Actually, this is no longer the case. After about fifty years just making
WD-40, they wound up merging with the folks that make 3-in-1 oil (another
source of nasty varnish) and some other products.
--scott

Well, there goes the neighborhood. Next they'll be producing cheap Chinese
large diaphragm microphones. BTW, I've only obtained one use from 3-in-1 oil.
What are the other 2?


Scott Fraser

"ScotFraser" wrote in message ...
: Actually, this is no longer the case. After about fifty years just making
: WD-40, they wound up merging with the folks that make 3-in-1 oil (another
: source of nasty varnish) and some other products.
: --scott
:
: Well, there goes the neighborhood. Next they'll be producing cheap Chinese
: large diaphragm microphones. BTW, I've only obtained one use from 3-in-1 oil.
: What are the other 2?
: Scott Fraser

According to the marketing text: lubricates, cleans and prevents rust

"ScotFraser" wrote in message ...
: Actually, this is no longer the case. After about fifty years just making
: WD-40, they wound up merging with the folks that make 3-in-1 oil (another
: source of nasty varnish) and some other products.
: --scott
:
: Well, there goes the neighborhood. Next they'll be producing cheap Chinese
: large diaphragm microphones. BTW, I've only obtained one use from 3-in-1 oil.
: What are the other 2?
: Scott Fraser

According to the marketing text: lubricates, cleans and prevents rust

CatGut wrote:
"Phil Allison" wrote in message ...

[deletions]

: Current can only *flow* in a circuit - ie a closed loop. But a
: voltage ( also called an " emf " in some texts ) will exist between the
: ends of a piece of wire exposed to a varying magnetic field.
: ............ Phil

So are you saying that the voltage will be present without any current?

If a coil is open, a voltage can be induced in it without current flowing.
I think that is what he is saying.

This isn't really a good way of thinking about it, but it'll do. Phil
seems to really obsess on simple theoretical points that don't actually
matter while totally missing the overall picture.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

CatGut wrote:
"Phil Allison" wrote in message ...

[deletions]

: Current can only *flow* in a circuit - ie a closed loop. But a
: voltage ( also called an " emf " in some texts ) will exist between the
: ends of a piece of wire exposed to a varying magnetic field.
: ............ Phil

So are you saying that the voltage will be present without any current?

If a coil is open, a voltage can be induced in it without current flowing.
I think that is what he is saying.

This isn't really a good way of thinking about it, but it'll do. Phil
seems to really obsess on simple theoretical points that don't actually
matter while totally missing the overall picture.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

ScotFraser wrote:

Well, there goes the neighborhood. Next they'll be producing cheap Chinese
large diaphragm microphones. BTW, I've only obtained one use from 3-in-1 oil.
What are the other 2?

I think kids huff it to get high with. Don't know what the third is.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

ScotFraser wrote:

Well, there goes the neighborhood. Next they'll be producing cheap Chinese
large diaphragm microphones. BTW, I've only obtained one use from 3-in-1 oil.
What are the other 2?

I think kids huff it to get high with. Don't know what the third is.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Scott Dorsey" wrote in message ...

I asked:

: So are you saying that the voltage will be present without any current?
:
: If a coil is open, a voltage can be induced in it without current flowing.
: I think that is what he is saying.

I never knew this was possible, but I don't know very much anyway.
I was under the impression that Ohm's law still applied. And if
V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
much and so this seems confusing.

: This isn't really a good way of thinking about it, but it'll do. Phil
: seems to really obsess on simple theoretical points that don't actually
: matter while totally missing the overall picture.
: --scott

Thanks!

"Scott Dorsey" wrote in message ...

I asked:

: So are you saying that the voltage will be present without any current?
:
: If a coil is open, a voltage can be induced in it without current flowing.
: I think that is what he is saying.

I never knew this was possible, but I don't know very much anyway.
I was under the impression that Ohm's law still applied. And if
V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
much and so this seems confusing.

: This isn't really a good way of thinking about it, but it'll do. Phil
: seems to really obsess on simple theoretical points that don't actually
: matter while totally missing the overall picture.
: --scott

Thanks!

CatGut wrote:

"Scott Dorsey" wrote in message ...

I asked:

: So are you saying that the voltage will be present without any current?
:
: If a coil is open, a voltage can be induced in it without current flowing.
: I think that is what he is saying.

