Re: Interesting inductor

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