino Controlled Vacuum Chamber  (Read 1113 times) 0 Members and 1 Guest are viewing this topic.
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 « on: November 08, 2012, 05:54:55 pm » Bigger Smaller Reset

So in my mechanical engineering class right now we have to create a product that will demonstrate some learning principal to younger students (somewhere in the K-12 range). In my last group our project was to build a glove that would measure acceleration as you threw a ball, at the time I had tried to use the arduino but was having problems with getting it, the accelerometer, and labview to interface correctly in time, so I ended up using a DAQ unit instead.

This time around, my new group and I have to rebuild another project from the last cycle, showing changes in size of a balloon (or another like apparatus) in a vacuum/pressure chamber. This seemed a whole lot less interesting to me, so to make it fun I want to computer control the **** out of it.

The chamber we were given from the last group wasn't even worth recreating in concept, so we are going to start over entirely. This time we will probably either modify a pressure cooker or an air tight food storage container for our vacuum/pressure chamber. Either way the volume of the chamber should be from 1-2 ft^3. I haven't decided on the pump yet, it would be nice to find a single unit that could provide both adequate vacuum/pressure levels, but for cost/availability reasons we might end up with separate vacuum and pressure pumps. If anyone has input on this I would appreciate it. Also limiting this would be my idea to use a computer power supply which would give several convenient voltage choices (3.3v, 5v, and of course 12v). Though according to the wikipedia page http://en.wikipedia.org/wiki/Power_supply_unit_%28computer%29 the maximum draw allowed is 18A at 12V, so the pumps would have to fall within that spec (since both pumps will never be running at the same time, they can both draw up to 18A). I will also need a pressure/vacuum sensor, and a solenoid valve to  regulate pressure, something of which I have been looking into, but am hoping for someone with experience to chime in here as well.

All of this will be controlled by an arduino uno with labview software, to control the pumps (with relays, of course) by using the readings from the pressure/vacuum sensor.

There are a lot of engineering problems with this, a few of which I can think of (besides the actual construction of the chamber itself) include:
If by using the pumps alone will I be able to accurately achieve the desired pressure/vacuum levels? I imagine they will not, so I might have to program it to "overshoot" the desired pressure/vac level and use the solenoid valve to adjust to to correct levels. Which means I will need a valve that can act quickly enough to bring within range (hopefully within 1-2in Hg).
Also as an apparatus, the balloon is pretty poor, since rubber is especially porous. Not really ideal for any sort of scientific measurement, but probably adequate for its intended purpose. I'd prefer something else, it just has to be reasonable to the vacuum/pressure levels achieved.

Another issue is cost, which is not too big of a deal since the school is paying for all of it. It just needs to be reasonable.
As far as what reasonable is, your guess is as good as mine.

Also something else was that my professor mentioned something about using a cell phone camera to track the size differences in whatever apparatus we use. I really haven't thought much about this as it is more "end game" right now, but I figured I would just mention it here anyway.

I'm sorry my questions on here are pretty vague, I am just hoping for some experienced input on ideas and feasibility on the different aspects of this. I love to overdo projects like this, and learning more on the arduino and electronics is a plus.

Thanks!
 « Last Edit: November 08, 2012, 06:03:58 pm by kro10000 » Logged

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 « Reply #1 on: November 08, 2012, 07:21:53 pm » Bigger Smaller Reset

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...the maximum draw allowed is 18A at 12V, so the pumps would have to fall withi n that spec (since both pumps will never be running at the same time, they can both draw up to 18A).
If the pumps require that much power, I'd suggest using 120V pumps (or 220V if you live in Europe).  I don't have a lot of experience with vacuum pumps, but I suspect you'll need a separate pressure pump.  I don't know if either one will work "backwards"...  I kind of think the vacuum pump could be used backwards, but I wouldn't push it much above 1 atmosphere.

Quote
Which means I will need a valve that can act quickly enough to bring within range (hopefully within 1-2in Hg).
If you use a very-small aperture, the vacuum/pressure will change slowly, and your valve won't have to be super-fast.   Most solenoid valves should operate in a matter of milliseconds.
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 « Reply #2 on: November 08, 2012, 08:01:09 pm » Bigger Smaller Reset

Your container is going to be transparent, isn't it?

(The pressure cookers I've seen have all been metal.)

To be sciencey, are you going to provide some method of measuring the volume or size of the balloon?
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Measurement changes behavior
 « Reply #3 on: November 08, 2012, 08:10:08 pm » Bigger Smaller Reset

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I will also need a pressure/vacuum sensor, and a solenoid valve to  regulate pressure, something of which I have been looking into, but am hoping for someone with experience to chime in here as well.

Well a single 'absolute pressure' sensor will read from absolute zero pressure ( a perfect vacuum) to some maximum pressure value, depending on the measurement range of the sensor you select, so no need for separate sensors unless you want them for other reasons.

