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"Invisible fence" for dogs
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Bob Engelhardt
Mar 10, 2016, 9:23:49 PM3/10/16
to
I have installed such a fence and it works fine. It is a single
conductor wire that completely encloses the area - i.e., both ends of
the wire are connected to the transmitter. It transmits an RF signal
that is received by the dog's collar and corrects him when he gets too
close to the wire/boundary.
My problem is that there is a section of the boundary where I don't want
the correction given. "Easy", I thought, "I'll just use coax in that
section and the signal will be shielded away". Well, the coax doesn't
shield/suppress it - the collar still reacts. This is with both ends of
the shield grounded. (The shield is a heavy layer of foil under a braid.)
What gives? Is there a better way to suppress the signal?
I don't know the frequency used, but I could look at it with my scope,
assuming the scope operates that high (it's a Tek 465B).
Thanks,
Bob
conductor wire that completely encloses the area - i.e., both ends of
the wire are connected to the transmitter. It transmits an RF signal
that is received by the dog's collar and corrects him when he gets too
close to the wire/boundary.
My problem is that there is a section of the boundary where I don't want
the correction given. "Easy", I thought, "I'll just use coax in that
section and the signal will be shielded away". Well, the coax doesn't
shield/suppress it - the collar still reacts. This is with both ends of
the shield grounded. (The shield is a heavy layer of foil under a braid.)
What gives? Is there a better way to suppress the signal?
I don't know the frequency used, but I could look at it with my scope,
assuming the scope operates that high (it's a Tek 465B).
Thanks,
Bob
Rheilly Phoull
Mar 10, 2016, 9:39:54 PM3/10/16
to
Winfield Hill
Mar 10, 2016, 10:05:25 PM3/10/16
to
Bob Engelhardt wrote...
but rather a medium-frequency AC current flowing through the
wire, creating a simple magnetic field surrounding the wire,
that's sensed by the electronic shock collar. Sorry, you
cannot use electrostatic shields to block magnetic fields.
I don't know if its possible to have a fixed opening. Yes,
you can create a non-functioning section: simply run the wire
back on itself, creating a cancelling field. Twisting the
two wires helps. Ahem, your problem is then what to do
with this folded-back wire, to continue on a complete-loop
path around your closed-in area, which blocks in the animal.
--
Thanks,
- Win
>
> I have installed such a fence and it works fine. It is a single
> conductor wire that completely encloses the area - i.e., both ends of
> the wire are connected to the transmitter. It transmits an RF signal
> that is received by the dog's collar and corrects him when he gets too
> close to the wire/boundary.
>
> My problem is that there is a section of the boundary where I don't want
> the correction given. "Easy", I thought, "I'll just use coax in that
> section and the signal will be shielded away". Well, the coax doesn't
> shield/suppress it - the collar still reacts. This is with both ends of
> the shield grounded. (The shield is a heavy layer of foil under a braid.)
>
> What gives? Is there a better way to suppress the signal?
You don't mention the brand, but it's likely not an RF system,
> I have installed such a fence and it works fine. It is a single
> conductor wire that completely encloses the area - i.e., both ends of
> the wire are connected to the transmitter. It transmits an RF signal
> that is received by the dog's collar and corrects him when he gets too
> close to the wire/boundary.
>
> My problem is that there is a section of the boundary where I don't want
> the correction given. "Easy", I thought, "I'll just use coax in that
> section and the signal will be shielded away". Well, the coax doesn't
> shield/suppress it - the collar still reacts. This is with both ends of
> the shield grounded. (The shield is a heavy layer of foil under a braid.)
>
> What gives? Is there a better way to suppress the signal?
but rather a medium-frequency AC current flowing through the
wire, creating a simple magnetic field surrounding the wire,
that's sensed by the electronic shock collar. Sorry, you
cannot use electrostatic shields to block magnetic fields.
I don't know if its possible to have a fixed opening. Yes,
you can create a non-functioning section: simply run the wire
back on itself, creating a cancelling field. Twisting the
two wires helps. Ahem, your problem is then what to do
with this folded-back wire, to continue on a complete-loop
path around your closed-in area, which blocks in the animal.
--
Thanks,
- Win
Carl Ijames
Mar 10, 2016, 10:36:09 PM3/10/16
to
"Winfield Hill" wrote in message news:nbtck...@drn.newsguy.com...
============================================================
Wild idea, but if it's detecting the magnetic field could you run the wire
through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe that
would provide enough shielding to give you a 3-4' door. I'm thinking 3/4"
pipe, or maybe 1".
-----
Regards,
Carl Ijames
Wild idea, but if it's detecting the magnetic field could you run the wire
through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe that
would provide enough shielding to give you a 3-4' door. I'm thinking 3/4"
pipe, or maybe 1".
-----
Regards,
Carl Ijames
legg
Mar 10, 2016, 10:51:52 PM3/10/16
to
RL
Phil Allison
Mar 10, 2016, 10:53:24 PM3/10/16
to
FYI:
Invisible dog fences are very controversial with many dog owners who have tried them strongly recommending against their use.
https://paws4udogs.wordpress.com/2013/06/10/should-i-get-an-invisible-fence/
In NSW where I liven their use is illegal ( under the Prevention of Cruelty to Animals Act, 2012 ) unless accompanied by a real fence that effectively contains the animal.
.... Phil
Bob Engelhardt
Mar 10, 2016, 11:19:25 PM3/10/16
to
On 3/10/2016 10:05 PM, Winfield Hill wrote:
> You don't mention the brand, but it's likely not an RF system,
> but rather a medium-frequency AC current flowing through the
> wire, creating a simple magnetic field surrounding the wire,
> that's sensed by the electronic shock collar. Sorry, you
> cannot use electrostatic shields to block magnetic fields.
It's a PetSafe brand, Yardmax model. I found a number of secondary
> You don't mention the brand, but it's likely not an RF system,
> but rather a medium-frequency AC current flowing through the
> wire, creating a simple magnetic field surrounding the wire,
> that's sensed by the electronic shock collar. Sorry, you
> cannot use electrostatic shields to block magnetic fields.
sources that said it did use a magnetic field. That's also consistent
with it needing both ends of the loop wire connected.
>
> I don't know if its possible to have a fixed opening. Yes,
> you can create a non-functioning section: simply run the wire
> back on itself, creating a cancelling field. Twisting the
> two wires helps. Ahem, your problem is then what to do
> with this folded-back wire, to continue on a complete-loop
> path around your closed-in area, which blocks in the animal.
to create an opening by raising the wire there. It will be a question
of how high it has to be.
Thanks,
Bob
Jasen Betts
Mar 11, 2016, 1:31:25 AM3/11/16
to
On 2016-03-11, Bob Engelhardt <BobEng...@comcast.net> wrote:
> I have installed such a fence and it works fine. It is a single
> conductor wire that completely encloses the area - i.e., both ends of
> the wire are connected to the transmitter. It transmits an RF signal
> that is received by the dog's collar and corrects him when he gets too
> close to the wire/boundary.
>
> My problem is that there is a section of the boundary where I don't want
> the correction given. "Easy", I thought, "I'll just use coax in that
> section and the signal will be shielded away". Well, the coax doesn't
> shield/suppress it - the collar still reacts. This is with both ends of
> the shield grounded. (The shield is a heavy layer of foil under a braid.)
>
> What gives? Is there a better way to suppress the signal?
it's a loop. it's also near-field, so you're picking up the magnetic
> I have installed such a fence and it works fine. It is a single
> conductor wire that completely encloses the area - i.e., both ends of
> the wire are connected to the transmitter. It transmits an RF signal
> that is received by the dog's collar and corrects him when he gets too
> close to the wire/boundary.
>
> My problem is that there is a section of the boundary where I don't want
> the correction given. "Easy", I thought, "I'll just use coax in that
> section and the signal will be shielded away". Well, the coax doesn't
> shield/suppress it - the collar still reacts. This is with both ends of
> the shield grounded. (The shield is a heavy layer of foil under a braid.)
>
> What gives? Is there a better way to suppress the signal?
field coax will give electrostatic shielding, but not magnetic.
dig a deep trench or make a high catenary so that the dog need
not approach the wire. or assuming the breach is for your back
door run the wire along the roof-line or across the basement floor.
or you may find that a large metal plate gives suffifient shielding.
> I don't know the frequency used, but I could look at it with my scope,
> assuming the scope operates that high (it's a Tek 465B).
--
\_(ツ)_
rickman
Mar 11, 2016, 2:03:02 AM3/11/16
to
On 3/10/2016 11:38 PM, Jasen Betts wrote:
> On 2016-03-11, Bob Engelhardt <BobEng...@comcast.net> wrote:
>> I have installed such a fence and it works fine. It is a single
>> conductor wire that completely encloses the area - i.e., both ends of
>> the wire are connected to the transmitter. It transmits an RF signal
>> that is received by the dog's collar and corrects him when he gets too
>> close to the wire/boundary.
>>
>> My problem is that there is a section of the boundary where I don't want
>> the correction given. "Easy", I thought, "I'll just use coax in that
>> section and the signal will be shielded away". Well, the coax doesn't
>> shield/suppress it - the collar still reacts. This is with both ends of
>> the shield grounded. (The shield is a heavy layer of foil under a braid.)
>>
>> What gives? Is there a better way to suppress the signal?
>
> it's a loop. it's also near-field, so you're picking up the magnetic
> field coax will give electrostatic shielding, but not magnetic.
It does when it is the return path for the current, but not in this case
> On 2016-03-11, Bob Engelhardt <BobEng...@comcast.net> wrote:
>> I have installed such a fence and it works fine. It is a single
>> conductor wire that completely encloses the area - i.e., both ends of
>> the wire are connected to the transmitter. It transmits an RF signal
>> that is received by the dog's collar and corrects him when he gets too
>> close to the wire/boundary.
>>
>> My problem is that there is a section of the boundary where I don't want
>> the correction given. "Easy", I thought, "I'll just use coax in that
>> section and the signal will be shielded away". Well, the coax doesn't
>> shield/suppress it - the collar still reacts. This is with both ends of
>> the shield grounded. (The shield is a heavy layer of foil under a braid.)
>>
>> What gives? Is there a better way to suppress the signal?
>
> it's a loop. it's also near-field, so you're picking up the magnetic
> field coax will give electrostatic shielding, but not magnetic.
where it carries little to no current.
> dig a deep trench or make a high catenary so that the dog need
> not approach the wire. or assuming the breach is for your back
> door run the wire along the roof-line or across the basement floor.
>
> or you may find that a large metal plate gives suffifient shielding.
>
>> I don't know the frequency used, but I could look at it with my scope,
>> assuming the scope operates that high (it's a Tek 465B).
>
> it'll be in an ISM band possibly 13.56Mhz or 25Khz
>
--
dca...@krl.org
Mar 11, 2016, 7:38:19 AM3/11/16
to
On Thursday, March 10, 2016 at 9:23:49 PM UTC-5, Bob Engelhardt wrote:
> I have installed such a fence and it works fine.
> I have installed such a fence and it works fine.
> What gives? Is there a better way to suppress the signal?
>
> I don't know the frequency used, but I could look at it with my scope,
> assuming the scope operates that high (it's a Tek 465B).
>
> Thanks,
> Bob
I would not expect the frequency to be very high. The first thing I would do is look at the signal and see what frequency is used.
>
> I don't know the frequency used, but I could look at it with my scope,
> assuming the scope operates that high (it's a Tek 465B).
>
> Thanks,
> Bob
Then assuming the frequency is reasonably low, I would connect a 1:1 transformer to the wire near where you want to suppress the signal. Now you can connect the secondary of the transformer to a loop of wire where you want the signal suppressed. Connect a sense coil to your scope and arrange the new loop so the signal is minimized.
This assumes you can get or make a transformer that will work at the frequency.
So the first thing to do is to measure the frequency.
A friend and I did something like this to see if the field from high voltage transmission lines could be cancelled. We made a large loop using regular house wire , probably 12-2 with ground. Connected the wires so we had a three turn coil and feed that with voltage from a Variac. We could cancel out the field from the high tension wires. We thought about the problem of the field from the high tension wires changing with the amount of power being used by the power grid, and figured we could design a system which would null the field, but never actually make such an apparatus.
Dan
Neon John
Mar 11, 2016, 8:57:08 AM3/11/16
to
On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
<carl.ija...@ZZxyz.verizon.net> wrote:
>
>Wild idea, but if it's detecting the magnetic field could you run the wire
>through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe that
>would provide enough shielding to give you a 3-4' door. I'm thinking 3/4"
>pipe, or maybe 1".
