Accuracy of AIMuhf system – AIM865A vs AIM882 vs AIM885 on a ferrite cored inductor

AIMuhfThis article builds on Accuracy of AIMuhf system – AIM865A vs AIM882 on a ferrite cored inductor by adding a measurement using AIM885 of the same test inductor.



Above is the test inductor. It comprises 6 turns of 0.5mm PVC insulated wire wound on a BN43-202 binocular balun core.

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Above is a plot of predicted inductor impedance. The model is calibrated for assumed self resonance around 15.5MHz based on measurement of the inductor using AIM software AIM882.

Note that the curve is smooth, R rises to a peak at the self resonant frequency, and X increases linearly at low frequencies until the effect of equivalent shunt capacitance turns the curve over and it passes through zero. Measurement with other instruments show this to be a quite good model for this type of inductor over this frequency range. Note though that tolerances on ferrite cores is quite wide and for #43 mix, variation of 20% in measured R and X is not out of the question.

You can calculate Z at other frequencies using Calculate ferrite cored inductor (from Al).

Screenshot - 25_03_2015 , 10_29_18

Above is an example calculation at 30MHz. (Al was determined by measurement of inductance with an RLC meter at 10kHz to be 90µH with 6t, so Al=90000/6^2=2500.)

Each version tested was calibrated using a standard cal, and the test fixture was a 920mm RG58 cable with SMA connectors, and a N-M to SMA-F adapter on the AIMuhf.

Screenshot - 29_03_2015 , 16_02_23Above is a measurement with AIM885 (current production version) and overlays of AIM865A (with circles) and AIM882 (with squares). The calibration and measurements were all done at room temperature of 23°.

The plots are all different in some parts of the domain, the differences are difficult to attribute to external factors and are probably caused by changes within the AIM software. The calibration process with AIM885 appeared slower than with the earlier versions, but it was not measured. It may be that the calibration process has changed.

I might note that there is variation in successive scans hinting that something inside AIMuhf warms up during measurements and its measurement is temperature sensitive to a small extent. That variation is less than shown on the chart above.

Nothing here inspires confidence in the AIM measurement system. The three successive versions produce very similar results below 6MHz, but different results above that frequency. (AIM880 was released in this version range, but in fairness it was pulled early and so has been ignored, AIM882 is now missing on the distribution page but it was production for about five months.)