I never knew this was possible, but I don't know very much anyway.
I was under the impression that Ohm's law still applied. And if
V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
much and so this seems confusing.

If that reasoning applied to transformers, it would have to apply to
batteries as well. And yet, I think it's pretty clear that batteries
have a voltage even when nothing is hooked up to them; in fact, it's
a chemical property of them.

- Logan

CatGut wrote:

"Scott Dorsey" wrote in message ...

I asked:

: So are you saying that the voltage will be present without any current?
:
: If a coil is open, a voltage can be induced in it without current flowing.
: I think that is what he is saying.

I never knew this was possible, but I don't know very much anyway.
I was under the impression that Ohm's law still applied. And if
V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
much and so this seems confusing.

If that reasoning applied to transformers, it would have to apply to
batteries as well. And yet, I think it's pretty clear that batteries
have a voltage even when nothing is hooked up to them; in fact, it's
a chemical property of them.

- Logan

On Fri, 9 Jul 2004 08:45:56 -0700, "CatGut"
wrote:

"Phil Allison" wrote in message ...

[deletions]

: Current can only *flow* in a circuit - ie a closed loop. But a
: voltage ( also called an " emf " in some texts ) will exist between the
: ends of a piece of wire exposed to a varying magnetic field.
: ............ Phil

So are you saying that the voltage will be present without any current?


To answer this, use a high voltage transformer, and put the ends of
the secondary close to each other. If there is no voltage, they won't
arc. If this were the case, car ignitions wouldn't work.

d
Pearce Consulting
http://www.pearce.uk.com

On Fri, 9 Jul 2004 08:45:56 -0700, "CatGut"
wrote:

"Phil Allison" wrote in message ...

[deletions]

: Current can only *flow* in a circuit - ie a closed loop. But a
: voltage ( also called an " emf " in some texts ) will exist between the
: ends of a piece of wire exposed to a varying magnetic field.
: ............ Phil

So are you saying that the voltage will be present without any current?


To answer this, use a high voltage transformer, and put the ends of
the secondary close to each other. If there is no voltage, they won't
arc. If this were the case, car ignitions wouldn't work.

d
Pearce Consulting
http://www.pearce.uk.com

"Logan Shaw" wrote in message ...

I said:
: I never knew this was possible, but I don't know very much anyway.
: I was under the impression that Ohm's law still applied. And if
: V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
: much and so this seems confusing.
:
: If that reasoning applied to transformers, it would have to apply to
: batteries as well. And yet, I think it's pretty clear that batteries
: have a voltage even when nothing is hooked up to them; in fact, it's
: a chemical property of them.
: - Logan

I thought the chemical reaction in a battery didn't happen until the
circuit was completed and that's what happens when you connect
the voltmeter? Thanks for all your help and info, sorry I'm such
a beginner, but still curious.

"Logan Shaw" wrote in message ...

I said:
: I never knew this was possible, but I don't know very much anyway.
: I was under the impression that Ohm's law still applied. And if
: V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
: much and so this seems confusing.
:
: If that reasoning applied to transformers, it would have to apply to
: batteries as well. And yet, I think it's pretty clear that batteries
: have a voltage even when nothing is hooked up to them; in fact, it's
: a chemical property of them.
: - Logan

I thought the chemical reaction in a battery didn't happen until the
circuit was completed and that's what happens when you connect
the voltmeter? Thanks for all your help and info, sorry I'm such
a beginner, but still curious.

** Currents have direction - voltages have polarity.



ok, got that. but what about when the cable runs next to an AC
transformer? that's the part that i don't quite get -- i don't see
how it could induce current in one conductor in opposite direction
with
the other. could you explain?


** Like many folk - you have not grasped the concept of what a circuit
is. Current can only *flow* in a circuit - ie a closed loop. But a
voltage ( also called an " emf " in some texts ) will exist between the
ends of a piece of wire exposed to a varying magnetic field.


ok, i can accept that. but as soon as i put an impedance across the
terminals, including a voltmeter, current flows. which is it? i'm
going insane! is it voltage or current? current or voltage?

i suppose elecrtic charge would be the pc term.

thanks, phil. i understand that so much of what we use is an accepted
vocabulary, so these discussions get confusing -- like that assumption
that electricity flows from + to - . . .

cheers,
chris deckard
saint louismo

** Currents have direction - voltages have polarity.



ok, got that. but what about when the cable runs next to an AC
transformer? that's the part that i don't quite get -- i don't see
how it could induce current in one conductor in opposite direction
with
the other. could you explain?


