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Expert: cleggsan Date: 12/14/2006 Subject: Experiment to find Inductance of inductor
Question This is one of a series of experiments for a project, this one is to calculate the inductance of an inductor, but I get a value way off the stated value of the inductor....
Here is how the experiment is carried out.
The inductor is measured with a multimeter to get its resistance (R).
The inductor is connected to a 50Hz supply and the impedance is calculated from Z = V(rms)/I(rms).
To get the reactance (X) the formula Z = sqrt(R^2 + X^2) is rearranged to X = sqrt(Z^2 - R^2).
the formula 2(pi)fL=V(rms)/I(rms) is rearranged to give L:
L = V/(2(pi)fLI)
Can you see anything wrong with the theory that would give the wrong value of L?
Thanks for your time.
Answer Yes, that is true only if the R is equal to the inductive reactance.
It may be a better choice to use the sampling resistor idea to calculate impedance. Use a sampling resister in series with the coil where the impedance of the coil is known to be much greater than the series resistor you are going to sample the current with. By measuring the voltage across the sampling resistor you can calculate the current through the coil; now you know the current and the voltage across the coil you can calculate Z. Then, solve for r + jwL.
