rfi power inlet filter

8/10/2019 RFI Power Inlet Filter

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Smart Measurement Solutions

Bode 100 - App lication No teRFI Power Inlet Filter Measurement

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RFI Power Inlet Filter Measurementwith Bode 100

by Florian Hmmerle

2010 Omicron Lab V1.0Visitwww.omicron-lab.comfor more information.

[email protected] technicalsupport.
http://www.omicron-lab.com/http://www.omicron-lab.com/http://www.omicron-lab.com/mailto:[email protected]:[email protected]:[email protected]:[email protected]://www.omicron-lab.com/


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Table of Contents

1 Executive Summary ....................................................................................................3

2 Measurement Task ......................................................................................................4

3 Measurement Setup & Results ...................................................................................5

3.1 Measurement Equipment ........................................................................................5

3.2 Test Object Specifications .......................................................................................5

3.3 Measurement Setup and Calibration .......................................................................6

3.3.1 Grabber DUT Connection ..................................................................................63.3.2 DUT Connection with Probe...............................................................................83.3.3 Soldered BNC Connection ...............................................................................10

3.4 Measurement Results ...........................................................................................12

4 Conclusion .................................................................................................................12

Note:Basic procedures like setting-up, adjusting and calibrating Bode 100 aredescribed 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 performmeasurements according to this application note.

Download the latest version athttp://www.omicron-lab.com/downloads.html
http://www.omicron-lab.com/downloads.htmlhttp://www.omicron-lab.com/downloads.htmlhttp://www.omicron-lab.com/downloads.htmlhttp://www.omicron-lab.com/downloads.html


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1 Executive Summary

This application note describes how to measure the common mode insertion loss of aRFI1power inlet filter with the Bode 100.

It explains the measurement principle how the common mode insertion loss ismeasured. This measurement principle is applied to a RFI filter using the Bode 100.Different methods how to contact the DUT

2are compared. The final measurement

results are compared with information from the datasheet.

The application note shows the importance of correct DUT connection and howconnection methods can influence the measurement.

1RFI...Radio Frequency Interference

2DUT...Device Under Test


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2 Measurement Task

RFI power inlet filters are used to prevent electronic devices from emitting RFI and toensure proper function of the device when RFI is present. A RFI power inlet filter helps

to achieve sufficient RFI quality by blocking conducted RFI over the power line. This isdone by filtering (blocking) the radio frequency spectrum.

The manufacturer of the DUT specifies the filter by measuring the insertion loss. Thefollowing picture shows how the common mode insertion loss is measured:

The reference setup is shown in the following picture. The RFI filter is replaced by a thruconnection, the 50termination stays active.


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3 Measurement Setup & Results

3.1 Measurement Equipment

Bode 100 Vector Network Analyzer

Test object (standard RFI power inlet filter)

Measurement accessories (probe, BNC cable with grabbers, wired 50 resistor)

3.2 Test Object Specifications

The datasheet of the filter provides information about the insertion loss of the RFI filter.The following table shows the guaranteed minimum insertion loss.

Minimum common mode insertion loss of the filter measured in a closed 50 System:

Frequency in MHz 0,15 0,5 1 5 10 30

Insertion loss in dB 14 23 30 41 45 50

The following figure from the datasheet shows the typical common mode insertion loss(black line) of the filter:

Using the Bode 100 we will compare the typical common mode insertion loss data withthe measurement data.


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3.3 Measurement Setup and Calibration

The used DUT has a standard rubber connector line inlet at the input and wire leads atthe output side. As we want to determine the attenuation of the filter both sides (input

and output) have to be connected.The first attempt to connect the DUT was to connect it via BNC cable and terminal plugson the line side and a BNC-Grabber adapter on the output side.

3.3.1 Grabber DUT Connection

The following figure shows the connection with the BNC-Grabber adapter cable.

The internal 50

resistor of channel 2 was switched on to achieve a terminated system.


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Thru calibration was performed as shown in the picture below.

After calibrating the measurement setup the DUT is connected as follows.

Using this configuration the following measurement results were achieved.

At 30MHz a strange peak appears.Extending the measurement range to 40MHz shows a resonance at approximately32MHz.

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TR1/dB

f/HzTR1: Mag(Gain)

Peak?


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To check if this resonance is caused by the connection setup or by the DUT itself ameasurement using an external probe was performed.

3.3.2 DUT Connection with Probe

To measure the filter with a probe the settings of the Bode 100 have to be changed. Theinput channel 2 has to be set to high impedance.

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20M 22M 24M 26M 28M 30M 32M 34M 36M 38M 40M

TR1/dB

f/HzTR1: Mag(Gain)


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To remove the probe influence on the measurement a thru calibration has to beperformed as shown in the following picture. As the probe has high input impedance the50termination is done by adding a resistor to the circuit.

During the measurement the DUT is connected as follows. The termination resistor isconnected at the output of the filter.


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The so measured insertion loss does not show the resonance any more.Some other effect seems to influence the measurement between 20 and 30MHz. Thearea with the unexpected measurement is marked with the circle in the picture below.

This disturbance may be caused by crosstalk from the input to the output of the filter.This effect can be decreased by shortening the connections and use shielded cable asclose to the DUT as possible.

3.3.3 Soldered BNC ConnectionBNC connectors were soldered to the filter trying to keep the connections as short aspossible.

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f/HzTR1: Mag(Gain)


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Again the input impedance of channel 2 was set to 50as explained with the firstconnection method. Thru calibration is performed by connecting the BNC cables with athru connection.

For the measurement the DUT is connected instead of the thru connection as shown inthe picture below.

This measurement leads to the following result:

The distortion between 20 and 30MHz was not entirely removed but reducedsignificantly.

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f/HzTR1: Mag(Gain)


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3.4 Measurement Results

We will now compare the measured common mode insertion loss with the chart from thedatasheet.

Datasheet: Measurement:

The dark solid line represents the typicalcommon mode insertion loss.The gray line displays the differential modeinsertion loss which is not part of thisapplication note.

The line represents the magnitude of themeasured common mode insertion loss.The red dotted line inidcates the linearinterpolated minimal common modeinsertion loss as specified in the datasheet.

4 Conclusion

The measurements show that very often the proper connection of the DUT is morechallenging than the measurement itself.To recognize errors caused by the connection one has to crosscheck the measureddata with the expected results.

The measured data and the information from the datasheet match well and the DUTcommon mode insertion loss is significantly higher than the specified minimum insertionloss.

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