Page 1 of 9 Capacitor ESR Measurement with Bode 100 and B-WIC by Florian Hämmerle 2010 Omicron Lab V1.0 Visit www.omicron-lab.com for more information. Contact support@omicron-lab.com for technical support.
Page 2 of 9 Table of Contents 1 Executive Summary...3 2 Measurement Task...3 3 Measurement Setup & Results...3 3.1 Measurement Equipment...3 3.1.1 Test Object Data...4 3.1.2 ESR Specification...4 3.2 Measurement Setup and Calibration...4 3.2.1 Set Up the Measurement...4 3.2.2 Calibrating the Impedance Adapter...5 3.2.3 Capacitor Measurement...7 3.3 Measurement Results...8 4 Conclusion...9 Note: Basic procedures like setting-up, adjusting and calibrating Bode 100 are described in the user manual of Bode 100. Note: All measurements in this application note have been performed with the Bode Analyzer Suite V2.30SR1. Use this Version or a higher Version to perform measurements according to this application note. Download the latest version at http://www.omicron-lab.com/downloads.html
Page 3 of 9 1 Executive Summary This application note describes how to measure the equivalent series resistance (ESR) of a capacitor using the Bode 100 vector network analyzer and the impedance adapter B-WIC. 2 Measurement Task The ESR (equivalent series resistance) of a capacitor influences strongly the characteristic behavior of a capacitor. A real capacitor can be modeled according to the equivalent circuit shown in the following picture. In some applications the series resistances influences the behavior of the system the capacitance is applied to. Generally the producers of capacitors do not provide much information about the ESR of the capacitors. This document shows the possibility of measuring the capacitor ESR using the Bode 100 vector network analyzer. 3 Measurement Setup & Results 3.1 Measurement Equipment Bode 100 Vector Network Analyzer Impedance Adapter (B-WIC or B-SMC) Test object (standard capacitor) In this case we use non polarized electrolytic capacitor with 1000µF and 16V operating voltage.
3.1.1 Test Object Data Bode 100 - Application Note The datasheet of the capacitor does only provide the following information about the ESR of the capacitor: At 120Hz and 20 C temperature the respectively the Dissipation Factor DF is specified with a maximum of 20% (= worst case). 3.1.2 ESR Specification Assuming the equivalent circuit mode shown in the previous page the following relation between dissipation factor and ESR is valid: Page 4 of 9 Using the data from the datasheet the ESR at 120Hz and 20 C temperature can be calculated as follows: Now we will use the Bode 100 to check this result. 3.2 Measurement Setup and Calibration 3.2.1 Set Up the Measurement The impedance adapter B-WIC is connected to the Bode 100 as shown in the following picture.
After starting the Bode Analyzer Suite the measurement mode is switched to the Frequency Sweep (Impedance Adapter) Mode. Page 5 of 9 3.2.2 Calibrating the Impedance Adapter When measuring with the impedance adapter an impedance calibration has to be performed before any measurement. Calibration of the B-WIC adapter is performed using the OMICRON Lab calibration board which is delivered with the B-WIC adapter. Open Calibration: No DUT 1 is connected to the impedance adapter and open calibration is performed. Attention: During the calibration is performed this measurement is very sensitive to changes in the electric field. Do not move your hands or any other parts close to the impedance adapter! 1 DUT...Device Under Test
Page 6 of 9 Short Calibration: The shorting bar of the calibration board is connected to the impedance adapter. Ensure good contacting by putting the board horizontal in the adapter before performing short calibration. Load Calibration: The load side of the calibration board is horizontally connected to the adapter and load calibration is performed.
3.2.3 Capacitor Measurement The capacitor is connected as shown in the following picture. Bode 100 - Application Note Page 7 of 9 Sweep start frequency is set to 10Hz. Sweep stop frequency is set to 1MHz. Sweep mode logarithmic, number of points 401. The Bode Analyzer Suite directly supports ESR and C measurements. To measure the series resistance the measurement is set to Impedance (Format: Rs). To measure the capacitance the measurement is set to Impedance (Format: C) Performing a single sweep measurement with all the settings and calibration mentioned above leads to the following measurement results:
TR2/F TR1/Ohm Bode 100 - Application Note Page 8 of 9 3.3 Measurement Results The following picture displays the ESR of the capacitor from 10 Hz to 1 MHz. It can be seen that the series resistance value is strongly dependent on the operating frequency. 10 0 10-1 10-2 10 1 10 2 10 3 10 4 10 5 10 6 TR1: Rs(Impedance) f/hz The next figure shows the series capacitance result. The capacitance at 10 Hz equals 990µF. At about 100 khz the capacitor shows a resonance due to the internal inductance. 5m 4m 3m 2m 1m 0-1m -2m -3m -4m -5m 10 1 10 2 10 3 10 4 10 5 10 6 TR2: Cs(Impedance) f/hz The exact series resistance value can easy be measured by switching on the cursor. To compare the measured ESR with the value from the datasheet the cursor is set to 120 Hz. The equivalent series resistance at 120Hz equals and is therefore approximately half the worst case value calculated from the datasheet information.
Page 9 of 9 4 Conclusion The Bode 100 with the impedance adapter B-WIC offers an easy and fast possibility to measure the series resistance and capacitance of a capacitor. From the results it can be seen that the ESR of the DUT strongly depends on the frequency. In addition to that the usable frequency range of a capacitor can be checked. The capacitance reduction at increasing frequency and eventual resonance points can be measured.