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NNTP-Posting-Date: Fri, 15 Mar 2024 19:14:01 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: Interesting inductor
Date: Fri, 15 Mar 2024 12:14:01 -0700
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On Fri, 15 Mar 2024 05:56:38 -0000 (UTC), Jasen Betts
<usenet@revmaps.no-ip.org> wrote:

>On 2024-03-14, 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.
>
>it's probably easier to just use the output terminals as a variable inductor.

I need a surface-mount motarized variac!

General Radio used to make Variacs. I think they had the patent. The
brush was tricky.

GR was interesting. Long gone now.