Trying to build a fluxgate magnetometer -- help!
Mark A. Haun
I am trying to build a fluxgate magnetometer sensitive enough to
monitor variations in the Earth's magnetic field, mostly to observe
magnetic storms caused by big flares on the sun (March 13, 1989
stuff especially :-) !).
I have seen an article about one of these designed to serve as a
solid state compass in Radio Electronics magazine's "Hardware
Hacker" column, and Radio Shack has also recently come out with a
fluxgate compass. Would such a circuit be readily adaptable for my
purposes? My main concern is whether it would have enough
sensitivity; I would like to measure changes at least as small as
10 gammas (.001 Gauss), and if possible, even smaller.
I envision having a setup with the magnetometer hooked up to a
chart recorder and running 24 hours a day. It would alert me to
the start of any magnetic storms and would show me the best times
to try and observe the northern lights from my location here in
California, if there are more *big* flares like this past March
(they were actually seen here then, but I wasn't aware of it until
a few days later).
I would appreciate hearing from anyone who has built any sort of
fluxgate magnetometer, anyone who has seen a construction article
for one, or anybody with suggestions/ideas/etc. on the feasibility
of this project. Please email to any of the addresses below.
Thanks!
--
( Mark A. Haun KJ6PC )( UUCP: ...ames!pacbell!sactoh0!mahaun )
( Sac-Unix, Sacramento CA )( AMPRNET: kj...@kj6pc.ampr.org )
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Vaso Bovan
>
>I am trying to build a fluxgate magnetometer sensitive enough to
>monitor variations in the Earth's magnetic field, mostly to observe
>magnetic storms caused by big flares on the sun (March 13, 1989
>stuff especially :-) !).
>
>10 gammas (.001 Gauss), and if possible, even smaller.
>
? You mean of course, nanotesla (nT), since 1954. :-)
John Sahr
Well, I don't know about the "official" state of "gamma" vs "nT", but
both are in common usage in "the business." For earth-based mags, the
_only_ unit I have heard used is "gamma".
How many of you circuit dweebs use the "right" term for inverse ohms?
I thought so.
(yearning for the days of furlongs per fortnight :*)
--
John Sahr, Dept. of Electrical Eng., Cornell University, Ithaca, NY 14853
johns@{alfven,calvin}.ee.cornell.edu, {rochester,cmcl2}!cornell!calvin!johns
--When the dust settles, each B2 bomber will fund NSF for more than a year--
Bill Katz
flux-gate magnetometers. It is the Technical Support Package for Tech
Brief LAR-13560, "Improved Flux-Gate Magnetometer, and includes a 23 item
bibliography. The package is about 35 pages long, and can be obtained
from NASA Langley Research Center, Hampton, VA 23665-5225. I got it from
a bingo card in _NASA Tech Briefs_ a couple years ago. I would assume it's
still available.
______________________________________________________________________________
_ /| -ACK! Bill (the) Katz Internet: bi...@hpsad.hp.com
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______________________________________________________________________________
Justin Masters~
Take a look inside the November 1989 Radio Electronics. I just got mine last
night and there is info for trying to build a fluxgate magnetometer.
-----------------------------------------------------------------------------
Is my car the only one in America where | Justin "Ice Cream Monster" Masters
someone breaks in and turns up my radio |
every time I park? - Steven Wright | jmas...@pcocd2.intel.com
John G. De Armond
>
>How many of you circuit dweebs use the "right" term for inverse ohms?
>I thought so.
>
You mean you don't sling your *ahem* Semen(s) around with wild abandon? :-)
(I no, I no, it ain't spelled rite but whot the hek?)
John
--
John De Armond, WD4OQC | Manual? ... What manual ?!?
Radiation Systems, Inc. Atlanta, GA | This is Unix, My son, You
gatech!stiatl!rsiatl!jgd **I am the NRA** | just GOTTA Know!!!
Robert Kelley
there's a description of a differential magnetometer capable of detecting a
minimum difference in field strength of 3e-5 oersted. The magnetic field of
the earth causes protons in water molecules to precess at a rate of about 2025 Hz.
The article describes a device consisting of two bottles of water with coils
wound around them, and a high-gain (2e6) tuned amplifier. A dc current is passed
through both coils to align the magnetic dipoles, then the current is removed and
the amplifier is connected to the coils. A beat frequency proportional to the
difference in the magnetic fields at each bottle is heard at the output of the
amplifier.
