**Impedance**

The impedance of an inductor is the total resistance to the flow of current, including the AC and DC component. The DC component of the impedance is simply the DC resistance of the winding. The AC component of the impedance includes the inductor reactance. The following formula calculates the inductive reactance of an ideal inductor (i.e., one with no losses) to a sinusoidal AC signal.

Z = X_{L} = 2πƒL

L is in henries and ƒ is in hertz. This equation indicates that higher impedance levels are achieved by higher inductance values or at higher frequencies. Skin effect and core losses also add to the impedance of an inductor. (see Skin Effect and Core Losses)

**Impedance Analyzer**

Test instrument capable of measuring a wide range of impedance parameters, gain and phase angle. In testing inductors, impedance analyzers can measure inductance, Q, SRF, insertion loss, impedance and capacitance. They operate in a much more automatic fashion in comparison to Q Meters. Some impedance analyzers have a wider test frequency range than a Q meter.

**Incremental Current**

The DC bias current flowing through the inductor which causes an inductance drop of 5% from the initial zero DC bias inductance value. This current level indicates where the inductance can be expected to drop significantly if the DC bias current is increased further. This applies mostly to ferrite cores in lieu of powdered iron. Powdered iron cores exhibit “soft” saturation characteristics. This means their inductance drop from higher DC levels is much more gradual than ferrite cores. The rate at which the inductance will drop is also a function of the core shape. (see Saturation Current)

**Inductance**

The property of a circuit element which tends to oppose any change in the current flowing through it. The inductance for a given inductor is influenced by the core material, core shape and size, the turns count and the shape of the coil. Inductors most often have their inductances expressed in microhenries (µH). The following table can be used to convert units of inductance to microhenries. Thus, 47 mH would be equal to 47,000 µH.

1 henry (H) = 10^{6} µH

1 millihenry (mH) = 10^{3} µH

1 microhenry (µH) = 1 µH

1 nanohenry (nH) = 10^{-3} µH

**Inductance Tolerance**

Standard inductance tolerances are typically designated by a tolerance letter. Standard inductance tolerance letters include:

Letter | Tolerance |
---|

F | ± 1% |

G | ± 2% |

H | ± 3% |

J | ± 5% |

K | ± 10% |

L | ± 15% * |

M | ± 20% |

* L = ± 20% for some Military Products

**Inductor**

A passive component designed to resist changes in current. Inductors are often referred to as “AC Resistors”. The ability to resist changes in current and the ability to store energy in its magnetic field, account for the bulk of the useful properties of inductors. Current passing through an inductor will produce a magnetic field. A changing magnetic field induces a voltage which opposes the field-producing current. This property of impeding changes of current is known as inductance. The voltage induced across an inductor by a change of current is defined as:

V=L di/dt

Thus, the induced voltage is proportional to the inductance value and the rate of current change. (see Inductance)

**Input Line Filter**

A power filter placed on the input to a circuit or assembly that attenuates noise introduced from the power bus. The filter is designed to reject noise within a frequency band. Typically these filters are lowpass filters meaning they pass low frequency signals such as the DC power and attenuate higher frequency signals which consist of mainly noise.

Bandpass or lowpass filters are commonly made up of inductor and capacitor combinations. (also see Noise, Attenuation, EMI and Pi-Filter)

**Input Voltage(s)**

The voltage applied to the primary winding.

**Iron Core Coil/Transformer**

Coil/transformer wound around an iron core to increase its inductance. At radio frequencies the core consists of powdered iron mixed in a binder which insulates the particles from each other.

**Isolation Transformer**

Transformer with a one-to-one turns ratio, connected between the AC power, input to a piece of equipment and the AC line, to minimize shock hazard.