>
>-----
>Regards,
>Carl Ijames
I think this will work. The steel should be lossy enough to absorb
<carl.ija...@ZZxyz.verizon.net> wrote:
>
>Wild idea, but if it's detecting the magnetic field could you run the wire
>through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe that
>would provide enough shielding to give you a 3-4' door. I'm thinking 3/4"
>pipe, or maybe 1".
>
>-----
>Regards,
>Carl Ijames
the signal. Small pipe should work - even 1/4".
Another solution is simply to bury the wire so deep that the collar
can't detect it in that segment.
John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address
Jeroen Belleman
Mar 11, 2016, 10:42:10 AM3/11/16
to
On 2016-03-11 14:51, Neon John wrote:
> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
> <carl.ija...@ZZxyz.verizon.net> wrote:
>
>>
>> Wild idea, but if it's detecting the magnetic field could you run the wire
>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe that
>> would provide enough shielding to give you a 3-4' door. I'm thinking 3/4"
>> pipe, or maybe 1".
>>
>> -----
>> Regards,
>> Carl Ijames
>
> I think this will work. The steel should be lossy enough to absorb
> the signal. Small pipe should work - even 1/4".
No. Pipe or no pipe, the magnetic field at a given distance
> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
> <carl.ija...@ZZxyz.verizon.net> wrote:
>
>>
>> Wild idea, but if it's detecting the magnetic field could you run the wire
>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe that
>> would provide enough shielding to give you a 3-4' door. I'm thinking 3/4"
>> pipe, or maybe 1".
>>
>> -----
>> Regards,
>> Carl Ijames
>
> I think this will work. The steel should be lossy enough to absorb
> the signal. Small pipe should work - even 1/4".
from the wire will remain exactly the same. Ampère's law.
>
> Another solution is simply to bury the wire so deep that the collar
> can't detect it in that segment.
Jeroen Belleman
dca...@krl.org
Mar 11, 2016, 12:41:48 PM3/11/16
to
On Friday, March 11, 2016 at 7:38:19 AM UTC-5, dca...@krl.org wrote:
> On Thursday, March 10, 2016 at 9:23:49 PM UTC-5, Bob Engelhardt wrote:
> > I have installed such a fence and it works fine.
> > What gives? Is there a better way to suppress the signal?
> >
> > Thanks,
> On Thursday, March 10, 2016 at 9:23:49 PM UTC-5, Bob Engelhardt wrote:
> > I have installed such a fence and it works fine.
> > What gives? Is there a better way to suppress the signal?
> >
> > Bob
>
I had another thought that would be fairly easy to try and cost very little.
How about connecting another two wires into the circuit. So where you want no signal, there would be three wires each with 1/3rd the current. The wires would need to be spaced maybe two or three feet apart, maybe more.
You would still have the signal , but not as strong.
Dan
rickman
Mar 11, 2016, 1:27:18 PM3/11/16
to
On 3/11/2016 10:41 AM, Jeroen Belleman wrote:
> On 2016-03-11 14:51, Neon John wrote:
>> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
>> <carl.ija...@ZZxyz.verizon.net> wrote:
>>
>>>
>>> Wild idea, but if it's detecting the magnetic field could you run the
>>> wire
>>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe
>>> that
>>> would provide enough shielding to give you a 3-4' door. I'm thinking
>>> 3/4"
>>> pipe, or maybe 1".
>>>
>>> -----
>>> Regards,
>>> Carl Ijames
>>
>> I think this will work. The steel should be lossy enough to absorb
>> the signal. Small pipe should work - even 1/4".
>
> No. Pipe or no pipe, the magnetic field at a given distance
> from the wire will remain exactly the same. Ampère's law.
That is *not* what Ampere's law says. Even if it did, it only applies
> On 2016-03-11 14:51, Neon John wrote:
>> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
>> <carl.ija...@ZZxyz.verizon.net> wrote:
>>
>>>
>>> Wild idea, but if it's detecting the magnetic field could you run the
>>> wire
>>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe
>>> that
>>> would provide enough shielding to give you a 3-4' door. I'm thinking
>>> 3/4"
>>> pipe, or maybe 1".
>>>
>>> -----
>>> Regards,
>>> Carl Ijames
>>
>> I think this will work. The steel should be lossy enough to absorb
>> the signal. Small pipe should work - even 1/4".
>
> No. Pipe or no pipe, the magnetic field at a given distance
> from the wire will remain exactly the same. Ampère's law.
to static fields.
>> Another solution is simply to bury the wire so deep that the collar
>> can't detect it in that segment.
>
> Yes, that should work.
>
> Jeroen Belleman
>
Rick
whit3rd
Mar 11, 2016, 3:23:24 PM3/11/16
to
On Friday, March 11, 2016 at 10:27:18 AM UTC-8, rickman wrote:
> On 3/11/2016 10:41 AM, Jeroen Belleman wrote:
> > On 2016-03-11 14:51, Neon John wrote:
> >> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
> >> <carl.ija...@ZZxyz.verizon.net> wrote:
> >>
> >>>
> >>> Wild idea, but if it's detecting the magnetic field could you run the
> >>> wire
> >>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe
> >>> that
> >>> would provide enough shielding
> On 3/11/2016 10:41 AM, Jeroen Belleman wrote:
> > On 2016-03-11 14:51, Neon John wrote:
> >> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
> >> <carl.ija...@ZZxyz.verizon.net> wrote:
> >>
> >>>
> >>> Wild idea, but if it's detecting the magnetic field could you run the
> >>> wire
> >>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe
> >>> that
> >>> would provide enough shielding
> > No. Pipe or no pipe, the magnetic field at a given distance
> > from the wire will remain exactly the same
It won't work, because the pipe would just be a lossy ferrite bead... it'll
> > from the wire will remain exactly the same
load the entire loop circuit, probably prevent normal function everywhere.
George Herold
Mar 11, 2016, 4:02:38 PM3/11/16
to
concentrate the B-field locally and make it smaller up above the dirt.
George H.
mixed nuts
Mar 11, 2016, 5:04:40 PM3/11/16
to
"How do I allow a place along the boundary wire where my pet can safely
cross?
To create the layout that you need, a double loop layout format will be
necessary.
First, run the wire around the perimeter. When you get to the end, make
a U-turn with your wire and backtrack around the coverage area.
Be sure to keep the wire 3 - 5 feet apart where you want signal. When
you want to cancel the signal, bring the wires together and twist them
10 times per foot."
http://www.petsafe.net/support/in-ground-fences/yardmax-rechargeable-in-ground-fence
I have a friend who wanted to allow free passage for his dog into the
house and garage but keep him away from flower beds, mailmen and the
like. Took a lot of wire for the double loopnbut it all worked after a
fashion.
An elevated section worked most of the time but the dog got zapped when
standing for a petting on the way to the play area a couple of times -
not a good thing.
--
Grizzly H.
M Philbrook
Mar 11, 2016, 5:45:37 PM3/11/16
to
In article <nbtgv...@news4.newsguy.com>, BobEng...@comcast.net
says...
Balanced path, tightly bunched.
Jamie
says...
Jamie
George Herold
Mar 11, 2016, 6:56:51 PM3/11/16
to
a twisted pair, but couldn't make it work.
George H.
mako...@yahoo.com
Mar 12, 2016, 12:56:24 AM3/12/16
to
When you say you grounded the shield,
Grounded it to what?
M
Grounded it to what?
M
Neon John
Mar 12, 2016, 9:53:07 AM3/12/16
to
On Fri, 11 Mar 2016 12:23:14 -0800 (PST), whit3rd <whi...@gmail.com>
wrote:
>> > No. Pipe or no pipe, the magnetic field at a given distance
>> > from the wire will remain exactly the same
No, the steel will serve as a one turn shorted secondary of a
transformer just like an induction heater works.
>
>It won't work, because the pipe would just be a lossy ferrite bead... it'll
>load the entire loop circuit, probably prevent normal function everywhere.
Doubtful, especially if he uses a larger pipe. The shorted turn
represented by the pipe will be reflected back to the primary as
essentially no reactance. Plus the mutual inductance will be quite
low.
Since it costs almost nothing to try, that's what I'd do.
wrote:
>> > No. Pipe or no pipe, the magnetic field at a given distance
>> > from the wire will remain exactly the same
transformer just like an induction heater works.
>
>It won't work, because the pipe would just be a lossy ferrite bead... it'll
>load the entire loop circuit, probably prevent normal function everywhere.
represented by the pipe will be reflected back to the primary as
essentially no reactance. Plus the mutual inductance will be quite
low.
Since it costs almost nothing to try, that's what I'd do.
Phil Hobbs
Mar 12, 2016, 10:34:39 AM3/12/16
to
coyotes, and the poor dogs can't run away from them because of the
invisible fence. A certain number get eaten as a result.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
John S
Mar 12, 2016, 1:18:43 PM3/12/16
to
circumstances. The fence might slow the dog down, but I suspect that the
result will ultimately be the same.
mixed nuts
Mar 12, 2016, 1:21:13 PM3/12/16
to
unrestrained and done-in in plain view. A lot of cats have evaporated
as well though there are a couple of outdoor cats in the area who seem
to have found a way. There has been a major reduction in coyote
population over the past 2-3 years. Mange may be one factor but there's
been some organized hunting as well (open season from Columbus Day
through mid-March). A couple of years back there was a pack that
apparently attempted to take some yarded-up deer behind my house. Deer
are not defenseless - my neighbor found 2 dead coyotes (stomped) behind
his house the next day.
--
Grizzly H.
Phil Hobbs
Mar 12, 2016, 1:55:25 PM3/12/16
to
A real fence can discourage the coyote. And I'm not at all sure that coyotes are always faster than dogs. Speed depends on age and condition, for one thing.
Cheers
Phil Hobbs
Cheers
Phil Hobbs
John S
Mar 12, 2016, 2:41:28 PM3/12/16
to
one, not one that will just discourage your own pet.
Have you ever encountered an old coyote? Coyotes are in better condition
than domesticated pets, even old ones. You should know why.
Ever heard the story of a coyote with 3 legs running all day after
chewing its leg off to get out of a trap?
Have you been in remote areas where you could observe them? I have.
Even if they cannot outrun a fast dog, they can always outlast them.
Try this: http://www.ct.gov/deep/cwp/view.asp?a=2723&q=325992
It is in your area, maybe.
Phil Hobbs
Mar 12, 2016, 3:40:32 PM3/12/16
to
Cheers
Phil Hobbs
DecadentLinuxUserNumeroUno
Mar 12, 2016, 3:48:22 PM3/12/16
to
On Sat, 12 Mar 2016 10:55:13 -0800 (PST), Phil Hobbs
<pcdh...@gmail.com> Gave us:
And breed. I am sure that a greyhound would give a coyote a run for
his hunger.
<pcdh...@gmail.com> Gave us:
his hunger.
DecadentLinuxUserNumeroUno
Mar 12, 2016, 3:49:20 PM3/12/16
to
On Sat, 12 Mar 2016 13:41:59 -0600, John S <Sop...@invalid.org> Gave
us:
>Have you ever encountered an old coyote? Coyotes are in better condition
>than domesticated pets, even old ones. You should know why.
All that cardboard based dog chow? The presence of smelly humans?
us:
>Have you ever encountered an old coyote? Coyotes are in better condition
>than domesticated pets, even old ones. You should know why.
krw
Mar 12, 2016, 5:32:08 PM3/12/16
to
On Sat, 12 Mar 2016 10:55:13 -0800 (PST), Phil Hobbs
<pcdh...@gmail.com> wrote:
>A real fence can discourage the coyote. And I'm not at all sure that coyotes are always faster than dogs. Speed depends on age and condition, for one thing.
...and whatever other food is available. "You don't have to be faster
>A real fence can discourage the coyote. And I'm not at all sure that coyotes are always faster than dogs. Speed depends on age and condition, for one thing.
than the bear..."
krw
Mar 12, 2016, 5:34:05 PM3/12/16
to
dca...@krl.org
Mar 12, 2016, 6:44:11 PM3/12/16
to
On Saturday, March 12, 2016 at 1:18:43 PM UTC-5, John S wrote:
>
> I seriously doubt that a dog can run away from a coyote under any
> circumstances. The fence might slow the dog down, but I suspect that the
> result will ultimately be the same.
http://www.nytimes.com/2010/04/26/sports/26greyhounds.html?_r=0
>
> I seriously doubt that a dog can run away from a coyote under any
> circumstances. The fence might slow the dog down, but I suspect that the
> result will ultimately be the same.