It might be interesting to build a more modern version of the system described
in the article. Another installation of _The_Amateur_Scientist_ describes another
NMR setup and suggests adding ferric nitrate to the water. Why?
Doug Gibson
>It might be interesting to build a more modern version of the system described
>in the article. Another installation of _The_Amateur_Scientist_ describes another
>NMR setup and suggests adding ferric nitrate to the water. Why?
In the NMR lab given in undergrad p-chem here, we added a decent amount
(millimolar, I think) of some ferric salt to water.... and all of a sudden, the
water peak was about 1000 Hz wide.
I suspect there's a connection.
-Doug Gibson
char...@csli.stanford.edu
"He's dead, Jim. You grab his tricorder, and I'll take his wallet."
pie...@cimnet.dec.com
simpler option is WWV. WWV includes a solar activity report in, in voice,
the 18th minute of every hour.
thanks
dave pierson |The facts as accurately as I can manage,
Digital Equipment Corporation |The opinions, my own.
600 Nickerson Rd
Marlboro, Mass
01752
smlg...@uxa.cso.uiuc.edu
I think the ferric salt is added to the water for the following
reason:q:
smlg...@uxa.cso.uiuc.edu
Adding ferric nitrate to the water makes this experiment one in
FMR, ferromagnetic resonance rather than nuclear magnetic resonance.
The total electronic spin of iron precesses with a static external
magnetic field just as the nuclear spins do. However, the contribution
of the iron electronic spin is much greater.
John Leroy
>
> I would appreciate hearing from anyone who has built any sort of
> fluxgate magnetometer, anyone who has seen a construction article
> for one, or anybody with suggestions/ideas/etc. on the feasibility
> of this project.
>
Dover Books for the theory and math behind the magnetometer described
in Sky and Telescope this month. Anybody got a good reference for the
fluxgate magnetometer?
--
-John LeRoy
Packet Radio: WA4VLV @ WX4S
Compuserve: 74136,401
UUCP: rti!tijc02!jkl141
Phone: 615-461-2440
Jeff Forbes
Ferric nitrate is a paramagnetic compound (One unpared electron),
ferrous nitrate is diamagnetic. The NMR experiment described in
"Scientific American" could only detect proton resonances. Proton have the
highest resonance frequency in a given field (except for tritium). You
could never see iron-57 at the field used in the experiment, its
gyromagnetic ratio is too low and its natural abundance is too low.
For example, when protons resonate at 360MHz (8.5T), iron-57 resonates at
ca. 15MHz. Adding paramagnets to a solution while change the magnetic
susceptibility of the solution, which will broaden the line considerably.
Some paramagnetic ions will cause a shift in the resonance rather than a
broadening, which is usefull for determining the structure of a compound.
Paramagnetic ions can also cause the spin system to relax faster, which
can be very useful. This discusion would be better in sci.chem than
sci.electronics.
Jeff Forbes
University of Illinois
Chemistry Dept.
David Cook
>>
>> I would appreciate hearing from anyone who has built any sort of
>> fluxgate magnetometer, anyone who has seen a construction article
>> for one, or anybody with suggestions/ideas/etc. on the feasibility
>> of this project.
>>
>
Mark... The very latest issue of Radio Electronics has an article
on connecting the Radio Shack Electronic COmpass to a computer system.
To make a long story short, they have an excellent discussion on
fluxgate magnetometers as a part of the article, including a description
as to how the windings are made (a control winding goes totally around
the core [ring] and a sine and cosine winding exist at 90 degree angles
to each other). Check out this article for at least a "feel" as to how
these devices are constructed.
John Leroy
>
> monitor variations in the Earth's magnetic field, mostly to observe
> magnetic storms caused by big flares on the sun (March 13, 1989
> stuff especially :-) !).
>
Some time back, I remember seeing an application note for Hall Effect
devices used to build a simple compass. Anybody have any insight as
to whether these devices might be available in a form suitable for
building a magnetometer?
John Leroy
>
> I am trying to build a fluxgate magnetometer sensitive enough to
> monitor variations in the Earth's magnetic field, mostly to observe
> magnetic storms caused by big flares on the sun (March 13, 1989
> stuff especially :-) !).
