measuring ac resistance of the inductor

[tauquir_iqbal]

hi . i am using diligent analog discovery 2 impedance analyzer to calculate the ac resistance of the inductor at a certain frequency. the value of the inductor is correct but i am getting the diffeernt value of ac resistance using a different setting. the inductance value is around 1.5 mH and ac resistance will be in milli of ohm. 
 

[jpeyron]

Hi @tauquir_iqbal,

Welcome to the Digilent forums!

I moved this thread to a section where more experienced AD2/WaveForms engineers look.

cheers,

Jon

[attila]

Hi @tauquir_iqbal

The component characteristics depend on current and voltage, or the measurement is inaccurate.

This is what i see with an 1uH:

Notice the warnings: at low frequency, the DUT voltage is low, and around 1MHz the reference resistor voltage/current (C2 in time view) is very low. In these cases the measurement might be inaccurate.

[tauquir_iqbal]

I don't need precision in low frequency or very high frequency. I need accurate even with +-10 % is no problem.
my inductor value is around 1.5 mH. my interest is in frequency around 10 kHz - 100 kHz only. I am interested in knowing ac resistance as inductor value is very accurately measured by AD2.
can you suggest setting for it. ac resistance will be in the range of mili ohm

[tauquir_iqbal]

how you got three parallel scopes. how can I add more scope? normally I have only 2 .

 

[attila]

Hi @tauquir_iqbal

Could you post some screenshots with your measurement results?

A window can be dragged from the tab bar (A) or the entire group of tabbed windows can be dragged from title bar (B), and dropped to other place. Make sure to have suffice space in the parent window to be able to perform such operation.

[tauquir_iqbal]

[attila]

Hi @tauquir_iqbal

Perform short compensation before the measurements and enable it.

This will eliminate/reduce the wiring, AD2 scope contacts, IA adapter relay, socket... resistance.
The open compensation is useful for low capacitance measurements, to eliminate the wiring capacitance.

Such measurements are very sensitive, it would ideally require kelvin connection...
Electrical contacts can have several mOhms resistance which is comparable or even higher than the inductor resistance and can ruin the measurement.

Here I tried to measure a low ESR 1uH coil.
The Short trance is the short compensation, NoComp is the inductor measurement without compensation and Comp the short compensated measurement.

 

[tauquir_iqbal]

any suggestion for " Such measurements are very sensitive, it would ideally require Kelvin connection...".
how can i implement kelvin connection in AD2? any reference will be so helful. 

[fonak]

Hi tauquir_iqbal

This should help.

https://en.wikipedia.org/wiki/Four-terminal_sensing

https://www.allaboutcircuits.com/textbook/direct-current/chpt-8/kelvin-resistance-measurement/

[attila]

Hi @tauquir_iqbal

Such measurements are on the edge or above of the device capabilities.
We are trying to compare 10 Ohms with mOhms, the AWG current is on the limits, voltage drop is close to scope resolution...
The contact resistance can also ruin the measurements... it would need special clips mentioned by @fonak

Here I tried to compare various setups, but after short compensation the results are pretty close to each other, given the conditions...

Traces:
- IA: using IA adapter
- IAComp: compensated

- Kelvin: the following single ended setup, with twisted (1+/- 2+/- W1/GND) wires hooked to a breadboard, trying to do 4 terminal sensing
- KComp: same with compensation

- Diff: differential measurement on breadboard, 4 terminal
- DiffComp: same with compensation

 

[tauquir_iqbal]

thanks for your kind reply. i do understand the problem with measuring ac resistance . can you share the pics of the set up you used for the measurement, i don't expect to get exact ac resistance as it needs some special device. i don't have the problem with +-25% error. moreover, my inductance is pretty large so its Rac value is also in the range of hundred of milliohm.

thanks again for the reply. 
can you share the pics of the test you did with the Kelvin clip so that other people who also want to measure ac resistance can see the procedure and complete the measurement?