LTspice tapped inductor

I have an inductor wound on some 22mm plastic pipe, so essentially 
air-cored.  It's over 120 turns, 700mm long and uses resistance wire. 
It's about 12uH.

There are 30 capacitors connected evenly along the coil commoned to a 
copper pipe busbar.  It simulates a long, peculiar transmission line.

I want to LTspice it.  OK, lots of small inductors with some resistance 
and the capacitors.

But these small inductors are coupled by virtue of being co-axial and 
adjacent and being part of a single larger inductor.  A tapped inductor 
is surely a transformer, so how would I enumerate the coupling 
coefficients, or is this something which can be ignored?

I know I can use an LTRA, but that doesn't simulate the discrete nature 
of the capacitance, and I really want to simulate the simulated line.

-- 
Cheers
Clive

On Monday, August 15, 2022 at 7:57:33 PM UTC+10, Clive Arthur wrote:
> I have an inductor wound on some 22mm plastic pipe, so essentially 
> air-cored. It's over 120 turns, 700mm long and uses resistance wire. 
> It's about 12uH. 
> 
> There are 30 capacitors connected evenly along the coil commoned to a 
> copper pipe busbar. It simulates a long, peculiar transmission line. 
> 
> I want to LTspice it. OK, lots of small inductors with some resistance 
> and the capacitors. 
> 
> But these small inductors are coupled by virtue of being co-axial and 
> adjacent and being part of a single larger inductor. A tapped inductor 
> is surely a transformer, so how would I enumerate the coupling 
> coefficients, or is this something which can be ignored? 

K L1 L2 ... Ln 0.2

lets you set up a single coupling coefficient (here 0.2) for a collection of inductors. Obviously more remote winding are less closely coupled.

I don't suppose that there's anything stop you doing a series of coupled inductors, say 

K1 L1 L2 0.2   K2 L2 L3 0.2  K3 L3 L4 0.2

which wouldn't be entirely right either

> I know I can use an LTRA, but that doesn't simulate the discrete nature 
> of the capacitance, and I really want to simulate the simulated line. 

My guess would be that the discrete nature of the capacitors won't make a lot of difference for frequencies where the wavelength is longer than a couple of sections.

-- 
Bill Sloman, Sydney

On Mon, 15 Aug 2022 10:57:25 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

>I have an inductor wound on some 22mm plastic pipe, so essentially 
>air-cored.  It's over 120 turns, 700mm long and uses resistance wire. 
>It's about 12uH.
>
>There are 30 capacitors connected evenly along the coil commoned to a 
>copper pipe busbar.  It simulates a long, peculiar transmission line.
>
>I want to LTspice it.  OK, lots of small inductors with some resistance 
>and the capacitors.
>
>But these small inductors are coupled by virtue of being co-axial and 
>adjacent and being part of a single larger inductor.  A tapped inductor 
>is surely a transformer, so how would I enumerate the coupling 
>coefficients, or is this something which can be ignored?
>
>I know I can use an LTRA, but that doesn't simulate the discrete nature 
>of the capacitance, and I really want to simulate the simulated line.

Why resistance wire? With enough resistance (namely many ns tau per
stage) it becomes a string of RCs, about as ugly a txline as possible.

What's total r ? How big are the caps?

Have you built one? What's the step response like?

What's the application?

On Tuesday, August 16, 2022 at 12:27:37 AM UTC+10, jla...@highlandsniptechnology.com wrote:
> On Mon, 15 Aug 2022 10:57:25 +0100, Clive Arthur 
> <cl...@nowaytoday.co.uk> wrote: 
> 
> >I have an inductor wound on some 22mm plastic pipe, so essentially 
> >air-cored. It's over 120 turns, 700mm long and uses resistance wire. 
> >It's about 12uH. 
> > 
> >There are 30 capacitors connected evenly along the coil commoned to a 
> >copper pipe busbar. It simulates a long, peculiar transmission line. 
> > 
> >I want to LTspice it. OK, lots of small inductors with some resistance 
> >and the capacitors. 
> > 
> >But these small inductors are coupled by virtue of being co-axial and 
> >adjacent and being part of a single larger inductor. A tapped inductor 
> >is surely a transformer, so how would I enumerate the coupling 
> >coefficients, or is this something which can be ignored? 
> > 
> >I know I can use an LTRA, but that doesn't simulate the discrete nature 
> >of the capacitance, and I really want to simulate the simulated line.
>
> Why resistance wire?

That might just be driven by application.

> With enough resistance (namely many ns tau per 
> stage) it becomes a string of RCs, about as ugly a txline as possible. 

He hasn't specified the resistance, or the capacitances, so the nature of the transmission line is obscure.

