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I need to measure inductors with a small DC bias current. Small is a relative term and here as in won't cause any significant voltage drop in the cables of the LCR meter but enough to put my inductor near saturation. There are a few high end production test models which has this built in but it's way above my price range. The ones which has DC bias are always rated in voltage only which makes perfect sense for a capacitor measurement but assuming my DC source does the constant current limitation, am I missing something? 10 V maximum, sure, but how much current can I pass though it? Will the L-measurement DC-block the DC voltage imposed by my external current over the resistance in the wire of the coil (DUT)?

Here is one example: datasheet

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  • \$\begingroup\$ Why do you need to have a small DC bias current flowing to do the measurement. As far as I know the value of an inductor does not change (significantly) for small DC currents. At the saturation current of course it does but not for small currents. \$\endgroup\$
    – Bimpelrekkie
    Commented Jul 5, 2016 at 8:31
  • \$\begingroup\$ Sorry about that, I'll edit the text to make it more clear. \$\endgroup\$
    – winny
    Commented Jul 5, 2016 at 8:37
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    \$\begingroup\$ Old question, I know, but you may be able to get the same effect by winding a second identical winding on the core and applying your DC bias through that one; it would have the same effect to saturate the core and you can use whatever bias circuitry you want without interfering with your LCR meter at all. \$\endgroup\$
    – Hearth
    Commented Dec 30, 2020 at 0:39
  • \$\begingroup\$ @Hearth That’s one interesting option. It would require it to be done before potting though. The inductor in question is already in mass production but I’m sure this question will become relevant sooner or later again. \$\endgroup\$
    – winny
    Commented Dec 30, 2020 at 9:35

2 Answers 2

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Feed a constant current (high compliance) through the inductor and couple the input lead of the LCR meter via a 100 uF capacitor. The capacitor should decouple the measurement circuit from the DC circuit adequately and not pose much of a significant measurement error when measuring inductance.

It's easy to try.

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  • \$\begingroup\$ This was my original thought, as per powerelectronics.com/site-files/powerelectronics.com/files/…, but since I need a more fancy LCR meter anyway, why not one with DC bias option I thought. This leaves me with the question, if I can't run current though the DC bias port of most LCR meters, is their purpose only to bias capacitors? \$\endgroup\$
    – winny
    Commented Jul 5, 2016 at 11:33
  • \$\begingroup\$ @winny Yes, just for capacitors. Applying a bias voltage is easier than a bias current. \$\endgroup\$
    – Hearth
    Commented Dec 30, 2020 at 0:40
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Keysight LCR Meter E4980A does have the DC bias in current option where u can change your signal to sourcing current instead of voltage for inductos

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    \$\begingroup\$ Excellent start of your EE.SE career! I should have mentioned that the Keysight one plus option “Option E4980A-001 power and DC bias enhancement” was the one out of my price range. Very high end precision model! In the meantime I changed the design to not depend on the inductance at high DC offset, but if there is any low cost model, I’m still interested. \$\endgroup\$
    – winny
    Commented Jul 25, 2019 at 12:40

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