>
> I would appreciate hearing from anyone who has built any sort of
> fluxgate magnetometer, anyone who has seen a construction article
> for one, or anybody with suggestions/ideas/etc. on the feasibility
> of this project. Please email to any of the addresses below.
My email to you bounces, so I'll post this.
I just stumbled across "Simple Magnetometers or How to Measure Your
Own K-Index" by Russell G. Wicker, W4WD in the Proceedings of the
22nd conference of the Central States VHF Society (1988). If you
want a copy and can't find the proceedings let me know.
Doug McDonald
>>I would like to measure changes at least as small as
>>10 gammas (.001 Gauss), and if possible, even smaller.
>>
>
>? You mean of course, nanotesla (nT), since 1954. :-)
I have been in the science business for over 20 years and have
never heard anyone refer to magnetic fields in Tesla - everyone
uses gauss. It is true that people know that someone somewhere
created a unit of magnetic field called a Tesla, but no one
remembers how many gauss are in one Tesla, and no one uses it.
Sometimes it might appear in a textbook (usually directed at
freshmen or sophmores - more advanced books use gauss).
There are lots of names of units out there that are simply not used.
(Also, I might add, a lot of people refer to actual physical
magnets, though not the fields they create, in megahertz - as
in "it's a 500 MHz magnet" meaning, of course, that the NMR
resonance frequency of protons in it would be 500 MHz." Even the
people who do this snicker a bit while doing it, however.)
Doug McDonald
Jeff Forbes
NMR spectroscopists refer to their magnets in proton resonance
frequency as well as field in TESLA. A 500 MHz magnet is 11.7 T, a 60 MHz
magnet is 1.6 T, etc.
Jeff Forbes
Mark Wilkins
>(Also, I might add, a lot of people refer to actual physical
>magnets, though not the fields they create, in megahertz - as
>in "it's a 500 MHz magnet" meaning, of course, that the NMR
>resonance frequency of protons in it would be 500 MHz." Even the
>people who do this snicker a bit while doing it, however.)
>
>Doug McDonald
Ummm... In the world of analytical chemistry and in some other areas
where large magnets are often in use the Tesla is used to measure large
fields. For example, Nicolet Instruments, the company which currently holds
the patent on Fourier transform mass spectrometers, advertises all of their
magnets in Tesla values as do most other manufacturers in the analytical
chemistry market.
In general, when I was working in analytical chemistry at UC Riverside,
the only place I heard the gauss values used was in the Bank of America's
specification that credit cards were unsafe past the 50 gauss line. The
magnets were always, to us, thirteen, seven, and three TESLA.
Of course, everybody also used "torr" to refer to "mm Hg," which people in
some fields would find odd. I suppose the point is that just because your
area of work has different conventions than someone else's it isn't really
yours to say that some unit or another is NEVER, EVER used.
-- Mark Wilkins
wil...@jarthur.claremont.edu
Bo Thide'
>>>10 gammas (.001 Gauss), and if possible, even smaller.
>>>
>>
>>? You mean of course, nanotesla (nT), since 1954. :-)
>
>I have been in the science business for over 20 years and have
>never heard anyone refer to magnetic fields in Tesla - everyone
>uses gauss.
I use Tesla (or, rather, nanoTesla) all the time. But I have only
been in the science business for 17 years so I had a chance to
learn the SI system properly ... :->
Bo
^ Bo Thide'--------------------------------------------------------------
| | Swedish Institute of Space Physics, S-755 91 Uppsala, Sweden
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~~U~~ -----------------------------------------------------------------sm5dfw
Henry Spencer
>never heard anyone refer to magnetic fields in Tesla - everyone
>Sometimes it might appear in a textbook (usually directed at
>freshmen or sophmores - more advanced books use gauss).
The gauss is the older unit, still used a lot, especially in older sources
and by older writers. The Tesla is the correct modern unit; if you look
around, you'll see increasing use of it in most fields.
--
A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology
megabyte of flaming. | uunet!attcan!utzoo!henry he...@zoo.toronto.edu
Larry Lippman
> >>I would like to measure changes at least as small as
> >>10 gammas (.001 Gauss), and if possible, even smaller.
