magnetic field

[John Larkin]

On Wed, 22 Jun 2005 17:58:46 GMT, "CWatters"
<colin.watters@pandoraBOX.be> wrote:

"redbelly" <redbelly98@yahoo.com> wrote in message
news:1119446904.126135.292690@f14g2000cwb.googlegroups.com...
I'm looking for a basic, easy-to-build constant current source to drive
thermistors, nominally at 0.1 mA. The thermistors would be the common
10 k-ohm @ 25 C variety.

Can't get much simpler..

http://zebu.uoregon.edu/~rayfrey/431/notes6.pdf

Ghastly analysis.

John

 

[CWatters]

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:g9hjb15giu7i16g9drhic5ai6m0bj40q81@4ax.com...

On Wed, 22 Jun 2005 17:58:46 GMT, "CWatters"
colin.watters@pandoraBOX.be> wrote:


"redbelly" <redbelly98@yahoo.com> wrote in message
news:1119446904.126135.292690@f14g2000cwb.googlegroups.com...
I'm looking for a basic, easy-to-build constant current source to drive
thermistors, nominally at 0.1 mA. The thermistors would be the common
10 k-ohm @ 25 C variety.

Can't get much simpler..

http://zebu.uoregon.edu/~rayfrey/431/notes6.pdf



Ghastly analysis.

Mine or the one in that paper?

 

[Dave]

"qude" <qmdynamics@yahoo.com> wrote in message
news:1119478533.527521.242700@g14g2000cwa.googlegroups.com...

Dave wrote:


no, its for those who have more money than brains. at the edges the
fields
wrap around so for a small shield like that it would only reduce the
field
slightly for a small distance on the other side of it. even when
shielding
transformer vaults it requires not only doing the whole wall between
the
transformer and the equipment being protected, but a large part of the
floor, ceiling and other walls... preferably wrapping the whole room.

I checked further. Is it possible the plate of cooper or
aluminum can be designed so that (by induction) it can produced
a third waveform, by some kind of circuit. ES or Electrosensitives
have so called neutralizing frequency and these swedish designers
created some kind of copper plate in which when you put it near
any source of magnetic field, it can produce a third waveform
oscilating at a certain frequency. For example. You are tasked
to design such circuit that is powered by induction (with power
requirement even 0.01 mA or less) and oscilating at 20 Hz. How
would you do that?


rfid tags pick up one rf frequency and then use that to power their
circuitry to respond on a different frequency. anti-theft labels in
retail
stores are even simpler and do a similar job but without the smart data
of
an rfid tag. adding a diode or two to a simple loop of wire you can
double
the frequency. you can also generate subharmonics of the exciting
current
with a properly tuned resonant circuit and a diode or two.

Supposed you are to design it with pure copper foil or plate with
no diode. Just wire perhaps imbedded in the copper surface. How
would you do that. Supposed the input frequency is 2 Hz (by
induction). And you want the output magnetic field to be 15 Hz.

i would say its not possible without active components. harmonics and
subharmonics require a non-linear component of some kind like a diode. non
integer frequency multiplication is much harder and would typically require
that the incident field be rectified and used to power some kind of active
signal device like on an rfid tag.

Also is it only magnetic field that can be used for contactless
induction. How about electric field. Can electric field be used
for contactless induction too? The former is Faraday law of
induction, what's the second called (if at all)?

yes, an electric field can be used by having two plates instead of a
coil.
as the electric field changes it will produce a voltage difference
between
the plates that can be used to power devices. i think some power
utilities
use this for 'unpowered' devices on high voltage lines. many years ago
one
of the 'popular' magazines published a free power motor that ran on the
clear air field gradient.

For example you have a battery, let's say a small calculator battery.
It should produce some electric field near it. If you put the copper
tag nearby. What possible induction transfer can occur when it's
clear you didn't put it in between the plates?

the electric field from a small battery is very small and static except for
when you physically move the battery or move the plate around it. but even
then the change in the field is so small it would even be hard to measure
without extremely sensitive instruments. also note that for a static field
source like a battery a current would only be created when it was moving.