Dan
Phil Hobbs
Mar 12, 2016, 7:42:19 PM3/12/16
to
I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
Cheers
Phil Hobbs
I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
Cheers
Phil Hobbs
krw
Mar 12, 2016, 8:09:25 PM3/12/16
to
On Sat, 12 Mar 2016 16:42:08 -0800 (PST), Phil Hobbs
<pcdh...@gmail.com> wrote:
>I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
>
>I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
I like dogs but they take too much work so we have a couple of cats
<pcdh...@gmail.com> wrote:
>I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
>
>I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
(one just climbed up on my feet). I agree, whatever the pet, their
welfare becomes your responsibility, once they're taken into your
home.
BTW, coyotes aren't the only predator that feeds on pets. Owls will
take cats and small dogs, too. A friend had an hawk grab his Fifi
from his back yard (but released it), while he was watching.
I'm not one who objects to hunting coaters with Greyhounds, though. I
could deal with fewer coyotes around here, too.
Jeroen Belleman
Mar 13, 2016, 7:42:10 AM3/13/16
to
On 11/03/16 19:27, rickman wrote:
> On 3/11/2016 10:41 AM, Jeroen Belleman wrote:
>> On 2016-03-11 14:51, Neon John wrote:
>>> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
>>> <carl.ija...@ZZxyz.verizon.net> wrote:
>>>
>>>>
>>>> Wild idea, but if it's detecting the magnetic field could you run the
>>>> wire
>>>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe
>>>> that
>>>> would provide enough shielding to give you a 3-4' door. I'm thinking
>>>> 3/4"
>>>> pipe, or maybe 1".
>>>>
>>>> -----
>>>> Regards,
>>>> Carl Ijames
>>>
>>> I think this will work. The steel should be lossy enough to absorb
>>> the signal. Small pipe should work - even 1/4".
>>
>> No. Pipe or no pipe, the magnetic field at a given distance
>> from the wire will remain exactly the same. Ampère's law.
>
> That is *not* what Ampere's law says. Even if it did, it only applies
> to static fields.
>
Ampère's law says that the integral of the magnetic field along a closed
> On 3/11/2016 10:41 AM, Jeroen Belleman wrote:
>> On 2016-03-11 14:51, Neon John wrote:
>>> On Thu, 10 Mar 2016 22:35:13 -0500, "Carl Ijames"
>>> <carl.ija...@ZZxyz.verizon.net> wrote:
>>>
>>>>
>>>> Wild idea, but if it's detecting the magnetic field could you run the
>>>> wire
>>>> through a 3 or 4' long piece of iron or galvanized steel pipe? Maybe
>>>> that
>>>> would provide enough shielding to give you a 3-4' door. I'm thinking
>>>> 3/4"
>>>> pipe, or maybe 1".
>>>>
>>>> -----
>>>> Regards,
>>>> Carl Ijames
>>>
>>> I think this will work. The steel should be lossy enough to absorb
>>> the signal. Small pipe should work - even 1/4".
>>
>> No. Pipe or no pipe, the magnetic field at a given distance
>> from the wire will remain exactly the same. Ampère's law.
>
> That is *not* what Ampere's law says. Even if it did, it only applies
> to static fields.
>
loop equals the current going through the surface enclosed by
that loop. I'm aware that that is not the whole story, but it's
near enough for a dog fence. It may seem odd to some, but the presence
of magnetic materials does not change that. The steel pipe does not
shield the field.
Jeroen Belleman
Jeroen Belleman
Mar 13, 2016, 7:45:10 AM3/13/16
to
We'll see if what I think I know is true. ;-)
Jeroen Belleman
Jeroen Belleman
Mar 13, 2016, 7:53:38 AM3/13/16
to
On 12/03/16 15:52, Neon John wrote:
> On Fri, 11 Mar 2016 12:23:14 -0800 (PST), whit3rd <whi...@gmail.com>
> wrote:
>
>
>>>> No. Pipe or no pipe, the magnetic field at a given distance
>>>> from the wire will remain exactly the same
>
> No, the steel will serve as a one turn shorted secondary of a
> transformer just like an induction heater works.
>
You are confused. A piece of metal pipe with unconnected ends
> On Fri, 11 Mar 2016 12:23:14 -0800 (PST), whit3rd <whi...@gmail.com>
> wrote:
>
>
>>>> No. Pipe or no pipe, the magnetic field at a given distance
>>>> from the wire will remain exactly the same
>
> No, the steel will serve as a one turn shorted secondary of a
> transformer just like an induction heater works.
>
is not a shorted turn for the current running through a wire
running through it. It would be if the wire had been enclosed
in the pipe over its full length and if the pipe ends were
connected together. (We're talking LF AC, of course.)
Jeroen Belleman
Jeroen Belleman
Mar 13, 2016, 7:56:21 AM3/13/16
to
On 11/03/16 23:04, mixed nuts wrote:
> There's a method on the Petsafe website speaking to that issue:
>
> "How do I allow a place along the boundary wire where my pet can safely
> cross?
>
> To create the layout that you need, a double loop layout format will be
> necessary.
>
> First, run the wire around the perimeter. When you get to the end, make
> a U-turn with your wire and backtrack around the coverage area.
>
> Be sure to keep the wire 3 - 5 feet apart where you want signal. When
> you want to cancel the signal, bring the wires together and twist them
> 10 times per foot."
Yes, that works.
> There's a method on the Petsafe website speaking to that issue:
>
> "How do I allow a place along the boundary wire where my pet can safely
> cross?
>
> To create the layout that you need, a double loop layout format will be
> necessary.
>
> First, run the wire around the perimeter. When you get to the end, make
> a U-turn with your wire and backtrack around the coverage area.
>
> Be sure to keep the wire 3 - 5 feet apart where you want signal. When
> you want to cancel the signal, bring the wires together and twist them
> 10 times per foot."
Jeroen Belleman
Neon John
Mar 13, 2016, 10:02:30 AM3/13/16
to
On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
<jer...@nospam.please> wrote:
>Ampčre's law says that the integral of the magnetic field along a closed
dissipates as heat the magnetic field. In effect, a tiny induction
heater.
I just tested this effect in my lab. 3 ft piece of 3/4" black iron.
#4 welding cable through the center connected to an induction heater
(80kHz). A length of hookup wire connected to a 10 ohm resistor and a
scope held along the length of the outside of the pipe. Rowgoski coil
shows 80 amps in the inner cable. About 5mv P-P across the 10 ohm
resistor. Yes, the pipe got hot dissipating that magnetic filed via
both ohmic losses and hysteresis losses.
Damn, but some of you people are narrow visioned!
<jer...@nospam.please> wrote:
>Ampčre's law says that the integral of the magnetic field along a closed
>loop equals the current going through the surface enclosed by
>that loop. I'm aware that that is not the whole story, but it's
>near enough for a dog fence. It may seem odd to some, but the presence
>of magnetic materials does not change that. The steel pipe does not
>shield the field.
Nothing to do with Ampere's law. The steel pipe absorbs and
>that loop. I'm aware that that is not the whole story, but it's
>near enough for a dog fence. It may seem odd to some, but the presence
>of magnetic materials does not change that. The steel pipe does not
>shield the field.
dissipates as heat the magnetic field. In effect, a tiny induction
heater.
I just tested this effect in my lab. 3 ft piece of 3/4" black iron.
#4 welding cable through the center connected to an induction heater
(80kHz). A length of hookup wire connected to a 10 ohm resistor and a
scope held along the length of the outside of the pipe. Rowgoski coil
shows 80 amps in the inner cable. About 5mv P-P across the 10 ohm
resistor. Yes, the pipe got hot dissipating that magnetic filed via
both ohmic losses and hysteresis losses.
Damn, but some of you people are narrow visioned!
John S
Mar 13, 2016, 11:51:00 AM3/13/16
to
John S
Mar 13, 2016, 11:54:02 AM3/13/16
to
preventative should be criminal. If you can't afford it for your dog,
then find him a home that can.
Phil Hobbs
Mar 13, 2016, 1:12:19 PM3/13/16
to
>I agree with you. Just as I believe that not giving them heart-worm
>preventative should be criminal. If you can't afford it for your dog,
>then find him a home that can.
Prison for not vaccinating a dog? What about the human suffering that entails?
>preventative should be criminal. If you can't afford it for your dog,
>then find him a home that can.
Some dog people need to get more of a life.
Cheers
Phil Hobbs
bloggs.fred...@gmail.com
Mar 13, 2016, 1:53:43 PM3/13/16
to
On Thursday, March 10, 2016 at 10:05:25 PM UTC-5, Winfield Hill wrote:
> Bob Engelhardt wrote...
> >
> > I have installed such a fence and it works fine. It is a single
> > conductor wire that completely encloses the area - i.e., both ends of
> > the wire are connected to the transmitter. It transmits an RF signal
> > that is received by the dog's collar and corrects him when he gets too
> > close to the wire/boundary.
> >
> > My problem is that there is a section of the boundary where I don't want
> > the correction given. "Easy", I thought, "I'll just use coax in that
> > section and the signal will be shielded away". Well, the coax doesn't
> > shield/suppress it - the collar still reacts. This is with both ends of
> > the shield grounded. (The shield is a heavy layer of foil under a braid.)
> >
> > What gives? Is there a better way to suppress the signal?
> Thanks,
> - Win
Right, if it's like the heart rate monitors, it would be around 5KHz, the range is small like 3 feet, and the signal is AM/PAM encoded for the dog collar receiver...false activation rate is near zero.
> Bob Engelhardt wrote...
> >
> > I have installed such a fence and it works fine. It is a single
> > conductor wire that completely encloses the area - i.e., both ends of
> > the wire are connected to the transmitter. It transmits an RF signal
> > that is received by the dog's collar and corrects him when he gets too
> > close to the wire/boundary.
> >
> > My problem is that there is a section of the boundary where I don't want
> > the correction given. "Easy", I thought, "I'll just use coax in that
> > section and the signal will be shielded away". Well, the coax doesn't
> > shield/suppress it - the collar still reacts. This is with both ends of
> > the shield grounded. (The shield is a heavy layer of foil under a braid.)
> >
> > What gives? Is there a better way to suppress the signal?
>
> You don't mention the brand, but it's likely not an RF system,
> but rather a medium-frequency AC current flowing through the
> wire, creating a simple magnetic field surrounding the wire,
> that's sensed by the electronic shock collar. Sorry, you
> cannot use electrostatic shields to block magnetic fields.
>
> You don't mention the brand, but it's likely not an RF system,
> but rather a medium-frequency AC current flowing through the
> wire, creating a simple magnetic field surrounding the wire,
> that's sensed by the electronic shock collar. Sorry, you
> cannot use electrostatic shields to block magnetic fields.
>
> I don't know if its possible to have a fixed opening. Yes,
> you can create a non-functioning section: simply run the wire
> back on itself, creating a cancelling field. Twisting the
> two wires helps. Ahem, your problem is then what to do
> with this folded-back wire, to continue on a complete-loop
> path around your closed-in area, which blocks in the animal.
>
>
> --
> you can create a non-functioning section: simply run the wire
> back on itself, creating a cancelling field. Twisting the
> two wires helps. Ahem, your problem is then what to do
> with this folded-back wire, to continue on a complete-loop
> path around your closed-in area, which blocks in the animal.
>
>
> Thanks,
> - Win
Right, if it's like the heart rate monitors, it would be around 5KHz, the range is small like 3 feet, and the signal is AM/PAM encoded for the dog collar receiver...false activation rate is near zero.
bloggs.fred...@gmail.com
Mar 13, 2016, 2:07:50 PM3/13/16
to
On Saturday, March 12, 2016 at 1:18:43 PM UTC-5, John S wrote:
https://en.wikipedia.org/wiki/Eastern_coyote
George Herold
Mar 13, 2016, 7:54:10 PM3/13/16
to
You just need enough room, :^)
Our dogs are no more work than the cats,
(maybe less... I'd rather do the ~one day spring clean up
of winter dog poop, than the kitty liter box through the winter...
Perhaps it's better there in the south..
(When there's no white stuff on the ground everyone poops
in the field. Well except for the wife, kids and I.)
We've got some coyote, more predators to control the deer
population would be good. Deer seem to be even more of a
problem in the suburbs, no human hunters... and more coyote?
I'm totally a dog person.
Cats are tolerated for their vermin control, funny antics
are the gravy.
George H.
