# Inductances

The purpose of the test is to check the presence and accuracy of the inductance value, signalling any anomalies.

The test consists in inputting a linear ramp of descending current into the component and measuring the voltage drop at the heads of the inductance, when the current ramp passes zero.

Since the initial value of the current and the slope of the ramp are well determined, at the time when the current equals zero, the voltage at the heads of the inductance is exclusively due to its reactive component, since there is no voltage contribution due to the series resistance.

The voltage at the heads of an inductor with current flowing through is given by the formula:

VL = I · RS + L ΔI / ΔT VL = L ΔI / ΔT = L I0 / T0

VT (1 + TOLmin) < VM < VT (1 + TOLmax)

Where:

VM drop in measured voltage

VT drop in theoretical voltage

VL voltage at the heads of the inductance

I the preset inputted current

RS value of the series resistance of the inductor

L value of the inductance

ΔI value of the current variation

ΔT time in which ΔI is measured

TOLmin minimum tolerance specified

TOLmax maximum tolerance specified