> >
> >? You mean of course, nanotesla (nT), since 1954. :-)
>
> I have been in the science business for over 20 years and have
> never heard anyone refer to magnetic fields in Tesla - everyone
> uses gauss. It is true that people know that someone somewhere
> created a unit of magnetic field called a Tesla, but no one
> remembers how many gauss are in one Tesla, and no one uses it.
> Sometimes it might appear in a textbook (usually directed at
> freshmen or sophmores - more advanced books use gauss).
Speaking as a Gauss-person who would prefer to see otherwise :-),
I regret to inform you that the Tesla is indeed being used in the real
world to replace the Gauss as a unit of magnetic flux density measurement.
Many magnetometer and magnetic instrument manufacturers, such
as F. W. Bell, Humphrey Inc., FRL Industries and Walker Scientific now
use the Tesla instead of the Gauss as their unit of specification.
However, it is somewhat amusing to note that while these vendors still
refer to certain products as "gaussmeters", they are now specified
using the Tesla as a unit of measurement; sort of an oxymoron, huh? :-)
Since I have already survived and coped with the Pascal, the
change to Tesla was less traumatic than I had imagined. Incidently,
the nanotesla (nT) seems to have replaced the gamma (.00001 Gauss) where
finer magnetic flux measurements are concerned.
<> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
<> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry
<> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry
<> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
Vaso Bovan
>>>10 gammas (.001 Gauss), and if possible, even smaller.
>>>
>>
>>? You mean of course, nanotesla (nT), since 1954. :-)
>
>I have been in the science business for over 20 years and have
>never heard anyone refer to magnetic fields in Tesla - everyone
>uses gauss. It is true that people know that someone somewhere
>created a unit of magnetic field called a Tesla, but no one
>remembers how many gauss are in one Tesla, and no one uses it.
>Sometimes it might appear in a textbook (usually directed at
>freshmen or sophmores - more advanced books use gauss).
>
>There are lots of names of units out there that are simply not used.
>
There are too many units out there that ARE being used. That is the reason
various international technical standardization organizations has strived
for a minimal set of clearly defined units. Unfortunately, there are many
authors who insist on dragging their feet on the changeover, so that one often
sees, for instance cgs and SI metric units intermingled, even within the same
equation ! I note that refereed journals usually require SI metric, but allow
obsolete cgs units "where traditional." This is an unfortunate loophole. I'm
an electrical engineer. I have to deal today with gauss, tesla, and microns,
all to describe the same parameter. (I won't even mention the profusion of
inch-based electro-magnetic units which are STILL found in new textbooks).
Let's not even start on the disgraceful reluctance of certain sectors of
U.S.A. engineering, mechanical engineers in particular, to expedite conversion
to metric measure.
John Sahr
>>>10 gammas (.001 Gauss), and if possible, even smaller.
>>? You mean of course, nanotesla (nT), since 1954. :-)
>I have been in the science business for over 20 years and have
>never heard anyone refer to magnetic fields in Tesla - everyone
>uses gauss. It is true that people know that someone somewhere
>created a unit of magnetic field called a Tesla, but no one
>remembers how many gauss are in one Tesla, and no one uses it.
>Sometimes it might appear in a textbook (usually directed at
>freshmen or sophmores - more advanced books use gauss).
>Doug McDonald
Whoa, thea, padnuh. The "Tesla" is alive and well, thank you. If I walk
over to the High Volt Lab, I find people quite comfortable with kilogauss
or tesla (not the same, of course), as they torture innocent protons.
Engineering textbooks through the graduate level tend to use MKS units,
which include Tesla. Physics textbooks, on the other hand, tend to use
cgs, which include gauss. I have several of each brand of text. For
genuine pandemonium, look at plasma physics texts. In ionospheric physics,
there is no standard at all, but a pretty free mix of cgs and MKS. Chen's
plasma physics 1st ed was in cgs: the second is MKS. You be the judge.
Actually, I prefer cgs all the way, myself, but I'm not dogmatic about it,
even though it ought to be obvious that cgs units are The One True Units. On
the other hand, E/B in MKS has units of velocity, which is convenient. But
on the other hand, E/B in cgs has no units at all, which is also convenient.
On the other hand, my Radio Shack voltmeter insists on giving me MKS units.
On the other hand, Jackson is a nice reference, and uses cgs, so it must be
good.
So, as I said, I don't insist upon cgs, because this is a free planet.
But, come the revolution, the MKSeoisie will be the first with
their backs against the wall.