** Like many folk - you have not grasped the concept of what a circuit
is. Current can only *flow* in a circuit - ie a closed loop. But a
voltage ( also called an " emf " in some texts ) will exist between the
ends of a piece of wire exposed to a varying magnetic field.


ok, i can accept that. but as soon as i put an impedance across the
terminals, including a voltmeter, current flows. which is it? i'm
going insane! is it voltage or current? current or voltage?

i suppose elecrtic charge would be the pc term.

thanks, phil. i understand that so much of what we use is an accepted
vocabulary, so these discussions get confusing -- like that assumption
that electricity flows from + to - . . .

cheers,
chris deckard
saint louismo

In article ,
"CatGut" wrote:

"Logan Shaw" wrote in message
...

I said:
: I never knew this was possible, but I don't know very much anyway.
: I was under the impression that Ohm's law still applied. And if
: V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
: much and so this seems confusing.
:
: If that reasoning applied to transformers, it would have to apply to
: batteries as well. And yet, I think it's pretty clear that batteries
: have a voltage even when nothing is hooked up to them; in fact, it's
: a chemical property of them.
: - Logan

I thought the chemical reaction in a battery didn't happen until the
circuit was completed and that's what happens when you connect
the voltmeter? Thanks for all your help and info, sorry I'm such
a beginner, but still curious.



Were that true, there would be no measurable voltage from a battery that was not
part of a closed circuit. The chemical half-cells produce a voltage regardless
of whether they are generating a current or not. Charge, which when moving is
referred to as current, can also accumulate on an insulated object and produce
quite high voltages without moving, hence the term "static" charge.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

In article ,
"CatGut" wrote:

"Logan Shaw" wrote in message
...

I said:
: I never knew this was possible, but I don't know very much anyway.
: I was under the impression that Ohm's law still applied. And if
: V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
: much and so this seems confusing.
:
: If that reasoning applied to transformers, it would have to apply to
: batteries as well. And yet, I think it's pretty clear that batteries
: have a voltage even when nothing is hooked up to them; in fact, it's
: a chemical property of them.
: - Logan

I thought the chemical reaction in a battery didn't happen until the
circuit was completed and that's what happens when you connect
the voltmeter? Thanks for all your help and info, sorry I'm such
a beginner, but still curious.



Were that true, there would be no measurable voltage from a battery that was not
part of a closed circuit. The chemical half-cells produce a voltage regardless
of whether they are generating a current or not. Charge, which when moving is
referred to as current, can also accumulate on an insulated object and produce
quite high voltages without moving, hence the term "static" charge.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

"Scott Dorsey" wrote in message
...
ScotFraser wrote:

Well, there goes the neighborhood. Next they'll be producing cheap
Chinese
large diaphragm microphones. BTW, I've only obtained one use from 3-in-1
oil.
What are the other 2?

I think kids huff it to get high with. Don't know what the third is.
--scott

Ice cream topping.

Glenn D.

"Scott Dorsey" wrote in message
...
ScotFraser wrote:

Well, there goes the neighborhood. Next they'll be producing cheap
Chinese
large diaphragm microphones. BTW, I've only obtained one use from 3-in-1
oil.
What are the other 2?

I think kids huff it to get high with. Don't know what the third is.
--scott

Ice cream topping.

Glenn D.

"Jay Kadis" wrote in message ...
: In article ,
: "CatGut" wrote:

[deletions]
I said:
: I thought the chemical reaction in a battery didn't happen until the
: circuit was completed and that's what happens when you connect
: the voltmeter? Thanks for all your help and info, sorry I'm such
: a beginner, but still curious.
:
: Were that true, there would be no measurable voltage from a battery that was not
: part of a closed circuit. The chemical half-cells produce a voltage regardless
: of whether they are generating a current or not. Charge, which when moving is
: referred to as current, can also accumulate on an insulated object and produce
: quite high voltages without moving, hence the term "static" charge.
: -Jay

Ok, I can understand that. So a static charge has no current until
it's discharged, correct? And when you measure the voltage, you
complete the circuit, hence current flows at that time. And Ohm's
law is only regarding a circuit.

And what does this have to do with crosstalk and common mode
rejection?

