Earlier than we delve right into a step-by-step information to good engineering apply, two ideas to bear in mind. First, there are too many subpar take a look at stories from engineers, who typically do glorious work however aren’t given sufficient time to doc it correctly. In consequence, when groups sit right down to evaluation the report weeks and even days later, vital particulars are lacking, and the take a look at engineers have merely forgotten a number of the extra refined factors.
Second, there’s a lack of strong tips for this course of. A fast search on Google doesn’t flip up a lot on the topic. These two components led to the creation this text.
This text received’t cowl the way to write an accredited EMC take a look at report, which requires detailed documentation of issues like take a look at circumstances, measurement uncertainty, and so forth. As a substitute, it’s geared toward design engineers and take a look at engineers who’re doing hands-on work in their very own labs.
After all, managers are greater than welcome to learn alongside too. And when you’re a supervisor who finds this text useful, be at liberty to share it along with your workforce.
To kick issues off, let’s begin by an instance of what to not do.
Determine 1 The screenshot exhibits a benchtop EMC report that the creator collected some time in the past. Supply: Min Zhang
Determine 1 exhibits a screenshot from a take a look at report. Discover something incorrect?
First, there’s no setup image. Anybody aware of EMC/RF testing is aware of that even a minor setup error can result in considerably totally different outcomes. If a system is incorrectly examined as a failure, the end result might result in pricey over-design. However, if a system is wrongly marked as a cross, discovering out it fails on the accredited EMC lab is not going to solely come as a shock however will even add further prices and influence your product’s time to market.
What else? The take a look at circumstances usually are not clearly outlined. For instance, what does the engineer imply by “prolonged the defend with further foil”? It might need made sense on the time however belief me—when the identical engineer revisits the report a month later, they most likely received’t bear in mind the specifics. Furthermore, we’d wish to know if this “further foil” was terminated and, in that case, how. Sadly, no supporting photograph was offered.
Lastly, the engineer made an announcement with out providing a proof or supporting proof. When stating “noise was frequent mode fairly than differential mode,” there have been no take a look at outcomes to again this up. In EMC/RF testing, assumptions usually are not sufficient. A easy RF present probe clamped on the cable bundle might have offered the required proof for this assertion.
So, how ought to we write a high-quality take a look at report? Primarily based on years of troubleshooting EMI points, right here is our step-by-step information to writing an efficient engineering report.
Step 1: Sharpening the instruments
Earlier than diving into the setup, it’s essential to make sure your tools is prepared for the duty—very like how a carpenter sharpens the instruments earlier than beginning a challenge. Whereas we’re not actually “sharpening” something, the concept is similar: earlier than any RF measurement, all the time test in case your tools is as much as the job. Let me share an instance to emphasise the significance of this step.
In a single case, a consumer’s costly receiver had a broken RF front-end, they usually have been unaware of it. It is a traditional case of what I name “engineers’ bias”—the idea that high-priced tools is inherently dependable. Engineers typically place full confidence in pricey devices, however even these can fail.
In case your spectrum analyzer has a monitoring generator, you possibly can simply test for this problem. Merely join the TG output and the spectrum enter utilizing a coaxial cable and carry out a TG scan. One ought to see a flat, straight line throughout the entire frequency vary on the provided TG energy degree (typically between -20 dBm and 0 dBm). That is proven in Determine 2.
Determine 2 Here’s a solution to test the RF front-end of a spectrum analyzer. Supply: Min Zhang
The identical precept applies to different take a look at tools. As an illustration, if an RF present probe is unintentionally dropped, its switch impedance could also be affected. In such a case, it’s best to recalibrate the probe earlier than continuing with the take a look at. Likewise, line impedance stabilization networks (LISNs) ought to be often checked to make sure their impedance conforms to the related requirements.
It’s additionally vital to doc the final calibration, characterization, or inspection date for all tools used within the take a look at. If an incident happens (like dropping the present probe), ensure that to file it within the report. This ensures traceability. Whilst you can proceed with the take a look at, take into account that such occasions improve measurement uncertainty.
Step 2: Take a look at set-up
You will need to clearly present detailed photographs of the take a look at set-up. This could embrace an total view of the take a look at association, in addition to close-up pictures of particular particulars, such because the bonding wire, the way it’s bonded, and whether or not a continuity test was carried out on the connections.
For performed emissions/immunities and transient exams, embrace photos displaying the bonding of the take a look at tools, cable format, and particulars of the gadget beneath take a look at (DUT) bonding, significantly if a bonding wire is used to connect with the take a look at floor airplane.
For radiated emissions exams, assuming you’re conducting them in your personal lab—since radiated immunity testing can intervene with the electromagnetic surroundings—you shouldn’t carry out radiated immunity take a look at with no shielded tent. Make certain to incorporate photos that present the antenna set-up.
Do we have to embrace a system diagram of the take a look at setup?
The brief reply is sure, ideally. Whereas drawing a system diagram could take extra time than merely snapping a photograph, it’s nonetheless vital to incorporate a easy diagram. Widespread instruments for creating system diagrams embrace Microsoft Visio and PowerPoint. Determine 3 exhibits a system diagram utilizing Keynote on a MacBook. In the event you’re extra artistically inclined, be at liberty to make use of different drawing instruments—some engineers favor this strategy.
Determine 3 The system diagram exhibits a take a look at set-up for CISPR 25 performed emissions. Supply: Min Zhang
Determine 4 exhibits the precise take a look at set-up used for the performed emission take a look at, highlighting an total view of the take a look at association. You may see how the take a look at tools is listed for the take a look at.