 

[John Larkin]

On Wed, 22 Jun 2005 21:35:55 GMT, "CWatters"
<colin.watters@pandoraBOX.be> wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:g9hjb15giu7i16g9drhic5ai6m0bj40q81@4ax.com...
On Wed, 22 Jun 2005 17:58:46 GMT, "CWatters"
colin.watters@pandoraBOX.be> wrote:


"redbelly" <redbelly98@yahoo.com> wrote in message
news:1119446904.126135.292690@f14g2000cwb.googlegroups.com...
I'm looking for a basic, easy-to-build constant current source to drive
thermistors, nominally at 0.1 mA. The thermistors would be the common
10 k-ohm @ 25 C variety.

Can't get much simpler..

http://zebu.uoregon.edu/~rayfrey/431/notes6.pdf



Ghastly analysis.


Mine or the one in that paper?

The paper. Assumes a transistor with infinite beta, infinite collector
impedance, and simple 0.6 volt Vbe. Plus a couple of silly statements.

John

 

[ehsjr]

CWatters wrote:

"redbelly" <redbelly98@yahoo.com> wrote in message
news:1119446904.126135.292690@f14g2000cwb.googlegroups.com...

I'm looking for a basic, easy-to-build constant current source to drive
thermistors, nominally at 0.1 mA. The thermistors would be the common
10 k-ohm @ 25 C variety.


Can't get much simpler..

What about a FET and a source-gate resistor?
Ed

http://zebu.uoregon.edu/~rayfrey/431/notes6.pdf

 

[Don Kelly]

"qude" <qmdynamics@yahoo.com> wrote in message
news:1119468145.845949.250390@f14g2000cwb.googlegroups.com...

Dave wrote:
"qude" <qmdynamics@yahoo.com> wrote in message
news:1119359115.474113.237760@o13g2000cwo.googlegroups.com...


Dave wrote:
"qude" <qmdynamics@yahoo.com> wrote in message
news:1119330643.140180.186910@f14g2000cwb.googlegroups.com...


Dave wrote:
"qude" <qmdynamics@yahoo.com> wrote in message
news:1119273009.300137.199390@z14g2000cwz.googlegroups.com...


CWatters wrote:
"qude" <qmdynamics@yahoo.com> wrote in message
news:1119223515.039007.79790@g47g2000cwa.googlegroups.com...


Suppose you have a current source with magnetic field
-----snip---------

I checked further. Is it possible the plate of cooper or
aluminum can be designed so that (by induction) it can produced
a third waveform, by some kind of circuit. ES or Electrosensitives
have so called neutralizing frequency and these swedish designers
created some kind of copper plate in which when you put it near
any source of magnetic field, it can produce a third waveform
oscilating at a certain frequency. For example. You are tasked
to design such circuit that is powered by induction (with power
requirement even 0.01 mA or less) and oscilating at 20 Hz. How
would you do that?
----------

Induction motors can be modified (essentially open circuited rotor
windings) to give an output that depends on speed. Thus a 60Hz motor with a
synchronous speed of 3600rpm, if driven at 2400 rpm, will have a rotor
frequency of 20Hz. Note that this is not a stationary device. However it is
easier to get the desired frequency by electronic means. A static device
such as some copper sheet will not do this.

However, this has nothing to do with a "third" waveform. Electrosensitivity
is one thing but the "shields" or other devices which claim great
protection, etc, are typically designed to do one thing -extract money from
suckers.

Also is it only magnetic field that can be used for contactless
induction. How about electric field. Can electric field be used
for contactless induction too? The former is Faraday law of
induction, what's the second called (if at all)?

