Measurement of the resistance of the wire of an inductor with LCR instrument

Thread Starter

roxi60

Joined Sep 2, 2018
73
Hello.
Measuring an inductor with a LCR bridge, gives Rs (series resistance)and Xl (reactance).
The measurement is made applying an AC sinusoidal voltage and measuring the resulting current.

But the value of Rs obtained has nothing to do with R of the coil measured in DC mode, has it?
Is there any correlation between the two values?
Why Rs is greater then R (DC)?

Thanks a lot for any explanation.
 

LesJones

Joined Jan 8, 2017
4,174
Hi Eric,
I would have thought that the the resistance and reactance should be vector added rather than simple addition.
(Z = root ( R^2 + (2 * pi * f *L)^2) )

Les.
 

Thread Starter

roxi60

Joined Sep 2, 2018
73
Thank you very much, Eric, Les.
But the question is: the R in the formula, has something to do with the R eventually measured with a DC multimeter? I guess no.
For instance, let's have an inductor that, measured with DC multimeter has R=5 ohm.
If I measure it in AC with LCR instrument, I will have a Rs value that is greater, I will not have 5 ohm.
Suppose Rs=8 ohm.
My concern is: is anyway this measurement index of the DC resistance of the coil (correlated)?

Thank you again
 

LesJones

Joined Jan 8, 2017
4,174
There can be other things that produce losses in an inductor as well as the actual DC resistance of the wire. I think the most significant thisng will be losses in the core. ( Assuming it has a ferromagnetic core.)

Les.
 

ebp

Joined Feb 8, 2018
2,332
It shouldn't be called resistance if it has other components such as losses or reactance, so it should be equal to what would be measured at DC. The manual for the instrument should spell out exactly what is being reported, otherwise it is rather useless. Losses are frequency dependent. Skin effect, which is also frequency dependent, can legitimately be regarded as a change in resistance (it is neither a loss nor reactance), but resistance reported based on skin effect is not useful in general characterization of an inductor.
 
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