magnetic field

[Watson A.Name - \"Watt Su]

"Kevin G. Rhoads" <kgrhoads@alum.mit.edu> wrote in message
news:4163EE81.D5AF7646@alum.mit.edu...

[snip]

N.B., you cannot expect to
make a good solder connection to aluminum foil -- have lots of short
jumpers will alligator clips on both ends.

A few weeks ago I tried an aluminum soldering technique that someone
mentioned here. I used a big 100W iron, and sanded the spot and then
put a drop of Oatley flux on it to keep the air away. The original
advice was to use oil, but the flux seemed to work okay. Anyway, the
aluminum got hot several inches away, but the solder flowed right into
the alumninum, wetting it nicely. With foil, it shouldn't take so much
heat, so a smaller iron should work okay. A little experimentation
might be worth a lot.

I was reading an article (in Popular Science?) about how mercury can
corrode a huge aamount of aluminum, and it showed an I-beam that had
been exposed to it for less than a day. The I-Beam was eaten away, and
turned to powder. It said something about how it could destroy an
airplane. Weird!

 

[Watson A.Name - \"Watt Su]

"Boris Mohar" <borism_-void-_@sympatico.ca> wrote in message
news:hpbim0dimgtounrilrn7da16i83nee0inm@4ax.com...

On Sun, 10 Oct 2004 01:44:06 -0700, "Watson A.Name - \"Watt Sun, the
Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:


"Greysky" <greyskynospam@sbcglobal.net> wrote in message
news:hjt8d.6675$nj.2550@newssvr13.news.prodigy.com...
Anyone know of a reliable way of detecting currents less than one
femtoamp
i.e. 1X10^-16 amp full-scale? I figure to perhaps use some
instrumentation

Let's see..
1 mA = 10^-3
1 uA = 10^-6
1 nA = 10^-9
1 pA = 10^-12
1 fA = 10^-15 _not_ 10^-16!


He said LESS than 1fA. 10^-16 is 100 attoamperes

It is doable with discrete front end of I/V op amp configuration. I
used
3N155

What's eye-opening is that at these ultra low currents, just a few
picofarads hold so much charge that it greatly affects the whole
measurement.

--
Boris Mohar

 

[Bob Masta]

On Mon, 11 Oct 2004 10:46:13 +0100, "Daniel Kelly \(AKA Jack\)"
<d.kellyNOSPAM@NOSPAM.ucl.ac.uk> wrote:

Hi,

I have just built a PCB which holds a switched power supply and a microphone
amplifier. The power supply runs a camera whilst the audio amp is powered
directly from the 3.7v lithium polymer battery. The problem is that the amp
picks up a lot of noise from the powersupply. So much noise that the amp is
unusable at the moment. If I turn off the power supply then the amp runs
perfectly. Please could I ask your advice as to how best to limit this
noise? I've had a few ideas myself:

1) The PCB is doublesided and the back of the PCB is a ground plane. This
ground plane is continuous across the entire PCB so the powersupply and the
amp both share the same ground plane. If I separate the ground plane by
cutting the copper with a knife at the boundary between the two circuits,
will this limit some of the noise that's leaking from the power supply to
the amp?

2) Use better shielding on the PSU's inducer.

3) Build a separate PCB for the amp (something I don't really want to do
because I'm quite short of time).

Things I've tried already (but with no success):

1) Running separate power leads from the PSU and amp to the battery

2) Putting coupling capacitors all over the place.

3) Shorting the length of the microphone cable to the absolute minimum.

4) Shielding the entire PCB with grounded silver foil

5) Shielding only one circuit with grounded silver foil.

Thanks,
Jack

Just a thought, but if you could increase the switcher
frequency to move the noise above the audio range,
you could use a simple low-pass filter on the mic amp.
Probably best used as a last resort after all the "good
design practice" stuff fails.

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Watson A.Name - \"Watt Su]

"Bob Haberkost" <cbclistener-really!-@canada.com> wrote in message
news:66had.811$5N6.412@trndny08...

[snip]

BTW, you are shamefully crossposting to too many newsgroups!

I show the list of only 5 groups....not excessive, but more than I
usually see
without it being tagged (and glommed) as spam.

That's after I deleted a half dozen newsgroups. I wouldn't be surprised
if some of the others chewed him out thoroughly for wasting their time.

> --

 

[Winfield Hill]

"mndflmr" wrote ...

Recently I purchased a low-power VHF transmitter kit from Ramsey.
After building this kit, I have discovered that it will not work
for my purpose. I am trying to transmit audio and video about 20
feet from a satellite receiver to my bedroom. The power output
from the transmitter is so low the picture quality is very poor.