Test papers will be returned on Monday :^)

"Jay Kadis" wrote in message ...
: In article ,
: "CatGut" wrote:

[deletions]
I said:
: I thought the chemical reaction in a battery didn't happen until the
: circuit was completed and that's what happens when you connect
: the voltmeter? Thanks for all your help and info, sorry I'm such
: a beginner, but still curious.
:
: Were that true, there would be no measurable voltage from a battery that was not
: part of a closed circuit. The chemical half-cells produce a voltage regardless
: of whether they are generating a current or not. Charge, which when moving is
: referred to as current, can also accumulate on an insulated object and produce
: quite high voltages without moving, hence the term "static" charge.
: -Jay

Ok, I can understand that. So a static charge has no current until
it's discharged, correct? And when you measure the voltage, you
complete the circuit, hence current flows at that time. And Ohm's
law is only regarding a circuit.

And what does this have to do with crosstalk and common mode
rejection?

Test papers will be returned on Monday :^)

mr c deckard wrote:
ok, i can accept that. but as soon as i put an impedance across the
terminals, including a voltmeter, current flows. which is it? i'm
going insane! is it voltage or current? current or voltage?

You just explained it perfectly. Induction causes a voltage. If
there were a path for the electricity to flow along (a circuit),
then there would be current.

i suppose elecrtic charge would be the pc term.

Electric charge is, in effect, an imbalance between positive and
negative charges (normally protons and electrons). In a transformer
coil suddenly subject to a magnetic field, the number of electrons
hasn't changed, so there is no change in the charge. Instead,
it's just that the magnetic field makes the electrons want to move
in a certain direction. If there is nowhere for them to go, they
won't move. If there is, they will, and the amount they move will
be related to how much they are impeded along the path they travel
(which is just another way of saying Ohm's Law).

- Logan

mr c deckard wrote:
ok, i can accept that. but as soon as i put an impedance across the
terminals, including a voltmeter, current flows. which is it? i'm
going insane! is it voltage or current? current or voltage?

You just explained it perfectly. Induction causes a voltage. If
there were a path for the electricity to flow along (a circuit),
then there would be current.

i suppose elecrtic charge would be the pc term.

Electric charge is, in effect, an imbalance between positive and
negative charges (normally protons and electrons). In a transformer
coil suddenly subject to a magnetic field, the number of electrons
hasn't changed, so there is no change in the charge. Instead,
it's just that the magnetic field makes the electrons want to move
in a certain direction. If there is nowhere for them to go, they
won't move. If there is, they will, and the amount they move will
be related to how much they are impeded along the path they travel
(which is just another way of saying Ohm's Law).

- Logan

In article ,
"CatGut" wrote:

"Jay Kadis" wrote in message
...
: In article ,
: "CatGut" wrote:

[deletions]
I said:
: I thought the chemical reaction in a battery didn't happen until the
: circuit was completed and that's what happens when you connect
: the voltmeter? Thanks for all your help and info, sorry I'm such
: a beginner, but still curious.
:
: Were that true, there would be no measurable voltage from a battery that
: was not
: part of a closed circuit. The chemical half-cells produce a voltage
: regardless
: of whether they are generating a current or not. Charge, which when moving
: is
: referred to as current, can also accumulate on an insulated object and
: produce
: quite high voltages without moving, hence the term "static" charge.
: -Jay

Ok, I can understand that. So a static charge has no current until
it's discharged, correct? And when you measure the voltage, you
complete the circuit, hence current flows at that time. And Ohm's
law is only regarding a circuit.

And what does this have to do with crosstalk and common mode
rejection?


Since conductors are coupled to other conductors both inductively and
capacitively, it is possible for signals from one circuit to appear in another
nearby circuit. This is considered to be cross-talk. When the two conductors
of a "balanced" (differential) line are properly twisted, they will see very
nearly the same coupled voltage in each wire and that will be attenuated by the
CMRR of the input, which rejects any signal common to both conductors while
amplifying the difference between them.

Test papers will be returned on Monday :^)

Grades will be kept confidential.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

In article ,
"CatGut" wrote:

"Jay Kadis" wrote in message
...
: In article ,
: "CatGut" wrote:

[deletions]
I said:
: I thought the chemical reaction in a battery didn't happen until the
: circuit was completed and that's what happens when you connect
: the voltmeter? Thanks for all your help and info, sorry I'm such
: a beginner, but still curious.
:
: Were that true, there would be no measurable voltage from a battery that
: was not
: part of a closed circuit. The chemical half-cells produce a voltage
: regardless
: of whether they are generating a current or not. Charge, which when moving
: is
: referred to as current, can also accumulate on an insulated object and
: produce
: quite high voltages without moving, hence the term "static" charge.
: -Jay

Ok, I can understand that. So a static charge has no current until
it's discharged, correct? And when you measure the voltage, you
complete the circuit, hence current flows at that time. And Ohm's
law is only regarding a circuit.