George Herold
Mar 13, 2016, 8:04:45 PM3/13/16
to
With iron there can also be magnetic polarizations....
I'm not sure of the time constants involved.
If you are seriously going to try something, will you do
copper and iron?
George H.
Bob Engelhardt
Mar 13, 2016, 10:06:46 PM3/13/16
to
On 3/11/2016 5:04 PM, mixed nuts wrote:
> There's a method on the Petsafe website speaking to that issue:
>
> ...
> There's a method on the Petsafe website speaking to that issue:
>
> First, run the wire around the perimeter. When you get to the end, make
> a U-turn with your wire and backtrack around the coverage area.
> ...
> a U-turn with your wire and backtrack around the coverage area.
I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
anyway. Bob
Bob Engelhardt
Mar 13, 2016, 10:10:57 PM3/13/16
to
On 3/12/2016 12:56 AM, mako...@yahoo.com wrote:
> When you say you grounded the shield,
> Grounded it to what?
> M
>
Ground. I.e., copper clad rods driven into the ground.
> When you say you grounded the shield,
> Grounded it to what?
> M
>
Ground. I.e., copper clad rods driven into the ground.
krw
Mar 13, 2016, 10:31:15 PM3/13/16
to
On Sun, 13 Mar 2016 16:54:05 -0700 (PDT), George Herold
<ghe...@teachspin.com> wrote:
>On Saturday, March 12, 2016 at 8:09:25 PM UTC-5, krw wrote:
>> On Sat, 12 Mar 2016 16:42:08 -0800 (PST), Phil Hobbs
>> <pcdh...@gmail.com> wrote:
>>
>> >I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
>> >
>> >I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
>>
>> I like dogs but they take too much work so we have a couple of cats
>> (one just climbed up on my feet). I agree, whatever the pet, their
>> welfare becomes your responsibility, once they're taken into your
>> home.
>>
>> BTW, coyotes aren't the only predator that feeds on pets. Owls will
>> take cats and small dogs, too. A friend had an hawk grab his Fifi
>> from his back yard (but released it), while he was watching.
>>
>> I'm not one who objects to hunting coaters with Greyhounds, though. I
>> could deal with fewer coyotes around here, too.
>
>Re: dog care,
>You just need enough room, :^)
> Our dogs are no more work than the cats,
>(maybe less... I'd rather do the ~one day spring clean up
>of winter dog poop, than the kitty liter box through the winter...
>Perhaps it's better there in the south..
You can't leave a dog alone for a long weekend. We leave the cats in
<ghe...@teachspin.com> wrote:
>On Saturday, March 12, 2016 at 8:09:25 PM UTC-5, krw wrote:
>> On Sat, 12 Mar 2016 16:42:08 -0800 (PST), Phil Hobbs
>> <pcdh...@gmail.com> wrote:
>>
>> >I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
>> >
>> >I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
>>
>> I like dogs but they take too much work so we have a couple of cats
>> (one just climbed up on my feet). I agree, whatever the pet, their
>> welfare becomes your responsibility, once they're taken into your
>> home.
>>
>> BTW, coyotes aren't the only predator that feeds on pets. Owls will
>> take cats and small dogs, too. A friend had an hawk grab his Fifi
>> from his back yard (but released it), while he was watching.
>>
>> I'm not one who objects to hunting coaters with Greyhounds, though. I
>> could deal with fewer coyotes around here, too.
>
>Re: dog care,
>You just need enough room, :^)
> Our dogs are no more work than the cats,
>(maybe less... I'd rather do the ~one day spring clean up
>of winter dog poop, than the kitty liter box through the winter...
>Perhaps it's better there in the south..
the house for a week to ten days, a couple of times a year, and have a
neighbor (high school) kid look in on them once or twice a day and
clean the (automatic) liter box once a week.
*Everything* is better in the South. ;-)
>(When there's no white stuff on the ground everyone poops
>in the field. Well except for the wife, kids and I.)
>We've got some coyote, more predators to control the deer
>population would be good. Deer seem to be even more of a
>problem in the suburbs, no human hunters... and more coyote?
presents in the yard. They *love* the roses.
>
>I'm totally a dog person.
>Cats are tolerated for their vermin control, funny antics
>are the gravy.
>
We're really dog people, too, but they do require more attention. Our
>I'm totally a dog person.
>Cats are tolerated for their vermin control, funny antics
>are the gravy.
>
cats have all been people cats (they sleep *on* my wife), so it's not
like they're just sharing the house with their servants.
Jasen Betts
Mar 14, 2016, 1:34:25 AM3/14/16
to
On 2016-03-13, Neon John <n...@never.com> wrote:
> On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
><jer...@nospam.please> wrote:
>
>
>>Ampère's law says that the integral of the magnetic field along a closed
> On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
><jer...@nospam.please> wrote:
>
>
>>loop equals the current going through the surface enclosed by
>>that loop. I'm aware that that is not the whole story, but it's
>>near enough for a dog fence. It may seem odd to some, but the presence
>>of magnetic materials does not change that. The steel pipe does not
>>shield the field.
>
> Nothing to do with Ampere's law. The steel pipe absorbs and
> dissipates as heat the magnetic field. In effect, a tiny induction
> heater.
>
> I just tested this effect in my lab. 3 ft piece of 3/4" black iron.
> #4 welding cable through the center connected to an induction heater
> (80kHz). A length of hookup wire connected to a 10 ohm resistor and a
> scope held along the length of the outside of the pipe. Rowgoski coil
> shows 80 amps in the inner cable. About 5mv P-P across the 10 ohm
> resistor. Yes, the pipe got hot dissipating that magnetic filed via
> both ohmic losses and hysteresis losses.
>
> Damn, but some of you people are narrow visioned!
Huh? the current on the inner surface of the pipe will tend to cancel
>>that loop. I'm aware that that is not the whole story, but it's
>>near enough for a dog fence. It may seem odd to some, but the presence
>>of magnetic materials does not change that. The steel pipe does not
>>shield the field.
>
> Nothing to do with Ampere's law. The steel pipe absorbs and
> dissipates as heat the magnetic field. In effect, a tiny induction
> heater.
>
> I just tested this effect in my lab. 3 ft piece of 3/4" black iron.
> #4 welding cable through the center connected to an induction heater
> (80kHz). A length of hookup wire connected to a 10 ohm resistor and a
> scope held along the length of the outside of the pipe. Rowgoski coil
> shows 80 amps in the inner cable. About 5mv P-P across the 10 ohm
> resistor. Yes, the pipe got hot dissipating that magnetic filed via
> both ohmic losses and hysteresis losses.
>
> Damn, but some of you people are narrow visioned!
the current in the wire, but the current on the outer surface of the
pipe will tend to match it.
--
\_(ツ)_
whit3rd
Mar 14, 2016, 2:15:27 AM3/14/16
to
On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
> On 2016-03-13, Neon John <n...@never.com> wrote:
> > On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
> ><jer...@nospam.please> wrote:
> >
> >
> >>Ampère's law says that the integral of the magnetic field along a closed
> >>loop equals the current going through the surface enclosed...
> On 2016-03-13, Neon John <n...@never.com> wrote:
> > On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
> ><jer...@nospam.please> wrote:
> >
> >
> >>Ampère's law says that the integral of the magnetic field along a closed
> > Nothing to do with Ampere's law. The steel pipe absorbs and
> > dissipates as heat the magnetic field. In effect, a tiny induction
> > heater.
> Huh? the current on the inner surface of the pipe will tend to cancel
> the current in the wire, but the current on the outer surface
The 'current on the inner surface' is induced eddy current, because the pipe
> the current in the wire, but the current on the outer surface
is getting magnetized. There's no current on the OUTER surface
until the magnetization starts changing on the outside (dB/dt nonzero), and
at high frequencies, that won't happen (there's a skin depth).
Eddy current heating of the pipe, and a whopping resistive + inductive impedance
as seen by whatever drives the buried wire, are to be expected,
Jeroen Belleman
Mar 14, 2016, 5:42:58 AM3/14/16
to
and fed it with 1MHz from my trusty HP3577, while sniffing
around with a pick-up coil. I tried the bare wire and also
with a 240mm piece of iron and then brass pipe around the
wire along the long edge of the rectangle. Sort of like
this (view with fixed-width characters):
---------------------
+-------------------------------------------+
| --------------------- |
| pipe |
| |
| |
| |
| |
| |
| |
| |
| |
| |
+------------------------------------------||
signal in
Verdict: Bare wire or pipe, the signal as a function of
distance is the same within a few dB.
I also tried back-tracking the wire along a larger perimeter,
580x480mm, bringing together and twisting the wires over some
200mm along one side. It's a bit hard to clearly show in
ASCII art how the connections go, but basically, the current
runs one way in the inner loop and back along the outer loop.
+---------------------+ +------------------+
| | | |
| | | |
| | | |
| +------------====================-----------+ |
| | twist | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| +----------------------------------------- + - |
| \ \ |
| \ \ |
| \ \ |
+-------------------------------------------------------+ +
Verdict: The signal has a clear drop, some 20dB, close to the
twisted section. Elsewhere along the inside perimeter, the signal
is a little weaker than before, ~6dB less @ 50mm, but still very
present. On the other hand, in the area in between the inner and
outer perimeter, the signal is about 6dB stronger than before.
No surprise there.
So, as I've said, pipe does not work to shield the signal.
Back-tracking and twisting the wires of some length *does*
work.
Jeroen Belleman
mixed nuts
Mar 14, 2016, 8:39:28 AM3/14/16
to
where you want to get fancy. Whether the feed for the doubled section
is from the actual box, or from gap in the wire, the result is the same.
--
Grizzly H.
Jeroen Belleman
Mar 14, 2016, 10:01:56 AM3/14/16
to
Jeroen Belleman
George Herold
Mar 14, 2016, 10:12:40 AM3/14/16
to
women down the road comes to care for them once a day.
>
> *Everything* is better in the South. ;-)
I was going to add that the one thing I don't miss
> *Everything* is better in the South. ;-)
about the south is all the ticks and chiggers that
the dogs bring back in the late summer.
George H.
George Herold
Mar 14, 2016, 10:22:51 AM3/14/16
to
What puzzles me is that I can use mu-metal to shield
static and low frequency B-fields... so in my model of
the world the iron should do something. Does one need
"soft" iron?
George H.
George Herold
Mar 14, 2016, 10:25:09 AM3/14/16
to
all the way around the perimeter.
George H.
amdx
Mar 14, 2016, 11:26:19 AM3/14/16
to
So hook up a small ferrite transformer and adjust turns for best
cancelling. Here's my thought, but I'm not to sure about it.
> http://s395.photobucket.com/user/Qmavam/media/Dog%20Fence%20cancelling._zpsufhfjmdu.png.html
Mikek
mixed nuts
Mar 14, 2016, 11:29:54 AM3/14/16
to
loop at _any_ point(s) and construct a double loop.
|---------------------------------|
| |
| |----------------------|
Feed |-----------------------|
| |
| |----------=====--------|
| |---------| |--------|
|---------------------------------| dog
passage
--
Grizzly H.
mako...@yahoo.com
Mar 14, 2016, 11:54:40 AM3/14/16
to
Isn't the H field inside a loop nearly constant ANYWHERE inside the perimiter of the loop?
I think the operation of the fence is NOT due to the magentic H field alone,.
If if was magnitic filed, then it would work in a similar fashion as those
magnetic loop audio assist devices. Those work anywhere inside the perimiter of the loop, not just near the wire.
Since the dog fence operates only near the wire, it must not be purley H magnetic field operated, it is obviously not electric E field operated so it must be EM field.
So we need to shield or cancel an EM field, not an H field.
Am I wrong?
Mark
George Herold
Mar 14, 2016, 3:30:37 PM3/14/16
to
On Monday, March 14, 2016 at 11:29:54 AM UTC-4, mixed nuts wrote:
> On 3/14/2016 10:01 AM, Jeroen Belleman wrote:
> > On 2016-03-14 13:39, mixed nuts wrote:
> >> On 3/13/2016 10:06 PM, Bob Engelhardt wrote:
> >>> On 3/11/2016 5:04 PM, mixed nuts wrote:
> >>>> There's a method on the Petsafe website speaking to that issue:
> >>>>
> >>>> ...
> >>>> First, run the wire around the perimeter. When you get to the end, make
> >>>> a U-turn with your wire and backtrack around the coverage area.
> >>>> ...
> >>>
> >>> I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
> >>> anyway. Bob
> >>
> >> You don't have to double loop the entire perimeter - just the section
> >> where you want to get fancy. Whether the feed for the doubled section
> >> is from the actual box, or from gap in the wire, the result is the same.