Here is the link to the kit manual:
http://www.ramseyelectronics.com/downloads/manuals/TV6.pdf

It's possible mndflmr's problem is misadjusted pots R3 and R7.


--
Thanks,
- Win

(email: use hill_at_rowland-dotties-org for now)

 

[Boris Mohar]

On 10 Oct 2004 06:55:45 -0700, Winfield Hill <Winfield_member@newsguy.com>
wrote:

Boris Mohar wrote...

He said LESS than 1fA. 10^-16 is 100 attoamperes

It is doable with discrete front end of I/V op amp
configuration. I used 3N155.

Tell us about your observed current offset and drifts.
(The 3n155 p-channel MOSFET is spec'd at 10pA maximum
gate leakage, for Vgs = -25V forward, admittedly a
rather silly and basically useless spec.)

Useless spec indeed. Actually we used 3N155A but do not have the data sheet
at the moment. We hand selected them for low Vgs because Igs varies
exponentially with Vgs

Also, did you use any input protection circuitry?

No. This was for ionization chamber which had the signal electrode enclosed
by the polarization electrode (can)

What was the size of your feedback/sense resistor?

1T Ohm in T feedback configuration. It was an I/V design.

Where did you get it?

The best at the time were from http://www.kandm.com/

Some others showed an inverse voltage coefficient. Manufacturer tested then
at 10 volts and higher but when we tested them at lower voltages the
resistance would start to increase rapidly. Of course it is not possible to
determine what the resistance is at 0V but when the electrometer is zeroed
this is what the feedback resistor sees.

The other big headache was the humidity. This was solved by potting the
front end in soft wax. We tried some fancy transparent potting gels but they
leaked. Potting also prevented parasitic ion chamber effects caused by the
interaction of nearby power leads and the input.


Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/

void _-void-_ in the obvious place

 

[E. Rosten]

Watson A.Name - \"Watt Sun, the Dark Remover\" wrote:

I was reading an article (in Popular Science?) about how mercury can
corrode a huge aamount of aluminum, and it showed an I-beam that had
been exposed to it for less than a day. The I-Beam was eaten away, and
turned to powder. It said something about how it could destroy an
airplane. Weird!

That is correct. Metals are often very good solvents for each other
(which is why alloys work well). Aluminium dissolves in mercury. When
the aluminium becomes exposed to oxygen in the air, it oxidises as
usual, but it is unable to form a protective hard coat since it isn't
sitting on a nice, solid base. Since the mercury essentially operates as
a catalyst, it can do pretty much unlimited damage.

-Ed






--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

 

[Guy Macon]

E. Rosten <look@my.sig> says...

Watson A.Name - \"Watt Sun, the Dark Remover\" wrote:

I was reading an article (in Popular Science?) about how mercury can
corrode a huge aamount of aluminum, and it showed an I-beam that had
been exposed to it for less than a day. The I-Beam was eaten away, and
turned to powder. It said something about how it could destroy an
airplane. Weird!

That is correct. Metals are often very good solvents for each other
(which is why alloys work well). Aluminium dissolves in mercury. When
the aluminium becomes exposed to oxygen in the air, it oxidises as
usual, but it is unable to form a protective hard coat since it isn't
sitting on a nice, solid base. Since the mercury essentially operates as
a catalyst, it can do pretty much unlimited damage.

In the aerospace factory I worked in mercury termometers and mercury-
wetted relays were banned.

 

[Rich Grise]

On Monday 11 October 2004 06:50 am, E. Rosten did deign to grace us with the
following:

Watson A.Name - \"Watt Sun, the Dark Remover\" wrote:

I was reading an article (in Popular Science?) about how mercury can
corrode a huge aamount of aluminum, and it showed an I-beam that had
been exposed to it for less than a day. The I-Beam was eaten away, and
turned to powder. It said something about how it could destroy an
airplane. Weird!

That is correct. Metals are often very good solvents for each other
(which is why alloys work well). Aluminium dissolves in mercury. When
the aluminium becomes exposed to oxygen in the air, it oxidises as
usual, but it is unable to form a protective hard coat since it isn't
sitting on a nice, solid base. Since the mercury essentially operates as
a catalyst, it can do pretty much unlimited damage.

I've also heard that mercury is one of very very few things that can

dissolve gold. Presumably, that's why it's used in tooth fillings.

