Electronics

Transients Take Many Shapes – Test Them All!

In the conclusion of Elite’s transient testing series, Tom Klouda and Tom Braxton review the family of magnetic-field and damped-wave immunity tests. Read more from our transient series in Part 1, Part 2, Part 3 and Part 4.

All transients have a common trait: they’re just passing through.  An electrostatic discharge (ESD) is a quick spark that passes in microseconds; an electrical fast transient (EFT) happens in rapid-fire bursts; and voltage surges wash over a device like a sudden wave hitting a boat.

Elite Electronic Engineering’s Tom Klouda has been running and observing these immunity tests for many years and explains that ESD, EFT, and surges are fast, high-energy events.  However, there are other transients that aren’t as dramatic but also pose threats to electronic devices. Among those are impulse magnetic fields, damped oscillatory magnetic fields, ring waves in low-voltage cables, and damped oscillatory waves.

The electrical threats are real and there are standards dealing with them all. Elite can help you navigate your way through the transient underbrush and run the immunity tests verifying your product’s ability to shrug them off.  This is why they’re called immunity tests: how immune is your product to a real-world disturbance?  Here’s a summary of the family of other transient standards and their tests.

Tom goes on to explain how these immunity tests apply and what conditions they’re designed to meet.

Impulse Magnetic Fields Immunity Tests

IEC 61000-4-9 spells out test and measurement techniques for impulse magnetic field immunity.  Those fields are used in the manufacture of permanent magnets, therapeutic medical services, and other specialized applications.  Like any other electrical event, effects of those impulses can find their way into unrelated equipment.  The immunity tests Elite performs under IEC 61000-4-9 measures how well a product continues to function.

The image below shows a typical setup. A combination wave generator (CWG) generates the currents specified in the standard, which are applied to a magnetic-field antenna coil that surrounds the equipment under test (EUT). Depending on the EUT’s shape and size, the test might be repeated with the coil in different positions surrounding the EUT.  The magnetic impulses are applied while the EUT is monitored for normal operation.

The images below show the waveform and a typical test setup as defined in the standard. Tests are specified at multiple current levels and for different size induction coils.

Magnetic pulses can originate from a variety of sources, including nearby lightning strikes, power plants, and high-voltage substations.  The test plan drawn up in concert with the regulatory test engineer will specify the EUT configuration and the specifics of the test application.

Damped Oscillatory Magnetic Fields Immunity Tests

Transient events take many forms, and magnetic fields are no exception.  Another version is the damped oscillatory magnetic field which also is a byproduct of power stations and high voltage switching. IEC 61000-4-10 is the standard spelling out test that determines a product’s oscillatory magnetic field immunity.

The figures below show the waveshape and configuration of the oscillatory pulse specified by IEC 61000-4-10.  The current level and repetition rate of the waveform will be specified in the test plan.  Those choices depend on the EUT’s intended application and the environment where it’s to be installed.  The EUT is monitored for any response during the test, following the failure criteria described in the test plan.

Ring Waves Immunity Tests

Yet another flavor of immunity verification for oscillating transients is the ring wave test, described in IEC 61000-4-12.  Ring waves are non-repetitive, like the single ring of a bell, hence the name.  Peak levels vary from 250 to 4000 volts and have a repetition rate between 1-60 per minute.

The figures below show the waveform specified in IEC 61000-4-12.  Note its difference from that of the damped oscillatory wave: it represents the ringing of a single transient event.  The image on the right is a schematic drawing of a simple coupling/decoupling network (CDN) that allows the ring wave generator to apply the wave to the EUT’s power lines.

Damped Oscillatory Waves Immunity Tests

In addition to the damped oscillatory field tests described in IEC 61000-4-10, there are damped oscillatory waves propagating along cables.  IEC 61000-4-18 defines the test for those.  Oscillatory waves are related to the oscillatory fields that result, but the path from interference source to victim is conducted, rather than radiated.  For that reason, it requires a different test.

Both slow-damped (100 kHz, 1 MHz) and fast-damped (3 MHz, 10 MHz, 30 MHz) waves are described in the standard, at levels for both common mode and differential mode injection through the CDN.  Again, the test plan crafted by the development and test engineers will identify what levels, rates, and modes are appropriate for the EUT’s application.