> >>
> >
> > I have trouble visualizing what you mean. ASCII drawing please?
>
>
> Just take the single loop and run it around the perimeter. Break that
> loop at _any_ point(s) and construct a double loop.
>
> |---------------------------------|
> | |
> | |----------------------|
> Feed Dog in here |-----------------------|
> > On 2016-03-14 13:39, mixed nuts wrote:
> >> On 3/13/2016 10:06 PM, Bob Engelhardt wrote:
> >>> On 3/11/2016 5:04 PM, mixed nuts wrote:
> >>>> There's a method on the Petsafe website speaking to that issue:
> >>>>
> >>>> ...
> >>>> First, run the wire around the perimeter. When you get to the end, make
> >>>> a U-turn with your wire and backtrack around the coverage area.
> >>>> ...
> >>>
> >>> I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
> >>> anyway. Bob
> >>
> >> You don't have to double loop the entire perimeter - just the section
> >> where you want to get fancy. Whether the feed for the doubled section
> >> is from the actual box, or from gap in the wire, the result is the same.
> >>
> >
> > I have trouble visualizing what you mean. ASCII drawing please?
>
>
> Just take the single loop and run it around the perimeter. Break that
> loop at _any_ point(s) and construct a double loop.
>
> |---------------------------------|
> | |
> | |----------------------|
> | |
> | |----------=====--------|
> | |---------| |--------|
> |---------------------------------| dog
> passage
>
>
But how does the dog get too the passage without stepping over
> | |----------=====--------|
> | |---------| |--------|
> |---------------------------------| dog
> passage
>
>
an un-cancelled section of wire.
(Or to put it another way, your dog passage goes from outside the fence
to outside the fence.)
George H.
> --
> Grizzly H.
Jeroen Belleman
Mar 14, 2016, 3:34:52 PM3/14/16
to
On 14/03/16 16:30, mixed nuts wrote:
> On 3/14/2016 10:01 AM, Jeroen Belleman wrote:
>> On 2016-03-14 13:39, mixed nuts wrote:
>>> On 3/13/2016 10:06 PM, Bob Engelhardt wrote:
>>>> On 3/11/2016 5:04 PM, mixed nuts wrote:
>>>>> There's a method on the Petsafe website speaking to that issue:
>>>>>
>>>>> ...
>>>>> First, run the wire around the perimeter. When you get to the end,
>>>>> make
>>>>> a U-turn with your wire and backtrack around the coverage area.
>>>>> ...
>>>>
>>>> I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
>>>> anyway. Bob
>>>
>>> You don't have to double loop the entire perimeter - just the section
>>> where you want to get fancy. Whether the feed for the doubled section
>>> is from the actual box, or from gap in the wire, the result is the same.
>>>
>>
>> I have trouble visualizing what you mean. ASCII drawing please?
>
>
> Just take the single loop and run it around the perimeter. Break that
> loop at _any_ point(s) and construct a double loop.
>
> |---------------------------------|
> | |
> | |----------------------|
> Feed |-----------------------|
> | Dog pen |Zap!
> On 3/14/2016 10:01 AM, Jeroen Belleman wrote:
>> On 2016-03-14 13:39, mixed nuts wrote:
>>> On 3/13/2016 10:06 PM, Bob Engelhardt wrote:
>>>> On 3/11/2016 5:04 PM, mixed nuts wrote:
>>>>> There's a method on the Petsafe website speaking to that issue:
>>>>>
>>>>> ...
>>>>> First, run the wire around the perimeter. When you get to the end,
>>>>> make
>>>>> a U-turn with your wire and backtrack around the coverage area.
>>>>> ...
>>>>
>>>> I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
>>>> anyway. Bob
>>>
>>> You don't have to double loop the entire perimeter - just the section
>>> where you want to get fancy. Whether the feed for the doubled section
>>> is from the actual box, or from gap in the wire, the result is the same.
>>>
>>
>> I have trouble visualizing what you mean. ASCII drawing please?
>
>
> Just take the single loop and run it around the perimeter. Break that
> loop at _any_ point(s) and construct a double loop.
>
> |---------------------------------|
> | |
> | |----------------------|
> Feed |-----------------------|
> | |----------=====--------|
> | |---------| |--------|
> |---------------------------------| dog
> passage
>
>
Sorry, maybe I'm dense, but how would the dog get from its pen to
> | |---------| |--------|
> |---------------------------------| dog
> passage
>
>
the passage without crossing a singular wire at least once?
Jeroen Belleman
George Herold
Mar 14, 2016, 3:38:41 PM3/14/16
to
George H.
Jeroen Belleman
Mar 14, 2016, 4:16:45 PM3/14/16
to
On 14/03/16 15:22, George Herold wrote:
> On Monday, March 14, 2016 at 5:42:58 AM UTC-4, Jeroen Belleman wrote:
[...]
> On Monday, March 14, 2016 at 5:42:58 AM UTC-4, Jeroen Belleman wrote:
>>
>> Well, I rigged a miniature dog fence,
>> [...]
>> Well, I rigged a miniature dog fence,
>> So, as I've said, pipe does not work to shield the signal.
>> Back-tracking and twisting the wires of some length *does*
>> work.
>>
>> Jeroen Belleman
>
> Interesting, thanks for the experiment.
> What puzzles me is that I can use mu-metal to shield
> static and low frequency B-fields... so in my model of
> the world the iron should do something. Does one need
> "soft" iron?
>
> George H.
>
Well, the flux density inside the iron of the tube is
>> Back-tracking and twisting the wires of some length *does*
>> work.
>>
>> Jeroen Belleman
>
> Interesting, thanks for the experiment.
> What puzzles me is that I can use mu-metal to shield
> static and low frequency B-fields... so in my model of
> the world the iron should do something. Does one need
> "soft" iron?
>
> George H.
>
certainly greater than elsewhere, but that does not reduce
the field outside the tube.
Magnetic shielding is different. Ampere's law really works
like that. Moreover, whereas a thin metal box can stop an
electric field, you need a thick-walled shield to guide a
magnetic field around your critical volume. Oddly enough, the
shield does not need to be closed. (Well strictly, that is
true for E-field shields too.)
Around 2006, I installed a box with little RF transformers
in the fringing field of the bending magnets of the Proton
Synchrotron here. The transformers were inside a little pill-box
style mu-metal shield with 1mm wall thickness. Near 10GeV, my
transformers suddenly stopped working. The shield was not good
enough!
I solved the problem by sandwiching the works between two 5mm
thick soft iron discs, taking care to align the discs' diameter
with the field. That way, the flux goes through the iron and
little is left in between the discs.
Jeroen Belleman
Jeroen Belleman
Mar 14, 2016, 4:33:35 PM3/14/16
to
On 14/03/16 16:54, mako...@yahoo.com wrote:
[...]
sum of several of those, so while it doesn't drop off as fast inside
as outside the perimeter, it's certainly not constant.
Jeroen Belleman
[...]
> this is an interesting problem.
>
> Isn't the H field inside a loop nearly constant ANYWHERE inside the perimiter of the loop?
>
The field of a single wire drops off as 1/d. The total field is the
>
> Isn't the H field inside a loop nearly constant ANYWHERE inside the perimiter of the loop?
>
sum of several of those, so while it doesn't drop off as fast inside
as outside the perimeter, it's certainly not constant.
Jeroen Belleman
amdx
Mar 14, 2016, 6:23:12 PM3/14/16
to
I think there is an arrangement like this that will cancel the signal.
Mikek
George Herold
Mar 14, 2016, 9:39:39 PM3/14/16
to
(with transmitter sending wrt the same "ground".)
George H.
amdx
Mar 14, 2016, 10:07:55 PM3/14/16
to
won't work.
Anyone have an idea about this? Or a transformer drive cancelling
circuit.
Mikek
Jasen Betts
Mar 15, 2016, 1:01:28 AM3/15/16
to
On 2016-03-14, whit3rd <whi...@gmail.com> wrote:
> On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
>> On 2016-03-13, Neon John <n...@never.com> wrote:
>> > On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
>> ><jer...@nospam.please> wrote:
>> >
>> >
>> >>Ampère's law says that the integral of the magnetic field along a closed
>> >>loop equals the current going through the surface enclosed...
>
>> > Nothing to do with Ampere's law. The steel pipe absorbs and
>> > dissipates as heat the magnetic field. In effect, a tiny induction
>> > heater.
>
>> Huh? the current on the inner surface of the pipe will tend to cancel
>> the current in the wire, but the current on the outer surface
>
> The 'current on the inner surface' is induced eddy current, because the pipe
> is getting magnetized.
No, because it's conductive, ferrite won't show the same current, copper will.
> On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
>> On 2016-03-13, Neon John <n...@never.com> wrote:
>> > On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
>> ><jer...@nospam.please> wrote:
>> >
>> >
>> >>Ampère's law says that the integral of the magnetic field along a closed
>> >>loop equals the current going through the surface enclosed...
>
>> > Nothing to do with Ampere's law. The steel pipe absorbs and
>> > dissipates as heat the magnetic field. In effect, a tiny induction
>> > heater.
>
>> Huh? the current on the inner surface of the pipe will tend to cancel
>> the current in the wire, but the current on the outer surface
>
> The 'current on the inner surface' is induced eddy current, because the pipe
> is getting magnetized.
> There's no current on the OUTER surface
> until the magnetization starts changing on the outside (dB/dt nonzero), and
> at high frequencies, that won't happen (there's a skin depth).
>
> Eddy current heating of the pipe, and a whopping resistive + inductive impedance
> as seen by whatever drives the buried wire, are to be expected,
--
\_(ツ)_
Jasen Betts
Mar 15, 2016, 1:32:26 AM3/15/16
to
On 2016-03-14, mixed nuts <melops...@undulatus.budgie> wrote:
> On 3/14/2016 10:01 AM, Jeroen Belleman wrote:
>> On 2016-03-14 13:39, mixed nuts wrote:
>>> You don't have to double loop the entire perimeter - just the section
>>> where you want to get fancy. Whether the feed for the doubled section
>>> is from the actual box, or from gap in the wire, the result is the same.
>>>
>>
>> I have trouble visualizing what you mean. ASCII drawing please?
>
>
> Just take the single loop and run it around the perimeter. Break that
> loop at _any_ point(s) and construct a double loop.
>
> |---------------------------------|
> | |
> | |----------------------|
> Feed |-----------------------|
> | (B) | (C)
> On 3/14/2016 10:01 AM, Jeroen Belleman wrote:
>> On 2016-03-14 13:39, mixed nuts wrote:
>>> You don't have to double loop the entire perimeter - just the section
>>> where you want to get fancy. Whether the feed for the doubled section
>>> is from the actual box, or from gap in the wire, the result is the same.
>>>
>>
>> I have trouble visualizing what you mean. ASCII drawing please?
>
>
> Just take the single loop and run it around the perimeter. Break that
> loop at _any_ point(s) and construct a double loop.
>
> |---------------------------------|
> | |
> | |----------------------|
> Feed |-----------------------|
> | |----------=====--------| (D)
> | |---------| |--------|
> |---------------------------------| dog
> passage
>
(A)
> |---------------------------------| dog
> passage
>
[ edit (A),(B),(C) and (D) added ]
where is the safe path from (A) to (B) ?
(A) to (C) is possible via the "passage" or via (D)
but not (A) to (B)
--
\_(ツ)_
Jasen Betts
Mar 15, 2016, 1:32:27 AM3/15/16
to
On 2016-03-14, mixed nuts <melops...@undulatus.budgie> wrote:
> On 3/13/2016 10:06 PM, Bob Engelhardt wrote:
>> On 3/11/2016 5:04 PM, mixed nuts wrote:
>>> There's a method on the Petsafe website speaking to that issue:
>>>
>>> ...
>>> First, run the wire around the perimeter. When you get to the end, make
>>> a U-turn with your wire and backtrack around the coverage area.
>>> ...
>>
>> I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
>> anyway. Bob
>
> You don't have to double loop the entire perimeter - just the section
> where you want to get fancy
true, you only need to double any perimeter that has an opening
>> On 3/11/2016 5:04 PM, mixed nuts wrote:
>>> There's a method on the Petsafe website speaking to that issue:
>>>
>>> ...
>>> First, run the wire around the perimeter. When you get to the end, make
>>> a U-turn with your wire and backtrack around the coverage area.
>>> ...