And what does this have to do with crosstalk and common mode
rejection?


Since conductors are coupled to other conductors both inductively and
capacitively, it is possible for signals from one circuit to appear in another
nearby circuit. This is considered to be cross-talk. When the two conductors
of a "balanced" (differential) line are properly twisted, they will see very
nearly the same coupled voltage in each wire and that will be attenuated by the
CMRR of the input, which rejects any signal common to both conductors while
amplifying the difference between them.

Test papers will be returned on Monday :^)

Grades will be kept confidential.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x-------- http://ccrma-www.stanford.edu/~jay/ ----------x

In article ,
says... [spewing of venom snipped]
Okay, I should've known it was flame-bait; I won't deal with
this Phil thing anymore.
---Michael (of APP)...

In article ,
says... [spewing of venom snipped]
Okay, I should've known it was flame-bait; I won't deal with
this Phil thing anymore.
---Michael (of APP)...

"Jay Kadis" wrote in message ...
[deletions]

I said:
: And what does this have to do with crosstalk and common mode
: rejection?
:
: Since conductors are coupled to other conductors both inductively and
: capacitively, it is possible for signals from one circuit to appear in another
: nearby circuit. This is considered to be cross-talk. When the two conductors
: of a "balanced" (differential) line are properly twisted, they will see very
: nearly the same coupled voltage in each wire and that will be attenuated by the
: CMRR of the input, which rejects any signal common to both conductors while

CMRR = common mode rejection ratio

: amplifying the difference between them.
:
: Test papers will be returned on Monday :^)
: Grades will be kept confidential.

You fot an 'A'... oops...

: -Jay

Thanks for all the info guys. I get it...

"Jay Kadis" wrote in message ...
[deletions]

I said:
: And what does this have to do with crosstalk and common mode
: rejection?
:
: Since conductors are coupled to other conductors both inductively and
: capacitively, it is possible for signals from one circuit to appear in another
: nearby circuit. This is considered to be cross-talk. When the two conductors
: of a "balanced" (differential) line are properly twisted, they will see very
: nearly the same coupled voltage in each wire and that will be attenuated by the
: CMRR of the input, which rejects any signal common to both conductors while

CMRR = common mode rejection ratio

: amplifying the difference between them.
:
: Test papers will be returned on Monday :^)
: Grades will be kept confidential.

You fot an 'A'... oops...

: -Jay

Thanks for all the info guys. I get it...

In article CatGut wrote:
: "Scott Dorsey" wrote in message ...

: I asked:

: : So are you saying that the voltage will be present without any current?
: :
: : If a coil is open, a voltage can be induced in it without current flowing.
: : I think that is what he is saying.

: I never knew this was possible, but I don't know very much anyway.
: I was under the impression that Ohm's law still applied. And if
: V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
: much and so this seems confusing.

Now that the smoke has cleared a bit and the shouting died down, I will
de-lurk and attempt a non-calculus "common-sense" explanation.

Time-varying magnetic fields such as exist around AC power lines which
are under load (AC current must be flowing) generate electric fields
whose characteristics around any closed path (loop) obey "Faraday's
law of magnetic induction", which basically says that the "electromotive
force" around any closed path is proportional to the rate of change of
the total magnetic field lines which pass through the loop defined by
that path. Read that again until you can visualize it. "Electromotive
force" is indeed measured in volts, and is (plug your ears for a moment
if calculus scares you) is the "integral" (accumulation, sort of) of
the electric field (volts per unit distance) along the path (units
of distance) around the loop in question.

Now, let's place a conductor almost but not quite all the way around
our path. We all agree that if there is any electric field within
a conductor current must flow (the charges in the conductor are
forced to follow the electric field). And momentarily (and for a
modest-sized experiment here "momentarily" is approximately the time
it takes light to travel around the path) current does flow. It
stops when the distribution of charges within the conductor
exactly cancels the electric fields within the conductor.