> What's total r ? How big are the caps? 
> 
> Have you built one? What's the step response like? 

He says he has got one - maybe he built it. Clearly, measuring the actual step response is difficult for some reason or other so he wants to simulate it

> What's the application?

Always a good question. Clive Arthur has posted here often enough that he should have known that he'd get asked it. He's not clueless newbie.

-- 
Bill Sloman, Sydney

On 15/08/2022 16:12, Anthony William Sloman wrote:
> On Tuesday, August 16, 2022 at 12:27:37 AM UTC+10, jla...@highlandsniptechnology.com wrote:
>> On Mon, 15 Aug 2022 10:57:25 +0100, Clive Arthur
>> <cl...@nowaytoday.co.uk> wrote:
>>
>>> I have an inductor wound on some 22mm plastic pipe, so essentially
>>> air-cored. It's over 120 turns, 700mm long and uses resistance wire.
>>> It's about 12uH.
>>>
>>> There are 30 capacitors connected evenly along the coil commoned to a
>>> copper pipe busbar. It simulates a long, peculiar transmission line.
>>>
>>> I want to LTspice it. OK, lots of small inductors with some resistance
>>> and the capacitors.
>>>
>>> But these small inductors are coupled by virtue of being co-axial and
>>> adjacent and being part of a single larger inductor. A tapped inductor
>>> is surely a transformer, so how would I enumerate the coupling
>>> coefficients, or is this something which can be ignored?
>>>
>>> I know I can use an LTRA, but that doesn't simulate the discrete nature
>>> of the capacitance, and I really want to simulate the simulated line.
>>
>> Why resistance wire?
> 
> That might just be driven by application.
> 
>> With enough resistance (namely many ns tau per
>> stage) it becomes a string of RCs, about as ugly a txline as possible.
> 
> He hasn't specified the resistance, or the capacitances, so the nature of the transmission line is obscure.
> 
>> What's total r ? How big are the caps?
>>
>> Have you built one? What's the step response like?
> 
> He says he has got one - maybe he built it. Clearly, measuring the actual step response is difficult for some reason or other so he wants to simulate it
> 
>> What's the application?
> 
> Always a good question. Clive Arthur has posted here often enough that he should have known that he'd get asked it. He's not clueless newbie.
> 
Trouble is, as ever, NDAs.  I have built a simulator (maybe emulator is 
a better word) as described.  The R is representative of the real R, as 
is the C - totalling 10R and 160uF,  The L (12uH) is guestimated from a 
reasonable assumption of propagation velocity and length. Yes, it's very 
low impedance.  It was quite a juggling act to get all the parameters 
about right.

It's simply not possible at this stage to test with the Real Thing, so 
my emulator will have to do, but I'd also like to Spice the emulator to 
speed up a few things.  The Real Thing cannot be changed.

So the question is, how to Spice it?  Is the mutual inductance between 
sections of a long air-cored inductor at all significant?  Top signal 
frequency 100kHz.

This sort of thing is a weakness of mine, though less so than it was, 
which is why I ask.

-- 
Cheers
Clive

On Mon, 15 Aug 2022 17:10:48 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

>On 15/08/2022 16:12, Anthony William Sloman wrote:
>> On Tuesday, August 16, 2022 at 12:27:37 AM UTC+10, jla...@highlandsniptechnology.com wrote:
>>> On Mon, 15 Aug 2022 10:57:25 +0100, Clive Arthur
>>> <cl...@nowaytoday.co.uk> wrote:
>>>
>>>> I have an inductor wound on some 22mm plastic pipe, so essentially
>>>> air-cored. It's over 120 turns, 700mm long and uses resistance wire.
>>>> It's about 12uH.
>>>>
>>>> There are 30 capacitors connected evenly along the coil commoned to a
>>>> copper pipe busbar. It simulates a long, peculiar transmission line.
>>>>
>>>> I want to LTspice it. OK, lots of small inductors with some resistance
>>>> and the capacitors.
>>>>
>>>> But these small inductors are coupled by virtue of being co-axial and
>>>> adjacent and being part of a single larger inductor. A tapped inductor
>>>> is surely a transformer, so how would I enumerate the coupling
>>>> coefficients, or is this something which can be ignored?
>>>>
>>>> I know I can use an LTRA, but that doesn't simulate the discrete nature
>>>> of the capacitance, and I really want to simulate the simulated line.
>>>
>>> Why resistance wire?
>> 
>> That might just be driven by application.
>> 
>>> With enough resistance (namely many ns tau per
>>> stage) it becomes a string of RCs, about as ugly a txline as possible.
>> 
>> He hasn't specified the resistance, or the capacitances, so the nature of the transmission line is obscure.
>> 
>>> What's total r ? How big are the caps?
>>>
>>> Have you built one? What's the step response like?
>> 
>> He says he has got one - maybe he built it. Clearly, measuring the actual step response is difficult for some reason or other so he wants to simulate it
>> 
>>> What's the application?
>> 
>> Always a good question. Clive Arthur has posted here often enough that he should have known that he'd get asked it. He's not clueless newbie.
>> 
>Trouble is, as ever, NDAs.  I have built a simulator (maybe emulator is 
>a better word) as described.  The R is representative of the real R, as 
>is the C - totalling 10R and 160uF,  The L (12uH) is guestimated from a 
>reasonable assumption of propagation velocity and length. Yes, it's very 
>low impedance.  It was quite a juggling act to get all the parameters 
>about right.