The images below show the waveform and coupling example as defined in the standard.

Transients, transients, everywhere

A product intended for use in a harsh environment, like near a power-distribution or generating station, should be tested for the full range of transient immunity.  The same immunity tests are applicable for devices used in places surrounded by sudden electrical events like lightning strikes or power switching.  Which ones apply to your product?  Contact the experts at Elite, and they can help you determine what combination of these immunity tests best fit your application requirements.

Elite’s expertise, timeliness, and trusted results have set a high bar for 65 years.  When you have questions on these or any other of the array of tests your product needs, contact Elite for the answers.

Learn more in A Seasonal Series on Transient Testing: Part 1, Part 2, Part 3, and Part 4.

A Sudden Spark Made My Screen Go Dark

Electrostatic Discharges (ESD) are everywhere. We feel them when we reach for a doorknob, a car-door handle, or pull off a sweater. Your electronic products feel them too, and often not in a good way. False displays, logic upsets, or even component damage can result.  In Part 4 of Elite’s transient testing series, Tom Klouda and Tom Braxton show how an ESD test is done and why you need to know more about it. Read more from our transient series in Part 1, Part 2, Part 3, and Part 5.

It’s a brisk morning in January and you slide off your coat, settle in the chair next to the equipment bench, and rub your hands together to get the chill off your fingers.  Rolling over to the bench, you reach for the power switch on the laptop and – zap! Your arm jerks back and the screen has gone blue. Reboot and hope for the best.

You could change a few details in this story, but we’ve all had this experience.  It doesn’t have to be a cold day in January – it could be any time of year in any office or lab.  Electrostatic discharge (ESD) has raised its head and bit your finger. ESD also bit the laptop, but the machine doesn’t have an arm to jerk back in response.  The laptop was knocked down after taking a punch and is getting back on its feet. You hope to see that no data was corrupted when it comes up again.

Digital devices are especially vulnerable to ESD upsets. The actions described above can build up a charge of 20kV or more between the finger and the surface. The current level is extremely low, but a jolt that size can throw off a device’s internal clock and, in the worst case, damage semiconductor devices.

IEC 61000-4-2, the basic standard for ESD immunity testing, spells out voltage severity levels, test environments, and test procedures.  Those specs aim for test repeatability while simulating a condition that is inherently not repeatable.  The table below shows the voltage severity levels for two different discharge types, contact and air.

Contact discharge (sometimes called “current injection”) is performed when the tip of the ESD test instrument is touching the test-point surface before the discharge is applied.  This simulates the case when there is direct contact between the EUT and the discharge source, as shown by Elite test engineer Brelon Weathersby in the figure to the right:

Air discharge is, as the name implies, a discharge passing from the instrument tip through the air to the test point. The illustration below shows the path of an air discharge.

A third discharge type is indirect, where discharges are applied to a nearby coupling plane.  This simulates the condition where the zap occurs in the vicinity of the EUT, creating a momentary RF field that can be induced into the EUT.  The illustration below shows the positions of the horizontal coupling plane (HCP) and the vertical coupling plane (VCP). Discharges are applied at the edges of the coupling planes while the EUT is monitored.

ESD behavior is statistical.  The equipment under test (EUT) can be zapped in the same place at the same level under the same conditions, and fail every time, half the time, or 1% of the time.  That’s why the standard calls for a minimum of ten discharges at each voltage level, negative and positive.  If a device is tested a 2kV, 4kV, and 8kV, at both polarities, that would mean 60 discharges at that test point.  If the EUT has ten specified test points, there would be 600 discharges applied.  It’s easy to see how that number could grow for a more complex EUT.

Any device going through an ESD test needs a test plan showing the EUT’s configuration and test point locations. Test points are chosen based on how likely they will be zapped in actual use.  For example, anywhere hands are going to touch, such as control panels and cable connectors, are obvious test points.  Conductive surfaces get contact discharges, and non-conductive surfaces (plastic enclosures, painted surfaces, etc.) get air discharges.  If an air discharge can’t be generated because the surface is heavily insulated, the non-discharge is noted along with other results.

