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Principle of Inductance and Impedance Test

Principle of Inductance and Impedance Test

Principle of Inductance and Impedance Test

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  • Categories:Company News
  • Time of issue:2021-09-02 14:54
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The resistance of any component can be expressed as R+Xi.

Among them, R is the resistance of the real part and X is the resistance of the imaginary part. The impedance is the modulus of the complex number, Z=√(R+X^2 ).

The characteristic of the real part R is that R does not change with the change of frequency, and is a fixed resistance.

The characteristic of the imaginary part X is that X will change with the change of frequency.

X>0 is called inductive, that is, inductance.

X<0 is called capacitive, that is, capacitance.

Resistance, inductance, and capacitance are defined in the following table:

 

Resistance

R>>|X|, the resistance of the real part is much larger than the imaginary part, indicating that this is a resistance. The smaller X is, the better, if X=0, this is the theoretical resistance

inductance

R≈0, X>0, indicating that this is an inductance. The smaller R is, the better, if R=0, this is the theoretical inductance

capacitance

R≈0, X<0, indicating that this is a capacitor. The smaller R is, the better, if R=0, this is the theoretical capacitance

 

  1. How to calculate L and Q

According to the above, the expression of inductance is: R+Xi X=2πfL then L=X/(2πf)

f is the frequency, X is directly tested by the LCR bridge. The quality factor Q=X/R, we know that the smaller the R, the better, then the larger the Q value, the better, indicating that the quality of the inductor is better.

  1. Selection of test frequency

Assuming we have a 1nH inductor here, what frequency should be used to test it, let’s look at the following list, the resistance value of the inductor at different frequencies:

 

frequency

X(Ω)= 2πfL

1kHz

6.28uΩ

10kHz

62.8 uΩ

100kHz

628 uΩ

1MHz

6.28mΩ

10MHz

62.8mΩ

100MHz

628mΩ

 

For the LCR Meter, the test accuracy will be worse if the impedance is less than 1mΩ. Therefore, it is more appropriate to choose a frequency above 1MHz for testing.

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