EMI Troubleshooting: How to Fix EMC Issues
Electromagnetic interference (EMI) issues are common in spaces where large amounts of electrical devices interact with one another. Units, circuits, and wires can never completely contain electricity, creating electromagnetic compatibility (EMC) problems. Unfortunately, this means EMI can be tricky to attribute to a specific source and solve.
The number of variables involved can seem daunting. An interference issue could result from a single problem or several, making identifying sources of EMI more difficult. On top of that, there isn't any one way to quickly pinpoint where your issue lies.
But, if you stick to a proven method of investigation and follow the steps in order, you can narrow the possibilities and identify the culprit. This EMI troubleshooting guide will walk you through EMI and EMC testing basics and provide a systematic process for you to follow.
Steps to EMI Troubleshooting
You'll need to follow a thorough investigative process to troubleshoot an EMI issue without guessing or spending time on false leads. The steps are similar to those you would use to solve other power quality issues.
Your investigation should consist of the following test procedures:
- Identify the source of EMI: By determining what is being affected by the EMI and how often, you can find the potential source of the issue.
- Test the source and analyze collected data: You'll need to perform tests and collect data about the potential source and emissions using specialized tools. The data will help you determine what kind of modification to make.
- Modify the current system: Determine and apply changes or solutions to the EMI source based on your data analysis. You may have more than one necessary fix.
- Verify changes and confirm: After applying a solution, you must re-test and check the source to ensure you've correctly identified and fixed the issue.
These steps will provide you with the source and a solution to your EMI problem. You'll need to repeat the process if you misidentify the origin and are still experiencing the same issues at the last step. It's essential that you complete these steps in order.
Here is each part of the test plan broken down:
1. Identify the Source of EMI
Beginning the investigative process correctly is crucial to solving your EMI problems successfully.
First, you'll need to gather information about the problem. This will provide you with the background necessary to complete the rest of the process.
Meet with everyone involved with the affected equipment and gather their input. Operators spend the most time in direct contact with the systems, so they may be able to provide more accurate or knowledgeable details about the issue. However, you need to keep an open mind, as they may not know the exact cause of the interference.
Once you've determined what the EMI affects, you'll need to identify the origin. Understanding how to find EMI sources and what to look for in your equipment will help you find the fault quickly and accurately.
Paying attention to the issue's frequency is a significant factor in narrowing options and determining the source. If it occurs sporadically, you should look into infrequently used equipment. Look into commonly used equipment to see if the problem is periodic or has a pattern.
Using these details will make it easier to find the possible sources of the interruption. The most common culprits include:
- Radio sources: Nearby TV or radio and fixed base transmitters can cause interference. Look for handheld radios, RF heaters, arc welders, and vehicle radio transmitters inside the facility. You can use handheld radios to test for radio frequency interference (RFI) by irradiating cables and equipment enclosures to find failures.
- Power disturbances: Industrial facilities and offices often have large motors and heavy equipment running, such as in air conditioner units and elevator shafts. If your area is experiencing stormy weather, lightning strikes can also play a role. You can use a power transient generator and power quality monitor to test for disturbances and cycle equipment to force a failure.
- Electrostatic discharge: If there are static generators — paper or plastic film rolling and conveyor belts, for example — near your equipment, they may cause electrostatic discharge (ESD) interference. It can also become an issue whenever your region experiences low humidity. You can use ESD guns to test equipment, but you'll need to ease into it, starting with indirect discharge or a low level of direct contact.
You may also need to conduct a power quality audit. This testing allows you to analyze whether or not your systems are operating correctly and efficiently by evaluating the electrical energy.
Finding the source of the problem quickly and accurately is crucial, as interference can cause service interruptions, data loss, permanent damage to equipment, and failures. The stakes are even higher in the medical and military industries.
2. Test the Source and Analyze the Collected Data
Once you've identified the possible source and interference recipient, you need to perform tests to verify and measure the specifics of the issue.
The first parameters you should identify are:
- Frequency: Measuring frequency is crucial in determining the nature of the problem and potential remedies.
- Amplitude: You need to know the amplitude compared to relative expectations, as it will help you understand how invasive or extensive the solutions will be.
- Time: Paying attention to when the problem occurs can provide crucial information. You can deduce different possible culprits from how frequent the interruptions are, during what season or time of day they happen, if weather comes into play, and the operational state of the equipment.
- Impedance: Impedance plays a role in designing filters and input/output.
- Dimensions: You may be able to find potential antennas in equipment, which are crucial to locating if the frequencies determine the issue is radiated.
These details will help you better understand the interference and why the source is producing it.
You'll also need to determine the nature of the problem. The four main possibilities are:
Emissions can come from various equipment and are potentially the most common reason for EMI test failure. Set limits prevent electrical interference with sensitive radio equipment, though emissions are often too low to create an issue. Typically, only EMI testing can identify emissions.
Immunity or Susceptibility
Equipment can be affected by a wide variety of external sources of interference. Because there are so many possibilities, there are many corresponding tests. The most common tests include power transients, conducted and radiated RFI, ESD, and lightning.
Power loads and other transients from equipment in close quarters can also become issues. Transients don't appear in emissions testing, so they need to be identified separately. Susceptibility tests measure interference coming in rather than going out, as with emissions.
In the case of radiated EMI, a metallic element on the electrical unit — functioning as a sort of antenna — conveys the interference. For this to be possible, the element serving as an antenna has to measure about 1/20th of the electrical unit's wavelength or another significant fraction like 1/4 or 1/2.