Determine 4 The precise take a look at set setup lists all of the tools. Supply: Min Zhang
Different key data
Your report must also embrace particulars concerning the energy provide settings, reminiscent of voltage and present. If there’s any supporting tools for the DUT, ensure that to seize this in each the photographs and the system diagram whereas documenting the operational standing within the report.
Environmental circumstances reminiscent of room temperature and humidity are usually not required for in-house exams, however when you’re conducting electrostatic discharge (ESD) investigations, it’s vital to doc these components, as humidity can have an effect on the take a look at outcomes.
It is suggested to all the time take a look at and measure ambient EM noise earlier than beginning any benchtop EMC take a look at, and these outcomes ought to be completely documented within the take a look at report. Usually, a benchtop energy provide can introduce inner noise, which can be picked up by the LISN throughout performed emission exams.
Moreover, LED lights and close by tools typically generate EM noise, which may simply couple to the DUT’s cable leads and influence the emission readings. When working with no shielded surroundings—which is commonly the case for design engineers testing and troubleshooting on the bench—one of the best apply is to benchmark the ambient noise. This may be carried out utilizing the spectrum analyzer itself or by utilizing software program to save lots of the ambient noise information for comparability in future research.
Step 3: Acquiring take a look at outcomes
It’s all the time a good suggestion to save lots of outcomes straight from the tools or by way of a linked pc (assuming the required software program is put in), fairly than counting on a photograph of the display screen. This strategy gives a number of benefits.
In the beginning, trendy tools software program sometimes supplies much more data than what’s seen on the display screen, such because the date, time, and sampling fee (for an oscilloscope, for instance). Moreover, saving information digitally avoids potential points like reflections which will happen in photographs.
One other profit is that a number of traces can later be processed for comparability functions. Some software program even means that you can doc in depth particulars, reminiscent of take a look at circumstances and operation modes, making the report extra complete and traceable.
An instance is proven in Determine 5.
Determine 5 Right here is an instance of take a look at outcomes generated by software program Tekbox EMCview. Supply: Min Zhang
Step 4: Analyzing take a look at outcomes
For a junior engineer, analyzing take a look at outcomes can appear daunting, however we encourage you to present it your greatest effort. To start, concentrate on figuring out the failure mode—typically it is perhaps a resonance within the spectrum scan, or a narrowband sign failure. It’s vital to supply some type of rationalization. instance is proven in Determine 6.
Determine 6 It’s vital to supply some type of rationalization whereas analysing the take a look at outcomes. Supply: Min Zhang
On this radiated emission end result, two points are evident. First, there’s a broadband noise profile within the 50 to 80 MHz frequency vary, and second, there are narrowband noise traits between 100 and 200 MHz. Moreover, a single narrowband spurious sign seems at 222 MHz.
On this case, we highlighted these areas of curiosity and offered explanations for every. As all the time, when you suspect a selected perpetrator is inflicting the noise, show it by offering additional outcomes—this considerably enhances the worth of your evaluation, as demonstrated in Determine 6.
What when you don’t absolutely perceive what’s occurring? On the take a look at stage, on the very least, provide just a few potential explanations. You may say, “We imagine it could possibly be one of many following causes,” and listing some prospects. You can too point out that additional testing or simulation could also be wanted to pinpoint the basis trigger. That is vital as a result of when a workforce of engineers evaluations the report collectively, different workforce members typically contribute worthwhile insights and strategies.
Step 5: Troubleshooting and fixing
If the take a look at report contains troubleshooting and fixes, the options have to be clearly said and supported with ample proof. This could embrace photographs, take a look at outcomes, and a transparent rationale for the repair. For instance, an engineer would possibly say, “The ability cable linked to the motor proved to be the primary radiating mechanism, and a ferrite sleeve on the mains cable solved the issue.”
Nonetheless, this strategy is problematic for the explanations we’ve mentioned earlier. A simpler assertion could be:
“The motor energy cable was recognized as the primary supply of radiated emissions, as disconnecting the cable considerably decreased the noise between 50 and 80 MHz. We then utilized XXX (half quantity) ferrite cores to the motor cable, inserting it close to the motor connector, and ensured the ferrite cores have been near the car chassis (the situation is essential). As proven in Determine 7, this resulted in improved efficiency. See the comparability of the earlier than and after leads to Determine 7.”
Determine 7 That is how the troubleshooting half in a report seems to be like. Supply: Min Zhang
By stating the troubleshooting outcomes on this method, you present much more confidence within the answer.
Step 6: Abstract and conclusion
We imagine a great report must also embrace strategies, suggestions, or actions that must be taken. Engineers could suggest design modifications, but it surely’s vital to listing the potential dangers related to these modifications. This highlights that EMC engineering typically entails compromise. Whereas engineers could make strong strategies, they need to additionally think about different components reminiscent of thermal or mechanical design, which could complicate implementation.
It’s additionally important to contemplate various fixes. Throughout troubleshooting, you’re typically restricted by the instruments at hand, and the answer you discover might not be probably the most cost-effective. That is particularly related for quantity producers, the place even small value variations can have a major influence.
By this level, we’ve offered readers with a strong information to writing a benchtop EMC take a look at report. The ideas outlined listed below are relevant throughout many areas of engineering. We welcome your strategies and suggestions.
Dr. Min Zhang is the founder and principal EMC guide at Mach One Design, a UK-based engineering agency specializing in EMC consulting, troubleshooting, and coaching. He at the moment chairs the IEEE EMC Chapter for the UK and Eire department. Zhang will be reached at min.zhang@mach1design.co.uk.
Associated Content material
- EMC EMI RFI ESD
- Discover EMI sources with an oscilloscope
- EMC design contest to concentrate on sign looking
- An introduction to troubleshooting EMI issues
- EMI emissions testing: peak, quasi-peak, and common measurements
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