If you're like Mike and Leon here,
you know that weighing things...
is fun.
But what do you do when your scales misbehave?
Take a few measurements and hope for the best?
Have your scales recalibrated -- again??
Try with increasing desperation
until you begin to question the accuracy
even of the weights you thought you knew?
If only there were a better way to weigh!
Hey, you two:
Are you tired of low-accuracy measurements?
Would you like to weigh household objects
with the precision of cutting-edge physics?
Well now you can,
with the "NIST Do-It-Yourself Watt Balance"
made with LEGO (R) bricks!
That's right,
the "NIST Do-It-Yourself Watt Balance"
is the answer to all your high-accuracy
mass measurement needs.
Use it to weigh peanuts!
Packing peanuts!
Your engagement ring!
Other LEGO (R) pieces!
A button!
And much, much more,
all with as low as 1% uncertainty!
Don't settle for calibrated mass artifacts.
Dropping, chipping, or even sneezing on them
will change their mass and require a new calibration.
Only the "NIST 'D.I.Y.' Watt Balance"
can be used again, and again,
and again, and again,
for endless measurement fun!
Before I built my own NIST demo watt balance,
I had to use real watt balances,
which are the size of a room and can only be found
at world-class metrology institutes.
Now I can measure mass with an accuracy of 1%
from the comfort of my living room!
Warning: Accuracy may vary.
And for a limited time, you too can get in
on the precision measurement action.
That's right,
there has never been a better time
to build your "NIST 'D.I.Y.' Watt Balance."
Because this tabletop weighing machine
is based on a real-life device
that is currently playing a real-life role
in the international effort
to redefine the world's basic unit of mass --
the kilogram!
When complete, the full-size watt balance pictured here
should be able to measure a mass of one kilogram
to within three millionths of a percent.
That's low enough to make the watt balance
the new official U.S. standard for mass,
a role currently played
by this golf ball-sized cylinder of metal.
But the technology is so powerful
that even when it's constructed out of LEGO (R) bricks,
this instrument can beat the accuracy
of some jewelry, cooking, and postage scales,
all of which need regular calibrations
to maintain their accuracy.
And you can be part of this world-wide quest
to explore the mysteries of quantum physics,
the key to ultra-accurate measurements.
Not convinced that something made of LEGO (R) pieces
can deliver high-precision measurements
using the same technology
as a world-class metrology machine?
Don't take our word for it --
just listen to these experts.
The NIST demo watt balance is a real device
that you can make at home,
and it really can measure mass with high accuracy,
using the same principle as a full-size watt balance.
Watt balances work by making an indirect comparison
between mechanical power and electrical power.
This allows us to measure the downward pull
of a gravitational force on a mass
by counteracting it with an upward
electromagnetic force.
What's maybe counterintuitive
when you look at these machines is that
they are not comparing the mass of an object
on one side of the balance beam
to another object on the other side.
Instead, they are comparing the weight of a mass
on one side of the beam to the force created
by a magnet-driven levitation system directly beneath it.
To illustrate,
here's a basic watt balance anatomy lesson:
First, each device has a balance beam.
The balance beam on the full-size watt balance
is a wheel that rotates as one side goes up or down.
This wheel pivots about a knife edge.
On the tabletop demo watt balance,
the balance beam pivots about these two T-bricks.
And here is the platform where we can set the mass
that we are weighing.
Unlike a full-size watt balance, the demo version
has a symmetric design,
allowing the user to choose which side
they want to conduct the weighing measurement.
We have a strong permanent magnet
system down here.
You can just see it peeking out at the bottom,
and beneath these mass platforms
on the LEGO (R) watt balance.
To create this system,
we set two permanent magnets one on top
of each other, in repulsion.
Their magnetic fields collide and spill outwards
in all directions.
This is very similar to the effect you see
creating a radial spray of water.
Finally, we create electromagnets,
which in both cases involve a coil of insulated wire
through which we can pass electrical current.
Here, they are on either side
of the tabletop watt balance.
In the full-size machine here,
we use a second electromagnet
on the other side of the device
to move the balance.
We also have an optical measurement system
including lasers and fiber optics on this table,
which we use to tell us the position and velocity
of the coil.
