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'[OT] HELP WITH COILS AND INDUCTANCE.'
1999\03\03@054926 by Walter Markiw

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I need to build a coil to provide an inductance in the range of 0,001 to
0,1 Henrys.
It is for a frecuency filter I am planning to build.
Thanks in advance.

1999\03\03@103555 by Dave VanHorn

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> I need to build a coil to provide an inductance in the range of
0,001 to
>0,1 Henrys.
>It is for a frecuency filter I am planning to build.
>Thanks in advance.


This will be rather difficult mechanically. This is a large inductance
value, and a large range.

1999\03\03@160602 by paulb

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Walter Markiw wrote:

>  I need to build a coil to provide an inductance in the range of 0,001
> to 0,1 Henrys.
> It is for a frequency filter I am planning to build.

 OK, enough is enough.  They've wagged you *mercilessly* on this one.

 If you *really* want to build a *fixed* or *tapped* coil in this
range, that is do-able, but you would usually use a laminated (soft)
iron core to achieve the value.  An air-cored coil is rather impractical
and a variable one, quite impractical, at least over the range you
specified.

 Audio (it is audio, isn't it?) frequency filters use active "gyrator"
circuits to synthesise inductance with op-amps and capacitors.  That's
how variable inductance is emulated.

 Generally, this is part of a well-recognised filter type using
op-amps, and I presume you should be pursuing a reference for these to
find your design.

 If there is something special which you think can't be handled this
way, perhaps you might state it and we can make suggestions accordingly.
--
 Cheers,
       Paul B.

1999\03\04@051318 by Stefan Sczekalla-Waldschmidt

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"Paul B. Webster VK2BZC" wrote:
>
> Walter Markiw wrote:
>
> >  I need to build a coil to provide an inductance in the range of 0,001
> > to 0,1 Henrys.
> > It is for a frequency filter I am planning to build.
>
>   Audio (it is audio, isn't it?) frequency filters use active "gyrator"
> circuits to synthesise inductance with op-amps and capacitors.  That's
> how variable inductance is emulated.
>
>   Generally, this is part of a well-recognised filter type using
> op-amps, and I presume you should be pursuing a reference for these to
> find your design.

I would suggest this way too.

Take a look into a good book about op-amps/electronics. Also you may
want do
a search at the National semiconducter Web-Site for applictaion-notes on
op-amps.

       Stefan

1999\03\04@131943 by Scott Dattalo

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On Thu, 4 Mar 1999, Paul B. Webster VK2BZC wrote:

> Walter Markiw wrote:
>
> >  I need to build a coil to provide an inductance in the range of 0,001
> > to 0,1 Henrys.
> > It is for a frequency filter I am planning to build.
>
>   OK, enough is enough.  They've wagged you *mercilessly* on this one.
>
>   If you *really* want to build a *fixed* or *tapped* coil in this
> range, that is do-able, but you would usually use a laminated (soft)
> iron core to achieve the value.  An air-cored coil is rather impractical
> and a variable one, quite impractical, at least over the range you
> specified.
>
>   Audio (it is audio, isn't it?) frequency filters use active "gyrator"
> circuits to synthesise inductance with op-amps and capacitors.  That's
> how variable inductance is emulated.

Yeah! 'Gyrating Impedance Converters' or GICs have less component
sensitivy than other opamp topologies such as the Sallen-Key. The down
side though is that they require 2 opamps per complex pole (where as S-K
requires only one). Another benefit is that GIC's can be designed such
that all of the capacitors are the same value - the resistors control the
pole (or possibly zero) locations.

I guess if you used a Pic to vary the inductance you'd have a PIC-GIC :)

1999\03\06@210633 by Walter Markiw

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Ok,thank you all.Perhaps I should give some more details on the project.

   I have a pulse width modulated source of 10-50 Hz,220 vac,
and I need to filter 5th (250 Hz),7th (350 Hz) and 11th (550 Hz)
harmonics(and yes,the H bridge is driven by a pic).
   The amount of current involved should be no more than
15 amps (the coils would have to be constructed with some wire
that can handle that current).
     According to my calculations this could be done by paralelling
aproppiate values of inductance an capacitance for each frecuency,
and putting the pairs in series.The values I calculated are:
0,01 H coil paralelled with  40,53 uF capacitor to block 250 Hz (5th harmonic)
0,005 H "      "        "    41,36 uF    "      "    "   350 Hz (7th   "     )
0,002 H "      "        "    41,87 uF    "      "    "   550 Hz (11 th "     )
     The question is,how do I build a 0,01 H coil to handle 15 amps,
220 Vac?
     Any help will be appreciated.




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