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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Interesting inductor
Date: Thu, 14 Mar 2024 11:31:27 -0000 (UTC)
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Clive Arthur <clive@nowaytoday.co.uk> wrote:
> On 13/03/2024 22:43, john larkin wrote:
>> On Wed, 13 Mar 2024 22:32:27 +0000, Clive Arthur
>> <clive@nowaytoday.co.uk> wrote:
>> 
>>> On 13/03/2024 04:18, John Larkin wrote:
>>> 
>>> <snip>
>>> 
>>>> I'm hassling with inductors now too, but at the other end of the speed
>>>> spectrum.
>>>> 
>>>> We want a programmable inductor, from maybe 1 mH to 500 mH or so,
>>>> maybe 100 mA. Sounds like an inductive DAC, a series string of
>>>> inductors with shorting relays. If the step inductance ratio were,
>>>> say, 1.8:1 we could have some hidden bits, more than the customer
>>>> sees, so we could get pretty close to his requested value.
>>>> 
>>>> We could test all 2^n steps, make a list, and select the closest to
>>>> his request.
>>>> 
>>>> We're simulating loads to an engine control computer, torque motors
>>>> and solenoids and steppers.
>>>> 
>>> 
>>> Gyrator?
>> 
>> We just yesterday had a brainstorm session about that. How can one
>> make a programmable electronic fake inductor?
>> 
>> A real inductor stores energy, and can do things like high voltage
>> flyback. So a fake inductor should store energy, or pretend to. It
>> could be done with a current shunt, a fast ADC, some math in an FPGA,
>> a fast DAC, and a big power amplifier with big power supplies. Too
>> much work.
> 
> Yes, I got part way down the road of designing a gyrator to block 
> telemetry signals on a power line comms device.  Soon realised it would 
> need lots of power.
> 
> Just thinking out loud, and not really a serious suggestion, but would a 
> variac with a fixed inductor on the secondary work as a variable 
> inductor?  I guess 500:1 would be impossible.
> 

Not a dumb idea at all.  To avoid using a motor to turn it, one or more
transformers with binary-weighted windings and relays, maybe. 

The inductance of the transformer needs to be large enough, of course. 

I’ve occasionally considered using a transformer to make an isolated
version of a dpot, but it’s never been quite the right solution, mostly on
account of limited inductance. 

Cheers 

Phil Hobbs 

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics