[volt-nuts] Anyone know how to make stable inductors?

[Dave M]

Here's a paragraph from IETLab's web site on how their inductance standards 
are made:

"Each standard inductor is a uniformly wound toroid on a ceramic core. It 
has a negligible external magnetic field and hence essentially no pickup 
from external fields. The inductor is resiliently supported in a mixture of 
ground cork and silica gel, after which the whole assembly is cast with a 
poƫting compound into a cubical aluminum case."

Sounds like their objective is to isolate the winding from as many external 
influences as possible.  Of course, the same couild be said of any physical 
or electrical standard.

Cheers,
Dave M



Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> I was looking to make some inductors that I can use as a sanity check
> for
> my HP 4284A LCR meter. I don't too much care what their values are,
> but I want them to be stable with time. Any suggestions about the
> best way to
> make or buy them? I'd like values in the range of 1 nH to 100 mH.
>
> The LCR meter has 4 terminal Kelvin connections, with 4 x BNC sockets
> on a 22 mm pitch.
>
> The meter is at Keysight at the moment being calibrated, along with a
> free software upgrade they are kindly providing. So I'd like to
> measure some inductors when it comes back, and track their values
> over time, to see if the meter is drifting.
>
> The meter covers 20 Hz to 1 MHz, and has a basic uncertainty of
> 0.05%, so ideally I'd like to keep inductor changes to less than
> 0.005% over a year, so the inductor is an order of magnitude better
> than the meter. Maybe that is not practical. As I say, the absolute
> value is not important, since I only want a comparison.
>
> The calibration costs on this meter are not too bad (£207 GBP), but
> the calibration interval is 6 months, which is a bit annoying. I'd
> rather not
> be sending it off every 6 months if I can satisfy to myself it has not
> drifted too much. Luckily I don't need to satisfy anyone else.
>
> Dr. David Kirkby Ph.D CEng MIET
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex,
> CM3 6DT, UK.
> Registered in England and Wales, company number 08914892.
> http://www.kirkbymicrowave.co.uk/
> Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)