But... and this is a big but!!!... Faraday's law must still apply.
This means that the entire emf around our path must be crowded
into the little gap in the loop which we left. If we measure this
with a voltmeter (ignore the tiny current which flows in most practical
voltmeters and assume we are not enlarging the "loop" with our
probe wires) we *must* see a voltage --- and indeed we do.

Now lets weld the ends of the wire together into a perfectly uniform
ring. Now a current will flow in the loop, as long as the magnetic
feild keeps changing. Two interesting things happen when this
occurs. Because a current is flowing in the conductor, there can
now exist an electric field in the conductor (think ohm's law,
only more general) because the charges will be at any moment in time
uniformly distributed around the ring so they cannot cancel the
electric field postulated by Faraday's law. If one now probes
any particular pair of points on our ring with our perfect
voltmeter, we will see no voltage. Yet a current is indeed flowing.

Now the other interesting thing that happens is that the current
flowing in the wire will *itself* generate a magnetic field through
the loop which will tend to cancel the original magnetic field.
Indeed a perfect conductor loop will allow no net change in the
magnetic field linking it as the currents necessary to exactly
counteract the change will necessarily be produced.

Sooo, do changing magnetic fields induce voltages or currents?
Theoretically speaking, the laws say "voltage", at least in terms
of "emf" and "electric fields" around a closed path. And they
indeed induce voltages across gaps in otherwise conducting loops.
But they also practically induce currents in closed loops
linked by the fields.

Now lets talk about audio (and we'll talk about balanced audio
here). If the signal source is an element connected solely
between pin2 and pin3 and the receiving amplifier is a
marvelous widget which is solely connected between pin 2 and
pin 3 and is influenced by nothing other than the difference
between these two pins (and let's for grins suggest that the
amplifier input is high impedance relative to the conductor
so we can call it a "gap"), we have a loop which can be affected
by changing stray magnetic fields. Any fields linking the loop
will induce a voltage at the "gap" and thus will be seen by the
perfect differential receiving amplifier.

So what do we do to minimize this? First, we make the loop area
as small as possible to minimize the field that can link the loop.
This we do by routing pin 2 and pin 3 together through a
multi-conductor cable. Second, we wrap the pair of conductors in
a conductive shield (which we do for other reasons but it helps
a bit here, too). Any magnetic field which tries to penetrate
the conductive sheet to link the loop inside will generate
currents in the shield (around little circular paths in the
sheet) which oppose and partially cancel the field, reducing
the net field strength (and its effect) inside. And finally,
we *twist* the pair of wires together. This has the effect
of making the changing field link each bit of loop *backwards* to
the bit a few inches away, which *subtracts* the effect of
the adjacent bit. Remember that the emf induced in the
loop is proportional to the *net* rate of change of the
magnetic field linking the *entire* loop and magnetic fields,
just like electric fields, voltages and currents, have direction.

OK, I've got to quit. All of this applies as well to
"ground loops", etc., but I am out of time and communication
energy for the moment. There are a lot of "but what about..."
side trips that hopefully others can help with...

relurking

Bob Miller
Agilent Technologies
(remove spammenot to email)

In article CatGut wrote:
: "Scott Dorsey" wrote in message ...

: I asked:

: : So are you saying that the voltage will be present without any current?
: :
: : If a coil is open, a voltage can be induced in it without current flowing.
: : I think that is what he is saying.

: I never knew this was possible, but I don't know very much anyway.
: I was under the impression that Ohm's law still applied. And if
: V = I x R, and if I = 0, then V = 0 too. Like I said, I don't know
: much and so this seems confusing.

Now that the smoke has cleared a bit and the shouting died down, I will
de-lurk and attempt a non-calculus "common-sense" explanation.

Time-varying magnetic fields such as exist around AC power lines which
are under load (AC current must be flowing) generate electric fields
whose characteristics around any closed path (loop) obey "Faraday's
law of magnetic induction", which basically says that the "electromotive
force" around any closed path is proportional to the rate of change of
the total magnetic field lines which pass through the loop defined by
that path. Read that again until you can visualize it. "Electromotive
force" is indeed measured in volts, and is (plug your ears for a moment
if calculus scares you) is the "integral" (accumulation, sort of) of
the electric field (volts per unit distance) along the path (units
of distance) around the loop in question.

