0
\$\begingroup\$

I have a High-Frequency inductor available and I want to measure the inductance using the Rohde&Schwarz HM8118 LCR meter. If I change the frequency to 100kHz and voltage level to 1.5V (max) I get a value of 0.5 Henry which is way too high.

User manual of the LCR meter:

https://cdn.rohde-schwarz.com/pws/dl_downloads/dl_common_library/dl_manuals/gb_1/h/hm8118_1/HM8118_UserManual_de_en_06.pdf

The inductor is made of two ferrite cores as shown in for example here:

https://www.picclickimg.com/d/l400/pict/112230606209_/Ferrite-E-Core.jpg

How can I correctly measure the inductance (should get a value in microhenries) ?

EDIT:

Square wave signal of 100kHz is applied across the inductor (having no DC component). The measured inductance value also has a negative sign in front of it.

\$\endgroup\$
8
  • 1
    \$\begingroup\$ Choose f to match nearest fundamental (application) and AC couple with external DC and increase until L drops 10%. If SRF affects Z(f) (i.e. resonant) , L(f) reading will be invalid. \$\endgroup\$
    – Tony Stewart EE75
    Apr 9, 2017 at 11:06
  • \$\begingroup\$ For my application I am generating a PWM signal with a frequency of 100kHz and after changing it from the default 1kHz I get this huge inductance value. Also, other settings are: BIAS = off, SPD = slow, OPEN = on, SHORT = on and LOAD = off. Any idea? \$\endgroup\$
    – user203
    Apr 9, 2017 at 11:12
  • \$\begingroup\$ Use small signal and large Dc current external It uses CC sine to measure Z . I assume this is for DC application if not scratch that \$\endgroup\$
    – Tony Stewart EE75
    Apr 9, 2017 at 11:16
  • \$\begingroup\$ Add DC current and AC voltage hysteresis causes correct L reading without DC hysteresis gives too high H. I think it has Ldc port for 100mA only, maybe 200mA. You may want to use lowZ plastic cap external and add X Amps DC to reduce L 10% ( just before saturation) \$\endgroup\$
    – Tony Stewart EE75
    Apr 9, 2017 at 11:24
  • \$\begingroup\$ Is application Flyback or linear i.e. DCM CCM \$\endgroup\$
    – Tony Stewart EE75
    Apr 9, 2017 at 11:27

1 Answer 1

Reset to default
2
\$\begingroup\$

Raising the frequency to 100 kHz could certainly mean that you are approaching the natural self resonant frequency and you will get stupidly high inductance values and sometimes, if the frequency is too high it will behave as a capacitor and your meter displays nF or pF.

The natural self resonance is brought about by the interwinding capacitance i.e. It becomes a parallel resonant impedance.

I'm not saying definite but I am saying there's a decent probability given the size of the core. I'd trust the inductance reading at 1 kHz but by no means is 1 kHz a panacea.

\$\endgroup\$
3
  • \$\begingroup\$ At 1kHz a get an even more unrealistic inductance value. \$\endgroup\$
    – user203
    Apr 9, 2017 at 11:53
  • \$\begingroup\$ What did it measure and what do you expect it to read? Also how many turns and what AL value did you use to calculate L? \$\endgroup\$
    – Andy aka
    Apr 9, 2017 at 12:01
  • \$\begingroup\$ I expect it to read a value around the microhenries, around 10 turns \$\endgroup\$
    – user203
    Apr 9, 2017 at 19:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.