--
John Sahr, | Electrical Engineering - Space Plasma Physics
jo...@alfven.spp.cornell.edu | Cornell University, Ithaca, NY 14853
Duke McMullan n5gax
writes:
>In article <1989Oct29.1...@ux1.cso.uiuc.edu>
mcdo...@aries.scs.uiuc.edu (Doug McDonald) writes:
>>I have been in the science business for over 20 years and have
>>never heard anyone refer to magnetic fields in Tesla - everyone
>>uses gauss...
>>Sometimes it might appear in a textbook (usually directed at
>>freshmen or sophmores - more advanced books use gauss).
>The gauss is the older unit, still used a lot, especially in older sources
>and by older writers. The Tesla is the correct modern unit; if you look
>around, you'll see increasing use of it in most fields.
Listen well to Henry, my friends. Picofarads have been in use for lothesemany
years, but when I was first getting interested in this stuff (late '50s),
the usage was micromicrofarad, usually abrev.d MMFD. Too, microfarads were
abrev.d MFD. Those fine days are past (Subhan Allah!).
It took several months before I even was able to discover wuthehell MMFD stood
for -- Pop'Tronics ran a nice basic article on capacitors. Still, it was MM
instead of pico for at least ten more years.
Only in the past ten years have nanofarads come into use, and it's still common
to see a cap rated in thousands of microfarads rather than millifarads.
Consider this one: how many hams and other electronikers do you know who pro-
nounce dB dee-bee, and how many of them actually know it means decibel? Then,
how many of them have ever heard of a bel? For the real joker, how many of 'em
know what a bel is? It's a lot easier (IMHO) to explain bels than decibels.
Think again: how often do you see something rated in tens of decibels, rather
than bels? WHY?
Habit, I suspect, coupled with the natural conservatism that we all possess.
This will change. How many people do you know who know the peta- and exa-
prefixes, and the femto- and atto- prefixes? (Admittedly not useful to most
of us, unless you're measuring the circumference of Pluto's orbit in electronic
radii....;^)
We all wear blinders of a sort, lacking omniscience...at least I do; maybe you
know all. But, with improved communication, and the old (unwilling) making
room for the younger, "these, too will pass away."
Too much rambling; good night.
d
I've been to Australia, so now I know what
the inside of a kangaroo's pouch feels like. -- Anon.
Duke McMullan n5gax nss13429r phon505-255-4642 ee53...@hydra.unm.edu
Vaso Bovan
>
>Consider this one: how many hams and other electronikers do you know who pro-
>nounce dB dee-bee, and how many of them actually know it means decibel? Then,
>how many of them have ever heard of a bel? For the real joker, how many of 'em
>know what a bel is? It's a lot easier (IMHO) to explain bels than decibels.
>Think again: how often do you see something rated in tens of decibels, rather
>than bels? WHY?
>
4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in
continental Europe, the neper is used instead of the bel." Is this true,
European readers ?
Myron A. Calhoun
[many lines deleted]
>.... I have to deal today with gauss, tesla, and microns,....
Someone once referred to the USA's "solution" to this problem as
"INCHING OUR WAY TO THE METRIC SYSTEM"!
--Myron
--
Myron A. Calhoun, PhD EE, W0PBV, (913) 532-6350 (work), 539-4448 (home).
INTERNET: m...@ksuvax1.cis.ksu.edu
BITNET: m...@ksuvax1.bitnet
UUCP: ...{rutgers, texbell}!ksuvax1!harry!mac
Robert Firth
>But, come the revolution, the MKSeoisie will be the first with
>their backs against the wall.
Hear hear! Not content with making us remember all kinds of
silly historical names, they have now removed one of the best
terms in the entire science of electromagnetism.
Who ever heard of "de-Tesla-ing" ?
Paul Koning
Tesla is the SI unit, gauss the (officially obsolete) unit from the
CGS system. Why is it still used? Partly because we're in the USA,
where the metric system is only barely understood. Partly because
engineers and amateurs tend not to care much about consistency in
units.
I still remember the grief I caught from my Physics prof. because I
had the nerve to write up a lab report on gamma ray experiments with
the energies listed in fJ (femtojoules) rather than his pet MeV
(megaelectronvolts, a mishmash if ever I saw one).
