Poor man’s compliance testing: The EnderEMC (#P50)
Such a bold title, such vague blog post – I recently had the pleasure of comparing two very different systems for EMC pre-testing at the lab bench, and one of them gave me an idea.
The two systems were a
- Y.I.C Technologies EMScanner / EMScanner+ / EMScannerR / EMScannerR+ (with an additional capital R, whatever SEO marketing genius came up with THAT idea), which is a base plate that has all of the signal pickup coils already integrated. Advantage being a fast scan since there’s no moving parts – with the drawback that the raster is fixed in X/Y but also Z direction, and the DUT more often than not needs to be placed upside down onto it. Which, by the way, caused me to total a 2000€ board by accident, pew-pew, sparks flying and lots of magic smoke escaped.
- Pendulum (former Detectus) SCN-500, which is a glorified 3D printer that had its printing head replaced with a rotating axis (hence 4 degrees of freedom) that carries a traditional EMC test probe, and optionally a web cam to overlook the test area and/or a single point laser scanner for depth gauging. Advantage being that this does allow free positioning in X, Y, Z and Θ with basically arbitrary probes, at the cost of speed, since scanning a point in space not only takes time to take the sample, but also to move to the location.
These are both instruments in the 20k to 60k Euro price range depending on size and options. I’m not going into more detail here, if that appeals to you, ask your local sales rep for a demo – but the simple setup of one of the devices gave rise to this on a Saturday evening:
That is my Ender 5 Plus(plus) with an EMC probe cable tied to the printing head, a preamplifier cable tied to the chassis at the end of the drag chain, a bit of wiring down to the spectrum analyzer (all of these borrowed from work for the weekend – much lower grade than the demo equipment I have to say!), a simple 12V power supply and finally a test PCB that already had its signature taken on both professional devices. The board does have a very shouty quad DC-to-DC converter running, but the CPU is basically quiet – I don’t know if that’s due to the thermal damage caused by the catastrophic failure of a nearby PCB, or if it can be started by the right program loading software and talking to it. In any way, the signature of the DC-DC was of interest, both in terms of spectral spewage, but also spatial resolution. Since there’s four inductors placed around it and every segment delivers a different voltage and has a different load level (including, apparently, moments of absolute silence of the two top coils!), we were interested if that can be observed by any of the EMC scanners in any level of detail.
So I had a go.
Forgive me, for I have not managed to export all data from the commercial machines. One of them has a separate tool that does convert the proprietary format, one of them just exports peak frequencies over the entire scan, or the feature is maybe hidden in a menu somewhere. So I can only put two of them in similar plotting setups for a fair comparison. All images rotated and mirrored to match the PCB as shown on the Ender (both professional devices allow embedding a photo of the DUT in software for better clarity).
So, which one is which?
Well, the blobby/static one is the mid-range YIC unit. Although the others also only made a scan above the highest header (so no resolution gain due to proximity effects to the RF source), they have a serious advantage in possible spatial resolution (this YIC unit only has a 7.5mm raster). On the other hand, the scan is about an order of magnitude faster, but this is basically as good as it gets. Fast, but blurry. There is a top-of-the-range unit with significantly better resolution – at a significant premium, of course.
And the other two? As much as I’d like to brag, the more grainy image is from the Ender setup. This could be advanced signal processing by Pendulum, but also my spectrum analyzer/probe/preamp setup is 1/10th the cost of what was used in the demo setup, and the kinetic stage, i.e. the printer, is 1/100th the cost of the professional unit.
And at THAT discount, I very much like my results.
I also uploaded my scripts, mainly generated with ChatGPT and lots of patience, to
–> the Githubs<--.
Use at your own risk, especially check the printer limits since my Ender 5 Plus is likely larger than your printer. I ran the commands (printermove.py) via the Moonraker API and WiFi, and used a Rohde & Schwarz FPC1000 spectrum analyzer over LAN (which, half-way, decided to fully lock up on the control panel, but it still beeped on key presses and delivered data just fine). make_images.py converts the amassed single scans into a single image or a spectral series of images, the final assembly to a GIF was done once again with ezgif, which is an excellent service that deserves more funding. emc_scan_plot.py does the same for ascii files that were converted from ms2d format via the manufacturer tools – since this format is not documented, YMMV (version 3.3.1).