Cheers!
Rich

 

[Clarence]

"Scorsi" <scorsi@earthlink.net> wrote in message
news:ea7e8dbc.0410111252.5d648332@posting.google.com...

I got into a debate recently regarding motors and the need for air
cooling,
can somebody confirm whether or not a normal motor can run in a vacuum
without overheating and if overheating is a problem, if there is any
type of motor that can run in a vacuum?

thanks Steve

Not for more than a few moments. There are special motors designed for running
in a vacuum. They are usually used on satellites. They ARE expensive. The
last one I encountered cost $80,000.00

Bearings are a problem, and heat is removed by conduction.

 

[sergio]

sitting on a nice, solid base. Since the mercury essentially operates as
a catalyst, it can do pretty much unlimited damage.

I've also heard that mercury is one of very very few things that can
dissolve gold. Presumably, that's why it's used in tooth fillings.

and why gold miners are poisoning Amazon's rivers

 

[Dave VanHorn]

Newer NIMH's, like the C type cells from Sanyo, can take long term
overcharge without problems. Check your data sheets.

--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR

 

[Ol' Duffer]

In article <W8SZd.19761$d5.149287@newsb.telia.net>, bos@hack.org says...

As stated above, I'm using veroboards (stripboard and breadboard is a
synonyme for the same thing, i think) for building my circuits. I also
own a licence of Electronic Workbench (Multisim and Ultiboard are the
ones I use most frequently). However, since I do not own any etching
equipment Ultiboard is of less use for me since it can only do
PCB-layout/routing. I have contacted the developers to hear if there was
any possibility to make Ultiboard output to veroboards, but regretfully
enough UB is designed for PCB only, was the answer.

I am not familiar with that package, but have used commercial
routing programs to do veroboard and thought it was a piece of
cake. At least compared to pencil, eraser, and graph paper.
Just snap to a 0.100" grid and remember that the traces on the
bottom only run one direction. No it won't tell you where to
make cuts, but is that really so hard to figure out?

2. When constructing on veroboards, I often have the need in cutting the
boards to smaller shapes and I've found that it's pretty cumbersome
since I haven't found any good tips of how to do it the right way. For
new boards, I could take a small saw and shape it up without much
problems. But for new circuits that I haven't done before, cutting the
boards could lead to a too small board in the end, requiring me to start
it all over again.

A bandsaw with a fine-tooth blade is a beautiful thing, but
a hacksaw can serve. With small boards, I sometimes find it
easier to clamp the saw in a bench vise and drag the board
across it.

Or with a little practice, you can score the board and break
it over a sharp table edge like you would a piece of glass.
It may help to cut through the foil at the desired break line,
as it is tougher than the board. The key is to create an
obvious path of least resistance.

Cut or score along the holes, as this is the weakest place,
and any random breaks will tend to occur here anyway. If you
need to trim down further to that 0.050" between holes, a
belt sander or bench grinder works well. Or a fine-tooth
file for inside corners.

 

[E. Rosten]

Rich Grise wrote:

On Monday 11 October 2004 06:50 am, E. Rosten did deign to grace us with the
following:

I've also heard that mercury is one of very very few things that can
dissolve gold. Presumably, that's why it's used in tooth fillings.

I expect most, or at least many metals can dissolve, ie alloy with gold.
As for reacting with gold (often referred to as dissolving), aqua regia
is one of the few things that can do it. That said, the difference
between dissolving and reacting (especially with regards to alloying) is
rather more subtle that shcool chemistry would have you believe (A level
only touched on it lightly when I did it), especially when you happen to
end up with a eutectic alloy.

-Ed

--
(You can't go wrong with psycho-rats.) (er258)(@)(eng.cam)(.ac.uk)

/d{def}def/f{/Times findfont s scalefont setfont}d/s{10}d/r{roll}d f 5/m
{moveto}d -1 r 230 350 m 0 1 179{1 index show 88 rotate 4 mul 0 rmoveto}
for /s 15 d f pop 240 420 m 0 1 3 { 4 2 1 r sub -1 r show } for showpage

 

[Winfield Hill]

AKA Jack\ wrote...

Now I can propperly sheild the two PCBs from each other.

Two comments: You may or may not be suffering from any magnetic
pickup, but to the extent you are, sheilding won't help. Second,
to the extent separation and shielding do help, the same result
can be achieved on one PCB by adding two separated ground planes,
and a small over-sheild with tabs soldered into the ground plane.


--
Thanks,
- Win

(email: use hill_at_rowland-dotties-org for now)

 

[Daniel Kelly (AKA Jack)]

Hi,

Thanks for the reply.

