I need to make EMC limit charts (Some people refer to them as EMI charts) on my Emissions posts, Standards like CISPR 11 and CISPR 25 list their Emmision limit in tables like the one below.
This post about EMC charts is not about Equilibrium Moisture Content but about Electromagnetic Compatibility limit and emission plots and charts.
When I was working at CASS Industries, we used the same method to produce the emissions graphs in test reports. When I worked at ARRIVAL setting up the EMC Lab and facilities, I used the same process for making the charts and graphs in the EMC Component Standard.
![BS EN 55011:2016+A2:2021 (CISPR 11:2015+A2:2019) Table 2 - Disturbance voltage limits for class A group 1 equipment measured on a test site (a.c. mains power port)](https://philipmcgaw.com/wp-content/uploads/2024/07/image-1019x1024.png)
Above is “Table 2 – Disturbance voltage limits for class A group 1 equipment measured on a test site (a.c. mains power port)” from BS EN 55011:2016+A2:2021 (CISPR 11:2015+A2:2019). For this example chart, I want to plot the emissions limits for a DUT with a rated power of ≤ 20 kVA.
Frequency Range (MHz) | Quasi-Peak dB(μV) | Average dB(μV) |
---|---|---|
0.15 – 0.5 | 79 | 66 |
0.5 – 5 | 73 | 60 |
5 – 30 | 73 | 60 |
While there is nothing difficult to look at about the data in the table above, both the Frequency Range (MHz) and the Limit are Logarigmithic values, and this is something Microsoft Excel struggles to plot natively.
![Simple Plotting of Table 2 Chart in Microsoft Excel.](https://philipmcgaw.com/wp-content/uploads/2024/07/image-1-1024x458.png)
![Second attempt at plotting of the data from Table 2 using Microsoft Excel.](https://philipmcgaw.com/wp-content/uploads/2024/07/image-2-1024x444.png)
Using DPlot to plot the Charts
There is an application for Microsoft Windows called DPlot, that works with Excel to make plotting more complex charts easier. The version that you need to download is called DPlot Jr, and while it is harder to find it on the website, is both free and available for download.
Once you have installed it, running it doesn’t do anything interesting, but from this, we can start to make proper charts.
![First run of DPlot JR.](https://philipmcgaw.com/wp-content/uploads/2024/07/dPlotJrInstalled.png)
Using the same data as the second attempt at plotting the data from Excel, (I have updated the dB(uV) to dB(μV), and switched back to a Windows machine). Highlighting the data, and from the “Add-ins” menu, select “XYYY” from the DPlot drop-down.
![DPlot drop down in the Add-ins menu on Microsoft Excel.](https://philipmcgaw.com/wp-content/uploads/2024/07/Excel-1024x549.png)
DPlot will now open up the following window:
![Initial DPlot Charts from the Microsoft Excel Data](https://philipmcgaw.com/wp-content/uploads/2024/07/dplot-initial-1024x883.png)
Making DPlot EMC/EMI Charts ‘pretty’
![Select "E Logarithmic X - Logarithmic Y" from the Options > Linear/Log Scaling menu.](https://philipmcgaw.com/wp-content/uploads/2024/07/dplot-log-x-log-y-1024x885.png)
![The data is now shown as Log X Log Y in the DPlot Chart area](https://philipmcgaw.com/wp-content/uploads/2024/07/Log-X-Log-Y.png)
![Right click on the axis data, and select "Extents/Intervals/Size"](https://philipmcgaw.com/wp-content/uploads/2024/07/Change-Axis-Extents.png)
![Due to the data being between 150 kHz and 30 MHz, we can set the X axis to only include them, and reduce the Y axis range as well.](https://philipmcgaw.com/wp-content/uploads/2024/07/Limit-Axis.png)
![The data is now shown on Axis that don't extend passed it.](https://philipmcgaw.com/wp-content/uploads/2024/07/Limit-Axis-Data-Plot.png)
This is a basic introduction to how to use DPlot to make nice EMC / EMI Charts and plots from data in Excel. I have finished up the basic chart below which shows more data, both Class A, and Class B limits.
![55011:2016+A2:2021 AC Power Port Class A and Class B emission limits (Table 2; rated power <20 kVA and Table 4)](https://philipmcgaw.com/wp-content/uploads/2024/07/55011-2016A2-2021-AC.png)
The Charts can be exported as image formats via the “Save As” menu if you save the charts as a GRF file, it can not be opened with DPlot Jr. The applied settings can be saved and loaded via Get and Save Preferences.
There are examples of test report charts in the post “Autopsy of a Phone Charger from China“, with additional data shown, including the actual emissions and peak values from a spectrum analyser, allowing you to see all the data on one chart.