Capacitor Guide

# Basics of capacitors [Lesson 7] Measurement Method for the Electrostatic Capacitance of Ceramic Capacitors

This technical column describes the basic facts about capacitors.
This lesson describes the method of measuring the electrostatic capacitance of ceramic capacitors.

## 1. Measuring instruments

The electrostatic capacitance of ceramic capacitors is generally measured using an LCR meter.

## 2. Measurement principle

The typical measurement system of LCR meters is the "automatic balancing bridge method," such as shown in the figure below. The measurement principle is as follows.
DUT is the abbreviation of "Device Under Test," and refers to the measured item. A high gain amplifier automatically adjusts the gain level so that the electric current flowing through the resistor R is equal to the current flowing through the DUT; that is to say, the low potential side (L-end side in the figure) of the DUT is always equal to the virtual ground level (electric potential = 0). The phase angles of the input voltage E1 and output voltage E2 at this time are also measured, and are as follows:

E1＝|E1|∠θ1＝|E1|cosθ1+ｊ|E1|sinθ1
E2＝|E2|∠θ2＝|E2|cosθ2+ｊ|E2|sinθ2

The DUT impedance Zx can be obtained from these phase angles and the feedback resistance R as follows:

Zx＝R･E1/E2
＝R・|E1/E2|・{cos(θ1-θ2)+ｊsin(θ1-θ2)}

Here, the real part is Rx, the imaginary part is Xx, and the DUT electrostatic capacitance Cx can be obtained from the acquired Xx using the equation Xx=ｊ/ωCx.