Earlier than we delve right into a step-by-step information to good engineering follow, two ideas to bear in mind. First, there are too many subpar check stories from engineers, who typically do glorious work however aren’t given sufficient time to doc it correctly. In consequence, when groups sit all the way down to overview the report weeks and even days later, essential particulars are lacking, and the check engineers have merely forgotten a few of the extra refined factors.
Second, there’s a lack of strong pointers 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 right way to write an accredited EMC check report, which requires detailed documentation of issues like check situations, measurement uncertainty, and so forth. As an alternative, it’s aimed toward design engineers and check 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 crew.
To kick issues off, let’s begin by taking a look at an instance of what to not do.
Determine 1 The screenshot exhibits a benchtop EMC report that the writer collected some time in the past. Supply: Min Zhang
Determine 1 exhibits a screenshot from a check report. Discover something unsuitable?
First, there’s no setup image. Anybody acquainted with EMC/RF testing is aware of that even a minor setup error can result in considerably completely different outcomes. If a system is incorrectly examined as a failure, the consequence might result in pricey over-design. Then again, if a system is wrongly marked as a move, discovering out it fails on the accredited EMC lab is not going to solely come as a shock however may also add additional prices and influence your product’s time to market.
What else? The check situations should not clearly outlined. For instance, what does the engineer imply by “prolonged the defend with additional foil”? It may need made sense on the time however belief me—when the identical engineer revisits the report a month later, they in all probability received’t keep in mind the specifics. Furthermore, we’d need to know if this “additional foil” was terminated and, in that case, how. Sadly, no supporting photograph was supplied.
Lastly, the engineer made a press release with out providing a proof or supporting proof. When stating “noise was frequent mode somewhat than differential mode,” there have been no check outcomes to again this up. In EMC/RF testing, assumptions should not sufficient. A easy RF present probe clamped on the cable bundle might have supplied the required proof for this assertion.
So, how ought to we write a high-quality check report? Based mostly 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 mission. Whereas we’re not actually “sharpening” something, the thought is similar: earlier than any RF measurement, all the time verify 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. This can be a basic case of what I name “engineers’ bias”—the assumption 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 may simply verify for this difficulty. 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 stage (typically between -20 dBm and 0 dBm). That is proven in Determine 2.
Determine 2 Here’s a method to verify the RF front-end of a spectrum analyzer. Supply: Min Zhang
The identical precept applies to different check tools. For example, if an RF present probe is by accident dropped, its switch impedance could also be affected. In such a case, you need to recalibrate the probe earlier than continuing with the check. Likewise, line impedance stabilization networks (LISNs) ought to be commonly checked to make sure their impedance conforms to the related requirements.
It’s additionally essential to doc the final calibration, characterization, or inspection date for all tools used within the check. If an incident happens (like dropping the present probe), be sure to document it within the report. This ensures traceability. Whilst you can proceed with the check, understand that such occasions improve measurement uncertainty.
Step 2: Check set-up
It’s essential to clearly present detailed photographs of the check set-up. This could embrace an total view of the check association, in addition to close-up photographs of particular particulars, such because the bonding wire, the way it’s bonded, and whether or not a continuity verify was carried out on the connections.
For performed emissions/immunities and transient assessments, embrace photographs displaying the bonding of the check tools, cable structure, and particulars of the system below check (DUT) bonding, notably if a bonding wire is used to hook up with the check floor airplane.
For radiated emissions assessments, 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 check with out a shielded tent. Ensure that to incorporate photos that present the antenna set-up.
Do we have to embrace a system diagram of the check setup?
The brief reply is sure, ideally. Whereas drawing a system diagram could take extra time than merely snapping a photograph, it’s nonetheless essential to incorporate a easy diagram. Well-liked instruments for creating system diagrams embrace Microsoft Visio and PowerPoint. Determine 3 exhibits a system diagram utilizing Keynote on a MacBook. In case 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 check set-up for CISPR 25 performed emissions. Supply: Min Zhang
Determine 4 exhibits the precise check set-up used for the performed emission check, highlighting an total view of the check association. You’ll be able to see how the check tools is listed for the check.
Determine 4 The precise check set setup lists all of the tools. Supply: Min Zhang
Different key info
Your report must also embrace particulars in regards to the energy provide settings, corresponding to voltage and present. If there’s any supporting tools for the DUT, be sure to seize this in each the photographs and the system diagram whereas documenting the operational standing within the report.
