Paper Done! & more....

Just turned in the paper to Dawn.  We are officially done with the hard part!  Working on tweaking my lesson plan and Dave is working on the tech fest game.  Tech Fest will be a blast this year!

Poster is finally done! I HOPE

We have tweaked and tweaked till this is what is considered complete. 

Looking Good

Dressed up the assemblies so that they would look more professional today.  Had to mount the two boards required for the CO2 sensor/transmitter on a piece of wood.  Used #6 screws with 1/4" teflon standoffs.  Hopefully it looks good enough for being a prototype.  Fan wires are soldered to the board now.  Sharin & I tested it and everything is working as planned.  There is a little difference in voltage readings, but this will get addressed on Monday.

Sensor Board Updates

Spent yesterday afternoon soldering.  Sharin & I wanted to get the protoype off the bread board and into a permanent home.  The specific board we worked on was the receiver that communicates with the computer.  Looks much better with appropriate length wires. :-)

This morning was also very productive.  I started out at the hardware store looking for screws to mount the CO2 sensor/transmitter boards.  Miss judged sizes, so I had to make a second trip.  (This time I took a generic board for reference.)  Bought #6 screws & 1/4" teflon standoffs for mounting the boards to a 4" x 4" piece of wood.  The boards are mounted next to each other and we are now working on shortening the wiring to make it look better.  Functioning great!  Blow into or talk over the CO2 sensor & the fan kicks on right on que.

More to come.

The Plan

Actually, the plans. As the last trial with the cinder block takes place, I start to design the Tech Fest carnival apparatus. I trying to decide whether we should have 3 or 4 stations. We have the technical equipment for 4, but would it benefit us to have one more? I'l go ahead an design it, but go to EESAT and see the size of the room before buying materials. Off to plan...
(insert time here)
OK, done.
I just gotta buy the stuff and build it now.
Parsons

oh yeah, and we put a cinder block in an enclosure with 20000ppm CO2 and in 3 hours or so, it dropped below 200ppm. The room we were in was at 700ppm.

Monday, the first thousand light bulbs

Over the weekend, I took my large syringe to my room at school and calibrated it with water and a triple beam balance. I wanted to see whether or not the markings on the side of the syringe were in fact legitimate. If not, at least I will have measurements so that I know what each gradation actually is. According to http://www.csgnetwork.com/waterinformation.html tap water at the temperature I measured it at, has a density of .99624g/mL (interpolated).

 The slope (also the density) from my data was .9965g/mL accurate to 3 sig figs, so I have no worries about the precision of my instrument.

So today, one of the goals will be to oblige Dr. Rudi and place various building materials in a container with some CO2 and see if there are any changes in that level. Do the building materials exude or absorb the CO2. I expect nothing to happen, but that remains to be seen. I will try to test in the region where our fan will operate, 1000-5000ppm.

• First up: 2 pieces of dry wall about 5" x 26"(unpainted, unplastered)- no appreciable change

• Second: 1 cinder block (new)- CO2 ppm drops more than expected. Must do a more rigorous test. Sealed the entire container with the cinder block and CO2. The CO2 level dropped down from 1200ppm to a lowly 200ppm. The room we are in is at about 800ppm, so there is no excusing the drop in CO2. Upon doing some research, I see that to create lime in cement (and cinder blocks) CaCo3 is heated to 500-600 degrees celcius to create CaO and CO2. This reaction is reversible. Technically, the cinder block is a combination of coal ash, and portland cement, which is 3CaO•SiO2 and 2CaO•SiO2. Perhaps the CaO is being coaxed out of the block. This would eventually reach an equilibrium state, but it could take months for a new cinder block to reach that point. Very interesting, indeed!

• Third: 3 bricks (old)- no appreciable change

• Fourth: 2- 1sq. ft. ceiling tiles- no appreciable change

• Fifth: 1 linoleum adhesive floor tile- 

• Sixth:  3 carpet samples- no appreciable change

• Seventh: 2 small plants (a fern and a caladium)- There seems to be a trend of rising CO2....hmmm. Have I been lied to all my life? I have just been told that plants generate CO2 and O2 in different situations. Does everybody know this? I could swear that my biology teacher said plants make O2 with no mention of CO2 production. What is the net result? Sheesh. Too many variables in this little test.

Later, Dave

Tuesday, grinding away...

So the CO2 sensor that we ordered has some issues... at least the spec sheets do. Yes, that was plural...spec sheets. On one spec sheet the output voltage is 30-50mV, and the graph it provides reads that the output voltage is 265-325mV. On the spec sheet for the module the CO2 sensor plugs into, it refers to the CO2 sensor having a voltage output of 100-600mV. What?!?!?!?

It appears we must do our own calibration, using the grey wolf as gospel truth. Over 2 hours of careful measuring, we plotted the voltage function of the sensor in relation to the CO2 ppm and took 37 points of data, more closely spaced where we would be using the sensor. We measured from 800ppm to 80000ppm and found that the sensor becomes less responsive at very high concentrations. On a log graph, it looks fairly linear. The y-axis is ppm and the x-axis is voltage output by our sensor.