Maintaining a record of the results is critically important.  The test plan will have defined failure criteria stating what is acceptable and not acceptable.  If the EUT responds in any way (blinking lights, interruptions, etc.), those are noted for the voltage level and polarity.  After many discharges a, pattern might become apparent, and that is useful information for those responsible for the product.

The final report emerging from an ESD test may contain a pass-or-fail determination, but it might be a set of data noting only the responses to the various discharges.  Those results are inconclusive and require engineering judgments to be made by the EUT’s responsible engineer.  An example of an inconclusive result is a toy that had flickering lights during the ESD test – was that a failure?  Maybe not, since it’s not a safety hazard or a loss of function.  On the other hand, it could be a hazard for critical displays like fluid levels if ESD causes erratic flashes.  These are the types of judgments that are made to determine whether an EUT’s response is actually a failure.

As with any transient phenomenon, the first order of business is understanding the EUT’s failure criteria. The upfront work to craft a test plan will take some time, but it will save both time and uncertainty when the results are known.  A thorough ESD test could have predicted the blue-screen reset seen after you slid into your chair and rolled near the bench. Better to know that might happen before your customer is charged to 20kV and finds out the hard way.

Contact Elite for more information on planning and executing your ESD immunity test.  You’ll be glad you did.

Learn more in A Seasonal Series on Transient Testing: Part 1, Part 2, Part 3, and Part 5.

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When lightning strikes, it can cause damaging electrical surges near and far. Are your electronic devices protected from surges on power and signal cables? Elite’s Tom Klouda and Tom Braxton are back with the third installment on transient events and their testing techniques. Read more in Part 1,  Part 2, Part 4, and Part 5.

Dark clouds move slowly as the sky changes from blue to purple. Rain begins to fall, and you hear distant thunder rumbling… Crack! Ka-boom! A flash of light and sudden thunder explodes with enough force that you can feel it.

Lightning strikes millions of times around the world and whenever it happens it takes us by surprise. But we share that surprise with our devices. A lightning strike is typically 300 million volts carrying a current between 10,000 and 200,000 amps, and all that energy has to go somewhere. Most of it goes into the ground and startles earthworms, but some is induced into power and signal cables.

If only one-tenth of one percent of that voltage finds its way into local wiring, that’s a 300,000-volt surge being spread around. It’s extremely brief and will quickly diminish, but it’s going to find its way into devices plugged into their power source. While not as dramatic, voltage surges are also produced from major power-system switching and short circuits.

Not to worry though – there’s a test for that. Elite’s Tom Klouda explains how it’s done.

IEC 61000-4-5 Surge Immunity Testing

The IEC 61000-4-5 standard spells out straightforward test procedures for surge immunity. The equipment under test (EUT) is connected via its power cables to a coupling-decoupling network (CDN), which is connected to a combination wave generator that creates the test-surge waveform, shown in the images below. The generator output waveform is defined for both voltage and current.

The levels applied during the test are chosen based on the severity levels appropriate for the EUT. The selection of test levels is shown in the table below.

Because electrical connectivity can be varied (single-phase AC, three-phase AC, DC power source), the form of the CDN is varied as well. The image below shows the connectivity of the CDN is shown in its simplest form. The combination wave generator is capacitively connected to the power lines going to the EUT and the decoupling network prevents the surges from going back into the power source.

Tests are done in configurations of line-to-ground and line-to-line, and in multiple combinations when three-phase power is involved.

The EUT is monitored during the test, with any response noted along with the test levels and operating conditions of the EUT.

Tests are also performed on interconnecting signal lines if the EUT has signal paths that could be affected by induced power surges. IEC 61000-4-5 specifies the CDN connectivity for both shielded and unshielded cables. As an example, the image below shows the configuration for shielded interconnecting cables.

The real value in this test, as for all immunity tests, is in the test plan. The test plan gives the EUT’s description as tested (model, version, connectivity, supporting hardware, etc.) and defines its failure criteria: what should the EUT be doing during the test and what should it not be doing? Any responses in the EUT are noted so that a determination can be made whether the response was acceptable or if it was an actual failure.

At Elite, we’ve tested hundreds of products for surge immunity. We draw on that experience for pre-test advice, compliments of our Regulatory EMC Team Leader, Rick King, NCE, shown in the photo in Elite’s surge-test lab.  

