Constant power calibration method for electrical field

[incognito]

Is it possible to perform a calibration of the Electrical Field using the method that is described as the 'Constant power calibration method' in the IEC 61000-4-3 2006?

[joro]

The IEC 61000-4-3 describes two different methods for the calibration of an electrical field in an area within a shielded room.
The 'constant field calibration method' describes that the generated power should be adjusted to generate the same electrical field in each and every measurement location.
The 'constant power calibration method' describes that the electrical field on each measurement location should be measured while the generated power is the same for each and every measurement location.

Both calibration methods can be performed in RadiMation (with RadiMation version 2012.1.16 or newer).
To perform the 'constant power calibration method', it is thus needed to generate the same power level, while the electrical field on one (or more) of the measurement locations is measured. This test can be configured using a Multiband Radiated Immunity test.

1. Create an EUT file that is used to store the calibration measurement results
2. Configure a Multiband Radiated Immunity test to generate a fixed power level over the required frequency range, while an electrical field probe is used to measure the generated field. For example:
   • 1% logarithmic frequency step
   • A short dwell time (for example 100 ms)
   • Constant frequency change mode
   • No modulation
   • A single antenna height
   • Horizontal or Vertical polarization
   • A single turntable angle
   • A fixed forward power test-level (a 'power closed loop method') with the to be generated power level.
   • Signal power measurement as an input
   • Electrical field probe measurement as an input

   

   Example of the configuration of a constant power TSF

   constant-power-tsf.png (39.14 KiB) Viewed 15099 times

3. Start the configured test, and wait until the measurement is finished.
4. Ensure that the measured electrical field graph is at least 1.0 V/m on all datapoints, as it is not allowed to have electrical field measurement values of 1.0 V/m or lower.
5. When the test is finished, the data of the measured electrical field graphline can be exported to a Calibration file (CAL-File)
6. Click the 'Graphs' button above the graph, and select the 'Export...' option
7. Select the electrical field graphline that should be exported to a Calibration file, then click the 'Next' button

   

   The graphline export window that allows the selection of the to be exported graphline

   constant-power-export.png (16.59 KiB) Viewed 15099 times

8. Select 'CAL-file' as the type of the file to which the graphline should be exported, then click the 'Export' button

   

   The graphline exort window that allows the selection of the export type

   constant-power-calfile.png (13.5 KiB) Viewed 15099 times

9. A 'Save Calibration as' dialog will be shown to determine the location and name where the final calibration file should be stored.
10. The exported Calibration file is the result of the 'constant power calibration method' for that measurement location. This calibration file can be used during substitution tests to generate a required electrical field strength.

If the power calibration should be performed on multiple measurement locations, it is possible to repeat the steps 3 to 9 to measure the eletrical field measurement on the other measurement locations at the same generated power levels.

Some additional tips:

• It is easiest to generate a forward power level that is +- 90% of the maximum power of the used amplifier, because this makes it easier to generate a sufficiently high electrical field for all measurement locations
• When multiple field probes are available, it is possible to measure the electrical field at multiple measurement locations during the same frequency sweep.
• It is also possible to export the electrical field graphline from already saved multiband Radiated Immunity tests.
• This same procedure can also be used for the 'constant field calibration method'. In that case the 'test-level' of the test configuration should be changed to a 'Electrical Field levelling' test-level, instead of a 'power levelling' test-level.

The big advantage of the 'constant power calibration method' is that it is possible to measure the generated electrical field on multiple measurement locations during a single power-sweep. This can significantly reduce the amount of time needed for the total calibration.

[solutionseeker]

I get an error when exporting the CAL file (step 7) when I press Export: "This graphline cannot be exported because: The data of the signal generator power graph cannot be determined." Any suggestions?

Screenshot error

graph export error.PNG (52.2 KiB) Viewed 15089 times

[joro]

For a Calibration file it is required that the Signal generator power is available.
During the exporting of a graphline, a lot of validations are performed, and the shown error message is an indication that the no signal power graphline was present in the performed test.
It seems that the test you performed is not configured to measure the signal geneator power.

Please go back to configuration of the 'constant power calibration method' test, and add a 'Power' input, where the 'Power Method' is set to 'Signal Generator level'.

Power input configuration for the measurement of the signalpower

constant-power-sginput.png (10.41 KiB) Viewed 15086 times

With this improved test configuration, the test will also measure the signal generator power, and it will be possible to export the data to a Calibration file.

[solutionseeker]

Thanks for the quick reply. Indeed the 'Power Method' was set to 'Forward Power' instead of 'Signal Generator level'. This adjustment solved the error and exported the Calibration file without any problems.

[solutionseeker]

We are only able to export when we select Electrical Field probe 1 and can't export all the others types eg Signal Power etc... Is that normal behavior?

[joro]

It is indeed possible that only the 'Electrical Field probe 1' graphline can be exported. This is not a problem, as the exported data will contain all the required information that is needed in the exported .CAL file.
The 'signal power' and other power graphlines can only be exported if a graphline is available for it. This is not necessary, but if you want to review or export this information also, it is best to specify a 'Signal power' and/or a 'Forward power' input in the Mulitband test configuration. Once one or more of those inputs is configured, a graphline will be created for it, and it is possible to review or export it.

Signal power input configuration

signalpowerinput.png (8.2 KiB) Viewed 14947 times

[solutionseeker]

Thank you for the clarification. I have another question; after saving a 'Calibration file' should we repeat step 3 to 9 to measure the electrical field data for maximum 16 points?

[joro]

It is possible to include multiple field strenght sensors in the same 'Constant Power calibration method test'.
If multiple field strenght sensors are included in the same test, multiple 'Field'-graphlines will be present in the graph, and it is possible to export those 'Field'-graphlines to seperate calibration files.

For the 16 point Uniform Field Area validation, it is necessary to calibratie the field strength on 16 individual points. There are several possibilities to ensure that the 16 individual points are calibrated:

• If 16 field probes are available, it is possible to use these 16 field probes in a single 'Constant Power Calibration method' run.
• If only 4 field probes are available, it is possible to include those 4 field probes in a 'Constant Power Calibration method', which is then performed 4 times.
• If only a single field probe is available, it is necessary to run the 'Constant Power Calibration method' 16 times.
• any other combination that results in the measurement of 16 points

Depending on the number of available field probes, it is thus necessary to export the field graph from a single 'Constant power calibration method' multiple times (steps 6 - 9) or to perform the 'Constant power calibration method' multiple times (steps 3 - 9).

[solutionseeker]

Thank you, these calibration methods are clear now. Can you explain how the 16 point calibration data file(s) can be used for the electrical field strength during a substitution test?

[joro]

The 16 calibration files of the 16 individual field strenght points, can be used as input for the 'Uniform Field Area calculation'. The output of this 'Uniform Field Area calculation' will generate a single calibration file, which is then usable in a Field Strength substitution file.

The documentation of the 'Uniform Field Area calculation' can be found in Chapter 12 of our user manual. (Available at: http://wiki.dare.nl/wiki/index.php/Chap ... alculation )