>>
>> I have a 1000' perimeter, so that would be a bit of a nuisance. Thanks
>> anyway. Bob
>
> You don't have to double loop the entire perimeter - just the section
> where you want to get fancy
in other words if you want an opening in the perimeter you need
to double all of it.
> Whether the feed for the doubled section is from the actual box, or
> from gap in the wire, the result is the same.
one option that might work is to split the current many ways until
it's too diluted to trigger the collar,
.----------------.
| |
| |
| D
| |
| `-e-e-e-e-e-e-e
| .............
| . .
| . .
| . .
| .............
| e-e-e-e-e-e-e-.
| .---------------'
| |
| |
`----------------'
D driver
e earth peg
... house
seems risky though, if some plumbing picks up most of the current
that could cause a peak in the signal.
--
\_(ツ)_
Jasen Betts
Mar 15, 2016, 1:32:29 AM3/15/16
to
--
\_(ツ)_
whit3rd
Mar 15, 2016, 3:19:20 AM3/15/16
to
On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
> On 2016-03-14, whit3rd <whi...@gmail.com> wrote:
> > On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
> >> On 2016-03-13, Neon John <n...@never.com> wrote:
> >> > On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
> >> ><jer...@nospam.please> wrote:
> >> >
> >> >
> >> >>Ampère's law says that the integral of the magnetic field along a closed
> >> >>loop equals the current going through the surface enclosed...
> >
> >> > Nothing to do with Ampere's law. The steel pipe absorbs and
> >> > dissipates as heat the magnetic field. In effect, a tiny induction
> >> > heater.
> >
> >> Huh? the current on the inner surface of the pipe will tend to cancel
> >> the current in the wire, but the current on the outer surface
That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> On 2016-03-14, whit3rd <whi...@gmail.com> wrote:
> > On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
> >> On 2016-03-13, Neon John <n...@never.com> wrote:
> >> > On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
> >> ><jer...@nospam.please> wrote:
> >> >
> >> >
> >> >>Ampère's law says that the integral of the magnetic field along a closed
> >> >>loop equals the current going through the surface enclosed...
> >
> >> > Nothing to do with Ampere's law. The steel pipe absorbs and
> >> > dissipates as heat the magnetic field. In effect, a tiny induction
> >> > heater.
> >
> >> Huh? the current on the inner surface of the pipe will tend to cancel
> >> the current in the wire, but the current on the outer surface
current carrying contacts at its endpoints.
> > The 'current on the inner surface' is induced eddy current, because the pipe
> > is getting magnetized.
>
> No, because it's conductive, ferrite won't show the same current, copper will.
response, there will be a small depth (skin depth) on the inside of the
pipe that gets magnetized, and no induced current on the outer
surface of the pipe. Laminations for 60 Hz are 1 mm, pipe walls are maybe
3mm thick, and the frequency of interest was described as kilohertz-to-megahertz.
There's no dB/dt near the outer surface of the pipe, so no EMF there.
Jeroen Belleman
Mar 15, 2016, 4:09:48 AM3/15/16
to
any significant difference, but ground both ends and you'll
open up a whole can of worms to keep this group busy for
months. ;-)
Jeroen Belleman
Jeroen Belleman
Mar 15, 2016, 4:23:43 AM3/15/16
to
On 2016-03-15 08:19, whit3rd wrote:
> On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
>> On 2016-03-14, whit3rd <whi...@gmail.com> wrote:
>>> On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
>>>> On 2016-03-13, Neon John <n...@never.com> wrote:
>>>>> On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
>>>>> <jer...@nospam.please> wrote:
>>>>>
>>>>>
>>>>>> Ampère's law says that the integral of the magnetic field along a closed
>>>>>> loop equals the current going through the surface enclosed...
>>>
>>>>> Nothing to do with Ampere's law. The steel pipe absorbs and
>>>>> dissipates as heat the magnetic field. In effect, a tiny induction
>>>>> heater.
>>>
>>>> Huh? the current on the inner surface of the pipe will tend to cancel
>>>> the current in the wire, but the current on the outer surface
>
> That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> current carrying contacts at its endpoints.
Jasen is right, this is exactly what happens: The current on
> On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
>> On 2016-03-14, whit3rd <whi...@gmail.com> wrote:
>>> On Sunday, March 13, 2016 at 10:34:25 PM UTC-7, Jasen Betts wrote:
>>>> On 2016-03-13, Neon John <n...@never.com> wrote:
>>>>> On Sun, 13 Mar 2016 12:42:01 +0100, Jeroen Belleman
>>>>> <jer...@nospam.please> wrote:
>>>>>
>>>>>
>>>>>> Ampère's law says that the integral of the magnetic field along a closed
>>>>>> loop equals the current going through the surface enclosed...
>>>
>>>>> Nothing to do with Ampere's law. The steel pipe absorbs and
>>>>> dissipates as heat the magnetic field. In effect, a tiny induction
>>>>> heater.
>>>
>>>> Huh? the current on the inner surface of the pipe will tend to cancel
>>>> the current in the wire, but the current on the outer surface
>
> That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> current carrying contacts at its endpoints.
the inner surface of the pipe (almost) cancels the current on
the wire, and the circuit is completed by that current flowing
back over the outside surface of the tube. Nett result: The
B-field outside the tube is the same as if the tube hadn't
been there.
My measurement confirms that well enough.
Jeroen Belleman
amdx
Mar 15, 2016, 7:17:55 AM3/15/16
to
tubes.
Mikek
mako...@yahoo.com
Mar 15, 2016, 8:28:28 AM3/15/16
to
you make a loop around the perimeter, at the end of the loop, you turn back and make a second concentric loop, so you have two concentric loops spaced apart by say 10 feet. The dog cannot cross the inner loop, the outer loop is far enough away so it does not cancel the inner loop.
Now you should see where this is going. At the location where you want to allow passage, you simply bring the two loops together, so they do cancel.
Two concetric loops, current flowing in opposite directions, located apart where you want the fence to work and located closly where you want an opening.
Mark
mako...@yahoo.com
Mar 15, 2016, 8:54:07 AM3/15/16
to
Yes H drops as 1/r outside the loop or relative to a long straight wire, but INSIDE a loop, as you move away from the perimeter, you are moving closer to all the rest of it.
They use two loops to make a volume that has a constant H field in 3 dimensions.
https://en.wikipedia.org/wiki/Helmholtz_coil
I think the dog fence cannot be based on MAGNETIC fields alone but rather uses EM fields.
If it was based on MAGNETIC fields alone, the entire area inside the loop would active the collar.
Mark
bloggs.fred...@gmail.com
Mar 15, 2016, 9:30:50 AM3/15/16
to
Jeroen Belleman
Mar 15, 2016, 10:10:58 AM3/15/16
to
On 2016-03-15 13:53, mako...@yahoo.com wrote:
> On Monday, March 14, 2016 at 4:33:35 PM UTC-4, Jeroen Belleman
> wrote:
>> On 14/03/16 16:54, mako...@yahoo.com wrote: [...]
>>> this is an interesting problem.
>>>
>>> Isn't the H field inside a loop nearly constant ANYWHERE inside
>>> the perimiter of the loop?
>>>
>>
>> The field of a single wire drops off as 1/d. The total field is
>> the sum of several of those, so while it doesn't drop off as fast
>> inside as outside the perimeter, it's certainly not constant.
>>
>> Jeroen Belleman
>
> I believe the MAGNETIC field INSIDE a loop is essentially constant
> in the plane of the loop.
You already said that. My measurement contradicts your belief
> On Monday, March 14, 2016 at 4:33:35 PM UTC-4, Jeroen Belleman
> wrote:
>> On 14/03/16 16:54, mako...@yahoo.com wrote: [...]
>>> this is an interesting problem.
>>>
>>> Isn't the H field inside a loop nearly constant ANYWHERE inside
>>> the perimiter of the loop?
>>>
>>
>> The field of a single wire drops off as 1/d. The total field is
>> the sum of several of those, so while it doesn't drop off as fast
>> inside as outside the perimeter, it's certainly not constant.
>>
>> Jeroen Belleman
>
> I believe the MAGNETIC field INSIDE a loop is essentially constant
> in the plane of the loop.
and so does the theory. (Which I also already said...)
Surely you have no trouble accepting that the H field would
be much stronger very close to one wire rather than near
the centre of the loop? This 'constant field inside a loop'
is only an approximation, and a pretty rough one at that,
valid only for certain geometries and if you're not too picky.
Jeroen Belleman
George Herold
Mar 15, 2016, 11:40:08 AM3/15/16
to
have to do my own experiment... I've got this image that once you are thicker than
the skin depth the inside and outside of a metal shield are decoupled. With separate current flowing around on each surface. I don't see how grounding on both ends
would make much difference. (Assuming the length of the shield is a lot less than
the wavelength of the AC signal on the wire.)
George H.
>
> Jeroen Belleman
Jeroen Belleman
Mar 15, 2016, 12:31:23 PM3/15/16
to
On 2016-03-15 16:40, George Herold wrote:
> On Tuesday, March 15, 2016 at 4:09:48 AM UTC-4, Jeroen Belleman
> wrote:
>> On 2016-03-15 02:39, George Herold wrote:
>>> On Monday, March 14, 2016 at 4:16:45 PM UTC-4, Jeroen Belleman
>>> wrote:
>>>> On 14/03/16 15:22, George Herold wrote:
>>>>> On Monday, March 14, 2016 at 5:42:58 AM UTC-4, Jeroen
>>>>> Belleman wrote:
>>>> [...]
>>>>>>
>>>>>> Well, I rigged a miniature dog fence, [...] So, as I've
>>>>>> said, pipe does not work to shield the signal.
>>>>>> Back-tracking and twisting the wires of some length *does*
>>>>>> work.
>>>>>>
>>>>>> Jeroen Belleman
>>>>>
>>>>> Interesting, thanks for the experiment. What puzzles me is
>>>>> that I can use mu-metal to shield static and low frequency
>>>>> B-fields... so in my model of the world the iron should do
>>>>> something. Does one need "soft" iron?
>>>>>
>>>>> George H.
[...]
> On Tuesday, March 15, 2016 at 4:09:48 AM UTC-4, Jeroen Belleman
> wrote:
>> On 2016-03-15 02:39, George Herold wrote:
>>> On Monday, March 14, 2016 at 4:16:45 PM UTC-4, Jeroen Belleman
>>> wrote:
>>>> On 14/03/16 15:22, George Herold wrote:
>>>>> On Monday, March 14, 2016 at 5:42:58 AM UTC-4, Jeroen
>>>>> Belleman wrote:
>>>> [...]
>>>>>>
>>>>>> Well, I rigged a miniature dog fence, [...] So, as I've
>>>>>> said, pipe does not work to shield the signal.
>>>>>> Back-tracking and twisting the wires of some length *does*
>>>>>> work.
>>>>>>
>>>>>> Jeroen Belleman
>>>>>
>>>>> Interesting, thanks for the experiment. What puzzles me is
>>>>> that I can use mu-metal to shield static and low frequency
>>>>> B-fields... so in my model of the world the iron should do
>>>>> something. Does one need "soft" iron?
>>>>>
>>>>> George H.
>>>
>>> Did you ground the cylinders, or just let them float
>>> electrically? (with transmitter sending wrt the same "ground".)
>>>
>>>
>>> George H.
>>>
>>
>> The pipes were floating. A single-point ground wouldn't make any
>> significant difference, but ground both ends and you'll open up a
>> whole can of worms to keep this group busy for months. ;-)
>
> Hmm I'd think a single point ground would make a big difference..
> maybe I'll have to do my own experiment... I've got this image that
> once you are thicker than the skin depth the inside and outside of a
> metal shield are decoupled. With separate current flowing around on
> each surface. I don't see how grounding on both ends would make
> much difference. (Assuming the length of the shield is a lot less
> than the wavelength of the AC signal on the wire.)
>
> George H.
On thinking this over, I still don't think a single-point
>>> Did you ground the cylinders, or just let them float
>>> electrically? (with transmitter sending wrt the same "ground".)
>>>
>>>
>>> George H.
>>>
>>
>> The pipes were floating. A single-point ground wouldn't make any
>> significant difference, but ground both ends and you'll open up a
>> whole can of worms to keep this group busy for months. ;-)
>
> Hmm I'd think a single point ground would make a big difference..
> maybe I'll have to do my own experiment... I've got this image that
> once you are thicker than the skin depth the inside and outside of a
> metal shield are decoupled. With separate current flowing around on
> each surface. I don't see how grounding on both ends would make
> much difference. (Assuming the length of the shield is a lot less
> than the wavelength of the AC signal on the wire.)
