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Unexpected LCR meter behavior change - dependent on measurement lead positioning
maelh:
Hello,
I have a Peaktech 2170 LCR meter, which comes with Kelvin clips/leads.
I am measuring an inductor in the 100-200nH range (measured at 100kHz), and I noticed wildly changing values, between 40nH and 600nH. It seemed erratic until I found a way to reproduce it.
When I hold the clips in a steady position (so that the inductor coil doesn't get squished/stretched, and the connection from the clip to the DUT remains stable, too), but I move around only the leads going to the LCR meter, the measured inductance changes a lot.
When I keep the leads in a relatively stable position and recalibrate in this position, then the measurement is in the right ballpark. But if I reposition the leads the measurement is off again.
Is that normal behavior or is that a sign there is an issue with the leads?
If it is an issue with the leads, is there a test I can perform on the leads themselves to find out if maybe some strands are broken or something else is wrong (for example using a signal generator and a scope)?
KungFuJosh:
Sounds like the leads to me. Can you unscrew the covers over the plugs and inspect the wire connections?
floobydust:
Try shielding the inductor, it might be acting like an antenna for something. Keep your cell phone, cordless phone, WiFi, iPad etc. away from the test setup.
TERRA Operative:
Are the leads shielded?
If not, it might be worth replacing the test clip cables with thin coax and terminate the meter end of the shield to a banana jack to plug into the guard terminals.
Kleinstein:
The inductance is tiny and the shield is only effective against the electric field, not much against a magnetic field. Even with Kelvin probing there is magnetic coupling between the wires.
So the behaviour is probably normal. To measure such small inductance it needs a more ridgit setup, more like the SMD part fixtures and than compare to a short.
Probably not a factir here, but a possible problem with higher value inductors: ferrite material, especially that with high permebility reacts to mechanical stress. This is especially a factor for inductors with a closed core and thus a large dependence on the µr.
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