Rick reminds clients to confirm the suitability of their transient voltage suppressors (TVS) and to keep in mind that TVS ratings should be chosen based on not only the maximum applied surge levels, (i.e., +/-2kV), but also considering that lower amplitudes of 500V and 1000V are generally required to be tested. Excessive surge energy can enter the EUT if the TVS does not clamp at the lower levels.  

Rick also cautions that the lab’s surge coupling networks contain inductors which may create problems for switched-mode and pulse-width modulated (PWM) power supplies. The problem manifests itself as the test item’s inability to power-up during the surge test. Check Annex I of IEC 61000-4-5 for an explanation of this issue or contact Rick King at Elite for more insight.

Lightning and unexpected switching events are going to happen. You can rest assured that with Elite’s deep experience in surge-immunity testing you’ll know how your product is going to behave. Your customers will be much happier when your product continues to work even after those lightning flashes make them flinch.

Contact Elite with your questions on product testing and confirm your compliance before lightning strikes.

Learn more in A Seasonal Series on Transient Testing: Part 1, Part 2, Part 4, and Part 5.

Electrical Fast Transients (EFTs) – What they are and how they are tested

Large equipment is switched on and off all the time, and when that happens the power line sputters with bursts of pulses.  These are electrical fast transients (EFTs) that can upset an electronic device. Elite’s Tom Klouda and Tom Braxton are back with the second installment on transient events and their testing techniques. Read Part 1 and Part 3, Part 4 and Part 5. 

The IT manager at Hypothetical Tech’s branch location is talking with his colleague at the home office:

“We settled into that new office park.  It’s the space next to the campus HVAC plant.  Lots of room, and we’re in business!  Well, except Tuesday — four terminals crashed and we had to reboot.  Then on Friday it happened again, and we checked for lost data.  While we were down the folks in the HVAC plant came by to visit while they waited for their system to start up.  Nice guys.”

Does any of this sound familiar?  It’s what can happen when digital systems are hit with an electrical fast transient (EFT).  That HVAC plant next door had large blowers with hefty startup currents.  When the switch closes and the motor commutators start connecting, voltage spikes flash through the building’s wires.

High-current motors are a common EFT source, as are the switch contacts themselves.  The sudden voltage change is like striking a bell – a series of bursts, each of which linger until the energy has run out. 

What do bursts look like?

Think of an old-school desk telephone with a mechanical bell.  The bell rings in repeating bursts and generates an acoustic waveform like that shown below. 

In an EFT event, the current from the sudden surge splatters through the conductors’ natural resonance and sends bursts flowing into devices connected to the common power wiring.  EFT bursts are electrical, not acoustic, but the pattern is similar. The EFT voltage bursts resemble the acoustic bursts of the ringing bell. 

What is EFT?

The International Electrotechnical Commission (IEC) characterizes EFT bursts in standard 61000-4-4.  Like most standards, the electrical specifications are tightly defined.

The staccato bursts of voltage in the field are like snowflakes: they are never quite the same twice.  But they do have common characteristics that are standardized to allow repeatable testing.  Each individual pulse has a waveform defined in IEC 61000-4-4, shown in the image below:

A series of these pulses are sent into the power line at a designated repetition rate, forming a burst of a specified duration, which is then repeated at 300ms intervals and resemble the telephone-bell acoustic pulses shown above:

The voltage levels and repetition rates of the bursts are set based on the severity level appropriate for the equipment under test (EUT) and are run for a minimum of one minute.

As with any immunity test, a test plan is needed to assure the product is receiving a realistic approximation of what happens in its intended environment.  The test plan would include a description of the product, its configuration during the test (connecting equipment, cabling, active software, etc.), and the criteria for failure conditions. 

The test plan and the description of failure criteria are important.  During the application of the bursts, the EUT is monitored for correct operation.  If the EUT reacts to the bursts, is it a failure or a benign response?  For example, flickering display lamps may not count as a failure for some consumer products but may be critical for medical equipment.  Whatever could be regarded as a failure needs to be described in the test plan.

Not all responses can be known ahead of time, so someone familiar with the EUT should be present during the test to watch for anything unusual.  Any response should be documented for later analysis.  It’s obviously important for the EUT’s designer to know how the product responds to these kinds of transients.