>
> George H.
ground on the tube would make any difference. The signal
voltage on the wire is very small because the impedance of
the loop is so low. Nothing changes if there is no current
flowing through the ground wire.
On the other hand, I admit that you are likely correct that
grounding both ends won't make much of a difference as
compared to a single-point ground. The major part of the
current flowing over the outside surface of the tube will
keep doing so because that's by far the lowest impedance
path available.
Now, where did I put that miniature dog fence...
Jeroen Belleman
George Herold
Mar 15, 2016, 12:45:52 PM3/15/16
to
You might be right. I've had very little success at trying to shield
magnetic fields. Whereas electrostatic fields are easy.
I did this hand-wavy skin depth argument, but to be honest I'm not
sure it applies when you have a near field situation as is the case here.
George H.
>
> Jeroen Belleman
whit3rd
Mar 15, 2016, 1:42:43 PM3/15/16
to
On Tuesday, March 15, 2016 at 1:23:43 AM UTC-7, Jeroen Belleman wrote:
> On 2016-03-15 08:19, whit3rd wrote:
> > On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
> >>>> Huh? the current on the inner surface of the pipe will tend to cancel
> >>>> the current in the wire, but the current on the outer surface
> >
> > That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> > current carrying contacts at its endpoints.
> ... The current on
> On 2016-03-15 08:19, whit3rd wrote:
> > On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
> >>>> Huh? the current on the inner surface of the pipe will tend to cancel
> >>>> the current in the wire, but the current on the outer surface
> >
> > That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> > current carrying contacts at its endpoints.
> the inner surface of the pipe (almost) cancels the current on
> the wire, and the circuit is completed by that current flowing
> back over the outside surface of the tube. Nett result: The
> B-field outside the tube is the same as if the tube hadn't
> been there.
This is getting silly. The current on the inner surface of the pipe is
> the wire, and the circuit is completed by that current flowing
> back over the outside surface of the tube. Nett result: The
> B-field outside the tube is the same as if the tube hadn't
> been there.
an eddy-current, there is electrical resistance and loss of energy, and
it changes the impedance of the loop.
The eddy current doesn't reach the outside surface of the pipe until and unless
it magnetizes (it's too thick to do so at the frequency of interest)
The "net result' is an impedance change in the loop, and yes, the B-field outside
the tube is the same as if the tube hadn't been there, UNLESS the impedance
change loads the generator. Eddy currents don't cancel the B-field
caused by the wire. There wasn't any hope that they would: the geometry is wrong.
The only way to make current in the pipe to cancel the B-field around the wire,
is to make a net axial current. There aren't any electrical connections at the pipe ends,
so there's no net axial current; Kirchoff insists.
mako...@yahoo.com
Mar 15, 2016, 2:05:25 PM3/15/16
to
On Tuesday, March 15, 2016 at 10:10:58 AM UTC-4, Jeroen Belleman wrote:
> On 2016-03-15 13:53, mako...@yahoo.com wrote:
> > On Monday, March 14, 2016 at 4:33:35 PM UTC-4, Jeroen Belleman
> > wrote:
> >> On 14/03/16 16:54, mako...@yahoo.com wrote: [...]
> >>> this is an interesting problem.
> >>>
> >>> Isn't the H field inside a loop nearly constant ANYWHERE inside
> >>> the perimiter of the loop?
> >>>
> >>
> >> The field of a single wire drops off as 1/d. The total field is
> >> the sum of several of those, so while it doesn't drop off as fast
> >> inside as outside the perimeter, it's certainly not constant.
> >>
> >> Jeroen Belleman
> >
> > I believe the MAGNETIC field INSIDE a loop is essentially constant
> > in the plane of the loop.
>
> You already said that. My measurement contradicts your belief
> and so does the theory. (Which I also already said...)
>
Got any references to the theory?
> On 2016-03-15 13:53, mako...@yahoo.com wrote:
> > On Monday, March 14, 2016 at 4:33:35 PM UTC-4, Jeroen Belleman
> > wrote:
> >> On 14/03/16 16:54, mako...@yahoo.com wrote: [...]
> >>> this is an interesting problem.
> >>>
> >>> Isn't the H field inside a loop nearly constant ANYWHERE inside
> >>> the perimiter of the loop?
> >>>
> >>
> >> The field of a single wire drops off as 1/d. The total field is
> >> the sum of several of those, so while it doesn't drop off as fast
> >> inside as outside the perimeter, it's certainly not constant.
> >>
> >> Jeroen Belleman
> >
> > I believe the MAGNETIC field INSIDE a loop is essentially constant
> > in the plane of the loop.
>
> You already said that. My measurement contradicts your belief
> and so does the theory. (Which I also already said...)
>
Are you sure "your experiment" was responding to H field ONLY?
> Surely you have no trouble accepting that the H field would
> be much stronger very close to one wire rather than near
> the centre of the loop? This 'constant field inside a loop'
> is only an approximation, and a pretty rough one at that,
> valid only for certain geometries and if you're not too picky.
>
> Jeroen Belleman
the magnetic field inside a loop is constant in the plane of the loop
http://physics.stackexchange.com/questions/14024/why-is-the-magnetic-field-inside-a-solenoid-constant
http://teacher.pas.rochester.edu/phy122/Lecture_Notes/Chapter31/chapter31.html
Don't worry, I won't say it a third time.
Mark
George Herold
Mar 15, 2016, 2:10:12 PM3/15/16
to
On Tuesday, March 15, 2016 at 1:42:43 PM UTC-4, whit3rd wrote:
> On Tuesday, March 15, 2016 at 1:23:43 AM UTC-7, Jeroen Belleman wrote:
> > On 2016-03-15 08:19, whit3rd wrote:
> > > On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
>
> > >>>> Huh? the current on the inner surface of the pipe will tend to cancel
> > >>>> the current in the wire, but the current on the outer surface
> > >
> > > That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> > > current carrying contacts at its endpoints.
>
> > ... The current on
> > the inner surface of the pipe (almost) cancels the current on
> > the wire, and the circuit is completed by that current flowing
> > back over the outside surface of the tube. Nett result: The
> > B-field outside the tube is the same as if the tube hadn't
> > been there.
>
> This is getting silly. The current on the inner surface of the pipe is
> an eddy-current, there is electrical resistance and loss of energy, and
> it changes the impedance of the loop.
Not silly to me... I've still got grounding and shielding confusions.
> On Tuesday, March 15, 2016 at 1:23:43 AM UTC-7, Jeroen Belleman wrote:
> > On 2016-03-15 08:19, whit3rd wrote:
> > > On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
>
> > >>>> Huh? the current on the inner surface of the pipe will tend to cancel
> > >>>> the current in the wire, but the current on the outer surface
> > >
> > > That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> > > current carrying contacts at its endpoints.
>
> > ... The current on
> > the inner surface of the pipe (almost) cancels the current on
> > the wire, and the circuit is completed by that current flowing
> > back over the outside surface of the tube. Nett result: The
> > B-field outside the tube is the same as if the tube hadn't
> > been there.
>
> This is getting silly. The current on the inner surface of the pipe is
> an eddy-current, there is electrical resistance and loss of energy, and
> it changes the impedance of the loop.
I took two air coils, aligned along z-axis, stimulated one and picked up
with the other. I stuck a piece of 1/16" Al between them.
No change for freq < ~100 Hz.
I started to see attenuation at ~1kHz.
(With also a bit of phase shift ?)
>
> The eddy current doesn't reach the outside surface of the pipe until and unless
> it magnetizes (it's too thick to do so at the frequency of interest)
>
> The "net result' is an impedance change in the loop, and yes, the B-field outside
> the tube is the same as if the tube hadn't been there, UNLESS the impedance
> change loads the generator. Eddy currents don't cancel the B-field
> caused by the wire. There wasn't any hope that they would: the geometry is wrong.
> The only way to make current in the pipe to cancel the B-field around the wire,
> is to make a net axial current. There aren't any electrical connections at the pipe ends,
So if one connected each end with a loop of wire...?
George H.
Jeroen Belleman
Mar 15, 2016, 4:35:05 PM3/15/16
to
On 15/03/16 18:42, whit3rd wrote:
> On Tuesday, March 15, 2016 at 1:23:43 AM UTC-7, Jeroen Belleman wrote:
>> On 2016-03-15 08:19, whit3rd wrote:
>>> On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
>
>>>>>> Huh? the current on the inner surface of the pipe will tend to cancel
>>>>>> the current in the wire, but the current on the outer surface
>>>
>>> That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
>>> current carrying contacts at its endpoints.
>
>> ... The current on
>> the inner surface of the pipe (almost) cancels the current on
>> the wire, and the circuit is completed by that current flowing
>> back over the outside surface of the tube. Nett result: The
>> B-field outside the tube is the same as if the tube hadn't
>> been there.
>
> This is getting silly. The current on the inner surface of the pipe is
> an eddy-current, there is electrical resistance and loss of energy, and
> it changes the impedance of the loop.
In what direction do you think that current runs?
> On Tuesday, March 15, 2016 at 1:23:43 AM UTC-7, Jeroen Belleman wrote:
>> On 2016-03-15 08:19, whit3rd wrote:
>>> On Monday, March 14, 2016 at 10:01:28 PM UTC-7, Jasen Betts wrote:
>
>>>>>> Huh? the current on the inner surface of the pipe will tend to cancel
>>>>>> the current in the wire, but the current on the outer surface
>>>
>>> That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
>>> current carrying contacts at its endpoints.
>
>> ... The current on
>> the inner surface of the pipe (almost) cancels the current on
>> the wire, and the circuit is completed by that current flowing
>> back over the outside surface of the tube. Nett result: The
>> B-field outside the tube is the same as if the tube hadn't
>> been there.
>
> This is getting silly. The current on the inner surface of the pipe is
> an eddy-current, there is electrical resistance and loss of energy, and
> it changes the impedance of the loop.
Jeroen Belleman
Jeroen Belleman
Mar 15, 2016, 4:56:32 PM3/15/16
to
encircled surface. This is one single-turn encircling a relatively
huge surface. A dog fence. Not at all the same geometry.
My probe is a small coil with just a few turns of thick wire between
the pins of a coaxial connector, not a geometry very receptive to
E-fields. It's easy to check for that, too, just by rotating the
coil 180 degrees so the H-field changes sign, while the E-field does
not. Should be clearly visible if that was the problem. It's not.
The theory is simply Ampere's law plus superposition.
Jeroen Belleman
George Herold
Mar 15, 2016, 9:49:11 PM3/15/16
to
Redrawing it, the tube and loop is a one turn
transformer.. (which Mike k. mentioned up thread)
And the transformer has to have the same current...
which turns into another piece of the dog fence.
(a fun puzzle.)
Thanks again for the experiment.
George H.
>
> Jeroen Belleman
mako...@yahoo.com
Mar 15, 2016, 10:52:41 PM3/15/16
to
Did you read this part...... the more surprising thing about the magnetic field inside a solenoid is not that it's uniform along the length, but that it's uniform in the perpendicular directions -- that is, that the field doesn't depend on whether you're close to the axis or far from it (as long as you're inside it). It'd be easy to imagine the field would either drop off or get stronger as you move perpendicular to the axis, but it doesn't (again, for a long solenoid when you're not near the ends).
whit3rd
Mar 16, 2016, 12:17:45 AM3/16/16
to
On Tuesday, March 15, 2016 at 11:10:12 AM UTC-7, George Herold wrote:
> On Tuesday, March 15, 2016 at 1:42:43 PM UTC-4, whit3rd wrote:
> > > >>>> Huh? the current on the inner surface of the pipe will tend to cancel
> > > >>>> the current in the wire
> On Tuesday, March 15, 2016 at 1:42:43 PM UTC-4, whit3rd wrote:
> > > >>>> Huh? the current on the inner surface of the pipe will tend to cancel
> > > >>>> the current in the wire
> > > > That's what happens in coax cable, NOT with a length of iron pipe that hasn't any
> > > > current carrying contacts at its endpoints.
> > ... Eddy currents don't cancel the B-field
> > > > current carrying contacts at its endpoints.
> > caused by the wire. There wasn't any hope that they would: the geometry is wrong.
> > The only way to make current in the pipe to cancel the B-field around the wire,
> > is to make a net axial current. There aren't any electrical connections at the pipe ends,
> Oh, (head slap), I was picturing the currents wrong! (Thanks)
> So if one connected each end with a loop of wire...?