10r and 160 uF is a time constant of 1.6 milliseconds. L/R is around a
microsecond. It's an RC network.

Really 160 uF?

>
>It's simply not possible at this stage to test with the Real Thing, so 
>my emulator will have to do, but I'd also like to Spice the emulator to 
>speed up a few things.  The Real Thing cannot be changed.
>
>So the question is, how to Spice it?  Is the mutual inductance between 
>sections of a long air-cored inductor at all significant?  Top signal 
>frequency 100kHz.

Not with a 1.6 ms time constant.

>
>This sort of thing is a weakness of mine, though less so than it was, 
>which is why I ask.

You could build a short section and measure it. Fiddle with Spice to
match the measurement. Then you can add sections in Spice.

Is this a high voltage delay line?

On 8/15/2022 6:43 AM, Anthony William Sloman wrote:
> On Monday, August 15, 2022 at 7:57:33 PM UTC+10, Clive Arthur wrote:
>> I have an inductor wound on some 22mm plastic pipe, so essentially
>> air-cored. It's over 120 turns, 700mm long and uses resistance wire.
>> It's about 12uH.
>>
>> There are 30 capacitors connected evenly along the coil commoned to a
>> copper pipe busbar. It simulates a long, peculiar transmission line.
>>
>> I want to LTspice it. OK, lots of small inductors with some resistance
>> and the capacitors.
>>
>> But these small inductors are coupled by virtue of being co-axial and
>> adjacent and being part of a single larger inductor. A tapped inductor
>> is surely a transformer, so how would I enumerate the coupling
>> coefficients, or is this something which can be ignored?
> 
> K L1 L2 ... Ln 0.2
> 
> lets you set up a single coupling coefficient (here 0.2) for a collection of inductors. Obviously more remote winding are less closely coupled.
> 
> I don't suppose that there's anything stop you doing a series of coupled inductors, say
> 
> K1 L1 L2 0.2   K2 L2 L3 0.2  K3 L3 L4 0.2
> 
> which wouldn't be entirely right either

Unfortunately LTSpice balks at doing the second and considers that a 
"non-physical winding possibility" and wants you to just do it the first way

>> I know I can use an LTRA, but that doesn't simulate the discrete nature
>> of the capacitance, and I really want to simulate the simulated line.
> 
> My guess would be that the discrete nature of the capacitors won't make a lot of difference for frequencies where the wavelength is longer than a couple of sections.
> 

On 8/15/2022 8:26 PM, bitrex wrote:
> On 8/15/2022 6:43 AM, Anthony William Sloman wrote:
>> On Monday, August 15, 2022 at 7:57:33 PM UTC+10, Clive Arthur wrote:
>>> I have an inductor wound on some 22mm plastic pipe, so essentially
>>> air-cored. It's over 120 turns, 700mm long and uses resistance wire.
>>> It's about 12uH.
>>>
>>> There are 30 capacitors connected evenly along the coil commoned to a
>>> copper pipe busbar. It simulates a long, peculiar transmission line.
>>>
>>> I want to LTspice it. OK, lots of small inductors with some resistance
>>> and the capacitors.
>>>
>>> But these small inductors are coupled by virtue of being co-axial and
>>> adjacent and being part of a single larger inductor. A tapped inductor
>>> is surely a transformer, so how would I enumerate the coupling
>>> coefficients, or is this something which can be ignored?
>>
>> K L1 L2 ... Ln 0.2
>>
>> lets you set up a single coupling coefficient (here 0.2) for a 
>> collection of inductors. Obviously more remote winding are less 
>> closely coupled.
>>
>> I don't suppose that there's anything stop you doing a series of 
>> coupled inductors, say
>>
>> K1 L1 L2 0.2   K2 L2 L3 0.2  K3 L3 L4 0.2
>>
>> which wouldn't be entirely right either
> 
> Unfortunately LTSpice balks at doing the second and considers that a 
> "non-physical winding possibility" and wants you to just do it the first 
> way