Several unit pieces can serve as an antenna, including internal or external cables, slots or openings in metallic enclosures, and internal circuit boards. The rule of thumb is that high frequencies are more likely to radiate, as few elements are large enough to serve as an antenna for low frequencies. Commercial radiated emissions tests begin at about 30 MHz.
The broadband type works well to test for radiated EMI, using test instruments like pocket AM radios, radio-frequency field-strength meters, spectrum analyzers, and specialized antennas.
In the case of conducted EMI, a cable directly conveys the interference. Since it travels without the need for radiation, it occurs in low-frequency units, typically below the 30 MHz mark.
To test for conducted EMI, you should use spectrum analyzers, high-frequency clamp-on CTs, and sometimes power-line monitors and oscilloscopes — you may need the training to set up and operate these units correctly. If you cannot determine whether the interference is radiated or conducted, begin testing with radiated, as it is the most common type of EMI.
Depending on the type of interference you identify, several tools will aid you in locating the point where interference is radiated or conducted. You can find the direct origin by testing components of power supplies and equipment.
Near-field probes — either H-field or E-field — will help point out energy sources and measure emission profiles. Sources might include DC-DC, D/A, or A/D converters, processors, clock oscillators, and other things that create fast-edged digital signals. Near-field probes also aid in locating non-sealed seams on shielded enclosures.
Current probes measure high-frequency currents in equipment cables. It's crucial to test cables, as they are the most likely source of emissions. To record the emission profiles, you move the probe along each cable you need to check.
A nearby antenna can help you analyze harmonic content and identify the issue. Compared to both the cable and internal measurements, you'll be able to find the origin of the interference.
Much of this testing requires knowledge of operating and reading finely tuned tools, so it may be appropriate to hire a testing facility or power system designer to perform tests. Using the correct troubleshooting techniques for each instrument is crucial.
After assembling all of the recorded data, look for patterns or paths that indicate why your source is interfering with other electrical units. Most of the time, it boils down to a leaky seam or poorly shielded cable.
3. Modify the Current System
Now that you've identified the source and nature of the interference problem, you can decide on the best course of action for solving the issue. You may even find that there are several sources rather than one, meaning you'll need either a single fix or a combination of solutions.
When deciding how to fix EMI issues, consider facility operations, affected equipment, and the electromagnetic environment, as well as safety, installation, overall cost, maintenance, and the potential solution's performance record. You should also reach out to operators or involved parties and review the options with them before settling on one.
Before looking for outside solutions, you should try to reduce or alter the path of the emission levels from your identified source. Some potential solutions include:
- Cable fixes: Cables are a common source for EMI issues, but the problem can stem from one or several places. The complication is most likely rooted in the connector termination for shielded cables. This includes terminations at each link between the cable shield, connector, mating connector, and bulkhead. For a temporary fix, you can close gaps with copper tape or create a shield from aluminum foil and ground it to the housing. For filtered cables, check to ensure the assembly is circumferentially terminated to the cable connector or housing.
- Enclosure shield fixes: Openings and penetrations can cause problems in shielded enclosures. Openings are any seams, displays, and ventilation in the unit; penetrations include switches, fasteners, and indicators. Most commonly, these are involved in ESD problems, so ESD testing can help you locate them. Closing openings with copper tape or aluminum foil sometimes works, but ventilators, displays, and areas that need to stay open require conductive screens or perforated foil.
- Circuit board fixes: On equipment without external shields; the next option is to work with the circuit boards. Handheld radios and sniffers, H-field, E-field, and high-impedance scope probes all help localize the issue to identify it better. Depending on the exact problem, you'll need to use filters, transient protectors, or a combination of the two or onboard shields and power and signal filters in case of an emissions issue.
If you can't solve the problem through general independent troubleshooting, you may need to resort to other EMI testing methods, such as purchasing and installing a more definite EMI solution. These include:
Using filters that target specific ranges of MHz can help eliminate emissions. These filters protect equipment from emitted RFI and prevent emissions from interfering with other devices. They are available for both consumer and commercial purchase and are commonly used for conducted emissions, although they are also applicable for radiated emissions.
Radiofrequency shielding is the standard for suppressing emissions. Incorporated RF shields can protect sections of circuit boards from interference or prevent emissions from affecting other equipment. Some common examples of shield types include metal films or boxes and conductive foam, but guards are available in different materials, thicknesses, and shapes to suit your needs. Shields are commonly used for radiated emissions.
Grounding configurations come in many different designs to solve EMI issues. However, all grounding systems share a common purpose — to create a path of zero-impedance for signals that use the system as a reference. Using an improper or inadequate configuration could cause interference, so finding the right design for your uses is crucial. Depending on the EMI problem's specifics, grounding techniques can reduce conducted and radiated emissions.
If at all possible, you'll want to test these solutions before you purchase and install one of them. During a test for one of these solutions, you may find that it doesn't work well or that the issue is different than you hypothesized.
4. Verify the Changes and Confirm
Once you initiate the necessary fixes, operations should return to normal. After you make the repairs, you have to monitor and re-measure the emissions through testing to be sure your solution is working and continues to work. Include these post-fix measurements in your final report.
If an issue persists after applying the solution, you must repeat the process in the same order. Even if the solution mitigates the effects, you should completely fix the issue to ensure no further complications occur.
Officially confirming that the solution has resolved the interference issue is crucial to the safety of your work environment, especially in the military and aerospace industries.
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