Environmental situations corresponding to room temperature and humidity are typically not required for in-house assessments, however when you’re conducting electrostatic discharge (ESD) investigations, it’s essential to doc these components, as humidity can have an effect on the check outcomes.
It’s endorsed to all the time check and measure ambient EM noise earlier than beginning any benchtop EMC check, and these outcomes ought to be totally documented within the check report. Sometimes, a benchtop energy provide can introduce inner noise, which can be picked up by the LISN throughout performed emission assessments.
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 out a shielded surroundings—which is usually the case for design engineers testing and troubleshooting on the bench—the perfect follow is to benchmark the ambient noise. This may be finished utilizing the spectrum analyzer itself or through the use of software program to avoid wasting the ambient noise knowledge for comparability in future research.
Step 3: Acquiring check outcomes
It’s all the time a good suggestion to avoid wasting outcomes instantly from the tools or via a related laptop (assuming the required software program is put in), somewhat than counting on a photograph of the display screen. This strategy presents a number of benefits.
In the beginning, fashionable tools software program usually offers way more info than what’s seen on the display screen, such because the date, time, and sampling price (for an oscilloscope, for instance). Moreover, saving knowledge 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 intensive particulars, corresponding to check situations 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 check outcomes generated by software program Tekbox EMCview. Supply: Min Zhang
Step 4: Analyzing check outcomes
For a junior engineer, analyzing check outcomes can appear daunting, however we encourage you to offer it your greatest effort. To start, concentrate on figuring out the failure mode—generally it is likely to be a resonance within the spectrum scan, or a narrowband sign failure. It’s essential to supply some type of rationalization. A very good instance is proven in Determine 6.
Determine 6 It’s essential to supply some type of rationalization whereas analysing the check outcomes. Supply: Min Zhang
On this radiated emission consequence, 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 supplied explanations for every. As all the time, when you suspect a selected offender 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 totally perceive what’s occurring? On the check stage, on the very least, supply a number of potential explanations. You’ll be able to say, “We consider it might be one of many following causes,” and record some potentialities. You can even point out that additional testing or simulation could also be wanted to pinpoint the basis trigger. That is essential as a result of when a crew of engineers opinions the report collectively, different crew members typically contribute precious insights and options.
Step 5: Troubleshooting and fixing
If the check report consists of troubleshooting and fixes, the options have to be clearly said and supported with ample proof. This could embrace photographs, check outcomes, and a transparent rationale for the repair. For instance, an engineer may say, “The ability cable related to the motor proved to be the principle radiating mechanism, and a ferrite sleeve on the mains cable solved the issue.”
Nevertheless, this strategy is problematic for the explanations we’ve mentioned earlier. A more practical assertion could be:
“The motor energy cable was recognized as the principle 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, putting it close to the motor connector, and ensured the ferrite cores have been near the automobile 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 appears like. Supply: Min Zhang
By stating the troubleshooting outcomes on this method, you present way more confidence within the resolution.
Step 6: Abstract and conclusion
We consider a very good report must also embrace options, suggestions, or actions that have to be taken. Engineers could suggest design adjustments, however it’s essential to record the potential dangers related to these adjustments. This highlights that EMC engineering typically entails compromise. Whereas engineers could make strong options, they have to additionally take into account different components corresponding to thermal or mechanical design, which could complicate implementation.
It’s additionally important to think about various fixes. Throughout troubleshooting, you might be typically restricted by the instruments at hand, and the answer you discover will not be essentially the most cost-effective. That is particularly related for quantity producers, the place even small value variations can have a big influence.
By this level, we’ve supplied readers with a strong information to writing a benchtop EMC check report. The ideas outlined listed below are relevant throughout many areas of engineering. We welcome your options and suggestions.
Dr. Min Zhang is the founder and principal EMC advisor at Mach One Design, a UK-based engineering agency specializing in EMC consulting, troubleshooting, and coaching. He at present chairs the IEEE EMC Chapter for the UK and Eire department. Zhang will be reached at min.zhang@mach1design.co.uk.
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- Discover EMI sources with an oscilloscope
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- An introduction to troubleshooting EMI issues
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