Huh, that's weird. Actually it seems to only complain about non-physical 
winding for certain values of coupling coefficient when you set it up 
that way, if you set it like 0.2 it seems ok but if you try to do say 
0.9 it balks

On Tuesday, August 16, 2022 at 2:11:20 AM UTC+10, Clive Arthur wrote:
> On 15/08/2022 16:12, Anthony William Sloman wrote: 
> > On Tuesday, August 16, 2022 at 12:27:37 AM UTC+10, jla...@highlandsniptechnology.com wrote: 
> >> On Mon, 15 Aug 2022 10:57:25 +0100, Clive Arthur 
> >> <cl...@nowaytoday.co.uk> wrote: 

<snip>

> >> What's the application? 
> > 
> > Always a good question. Clive Arthur has posted here often enough that he should have known that he'd get asked it. He's not clueless newbie. 
> >
> Trouble is, as ever, NDAs. I have built a simulator (maybe emulator is 
> a better word) as described. The R is representative of the real R, as 
> is the C - totalling 10R and 160uF, The L (12uH) is guestimated from a 
> reasonable assumption of propagation velocity and length. Yes, it's very 
> low impedance. It was quite a juggling act to get all the parameters 
> about right. 
> 
> It's simply not possible at this stage to test with the Real Thing, so 
> my emulator will have to do, but I'd also like to Spice the emulator to 
> speed up a few things. The Real Thing cannot be changed. 
> 
> So the question is, how to Spice it? Is the mutual inductance between 
> sections of a long air-cored inductor at all significant? Top signal 
> frequency 100kHz. 

https://www.amazon.com/Inductance-Calculations-Dover-Electrical-Engineering/dp/0486474402

should let you work it out . I've even got a copy.

Chapter 16  - single layer coils on cylindrical winding forms - seems to be what you want. It goes from page 142 to page 162. 
I could scan them and e-mail you the images. Making sense of the content isn't easy.

> This sort of thing is a weakness of mine, though less so than it was, which is why I ask. 

Resistance is futile, but at least it is calculable.

-- 
Bill Sloman, Sydney

On 16/08/2022 01:45, bitrex wrote:
> On 8/15/2022 8:26 PM, bitrex wrote:
>> On 8/15/2022 6:43 AM, Anthony William Sloman wrote:
>>> On Monday, August 15, 2022 at 7:57:33 PM UTC+10, Clive Arthur wrote:
>>>> I have an inductor wound on some 22mm plastic pipe, so essentially
>>>> air-cored. It's over 120 turns, 700mm long and uses resistance wire.
>>>> It's about 12uH.
>>>>
>>>> There are 30 capacitors connected evenly along the coil commoned to a
>>>> copper pipe busbar. It simulates a long, peculiar transmission line.
>>>>
>>>> I want to LTspice it. OK, lots of small inductors with some resistance
>>>> and the capacitors.
>>>>
>>>> But these small inductors are coupled by virtue of being co-axial and
>>>> adjacent and being part of a single larger inductor. A tapped inductor
>>>> is surely a transformer, so how would I enumerate the coupling
>>>> coefficients, or is this something which can be ignored?
>>>
>>> K L1 L2 ... Ln 0.2
>>>
>>> lets you set up a single coupling coefficient (here 0.2) for a 
>>> collection of inductors. Obviously more remote winding are less 
>>> closely coupled.
>>>
>>> I don't suppose that there's anything stop you doing a series of 
>>> coupled inductors, say
>>>
>>> K1 L1 L2 0.2   K2 L2 L3 0.2  K3 L3 L4 0.2
>>>
>>> which wouldn't be entirely right either
>>
>> Unfortunately LTSpice balks at doing the second and considers that a 
>> "non-physical winding possibility" and wants you to just do it the 
>> first way
> 
> Huh, that's weird. Actually it seems to only complain about non-physical 
> winding for certain values of coupling coefficient when you set it up 
> that way, if you set it like 0.2 it seems ok but if you try to do say 
> 0.9 it balks


I wonder if that's because, say, L8 has 0.9 coupling to L7 which has 0.9 
to L6 etc, so L8 has 0.9 to L7 plus 0.9 x 0.9 to L6 (etc) which is >1 ? 
  In which case, 0.5 would be the absolute max for a large number of 
inductors?

So I tried it (LTspice) with 5 inductors and 4 couplings, all equal.
K = 0.58 fails, K = 0.57 works, and that's what passes for solid proof 
round these parts.  I think "Clive's Constant" has a certain ring to it.

That could be a clue, but like I said, not really my area.

-- 
Cheers
Clive