In the LEGO (R) watt balance,
we accomplish this with two laser pointers.
How much current we pump through the coil
determines how magnetic it is.
Enough current and we can raise the electromagnet
up against the permanent magnets,
until it exactly offsets the gravitational force
pulling down on the object.
Yes, folks, it's that simple!
And building your balance is easy too.
All you need are:
LEGO (R) bricks!
Laser pointers!
Cardboard!
Wire!
Magnets!
PVC piping!
A computer!
This free software!
A data acquisition electronics system!
And measuring tape!
A few more items required
for "NIST 'D.I.Y.' Watt Balance" as shown,
such as nuts, screws, screwdriver, printer, photodiode,
length of threaded rod, solder, soldering iron,
display case, wooden base board, and additional
electronics including a digital-analog converter,
each sold separately.
First, use your LEGO (R) bricks
to build the foot-tall tower and balance beam.
Next, create your very own weighing platforms!
Simply print out our custom target patterns
with their easy-to-use adjustment lines
and glue them to a piece of cardboard.
Now place the balance beam onto the tower,
and the weighing platforms onto the balance beam.
The T brick is the fulcrum!
Just look at that balance go!
Next, mount your two laser pointers here and here,
with a light-sensitive sensor here.
No need for guesswork -- these lasers
will let you track the balance beam's motion
in one dimension.
One dimension!
But wait -- there's more!
Why settle for store-bought electromagents
when you can build your own?
To make them, simply wrap two lengths
of insulated wire around two pieces of PVC piping.
You can even use a power drill to speed things up
and ensure your coils are smooth and even.
Smooth and even!
When electricity flows through the wire,
the coils become magnetic!
Magnetic!
Now suspend your new coils
from either side of the balance beam.
And that's not all!
What good is an electromagnet
without something to be attracted to?
Just attach a pair of super-strong neodymium
magnets -- in repulsion -- to a length
of threaded rod.
Warning: Magnets are extremely strong.
Handle with caution to avoid injury to self and others.
Finally, you're ready to place a pair of magnets
directly beneath each coil.
Then hook up your electronics,
connect to your computer, and launch the free software.
Free software!
And presto!
Now you can move the balance beam up or down
by changing the amount of current
flowing through the electromagnets!
It's the hands-free precision control
you've always dreamed of.
I used to carry a standard set of weights with me
wherever I went,
just in case I needed to calibrate a scale.
Now I know my measurements are accurate
without weighing my pockets down.
It's a dream come true!
And don't forget:
The "NIST Do-It-Yourself Watt Balance" features
not one, not two, but THREE modes of measurement!
First, calibrate your lasers in laser calibration mode!
Attach your measuring tape to a wall
and turn on your laser pointers.
It's quick work to gauge the position of the balance
at several angles and perform a few calculations
using the free software.
Free software!
Next, run velocity mode!
Our experts explain:
Before you can weigh an object on the balance,
you need to measure your magnetic field.
To do that, turn off Coil A.
Next, use the software to physically move Coil A
up and down next to the permanent magnet beneath it.
You'll be using Coil B,
on the other side of the balance beam,
as the driving force that creates this movement.
The motion induces a voltage in Coil A
that you can now measure,
and that voltage allows you to calculate
the magnetic field.
You said it!
Simply apply a current through one coil
and use it to move the weighing platform up and down
on the other side of the balance.
Just look at that sinusoidal trend
of induced voltage!
Finally, there's the mode you've all been waiting for:
weighing mode!
This is where we actually compare
the gravitational force pulling the object down
against the magnetic force that we use to
push it back up.
Yes, weighing mode is as easy as 1-2-3!
4!
5!
6!
and 7!
If your calibrations were correct,
you should get an answer within minutes
or less!
Fast and accurate!
But don't delay!
Start working on your
"NIST Do-It-Yourself Watt Balance"
within the next THIRTY SECONDS,
and we'll throw in this free link to a journal paper
with step-by-step instructions
for building the balance in your home or classroom.
Disclaimer: Journal article also free
to those who don't start building balance
in the next thirty seconds. See link below.
Act now!
Join the growing number of happy
"NIST Do-It-Yourself Watt Balance" builders
and you too can "measure smarter!"
Thanks, NIST Demo Watt Balance!