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  • Author Author: dwinhold
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ITO - In the Air Degign Challenge - Portable Field Tester #5

dwinhold

Hello to everyone!!

 

So, my update last week didn't get posted due to a drastic change in our project. With the focus on clean air, water and soil sensing, I was creating sensor boards for.. well sensors. This was starting to work well until my daughter (Chrystal/Project Partner) asked how does the sensor tell if the water is ok to drink? I explained that we test for PPM, PH and other sensor tests we add. Chrystal, being a perfectionist and aspiring biologist said that my tests wouldn't give accurate enough results. She asked how I figure that it could, with so little information from a sensor? (I started to see a lecture coming). She added, if we are to make a field tester that can be used and trusted we have to do it right. So in my great wisdom I told her to tell me how to do this right. (I say my great wisdom because she was right and I let her tell me.. And I listened!! I'm very glad I did.)

 

Same but different:

 

Our change is now more biology directed. We are still using the sensors but adding in more biology for better results. This won't add too much more space to our project (Well, it will add 50% more) but the accuracy will be worth it. We are making a digital microscope and (Believe it or not) a small 4 vial centrifuge (Yes, centrifuge). As Chrystal pointed out to me, this is the most accurate way to find bacteria in the water or soil. The findings in the sample after the centrifuge can be checked against a database for safety. This redirection for accuracy is more important to our project as we require more information then what a sensor could give.

 

Our centrifuge is being made from a cordless rotary tool with a plastic molded vial holder attached. This is the only inexpensive and high speed way I could come up with as we require at least 18,000 rpm to reach the required G-force for separation of particles. (Pictures to come)

 

Our digital microscope is made from lenses and a web cam. We require 150-400x to see the small bacteria, viruses are a different story which we won't get near, as that is far beyond our knowledge. We may look into this later if time allows, I would rather leave that for more experienced virologists.

 

That is our update for now, Chrystal will be writing the next report later this week,

 

Dale and Chrystal Winhold

  • in reply to dwinhold

    Sounds a much safer option, but just remember the mass of the housing and the need to ensure IT doesn't escape.

     

    Mark

  • My original speed of 18000 rpm - RFC 27167 would have accomplished separation in around 2 minutes. the vials are small, 1.5 ml and rated for up to 30000 RFC. I have also got a friend (who owns a machine shop) to donate his time and make me the rotor from a solid block of aluminum, balance and fit everything. We will be using the lower speed and more time for separation. Below are the centrifuge calculations:

    RCF=(RPM/1000)^2 x r x 1.118

  • I really like the feedback, thank you to everyone. Safety is first, the centrifuge will be enclosed and housed safely, nothing is worth risk taking.

    My research on speed, g-force and time required:

    Time for bacteria separation with below calculations - 15 + minutes

    RPM - 9500

    Radius from center to tip of vial - 75mm (3")

    G-force or RFC - 7567

  • in reply to jw0752

    "... you can give yourselves some protection by holding the unit above your heads ..."

    I'm thinking a large solid object to cover it and standing on top.

    I presume braking is an option when it detects out of balance??

     

    How much G Force (and for how long) is required to seperate the particles.

     

    Mark

  • in reply to michaelwylie

    Hi Michael, Well let's assume that the centrifuge disk has a diameter of 31 centimeters (not unusual for commercial units) which would mean that the outer circumfirance is 1 meter. Dale is talking about 18,000 RPM which means that the outer edge of the disk is traveling at 300 meters per second. I believe that this is in the neighborhood of the muzzle velocity of some handguns. If you square this velocity and multiply it by the mass of the piece that just broke off (in Kg) you have the energy in Joules of the projectile. The aftermath of a piece breaking off is that at 18,000 rpm the machine is badly out of balance and then will jump around and break other things. Not a situation one wants to be close to.

    John