Does all this matter, you ask? It sure does. I recently tried to
read an apparently well-regarded textbook on switching power supplies.
The section on inductor design was totally unintellegible. The
reason: careless random mixing of units, particularly centimeters
or square centimeters vs. "circular mils" [sic].
paul, ni1d
PS. Remember the Hz vs. cps flaming in QST some years ago?
S Schaper
gibberish!
:-)
UUCP: {amdahl!bungia, uunet!rosevax, chinet, killer}!orbit!pnet51!schaper
ARPA: crash!orbit!pnet51!sch...@nosc.mil
INET: sch...@pnet51.cts.com
Andrew Karanicolas
>writes:
(lots of stuff deleted)
>Habit, I suspect, coupled with the natural conservatism that we all possess.
>This will change. How many people do you know who know the peta- and exa-
>prefixes, and the femto- and atto- prefixes? (Admittedly not useful to most
>of us, unless you're measuring the circumference of Pluto's orbit in electronic
>radii....;^)
>
In the microelectronics world, thinking in terms of femtofarads is
fairly commonplace. For example, in calculations of gate-source capacitances
for a minimum feature size MOS device. .
Joe Keane
taking over.
Question: How do you usually measure thermal conductivity in British units?
Answer: (Btu / hr) / (ft^2) / (*F / in)
Put that in your units program and smoke it! I'll take watts / meter-*K.
Jeremy G Harris
>4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in
>continental Europe, the neper is used instead of the bel."
Obsolete, I think. A faint memory tells me that the neper is natural-log based
rather than log-base-10 based. Never seen it used.
--
Jeremy Harris j...@root.co.uk
John Dillon
>
> Tesla is the SI unit, gauss the (officially obsolete) unit from the
> CGS system. Why is it still used? Partly because we're in the USA,
> where the metric system is only barely understood. Partly because
> engineers and amateurs tend not to care much about consistency in
> units.
Ahh, unit bigotry! Just what we need. The author suggests that
SI units are the answer regardless of the question.
It is true that several systems of units carry an enormous burden
of historical chaos, but the CGS system is NOT one of them. In fact,
were it not for the burden of real-life test instruments calibrated
in volts and amps, a person seriously schooled in classical
electrodynamics would choose to work in either the CGS or
Heaviside-Lorentz systems*. If you wish to explore this further,
I would suggest reading J.D. Jackson's "Classical Electrodynamics",
which has an excellent appendix on units and dimensions.
> I still remember the grief I caught from my Physics prof. because I
> had the nerve to write up a lab report on gamma ray experiments with
> the energies listed in fJ (femtojoules) rather than his pet MeV
> (megaelectronvolts, a mishmash if ever I saw one).
This makes as much sense as complaining about astronomers' use of
parsecs and light-years. The use of electron-volt (eV) and its
derivatives in this assignment gives the student familiarity and
appreciation of it's utility. Ignoring the utility misses the point.
That utility is the same as the real-world utility of SI units.
Sure, many folks have amused themselves by computing plate tectonic
movement in mils per fortnight or microchip die area in femto-acres.
To be saddled with systems of units where this a constant necessity
would be a horror. But even more horrible would be an educational
system which did not teach students to cope with the various units
found in the real world, or to take advantage of specialized units
where practical.
-- John
* extra credit question: do you know why the vacuum permeability
in rationalized MKSA (a subset of SI) is exactly 4*pi*1e-7 ? If not,
please direct flames to /dev/null.
Torkil Hammer
#4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in
#continental Europe, the neper is used instead of the bel." Is this true,
#European readers ?
Nobody I knew of used neper. Isn't it supposed to pertain to RF levels?
Nobody used bels either. But everybody used decibels about sound levels.
And volume was something we measured in cubic meter.
Which leads to the next interesting question: Why is sound level or
sound level control called 'volume?'
John Woods
> Consider this one: how many hams and other electronikers do you know who pro-
> nounce dB dee-bee, and how many of them actually know it means decibel?
Now hol' on thar! *I* pronounce it "dee bee", and I *know* that it means
one-tenth of a bel. How one pronounces a unit often has more to do with
convenience than with knowledge of the underlying unit (just TRY to tell
me you've never referred to a "5 puff capacitor" :-).
>
> Habit, I suspect, coupled with the natural conservatism that we all possess.
> This will change. How many people do you know who know the peta- and exa-
> prefixes, and the femto- and atto- prefixes?
