Monday, July 9, 2012

A Horse Trough a Quonset Hut and Data Acquisition


It gets hot in Las Cruces, and sometimes there's nothing to do for it but take a dip.  That's how I found myself sitting in our horse trough with Junior this weekend cogitating about the new data acquisition system.  I had a glass of McAllen, and Junior had her boat, (at 17 months, she's much too young for McAllen), and a good time was had by all.  The horse trough is left over from when we lived in a Quonset hut.  The building didn't come with a bathtub, but a short trip to the local feed store a few blocks away and we were set.  It was kind of cush, the trough sat near the back door about five paces from the train tracks, so you could sit there and watch the trains go by, (see the video below).



That was before our landlord decided the space would make a better art gallery.

I digress though!  Back to the data acquisition system and its requirements.  I've come across two articles about the effect of alternating current magnetic fields on superconductors that seem to have contradictory findings.

http://copaseticflow.blogspot.com/2012/07/superconductor-trapped-field-and-its-ac.html

Both agree that AC magnetic fields will gradually 'erase' any pinned magnetic flux in a YBCO superconductor.  Where they disagree is how the frequency of the AC field influences things.  Ueda et. al. see a decrease in the attenuation of the pinned field with increasing frequency.  They took there measurements between .1 and 1 Hz and extrapolated up to 50 Hz.  Ogawa et. al. see a pronounced increase in the attenuation of pinned field with increase in frequency.  They took their data between 7 and 61 Hz.  Ogawa et. al. attribute this attenuation to AC heating in the superconductor.  If Ogawa is correct, then I should see the levitation force on my superconductor decrease with time.

So, there are two things that I need to measure this week: what the strength of the AC field is that first accomplishes levitation at a variety of frequency, and how long levitation can be maintained.  I'll be using the little Arduino board for data acquisition again.  I've rigged a contact breaker on the superconductor sample holder.  When the superconductor levitates, an electrical contact will be broken and the Arduino print a message to my laptop screen and start a timer.  When the superconductor falls again, the Arduino will output the amount of time the superconductor was levitated.  I'll post in more detail on all this as the week progresses.  Hopefully, there will also be a video post on whether or not liquid nitrogen conducts.

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