58 September/October 2018
Nowadays, 10 volt Josephson Voltage Standard (JVS)
systems are located in over 70 facilities around the world,
If you want to know even more about Josephson
junctions, there are quite a few scientific papers on the
Internet. Check Wikipedia too.
BTW, if you have some extra cash laying around,
you can buy a turnkey 10V programmable Josephson
instrument from the NIST (National Institute of Standards
and Technology) for the bargain price of $220,600. Or …
you could build one in your basement.
ARE MY METERS ACCURATE OR
Finally, I checked all the voltmeters in my shop against
a trimmed 5.00000V IC reference as shown in Figure 12.
It was kind of anticlimactic because ALL the meters were
right on the nose, including some analog panel meters.
So now, I have no doubts about the accuracy of any DC
voltage measurements I make in the future.
You might wonder why meters need to be periodically
calibrated if they always seem to be right on. The answer is
simple. In my youth, I briefly worked in the calibration lab
of a large aerospace company and asked the supervisor
the same question. He said “You may think they’re alright,
but they could have been dropped or zapped out on the
[production] line. You never know until you check ‘em.”
WRAPPING IT UP
While it might be fun to have your own world-class
super-precision Josephson instrument in your basement,
taking delivery of liquid helium each month might make
the neighbors wonder.
In lieu of that, you can easily build or buy a perfectly
good IC voltage reference and set your mind at ease about
the accuracy of your meters. At least you’ll know for sure
which meter you can trust. NV
FIGURE 11. The value of the DC output of this simplified array
diagram is locked to the frequency of the input microwave power.
FIGURE 12. My Fluke DMM is right on the nose compared
to a precision voltage source.
ITEM DESCRIPTION SUPPLIER
C1, C2 Capacitor, 0.1 µF, 50V Digi-Key, P4525-ND
D1 Diode, 1N914 Digi-Key, 1N914BCT-ND
LED LED, Red Junkbox
R1 Resistor, 20K ohms Digi-Key, 20KQBK-ND
U1 Regulator, 15V, 100 mA, 78L15 Digi-Key, MC78L15ACPFS-ND
U2 Voltage Reference, AD584K Digi-Key, AD584KNZ-ND
SW1 Switch, Slide, SPDT Digi-Key, EG1903-ND
TP1-4 Binding Post, Pair, Red & Black Jameco 77691 (get three pair)
Breadboard Solderless Breadboard Jameco 2155452
Battery ( 2) 9V Alkaline Walmart
Holder ( 2) Battery Holder, 9V Digi-Key, BH9VW-ND
FIGURE 10. A primary voltage standard setup uses a tank of liquid
helium to cool the Josephson junction array inside it to 40K. Photo
courtesy of NIST.
Voltage Standards Parts List