>
I do (despite a highly embarrasing article recently in which I interchanged
peta and exa...:-). Two habits I do refuse to part with, however, are "mhos"
and "cycles [per second]" (especially the former). "Mho"s are not only
meaningful, but FUN as well.
Vaso Bovan
>In article <58...@shlump.nac.dec.com>, kon...@koning.dec.com (Paul Koning) writes:
>>
>> Tesla is the SI unit, gauss the (officially obsolete) unit from the
>> CGS system. Why is it still used? Partly because we're in the USA,
>> where the metric system is only barely understood. Partly because
>> engineers and amateurs tend not to care much about consistency in
>> units.
>
>Ahh, unit bigotry! Just what we need. The author suggests that
>SI units are the answer regardless of the question.
>
>It is true that several systems of units carry an enormous burden
>of historical chaos, but the CGS system is NOT one of them. In fact,
>were it not for the burden of real-life test instruments calibrated
>in volts and amps, a person seriously schooled in classical
>electrodynamics would choose to work in either the CGS or
>Heaviside-Lorentz systems*. If you wish to explore this further,
>I would suggest reading J.D. Jackson's "Classical Electrodynamics",
>which has an excellent appendix on units and dimensions.
>
Which CGS system do you prefer: electromagnetic or electrostatic ? Should
I have to remember that 1 abvolt = 10^-8 practical volts and 1 abampere
= 10 practical amperes ? Or is easier that 1 stat volt = 300 practical volts,
and 1 stat ampere = (1/3)10^-9 practical amperes ? Which system do you
recommend ?
>
>* extra credit question: do you know why the vacuum permeability
>in rationalized MKSA (a subset of SI) is exactly 4*pi*1e-7 ?
For bonus points, explain why the CGS electromagnetic unit of capacitance
is the gigafarad.
Cees Keyer
+>In article <30...@buckaroo.mips.COM> va...@mips.COM (Vaso Bovan) writes:
+>>The bel is of rather recent vintage, 1923 [ A Dictionary of Scientific Units,
+>>4th Ed., Chapman & Hall, 1980]. This source contains the statement that "in
+>>continental Europe, the neper is used instead of the bel."
In Europe we use the bell instead of the neper.
The bell is a measure for good things but is a large unit hence
picobello :-).
+>
+>Obsolete, I think. A faint memory tells me that the neper is natural-log based
+>rather than log-base-10 based. Never seen it used.
+>--
The neper is used in transmision technology.
--
DISCLAIMER: I am not insane, I am a plane. pjew!
Cees Keyer, Algemene Hogeschool Amsterdam. | fax: (+31) 20-443215
department of electrical engineering. | phone (+31) 20-429333
Email: ce...@maestro.htsa.aha.nl ce...@tamtam.htsa.aha.nl
Snail: AHA-TMF, Europaboulevard 23, 1079 PC Amsterdam, The Netherlands.
John G. De Armond
>Nobody used bels either. But everybody used decibels about sound levels.
>And volume was something we measured in cubic meter.
>Which leads to the next interesting question: Why is sound level or
>sound level control called 'volume?'
That's easy. The control varies how many cubic feet of sound get produced
by the speakers. Didn't you know that the standard bell (of the church
variety) held about 1 cubic foot? Or that the home version was about
a tenth as spaceous, ergo the decibel? Of course, if you have a hundred
or so of these decibels, the great pressure of the large volume
of sound, especially the higher density sounds, can cause damage such
as cracked plaster, damaged ear drums and so on.
Oh yeah, .... :-)
John
--
John De Armond, WD4OQC | Manual? ... What manual ?!?
Radiation Systems, Inc. Atlanta, GA | This is Unix, My son, You
emory!stiatl!rsiatl!jgd **I am the NRA** | just GOTTA Know!!!
Henry Spencer
>is the gigafarad.
Now *there's* a filter capacitor!
Frederic W. Brehm
>fairly commonplace. For example, in calculations of gate-source capacitances
>for a minimum feature size MOS device. .
The microelectronics world does not use SI units everywhere, however. It
is commonplace to put (ignore the magnitudes, look at the mish-mash of
units) a 5000 Angstrom thick 1 micron wide line on a 2000 square mil die on
a 4 inch diameter wafer! This is changing, though.
