The previous slides reviewed DWV, insulation resistance, and leakage current which are all DC quantities. The following slides will now cover AC quantities starting with impedance, equivalent series resistance (ESR), and equivalent series inductance (ESL). A ceramic capacitor can be modeled using a simple RLC circuit which contains a capacitor, resistor and inductor. Impedance can be thought of as the total opposition to current and is the sum of all real and imaginary components of the RLC model. The resistance in the circuit, which is expressed in Ohms, represents the total Ohmic losses in the capacitor. This is the real part of the complex impedance equation. The reactance, which is also expressed in Ohms, is a property that opposes a change in current and is comprised of the capacitive reactance, which dominates at low frequencies, and the inductive reactance, which dominates at high frequencies. This is the imaginary part of the complex impedance equation. Both the capacitive reactance and inductive reactance are frequency dependent quantities. As frequency increases, the capacitive reactance decreases and the inductive reactance increases. At low frequencies this causes the impedance to decrease with increasing frequency as seen in the graph on the right. This is known as the capacitive region of the impedance plot. At some point, the capacitive reactance and the inductive reactance will cancel each other out leaving only the ESR component in the impedance equation. This is where the impedance is at a minimum and represents the inflection point in the impedance plot. This point is called the series resonant frequency, or SRF. As frequency increases above this point, the impedance will begin to increase. This is known as the inductive region of the impedance plot.