A solenoid valve can only be controlled to be fully on or fully off, so not capable of regulating a pressure or vacuum stream, you need to either have variable speed control on the pumps or variable 'control values', where you can control the position of the valve from anywhere from fully closed to fully opened.

Lefty
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 « Reply #4 on: November 09, 2012, 12:16:54 am » Bigger Smaller Reset

Your container is going to be transparent, isn't it?

(The pressure cookers I've seen have all been metal.)

To be sciencey, are you going to provide some method of measuring the volume or size of the balloon?

If we used a pressure cooker we would have to modify the lid anyway because they won't hold vacuum, so we would then have to put in a window made of probably lexan. As far as measuring goes, I have been discussing with my instructor using an android camera phone, some unknown software, and a lot of maths to measure the balloon size, however I am not sure if this will be possible to do in time (depends how long the rest takes).

Well a single 'absolute pressure' sensor will read from absolute zero pressure ( a perfect vacuum) to some maximum pressure value, depending on the measurement range of the sensor you select, so no need for separate sensors unless you want them for other reasons.

A solenoid valve can only be controlled to be fully on or fully off, so not capable of regulating a pressure or vacuum stream, you need to either have variable speed control on the pumps or variable 'control values', where you can control the position of the valve from anywhere from fully closed to fully opened.

Lefty

I was thinking that if the data from the sensor was used, that the arduino would energize the solenoid to open the valve when pressure/vacuum was too high and close it when pressure was optimal or too low. You don't think that will be accurate enough (honest question)?

If the pumps require that much power, I'd suggest using 120V pumps (or 220V if you live in Europe).  I don't have a lot of experience with vacuum pumps, but I suspect you'll need a separate pressure pump.  I don't know if either one will work "backwards"...  I kind of think the vacuum pump could be used backwards, but I wouldn't push it much above 1 atmosphere.

If you use a very-small aperture, the vacuum/pressure will change slowly, and your valve won't have to be super-fast.   Most solenoid valves should operate in a matter of milliseconds.

I doubt the pumps will need any more than 18A, personally 90% of all my electronics experience is with automotive systems, so I'm preferable to DC. I also sort of like the idea of running everything from the pumps to the arduino to any lighting off of the same power supply. I'm not necessarily against AC, just that my technical knowledge of AC isn't much better than believing it's witchcraft. As far as the solenoid goes, that was what I was thinking. If I got really wild with it I could have a second solenoid that was bigger for quick release.

Thanks for the responses, I'm starting to get excited about building this now.
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 « Reply #5 on: November 09, 2012, 09:27:01 am » Bigger Smaller Reset

What range of pressures do you intend to use? Vacuum is less dangerous than pressure and in any case you're limited to 1 bar differential but a couple of cubic feet of air under pressure could be very dangerous indeed. It would be much safer if your working fluid was water, and this would also be easier to pump.
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Measurement changes behavior
 « Reply #6 on: November 09, 2012, 10:26:54 am » Bigger Smaller Reset

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I was thinking that if the data from the sensor was used, that the arduino would energize the solenoid to open the valve when pressure/vacuum was too high and close it when pressure was optimal or too low. You don't think that will be accurate enough (honest question)?

Hard to say, you can only try and see. Also be sure any solenoid values you obtain will work in vacuum service, many won't so check their datasheets carefully or contact a manufacture rep and ask.

Lefty
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 « Reply #7 on: November 09, 2012, 11:27:51 am » Bigger Smaller Reset

What range of pressures do you intend to use? Vacuum is less dangerous than pressure and in any case you're limited to 1 bar differential but a couple of cubic feet of air under pressure could be very dangerous indeed. It would be much safer if your working fluid was water, and this would also be easier to pump.
For my intended purpose I can't see any reason why I would need to go much over 4 atm, so pressures should stay < 60 psi, unless something were to go wrong. Bringing hydraulic principals into it would be interesting, definitely something to think about anyway.

Hard to say, you can only try and see. Also be sure any solenoid values you obtain will work in vacuum service, many won't so check their datasheets carefully or contact a manufacture rep and ask.

Lefty
Hmm, I think like what DVDdoug said, a small aperture will be crucial, as well as a quick action. So the change in pressure/vac will be minimal when the solenoid shuts. I suppose it would be possible to do some programming to adjust shut time advance/delay in proportion to pressure/vac if there is a huge difference.
 « Last Edit: November 09, 2012, 12:44:51 pm by kro10000 » Logged

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 « Reply #8 on: November 09, 2012, 03:58:30 pm » Bigger Smaller Reset

A couple of cubic feet of air at four bar is enough to do a huge amount of damage, and if your container failed it would turn into so much shrapnel. If you're going to go ahead with this I would urge you to get a commercial pressure vessel designed for that job.

Using water would be much safer, because water doesn't compress significantly so it doesn't have any energy in it.
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