Fred
--
Frederic W. Brehm Siemens Corporate Research Princeton, NJ
f...@demon.siemens.com -or- princeton!siemens!demon!fwb
Frederic W. Brehm
>... Two habits I do refuse to part with, however, are "mhos" ...
>..."Mho"s are not only meaningful, but FUN as well.
Horrors! You should use the correct unit (siemens). We use it a lot
around here.
:-) Fred
Marc de Groot
>This will change. How many people do you know who know the peta- and exa-
What are the values for peta- and exa- ?
--
Marc de Groot (KG6KF) These ARE my employer's opinions!
Noe Systems, San Francisco
UUCP: uunet!hoptoad!noe!marc
Internet: ma...@kg6kf.AMPR.ORG
Larry Lippman
> In article <30...@buckaroo.mips.COM> va...@mips.COM (Vaso Bovan) writes:
> >For bonus points, explain why the CGS electromagnetic unit of capacitance
> >is the gigafarad.
>
> Now *there's* a filter capacitor!
Yup, that's a pretty large unit. Actually, I've not heard of the
term gigafarad, although the CGS emu unit of the abfarad would be 10^9
farads. I suspect that emu folks who deal in abvolts, abamperes, abohms,
and abcoulombs would prefer to stay with abfarads instead of gigafarads,
though.
Now, for a unit that is truly bizarre, consider the reciprocal of
capacitance, referred to as "elastance", which is measured in "darafs".
I kid you not.
For those Net readers who deal with purchasing departments, for
some fun, next time you need a small ceramic disc capcitor, specify
the capacitor value in elastance using the unit of gigadaraf. :-)
Paul O'Neill
from EE Times -- 17 Aug 81
Earl rogers, president of Precision Monolithics, has uncovered the
following useful conversion factors.
10^12 microphones = 1 megaphone
10^12 pins = 1 terrapin
10^-12 picolos = 1 pico-boulevard
10^21 picolos = 1 gigolo
10 rations = 1 decoration
10 millipedes = 1 centipede
1 centipede/second = 1 velocipede
3 1/3 tridents = 1 decadent
5 holocausts = 1 Pentecost
10^6 bicycles = 2 megacycles
10^9 micrometers = 1 kilometer = 200 pentameters
10 monologues = 5 dialogues = 1 decalogue
2 x 10^3 millinaries = 4 seminaries (*) = 1 binary
10^-5 dollars = 1 Millicent
1 milli-Helen = the amount of beauty required to
launch 1 ship
nano-nano = a prefix designating 10^18
(*) The enlightenment generated by a seminary is measured in luminaries.
Paul O'Neill p...@oce.orst.edu
Coastal Imaging Lab
OSU--Oceanography
Corvallis, OR 97331 503-754-3251
John Eaton
< Now, for a unit that is truly bizarre, consider the reciprocal of
< capacitance, referred to as "elastance", which is measured in "darafs".
< I kid you not.
Well, that makes it consistant with the mho (1/Resistance).
John Eaton
!hpvcfs1!johne
Phil R. Karn
So far the unit seems to be most popular in Europe. Unfortunately, it's
still almost unknown in the US. It's so much easier to say "10 nF" (a
common enough value) instead of .01uF or 10000 pF.
How many people do you know who know the peta- and exa-
>prefixes, and the femto- and atto- prefixes? (Admittedly not useful to most
>of us, unless you're measuring the circumference of Pluto's orbit in electronic
>radii....;^)
Some of these larger prefixes are becoming useful when describing the
size of digital databases, or the number of bits you can send over a
fiber in a day, or the average age of the US ham population. :-)
Actually, the differences between cgs and MKS are trivial in comparison
to the *real* problem, which is the brain-damaged English system of
units. It's a considerable embarassment to me as an American that we're
still not metric. I for one would love to take all the money that's
currently being wasted on "OSI migration" in the US and put it into
going metric. (See? I'm not an American with an NIH syndrome. When the
Europeans -- even the French -- come up with an idea that's actually
*better* than what we're already using, I'm all in favor of converting.)
Phil
joseph geller
I would like to send some notes on magnetometers to mahaun@sactoh0
but, my email keeps bouncing; please send your full email address or regular
mail address to gel...@bnlux0.bnl.gov or to bnl, bldg911A (ags), Upton,
NY, 11973.