Thanks.
---------

There are electric devices- it is possible to build an electromechanical
device that depends on fields. An electrostatic voltmeter is one such
device. However, the typical energy density of electrostatic devices is much
lower than that of electromagnetic devices so that for a given power level,
the electrostatic device is very much larger (and generally involves rather
nasty voltage levels)
--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer

 

[CWatters]

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:h3sjb1hg3pupqi89176ipfm7gphf328uer@4ax.com...

The paper. Assumes a transistor with infinite beta, infinite collector
impedance, and simple 0.6 volt Vbe. Plus a couple of silly statements.

Oh that. Yes well it depends what level the pupils are at. They aren't
unreasonable assumptions for many applications.

 

[Tony Williams]

In article <1119446904.126135.292690@f14g2000cwb.googlegroups.com>,
redbelly <redbelly98@yahoo.com> wrote:

I'm looking for a basic, easy-to-build constant current source to
drive thermistors, nominally at 0.1 mA. The thermistors would be
the common 10 k-ohm @ 25 C variety.

A good way of stimulating a thermistor is with a
resistor whose value is equal to the thermistor's
resistance at the centre of the req'd temperature
range. This gives an automatic linearisation of the
thermistor's curve over a moderate range. It's not
perfect linearisation, but good enough for most
government jobs.
--+--Vr
|
[Rs] = Rth at T-centre.
|
+---->Vth = Vr*Rth/(Rs+Rth).
|
[Rth]
|
--+--0v

eg. For 25C centre-temperature and 0.1mA,
Rs = 10k and Vr = 2V.

Plug in various values of Rth and look at the
change in Vth per degree. Compare the linearity
of DVth/dC with a 0.1mA constant current stimulus.

Usually there is no convenient Vr, so a higher
voltage can be tapped down with a pair of resistors.

Vsupply ---+---------------+
| |
[R1] [R3]
| |
+-->V(0C) +--------+-->Vth
| | |
[R2] [R4] [Rth]
| | |
0v----+---------------+--------+

Vr = Vsupply*R4/(R3+R4) and Rs = R3*R4/(R3+R4).

eg. If Vsupply is 5V, then R3= 25k and R4= 16.666k.
Nearest preferred values are 24k and 16k, and that
could be viable.

R1 and R2 provide the 0C voltage reference, equal
to Vth when the thermistor is at 0C.

--
Tony Williams.

 

[Alan Adrian]

"siliconmike" <siliconmike@yahoo.com> wrote in message
news:1119557583.922679.177430@g49g2000cwa.googlegroups.com...

I have a pcb with 10 electrical gold plated contacts in a single line
with 5 mil isolation between them.

At any time, a small gold plated copper part "C" makes a very *light*
contact with only one of the contacts.

A *weak* force is responsible to move C over the range of contacts.

Is there some lubricant I can apply on the contacts to reduce the
friction between C and the contacts?

Please don't advise to change this setup as nothing can be changed, for
certain reasons.

This can be done with math... but quantities such as *weak* and *light*
won't get you (or anyone else) there...

Al...

 

[Chris Berry]

Graphite?
cb

 

[Tom Biasi]

"Chris Berry" <christoforos@Notmail.com> wrote in message
news:d9farr$f79$05$1@news.t-online.com...

Graphite?
cb


Chris, graphite is conductive.

 

[Yukio YANO]

siliconmike wrote:

I have a pcb with 10 electrical gold plated contacts in a single line
with 5 mil isolation between them.

At any time, a small gold plated copper part "C" makes a very *light*
contact with only one of the contacts.

A *weak* force is responsible to move C over the range of contacts.

Is there some lubricant I can apply on the contacts to reduce the
friction between C and the contacts?

Please don't advise to change this setup as nothing can be changed, for
certain reasons.