With that many data points, it should be fairly easy to interpolate ppm based on voltage. Our range of concern is between primarily 1000-5000ppm. The actual data looked like this, although the program cut off the first 25 minutes.

Testing stuff!!!!!!!!!

Whew! 2 solid days of testing. Monday was spent testing different places we could place the CO2 sensor.
First, I tested with the CO2 sensor on the bottom of the enclosure.

I had expected the CO2 to settle on the bottom and give a much larger reading than the true reading. I knew how much CO2 I was putting in because I was measuring it with a large syringe. I would put the mouth of the syringe in the bottom of a bucket that had dry ice in it for quite awhile. I would slowly draw the gaseous CO2 into the  syringe, and then set the syringe in a vertical orientation so that when it came to room temp, it would push the excess CO2 out of the top end of the syringe. I made some calculations to arrive at 5mL of room temp CO2 was adding 80.3ppm by mass (79.7 by volume) to the container we were using. Anyway, back to my hypothesis. I figured that if I added CO2 to the enclosure (to bring it up to 1000ppm), it would pool in the bottom where the sensor was and give a reading far above 1000ppm. I was half right. If I can put a copy of the graph in this I will. The reading from the grey wolf spiked high every time I put CO2 in (50mL per injection), but after about 6 minutes, it would achieve a steady state.

The steady state value almost agreed with the ppm I thought I was putting in (700ppm compared to the 800ppm I believed i was putting in), but I had not anticipated this. My interpretation of the spike goes along with my initial hypothesis. The CO2 is just really heavy compared to air. However, I thought it would stay at that high level. I was really surprised that the CO2 diffused throughout the enclosure.

Next came the middle test where the sensor was located vertically in the middle of he chamber.

I kept the 50mL addition the same every time, but the initial spike from the low test was smaller, and the time to reach equilibrium was much longer, about 15 minutes.

Even though I was adding 800ppm every time (from calculations based on the syringe), the steady state averaged out to about a 500ppm increase each time....hmmm.

High test

The grey wolf was put at the top of the container as well as our sensor, to do some initial voltage measurements.

I was concerned about this last graph, because I thought something had gone wrong. I couldn't find anything wrong with the set-up, so it must be accurate. As Julius Sumner Miller stated "Experiments do not fail, you must provide Nature the necessary provisions, or she won't do what you want her to do."

We added 160ppm at 3:51 and got a reading of about a 21ppm increase 3 minutes later.

We added 320ppm at 3:54 and got a reading of about a 400ppm increase 8 minutes later.

We added 320ppm at 4:03 and got a reading of about a 260ppm increase 7 minutes later.

We added 480ppm at 4:10 and got a reading of about a 410ppm increase 6 minutes later.

We added 800ppm at 4:16 and got a reading of about a 630ppm increase 11 minutes later.

The ideas of what was going on was starting to coalesce in my head. I had imagined the CO2 like it was water, sinking to the bottom of the container and staying there. That was the model in my head of the system. To paraphrase Kenn Amdahl, when pretending the universe is like a watermelon, with the seeds like stars, don't forget that the universe isn't actually a watermelon. What I had failed to account for was that CO2 is a compressible fluid and water is not. This new-found realization crystallized and it made sense of the data. What actually was occurring when CO2 was added, was an initial plunge as the CO2 dropped to the bottom of the container. As the gas diffused, it also set up a density gradient, with the highest density at the bottom, and decreasing as you go vertically upward. That at least partially explains the discrepancy between the ppm injected and the ppm measured. I need to do a little research a little into this phenomenon. The fluid mechanics class I took was a long time ago, and I'm not sure if we covered compressible fluids.

Dave out

Ready to test!

Ok, I think we're at a stage where we can begin testing.

• First, measuring CO2 at different heights of the big tub. Hoping it will answer a question I have about how fast the CO2 will sink since it is much denser than air. Measure the concentration low, middle, high with the grey wolf given a known ppm.  
• I have calculated the ppm CO2 (by weight and by volume (for those of you playing at home, its only .16% different)) we will be adding to each of our containers per mL of CO2 we add from a large syringe.
• I measured and calculated the actual volume of our enclosures +/- 2% for the bucket, and +/- 5% on the enclosure.  These measurements were about 10% off from the listed size of the bucket, and less than 1% off for the enclosure.
• I should be able to show my team and whoever else the bubbles floating on the CO2 that we were going to employ at Tech Fest. I'll insert a video later today 

Parsons

Vaisala CO2 info

I have looked & looked for a company that deals with CO2 sensing combined with ventilation.  I found lots of good information on several types of sensing units from a company called Vaisala.  I have sent an email requesting more information about the company & where the sensor are manufactured.  I could only locate sales offices from the web page, but was able to get spec sheets for the sensors.  This company advertizes that they have applications appropriate for home, school, and business.  I will see what else I can determine about the company that is not on the web page.