Skip to main content

Levitation Frequency Characterization: Train of Lab Work Notes

Great news!  The bridged output mode on the Peavey amplifier I'm using here works!  That means I can apply roughly twice as much power to the levitation force providing electromagnet.  The bridge mode appeared not to be working two days ago.  A little reading of the manual provided the reason.  When in bridge mode, the speaker outputs don't like to be applied to any kind of ground.  I was trying to measure the output of the amplifier using a grounded oscilloscope.  Apparently this is what was causing the amplifier to shut itself off in bridged mode.  After removing the oscilloscope from the speaker outputs today, everything is working great.  Instead of hooking the scope directly to the electromagnet inputs, I attached it to  the pick-up coil.  As I mentioned a few days ago, this a better measure of the power available for levitation anyway.

I don't have time to write up everything in a classy fashion at this point, but I would still like to post on what's going on around the lab, so today I'm going to try something new.  This post is more or less what was going on around the lab as it was happening, (stream of lab work).  Hopefully in addition to showing what's going on in the lab as it happens, this type of post will give an idea of how results have to be reviewed, questions asked, and new tests performed.  I put in some notes after the fact, and they're marked.

A quick disclaimer.  I'm characterizing our equipment right now, so if it seems like there's not a great experimental procedure yet, that's because there's not.  All the data right now is just quick and dirty to get an idea of what our minimum and maximum experimental parameters are.

There are two questions for today:

What is the highest frequency that levitation can be attained at with the new bridged amplifier mode?  The old record is 152.62 Hz.

What is the minimum voltage at which levitation is achieved for each frequency?  [It looks like this question will have to wait for tomorrow].

Lev was immediately attained at 200 Hz!  Lev available at 400 Hz!  No lev at 600 Hz with power ramped up until the amplifier protection circuits kicked in.

400 Hz seems to be associated with changes in the level.  300 Hz looks like it might be level change related as well.

Comments after the fact
There are two types of levitation that we can get with the apparatus.  Each of them is shown in the following video.  The first one is what I'm calling steady-state levitaiton for the moment.  The superconductor floats up when the current is ramped up and stays up with no further changes in the current level.

The second one has to do with quickly changing magnetic fields.  If the electromagnet is quickly switched off, (as seen at the end of the video), there is a rather large, rather fast change in the magnetic field.  The amount of electromotive force induced in the superconductor is proportional to the rate of change of the magnetic field.  Consequently, you see a larger though very short jump in the levitation force.  (Look up Faraday's law of induction and Lenz's law for more information).

Back to train of lab work
200 Hz actually does provide steady levitation after a slow ramp up of power.

Trying again at 250 Hz.  Got steady levitation from 250 up to 300 Hz.  See the data on movie 108...:

Starting at 300 Hz, cannot get steady levitation.  The protection circuits kick off immediately after the superconductor moves the first time.

Trying again at 250 Hz after giving the SC time to cycle.  Got steady lev.  Did a successful run at 275 Hz as well.


Popular posts from this blog

Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

The Valentine's Day Magnetic Monopole

There's an assymetry to the form of the two Maxwell's equations shown in picture 1.  While the divergence of the electric field is proportional to the electric charge density at a given point, the divergence of the magnetic field is equal to zero.  This is typically explained in the following way.  While we know that electrons, the fundamental electric charge carriers exist, evidence seems to indicate that magnetic monopoles, the particles that would carry magnetic 'charge', either don't exist, or, the energies required to create them are so high that they are exceedingly rare.  That doesn't stop us from looking for them though!

Keeping with the theme of Fairbank[1] and his academic progeny over the semester break, today's post is about the discovery of a magnetic monopole candidate event by one of the Fairbank's graduate students, Blas Cabrera[2].  Cabrera was utilizing a loop type of magnetic monopole detector.  Its operation is in concept very simpl…

Unschooling Math Jams: Squaring Numbers in their own Base

Some of the most fun I have working on math with seven year-old No. 1 is discovering new things about math myself.  Last week, we discovered that square of any number in its own base is 100!  Pretty cool!  As usual we figured it out by talking rather than by writing things down, and as usual it was sheer happenstance that we figured it out at all.  Here’s how it went.

I've really been looking forward to working through multiplication ala binary numbers with seven year-old No. 1.  She kind of beat me to the punch though: in the last few weeks she's been learning her multiplication tables in base 10 on her own.  This became apparent when five year-old No. 2 decided he wanted to do some 'schoolwork' a few days back.

"I can sing that song... about the letters? all by myself now!"  2 meant the alphabet song.  His attitude towards academics is the ultimate in not retaining unnecessary facts, not even the name of the song :)

After 2 had worked his way through the so…