Mike

POLYPHENYLETHER

example SANTOVAC 5
Found in some "Contact Kleaners" as "with PPE"
Extremely Low Vapour Pressure, very stable, inert, great lubricant,
expensive, "same price range as Gold !"
Also available as a "High performance Ulta high Vacuum Grease "Fomblin"

Yukio YANO

 

[The Phantom]

On 23 Jun 2005 13:13:03 -0700, "siliconmike" <siliconmike@yahoo.com> wrote:

I have a pcb with 10 electrical gold plated contacts in a single line
with 5 mil isolation between them.

At any time, a small gold plated copper part "C" makes a very *light*
contact with only one of the contacts.

A *weak* force is responsible to move C over the range of contacts.

Is there some lubricant I can apply on the contacts to reduce the
friction between C and the contacts?

Please don't advise to change this setup as nothing can be changed, for
certain reasons.

Mike

There is a product called "Gold Guard", whose active ingredient is polyphenylether, which
is just for this job.
http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=75&M=CP420E

 

[CWatters]

"siliconmike" <siliconmike@yahoo.com> wrote in message
news:1119557583.922679.177430@g49g2000cwa.googlegroups.com...

I have a pcb with 10 electrical gold plated contacts in a single line
with 5 mil isolation between them.

Contact Cleaner Lubricant

http://www.google.com/search?hl=en&lr=&biw=1014&q=switch+cleaner+contact+lubricant

http://www.computronics.com.au/electrolube/oil_lub/

 

[Chris Berry]

That's one reason why I suggested it.
Not knowing anything about the application itself, it might be a solution.
cb

--
=================================
Some people have something to say... others have to say something!

 

[Ross Herbert]

On 23 Jun 2005 13:13:03 -0700, "siliconmike" <siliconmike@yahoo.com>
wrote:

I have a pcb with 10 electrical gold plated contacts in a single line
with 5 mil isolation between them.

At any time, a small gold plated copper part "C" makes a very *light*
contact with only one of the contacts.

A *weak* force is responsible to move C over the range of contacts.

Is there some lubricant I can apply on the contacts to reduce the
friction between C and the contacts?

Please don't advise to change this setup as nothing can be changed, for
certain reasons.

Mike

Stabilant 22 should do the trick http://www.stabilant.com/techt02h.htm
While not marketed as either a contact cleaner or lubricant, it does
do both. Expensive but good.

 

[Dave]

"qude" <qmdynamics@yahoo.com> wrote in message
news:1119572716.672121.209850@g43g2000cwa.googlegroups.com...

Dave wrote:
"qude" <qmdynamics@yahoo.com> wrote in message
news:1119478533.527521.242700@g14g2000cwa.googlegroups.com...

Dave wrote:


no, its for those who have more money than brains. at the edges
the
fields
wrap around so for a small shield like that it would only reduce
the
field
slightly for a small distance on the other side of it. even when
shielding
transformer vaults it requires not only doing the whole wall
between
the
transformer and the equipment being protected, but a large part of
the
floor, ceiling and other walls... preferably wrapping the whole
room.

I checked further. Is it possible the plate of cooper or
aluminum can be designed so that (by induction) it can produced
a third waveform, by some kind of circuit. ES or Electrosensitives
have so called neutralizing frequency and these swedish designers
created some kind of copper plate in which when you put it near
any source of magnetic field, it can produce a third waveform
oscilating at a certain frequency. For example. You are tasked
to design such circuit that is powered by induction (with power
requirement even 0.01 mA or less) and oscilating at 20 Hz. How
would you do that?


rfid tags pick up one rf frequency and then use that to power their
circuitry to respond on a different frequency. anti-theft labels in
retail
stores are even simpler and do a similar job but without the smart
data
of
an rfid tag. adding a diode or two to a simple loop of wire you can
double
the frequency. you can also generate subharmonics of the exciting
current
with a properly tuned resonant circuit and a diode or two.