Yes, I tried separating the ground plane before I cut the board apart, but
that didn't seem to work (although maybe I didn't separate the ground planes
far enough - I only made a thin stanley knife cut).

Next time I design a PCB like this, I will do as you suggest.

Thanks,
Jack


"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:ckgd2j01s38@drn.newsguy.com...

AKA Jack\ wrote...

Now I can propperly sheild the two PCBs from each other.

Two comments: You may or may not be suffering from any magnetic
pickup, but to the extent you are, sheilding won't help. Second,
to the extent separation and shielding do help, the same result
can be achieved on one PCB by adding two separated ground planes,
and a small over-sheild with tabs soldered into the ground plane.


--
Thanks,
- Win

(email: use hill_at_rowland-dotties-org for now)

 

[CWatters]

"Scorsi" <scorsi@earthlink.net> wrote in message
news:ea7e8dbc.0410111252.5d648332@posting.google.com...

I got into a debate recently regarding motors and the need for air
cooling,
can somebody confirm wether or not a normal motor can run in a vacuum
without overheating and if overheating is a problem, if there is any
type of motor that can run in a vacuum?

A permanant magnet DC brushless motor should survive if you can conduct
enough heat away through the case and it's mounting.

You might have problems with the oil in the bearings though. Might boils off
and become thick.

 

[Tim Auton]

scorsi@earthlink.net (Scorsi) wrote:

I got into a debate recently regarding motors and the need for air
cooling,
can somebody confirm wether or not a normal motor can run in a vacuum
without overheating and if overheating is a problem, if there is any
type of motor that can run in a vacuum?

Cooling is a big problem, you need some hefty heatsinks. NASA have
used some largely unmodified Maxon precious metal brushed motors on
Mars (Spirit, Opportunity and Sojourner). It's not a vacuum, but it is
very low pressure (~10 millibars). There are a few mentions in some
NASA papers and on the Maxon site, dig around a bit. You might want to
find out what motors NASA used on its space probes (particularly the
"cheap" Discovery missions).


Tim
--
Copyright, patents and trademarks are government-granted, time-limited monopolies.
Intellectual property does not exist.

 

[Charles Schuler]

"Scorsi" <scorsi@earthlink.net> wrote in message
news:ea7e8dbc.0410111252.5d648332@posting.google.com...

I got into a debate recently regarding motors and the need for air
cooling,
can somebody confirm wether or not a normal motor can run in a vacuum
without overheating and if overheating is a problem, if there is any
type of motor that can run in a vacuum?

thanks Steve

Air is not great as a thermal conductor. A motor can be run in a vacuum by
providing a thermal circuit. Copper is an excellent choice as are other
metals and liquids.

 

[Kryten]

"Dr. Slick" <radio913@aol.com> wrote in message
news:1d15af91.0410121257.7cd31dd0@posting.google.com...

This will power two 40-60 watt lights, with a
motion detector attached.

More info please.

Are these lights going to be moved around much, or stay put?

If they are for camping expeditions, nickel cells are going to be less mass
to haul up hills.
If you take a camper van, then weight isn't so important.
If it lights up an isolated survival hut, it isn't very important at all.

Are lead-acid batteries really the way to go?

Depends how they are being used.

All cell chemistries have their own care requirements.

See http://www.batteryuniversity.com/

Most people just see them as things you charge up and use, like a fuel tank.
It usually doesn't matter if mistreated cells wear out earlier,
if a MP3 player runs out at an inconvenient time.
You can pop into a store and get some new ones (and send old to recyclers).

If your cells are in a radio repeater in the desert, a fortnight camel
journey away, then one should make sure the cells are managed as best as
possible. This example just avoids tedious trips. If your cells are in a
survival shelter, it could save lives.

I bough some solar garden lamps out of curiosity. The instructions recommend
changing the two AA nickel cells every year.

Some charge regulators don't have a low voltage disconnect
circuits, so the battery can be drained if you aren't
careful. If I'm not mistaken, NiMH don't have this
problem, right?

IIRC no cells like being drained as flat as a witch's tit.

How likely is this going to be?

If it is motion detector driven, it would need something moving for a long
time.

Your battery is 36 WHr energy, so 2x50W would drain it in 0.36 Hrs.

I have a mental image of some mischievous Gary Larson bears investigating
your lamps on a woodland cabin.

They can do so for 21.6 minutes, at night.

Which reminds me you could do with a sensor to disable the lights during the
day, so passing bears don't waste the battery energy.

BTW I can send you a copy of the solar cell pages from the A of E.

K.