Now, let's place a conductor almost but not quite all the way around
our path. We all agree that if there is any electric field within
a conductor current must flow (the charges in the conductor are
forced to follow the electric field). And momentarily (and for a
modest-sized experiment here "momentarily" is approximately the time
it takes light to travel around the path) current does flow. It
stops when the distribution of charges within the conductor
exactly cancels the electric fields within the conductor.

But... and this is a big but!!!... Faraday's law must still apply.
This means that the entire emf around our path must be crowded
into the little gap in the loop which we left. If we measure this
with a voltmeter (ignore the tiny current which flows in most practical
voltmeters and assume we are not enlarging the "loop" with our
probe wires) we *must* see a voltage --- and indeed we do.

Now lets weld the ends of the wire together into a perfectly uniform
ring. Now a current will flow in the loop, as long as the magnetic
feild keeps changing. Two interesting things happen when this
occurs. Because a current is flowing in the conductor, there can
now exist an electric field in the conductor (think ohm's law,
only more general) because the charges will be at any moment in time
uniformly distributed around the ring so they cannot cancel the
electric field postulated by Faraday's law. If one now probes
any particular pair of points on our ring with our perfect
voltmeter, we will see no voltage. Yet a current is indeed flowing.

Now the other interesting thing that happens is that the current
flowing in the wire will *itself* generate a magnetic field through
the loop which will tend to cancel the original magnetic field.
Indeed a perfect conductor loop will allow no net change in the
magnetic field linking it as the currents necessary to exactly
counteract the change will necessarily be produced.

Sooo, do changing magnetic fields induce voltages or currents?
Theoretically speaking, the laws say "voltage", at least in terms
of "emf" and "electric fields" around a closed path. And they
indeed induce voltages across gaps in otherwise conducting loops.
But they also practically induce currents in closed loops
linked by the fields.

Now lets talk about audio (and we'll talk about balanced audio
here). If the signal source is an element connected solely
between pin2 and pin3 and the receiving amplifier is a
marvelous widget which is solely connected between pin 2 and
pin 3 and is influenced by nothing other than the difference
between these two pins (and let's for grins suggest that the
amplifier input is high impedance relative to the conductor
so we can call it a "gap"), we have a loop which can be affected
by changing stray magnetic fields. Any fields linking the loop
will induce a voltage at the "gap" and thus will be seen by the
perfect differential receiving amplifier.

So what do we do to minimize this? First, we make the loop area
as small as possible to minimize the field that can link the loop.
This we do by routing pin 2 and pin 3 together through a
multi-conductor cable. Second, we wrap the pair of conductors in
a conductive shield (which we do for other reasons but it helps
a bit here, too). Any magnetic field which tries to penetrate
the conductive sheet to link the loop inside will generate
currents in the shield (around little circular paths in the
sheet) which oppose and partially cancel the field, reducing
the net field strength (and its effect) inside. And finally,
we *twist* the pair of wires together. This has the effect
of making the changing field link each bit of loop *backwards* to
the bit a few inches away, which *subtracts* the effect of
the adjacent bit. Remember that the emf induced in the
loop is proportional to the *net* rate of change of the
magnetic field linking the *entire* loop and magnetic fields,
just like electric fields, voltages and currents, have direction.

OK, I've got to quit. All of this applies as well to
"ground loops", etc., but I am out of time and communication
energy for the moment. There are a lot of "but what about..."
side trips that hopefully others can help with...

relurking

Bob Miller
Agilent Technologies
(remove spammenot to email)

Phil Allison wrote:

** Bet you never eat Kentucky Fried either - those 11 secret herbs
and spices are a REAL worry !!

I do occasionally. But I wouldn't dream of sticking it in a potentiometer.

geoff

Phil Allison wrote:

** Bet you never eat Kentucky Fried either - those 11 secret herbs
and spices are a REAL worry !!

I do occasionally. But I wouldn't dream of sticking it in a potentiometer.

geoff

I've actually seen a couple people use WD-40 on a sctachy pot. I've
never tried it myself for fear of gunking it up but it did make it
quiet. I don't know what happened later. Is it as bad as I think it
would be?? I'm afraid to try it on anything I own.


bob






I used it on an entire board once. It was good for about three months and then
was worse than ever.

I cleaned it out with DeOxit and haven't had a problem since.

I don't care what it's made of, WD40 is not good on potentiometers.

Not a very good lubricant either, ( the can doesn't say that it is a lubricant,
either) but works fine as a grease remover.

I believe that WD stands for water Displacement and for that, it works very
well.