Supposed you are to design it with pure copper foil or plate with
no diode. Just wire perhaps imbedded in the copper surface. How
would you do that. Supposed the input frequency is 2 Hz (by
induction). And you want the output magnetic field to be 15 Hz.

i would say its not possible without active components. harmonics and
subharmonics require a non-linear component of some kind like a diode.
non
integer frequency multiplication is much harder and would typically
require
that the incident field be rectified and used to power some kind of
active
signal device like on an rfid tag.


Do you have samples of how a diode can be used in a circuit
to adjust the frequency of the incoming magnetic field and
output another one with different frequency? Do you have any
schematics of the tags that use this principle? Can this also work
when the diode is put inside an IC with copper foil stick on it
as the magnetic field sensor?

a diode can not 'adjust' the frequency. it can rectify an incoming sine
wave which creates all sorts of harmonics that can then be filtered out to
get multiples of the incoming signals frequency. the subharmonics is a bit
tougher, requiring a tuned circuit that is pumped by the rectified incoming
wave at the right rate to produce the desired output.

for the rfid tags you would have to contact one of the manufacturers... i'm
sure they would gladly share their schematics with you.

a diode in an ic is still a diode. to detect a magnetic field you normally
use a loop not a stick.

the electric field from a small battery is very small and static except
for
when you physically move the battery or move the plate around it. but
even
then the change in the field is so small it would even be hard to measure
without extremely sensitive instruments. also note that for a static
field
source like a battery a current would only be created when it was moving.

I know changing magnetic field can induce current. But what law have
you heard that changing electric field can also induce current?
Pls. elaborate. Thanks.

time to go study the basics a bit more my friend... i'm not going to give
you all the answers, if you really want to understand this you need to get a
good book on electromagnetic fields and waves. study maxwell's equations,
especially the one with the dE/dt and =J as parts of it.

 

[CWatters]

<denbigh1974@boltblue.com> wrote in message
news:1119619805.635322.279210@z14g2000cwz.googlegroups.com...

I am looking for cable with two twisted pairs: one which can carry
500mA/12VDC power up to 80 metres and and another which is screened +
twisted and suitable for a RS485 network. The cable will be used for a
variety of applications - CCTV control, a small RS485 network
including a security alarm keypad, lighting control system.

Is there something suitable available in the UK? (I've looked at Cat5
cable but would prefer not to use this for various reasons.)

You don't like the Power Over Ethernet spec? That uses regular CAT 5 for
this sort of thing.

http://www.panduit.com/enabling_technologies/098749.asp
http://www.poweroverethernet.com/

 

[CWatters]

"redbelly" <redbelly98@yahoo.com> wrote in message
news:1119648612.600600.127250@z14g2000cwz.googlegroups.com...

ehsjr wrote:

What about a FET and a source-gate resistor?
Ed

Ed,

Thanks for responding. Could you provide some more details? Perhaps
point to a URL with a schematic. Which leg of the FET is used for the
current source? Where is the power supply to be connected to?

http://www.vishay.com/document/70596/70596.pdf

 

[Watson A.Name - \"Watt Su]

"siliconmike" <siliconmike@yahoo.com> wrote in message
news:1119557583.922679.177430@g49g2000cwa.googlegroups.com...

I have a pcb with 10 electrical gold plated contacts in a single line
with 5 mil isolation between them.

At any time, a small gold plated copper part "C" makes a very *light*
contact with only one of the contacts.

A *weak* force is responsible to move C over the range of contacts.

Is there some lubricant I can apply on the contacts to reduce the
friction between C and the contacts?

Please don't advise to change this setup as nothing can be changed,
for
certain reasons.

I have (or had, I should say) a flashlight that I converted over to
white LEDs. Well, to my surprise, when I shut off the swtch, the LEDs
continued to glow dimly. I came to the conclusion that the grease they
used on the slide switch contacts was somewhat conductive. This wasn't
noticeable on a ragular filament lamp, but the LEDs showed it easily.
So if you do use a lubricant, make sure it is a good insulator.

Mike