Gyrator as a precision inductor for LCR meter Cal Checks

[scopeman]

Does anyone have experience creating a precision inductor using a gyrator circuit for checking the calibration of an LCR meter? If such an idea could be made to work
it would be a very inexpensive way to create precision inductors. I would think that a quality capacitor like polystyrene or PP film would be a good start.

Sam
W3OHM

[mawyatt]

Interesting idea!! Used gyrators and NIC converters but never thought about creating a "reference" inductor.

Agree, a stable cap, even with low TC is available, and of course precision op-amps and resistors are available. One could even tweak the cap TC by paralleling various different type caps to achieve a very low overall TC, then simply tweak the effective inductance with a select resistor(s) to achieve the desired inductance value.

Edit: One could even use the TC of the resistor to compensate for the TC of the Cap, and get a very low overall effective "Inductor" TC 

Thanks for posting 

Best,

[MaxZ]

This Edit: something similar has actually been recommended by HP in the 80s. I attached a screenshot from the manual of their 4274A LCR meter. I assume it's been done by others for a long time, too.

Corrected, thanks Kleinstein


Kind regards,
Max

[Kleinstein]

Low value inductors, that can be mode without an iron core can be quite stable and the temperature coefficient is even predictable from the thermal expansion of coppper. Even the inductors with a gapped  iron core can be relatively stable (and linear), as the main point it the length of the gap and less the core material itself.  Closed core inductors may be tricky however, as there the material TC and also external fields could have an effect.   So if at all the gyrator way makes sense for the larger inductors (e.g. > 1 H), less for the smaller ones. AT least this usually means a more lower test frequency.

The circuit that HP suggests is not a gyrator, but more like fooling the LCR meter in thinking it sees an indutor, using an unusual configuration for a 4 wire DUT.

[mawyatt]

Just for a fun test while waiting for doctors result, we grabbed some components from the scrap parts bin and kludged up a Gyrator Synthesized Inductor Resistor LR equivalent.

A Polystyrene 10nF, a 1K and 100K MF resistor and a OP07 were used. These components should yield a 1H inductor with 1K series R which it did when measured with a TH2830 LCR meter at 100Hz. We then measured these components to get a better value to use in the L = R1*R2*C equivalent value. Equivalent Inductor results were within 0.5% for frequencies of 50, 100, 500Hz.

Quickly used both the TH2830 and IM3536 LCR meters to verify results, also got a good reading at 1KHz with the IM3536, however the TH2830 became erratic here.

Best,

[tautech]

Just for a fun test while waiting for doctors result, ............

Much hoping it's good news.