Richard H. Kuschel
"I canna change the law of physics."-----Scotty

I've actually seen a couple people use WD-40 on a sctachy pot. I've
never tried it myself for fear of gunking it up but it did make it
quiet. I don't know what happened later. Is it as bad as I think it
would be?? I'm afraid to try it on anything I own.


bob






I used it on an entire board once. It was good for about three months and then
was worse than ever.

I cleaned it out with DeOxit and haven't had a problem since.

I don't care what it's made of, WD40 is not good on potentiometers.

Not a very good lubricant either, ( the can doesn't say that it is a lubricant,
either) but works fine as a grease remover.

I believe that WD stands for water Displacement and for that, it works very
well.





Richard H. Kuschel
"I canna change the law of physics."-----Scotty

On Fri, 9 Jul 2004 21:08:08 +0000 (UTC),
wrote:

excellent and clear explanation snipped

Just two comments. One: the following point is critical and
might be punched up.

Now the other interesting thing that happens is that the current
flowing in the wire will *itself* generate a magnetic field through
the loop which will tend to cancel the original magnetic field.
Indeed a perfect conductor loop will allow no net change in the
magnetic field linking it as the currents necessary to exactly
counteract the change will necessarily be produced.

Forces "act" to balance themselves, and your point if amplified
will go a long way toward removing the current/ voltage
confusion.


And two: this next can easily be misread. I did myself the first
couple times, interpreting it to mean that the *twisting*
causes a net subtraction. That's not correct and not what
you actually mean.

And finally,
we *twist* the pair of wires together. This has the effect
of making the changing field link each bit of loop *backwards* to
the bit a few inches away, which *subtracts* the effect of
the adjacent bit.

And, the subtraction occurs at the differential receiving end,
just to be picky picky.

Thanks, and I hope you'll de-cloak again and amplify,

Chris Hornbeck
"That's where my forebears came from;
well, three of them anyway.
Who's been sleeping in my porridge?"
-Flanders and Swann

On Fri, 9 Jul 2004 21:08:08 +0000 (UTC),
wrote:

excellent and clear explanation snipped

Just two comments. One: the following point is critical and
might be punched up.

Now the other interesting thing that happens is that the current
flowing in the wire will *itself* generate a magnetic field through
the loop which will tend to cancel the original magnetic field.
Indeed a perfect conductor loop will allow no net change in the
magnetic field linking it as the currents necessary to exactly
counteract the change will necessarily be produced.

Forces "act" to balance themselves, and your point if amplified
will go a long way toward removing the current/ voltage
confusion.


And two: this next can easily be misread. I did myself the first
couple times, interpreting it to mean that the *twisting*
causes a net subtraction. That's not correct and not what
you actually mean.

And finally,
we *twist* the pair of wires together. This has the effect
of making the changing field link each bit of loop *backwards* to
the bit a few inches away, which *subtracts* the effect of
the adjacent bit.

And, the subtraction occurs at the differential receiving end,
just to be picky picky.

Thanks, and I hope you'll de-cloak again and amplify,

Chris Hornbeck
"That's where my forebears came from;
well, three of them anyway.
Who's been sleeping in my porridge?"
-Flanders and Swann

In article , rickpv8945
@aol.com says...

I've actually seen a couple people use WD-40 on a sctachy pot. I've
never tried it myself for fear of gunking it up but it did make it
quiet. I don't know what happened later. Is it as bad as I think it
would be?? I'm afraid to try it on anything I own.


bob






I used it on an entire board once. It was good for about three months and then
was worse than ever.

I cleaned it out with DeOxit and haven't had a problem since.

I don't care what it's made of, WD40 is not good on potentiometers.

Not a very good lubricant either, ( the can doesn't say that it is a lubricant,
either) but works fine as a grease remover.

That's what I was told also. When I look at the web site for the WD-40
Big Blast can:

www.wd40.com/Brands/wd40_big_glast.html

The can states:

"Cleans and Protects
Lubricates
Drives Out Moisture
Prevents Rust
Keeps Dirt and Debris
from Sticking"



I believe that WD stands for water Displacement and for that, it works very
well.





Richard H. Kuschel
"I canna change the law of physics."-----Scotty

I know we didn't use it in any electronic equipment I worked on in my 35
+ electronics career, unless it was for mechanical latches, screws etc.
--
I. Care
Address fake until
the spam goes away