Then the pipe and the loop of wire would constitute a secondary winding transformer-coupled
> > The only way to make current in the pipe to cancel the B-field around the wire,
> > is to make a net axial current. There aren't any electrical connections at the pipe ends,
> Oh, (head slap), I was picturing the currents wrong! (Thanks)
> So if one connected each end with a loop of wire...?
to the primary loop. By Lenz's law, it'd attenuate the B-field around the pipe-enclosed
primary wiring, and the secondary loop might carry enough current to make the
fence effect.
krw
Mar 16, 2016, 12:23:12 AM3/16/16
to
On Mon, 14 Mar 2016 07:12:27 -0700 (PDT), George Herold
<ghe...@teachspin.com> wrote:
>On Sunday, March 13, 2016 at 10:31:15 PM UTC-4, krw wrote:
>> On Sun, 13 Mar 2016 16:54:05 -0700 (PDT), George Herold
>> <ghe...@teachspin.com> wrote:
>>
>> >On Saturday, March 12, 2016 at 8:09:25 PM UTC-5, krw wrote:
>> >> On Sat, 12 Mar 2016 16:42:08 -0800 (PST), Phil Hobbs
>> >> <pcdh...@gmail.com> wrote:
>> >>
>> >> >I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
>> >> >
>> >> >I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
>> >>
>> >> I like dogs but they take too much work so we have a couple of cats
>> >> (one just climbed up on my feet). I agree, whatever the pet, their
>> >> welfare becomes your responsibility, once they're taken into your
>> >> home.
>> >>
>> >> BTW, coyotes aren't the only predator that feeds on pets. Owls will
>> >> take cats and small dogs, too. A friend had an hawk grab his Fifi
>> >> from his back yard (but released it), while he was watching.
>> >>
>> >> I'm not one who objects to hunting coaters with Greyhounds, though. I
>> >> could deal with fewer coyotes around here, too.
>> >
>> >Re: dog care,
>> >You just need enough room, :^)
>> > Our dogs are no more work than the cats,
>> >(maybe less... I'd rather do the ~one day spring clean up
>> >of winter dog poop, than the kitty liter box through the winter...
>> >Perhaps it's better there in the south..
>>
>> You can't leave a dog alone for a long weekend. We leave the cats in
>> the house for a week to ten days, a couple of times a year, and have a
>> neighbor (high school) kid look in on them once or twice a day and
>> clean the (automatic) liter box once a week.
>Yeah, if we go away the cats and dogs stay in the garage and a
>women down the road comes to care for them once a day.
Too hot in the garage.
>>
>> *Everything* is better in the South. ;-)
>I was going to add that the one thing I don't miss
>about the south is all the ticks and chiggers that
>the dogs bring back in the late summer.
We've never had ticks as badly as we had them in NY (and at my
grandparents in the MI UP). Actually, the bugs in the South have been
minimal. We did have a scorpion in the living room last summer. One
of the cats was playing with it.
>
>George H.
>>
>> >(When there's no white stuff on the ground everyone poops
>> >in the field. Well except for the wife, kids and I.)
>>
>> ;-)
>>
>> >We've got some coyote, more predators to control the deer
>> >population would be good. Deer seem to be even more of a
>> >problem in the suburbs, no human hunters... and more coyote?
>>
>> We have a lot of deer around. They munch on our plants and leave
>> presents in the yard. They *love* the roses.
>> >
>> >I'm totally a dog person.
>> >Cats are tolerated for their vermin control, funny antics
>> >are the gravy.
>> >
>> We're really dog people, too, but they do require more attention. Our
>> cats have all been people cats (they sleep *on* my wife), so it's not
>> like they're just sharing the house with their servants.
<ghe...@teachspin.com> wrote:
>On Sunday, March 13, 2016 at 10:31:15 PM UTC-4, krw wrote:
>> On Sun, 13 Mar 2016 16:54:05 -0700 (PDT), George Herold
>> <ghe...@teachspin.com> wrote:
>>
>> >On Saturday, March 12, 2016 at 8:09:25 PM UTC-5, krw wrote:
>> >> On Sat, 12 Mar 2016 16:42:08 -0800 (PST), Phil Hobbs
>> >> <pcdh...@gmail.com> wrote:
>> >>
>> >> >I'm not a dog person myself, so (as they say) I don't have a dog in this fight. ;)
>> >> >
>> >> >I do think it's a shame if some animal gets chewed up because its owner didn't care, though.
>> >>
>> >> I like dogs but they take too much work so we have a couple of cats
>> >> (one just climbed up on my feet). I agree, whatever the pet, their
>> >> welfare becomes your responsibility, once they're taken into your
>> >> home.
>> >>
>> >> BTW, coyotes aren't the only predator that feeds on pets. Owls will
>> >> take cats and small dogs, too. A friend had an hawk grab his Fifi
>> >> from his back yard (but released it), while he was watching.
>> >>
>> >> I'm not one who objects to hunting coaters with Greyhounds, though. I
>> >> could deal with fewer coyotes around here, too.
>> >
>> >Re: dog care,
>> >You just need enough room, :^)
>> > Our dogs are no more work than the cats,
>> >(maybe less... I'd rather do the ~one day spring clean up
>> >of winter dog poop, than the kitty liter box through the winter...
>> >Perhaps it's better there in the south..
>>
>> You can't leave a dog alone for a long weekend. We leave the cats in
>> the house for a week to ten days, a couple of times a year, and have a
>> neighbor (high school) kid look in on them once or twice a day and
>> clean the (automatic) liter box once a week.
>Yeah, if we go away the cats and dogs stay in the garage and a
>women down the road comes to care for them once a day.
Too hot in the garage.
>>
>> *Everything* is better in the South. ;-)
>I was going to add that the one thing I don't miss
>about the south is all the ticks and chiggers that
>the dogs bring back in the late summer.
We've never had ticks as badly as we had them in NY (and at my
grandparents in the MI UP). Actually, the bugs in the South have been
minimal. We did have a scorpion in the living room last summer. One
of the cats was playing with it.
>
>George H.
>>
>> >(When there's no white stuff on the ground everyone poops
>> >in the field. Well except for the wife, kids and I.)
>>
>> ;-)
>>
>> >We've got some coyote, more predators to control the deer
>> >population would be good. Deer seem to be even more of a
>> >problem in the suburbs, no human hunters... and more coyote?
>>
>> We have a lot of deer around. They munch on our plants and leave
>> presents in the yard. They *love* the roses.
>> >
>> >I'm totally a dog person.
>> >Cats are tolerated for their vermin control, funny antics
>> >are the gravy.
>> >
>> We're really dog people, too, but they do require more attention. Our
>> cats have all been people cats (they sleep *on* my wife), so it's not
>> like they're just sharing the house with their servants.
whit3rd
Mar 16, 2016, 1:08:54 AM3/16/16
to
1mm from the inner surface of the pipe, it is parallel to the enclosed wire current.
2mm from the inner surface of the pipe, there is negligible current.
The outer diameter of the pipe is 3mm from the inner surface.
Jasen Betts
Mar 16, 2016, 4:01:03 AM3/16/16
to
added is probably insignificant.
--
\_(ツ)_
Jasen Betts
Mar 16, 2016, 4:01:03 AM3/16/16
to
On 2016-03-15, amdx <noj...@knology.net> wrote:
it will reduce the magnetic field round the whole perimiter
and concentrating the electric field at the feed point and
at the locaton of the beads.
--
\_(ツ)_
Jeroen Belleman
Mar 16, 2016, 4:39:52 AM3/16/16
to
direction right. Do I read you correctly? Do you state
there is no current on the outer surface because it's
several skin-depths away from the inner surface?
At my 1MHz frequency, the current essentially flows over
the surface everywhere, anti-parallel inside the tube,
indeed, but parallel on the outside surface. There's
almost nothing in the bulk metal.
Jeroen Belleman
Jasen Betts
Mar 16, 2016, 5:01:29 AM3/16/16
to
On 2016-03-15, mako...@yahoo.com <mako...@yahoo.com> wrote:
> On Monday, March 14, 2016 at 4:33:35 PM UTC-4, Jeroen Belleman wrote:
>> On 14/03/16 16:54, mako...@yahoo.com wrote:
>> [...]
>> > this is an interesting problem.
>> >
>> > Isn't the H field inside a loop nearly constant ANYWHERE inside the perimiter of the loop?
>> >
>>
>> The field of a single wire drops off as 1/d. The total field is the
>> sum of several of those, so while it doesn't drop off as fast inside
>> as outside the perimeter, it's certainly not constant.
>>
>> Jeroen Belleman
>
> I believe the MAGNETIC field INSIDE a loop is essentially constant in the plane of the loop.
That's an over-simplification, if you get close enough to wire you'll
> On Monday, March 14, 2016 at 4:33:35 PM UTC-4, Jeroen Belleman wrote:
>> On 14/03/16 16:54, mako...@yahoo.com wrote:
>> [...]
>> > this is an interesting problem.
>> >
>> > Isn't the H field inside a loop nearly constant ANYWHERE inside the perimiter of the loop?
>> >
>>
>> The field of a single wire drops off as 1/d. The total field is the
>> sum of several of those, so while it doesn't drop off as fast inside
>> as outside the perimeter, it's certainly not constant.
>>
>> Jeroen Belleman
>
> I believe the MAGNETIC field INSIDE a loop is essentially constant in the plane of the loop.
see the field strength following a 1/r curve but once you get 1 quarter of
the way across the yard the field looks pretty reasonably constant.
If you cycle on the streets when there's little traffic you'll see that
a bicycle doesn't have enough metal to trigger the buried metal detector
loop that drives the traffic lights if parked in the centre of the
loop, but put one rim over the seam where they cut the loop in and the
light will soon go green.
clearly the field is stronger next to the wire.
> If it was based on MAGNETIC fields alone, the entire area inside the loop would active the collar.
--
\_(ツ)_
mako...@yahoo.com
Mar 16, 2016, 8:52:58 AM3/16/16
to
The field near of an infinte straight wire varies as is 1/r, no issue there.
If we start with a RECTANGULAR loop say 100 feet on a side, when you get close enough to one wire, it approximates to an infinte straight wire. So I agree in that case.
So then I thought perhaps a CIRCULAR loop might be different.
But no, as you get closer and closer to the wire of a circular loop, the curvature appears to reduce and again we approach the infinte straight wire case.
So I guess you are correct, the field may be relatively constant inside the loop away from any wire, but as you get "close enough" to any wire, it __must__ approach the infinite straight wire case which is of course 1/r.
Thanks for maintaining a civil discussion, a rarity on usenet these days.
Mark
Bob Engelhardt
Mar 16, 2016, 7:17:27 PM3/16/16
to
Wow - what a long discussion. I couldn't follow most of it and since
there was so much disagreement, I wouldn't have known what to believe
anyhow.
I tried the iron pipe thing - I used a 1/2" Sch 40 pipe about 4' long.
I could not detect any difference in the receiver's detection.
My solution was to run the wire in the basement, low enough to not
trigger when passed over (3=4' min). Otherwise, I probably would have
used Dan's idea of paralleling 2 more wires several feet apart.
Thanks for all the replies,
Bob
there was so much disagreement, I wouldn't have known what to believe
anyhow.
I tried the iron pipe thing - I used a 1/2" Sch 40 pipe about 4' long.
I could not detect any difference in the receiver's detection.
My solution was to run the wire in the basement, low enough to not
trigger when passed over (3=4' min). Otherwise, I probably would have
used Dan's idea of paralleling 2 more wires several feet apart.
Thanks for all the replies,
Bob
whit3rd
Mar 16, 2016, 9:06:36 PM3/16/16
to
On Wednesday, March 16, 2016 at 1:39:52 AM UTC-7, Jeroen Belleman wrote:
> On 2016-03-16 06:08, whit3rd wrote:
[about wire carrying signal, inside a buried pipe section]
> On 2016-03-16 06:08, whit3rd wrote:
> OK, you want to talk skin depth. At least you have the
> direction right. Do I read you correctly? Do you state
> there is no current on the outer surface because it's
> several skin-depths away from the inner surface?
>
> At my 1MHz frequency, the current essentially flows over
> the surface everywhere, anti-parallel inside the tube,
> indeed, but parallel on the outside surface. There's
> almost nothing in the bulk metal.
depth of 82 um, and iron pipe would be an order of magnitude less, because it's MAGNETIC.
That current distribution you describe is of a pipe magnetized in
the circumferential direction, but you can't magnetize iron that
fast: that's why megahertz inductors have ferrite or air cores.
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