Applying the burst to the equipment under test (EUT)

The burst defined in IEC 61000-4-4 is applied to the EUT through its external cables.  The EUT’s vulnerability is tested by connecting the burst generator to the power cables through a coupling-decoupling network (CDN). 

The image below shows a schematic view how it’s done inside the CDN.   The right-hand side of the image represents the coupling section injecting the burst directly into the power lines.  The left-hand side is the decoupling section preventing the burst from propagating into the external power grid.  The photo shows the CDN application in Elite’s laboratory.

The next image shows how the burst is applied to signal cables in a tabletop configuration.  The cables are laid inside a coupling clamp that capacitively applies the burst.  The photograph shows a typical configuration.

These tests are best done in a laboratory, but if that’s not practical the test can be done in situ (on site in its installed condition). The IEC 61000-4-4 standard shows alternative test configurations that can be applied.

The EUT is monitored for normal operation for the duration of the test and any responses are recorded.  The failure criteria defined in the test plan determines if the responses are failures.  If not, the EUT has passed.

If your product is to carry the CE Mark so that it is eligible for sale in the European Union, IEC 61000-4-4 is among the suite of standards it needs to meet.  Be aware of how your devices respond to an EFT burst. Then if your customers install your equipment near some heavy machinery, you’ll have fewer things to worry about.

Contact us today to get more information and schedule your product’s transient tests to achieve CE Mark compliance, along with the range of FCC, ISED, and others your product needs.  When your customers hear the big motors start up next to their site, they won’t spend time recovering lost data and you won’t spend time trying to find out why. 

Learn more in A Seasonal Series on Transient Testing: Part 1 and Part 3, Part 4 and Part 5.

The weeks and months pass quickly this time of year.  The days are transient things, popping on the calendar and vanishing before we notice. 

This is the first of our new series with Elite’s Tom Klouda and Tom Braxton. Stay tuned for more transient talk in future blogs. Read Part 2, Part 3, Part 4 and Part 5.

Transient events are everywhere, including the space around your product.  Can your device tolerate a voltage surge?  An electrical fast transient?  An electrostatic discharge?  A magnetic impulse?  The only way to find out is to test it, and your product will need to navigate that test.  You’ll need an experienced guide to get you there.  The International Electrotechnical Commission (IEC) provides the standards, and Elite Electronic Engineering is the guide you need to lead you through.

What are transients and where do they come from?

A transient is a short-duration pulse brought about by stored energy or a disruption in current flow.  Anyone who has experienced electrostatic discharge (ESD) when pulling off a sweater during low humidity then reached for a metal doorknob has dealt with transients.  The ESD between the metal surface and the finger is a stored-energy phenomenon. 

Voltage surges on power lines are examples of a transient brought on by current-flow disruption. When an electrical contact is interrupted by opening or closing, voltage arcs and mechanical bouncing of the contacts create random pulses.  There will be uncontrolled transients that depend on several factors: the contact type, the voltage and current levels, whether current is AC or DC, and the conductors’ geometry.  Devices in line or adjacent to the source of those transients are all vulnerable to disruption or damage.  The figure below gives a simple illustration of a switch contact being closed and the arcs that would bring about transient pulses.

These transients can cause digital logic upsets that appear as process interruptions or corrupted data.  Some transients can cause actual damage, like that shown in the picture below.  Logic upsets are more common and can range from a simple annoyance to a critical malfunction and can be minimized with error-correcting software.  Component damage is clearly a larger concern as it results in a costly repair or replacement.

Transients can be radiated or conducted, or sometimes both.  For example, energizing a high-current device will almost certainly generate a series of electrical fast transients (EFT) on the power circuit, which will propagate to other devices drawing energy through power cables in that building.  In addition, that event will create a momentary radiated field that can be induced into other conductors or directly into nearby devices. 

Though transients are uncontrolled when they occur, repeatable test procedures are in place that offer confidence in your product’s ability to operate normally when transients happen.

How are products tested for transient immunity?

There are different types of transients and different types of products.   The IEC standards and guidelines establish product categories and test procedures for a wide range of transient phenomena.  For example, IEC 61000-4-2 addresses ESD immunity, laying out test procedures and severity-level choices that can be chosen depending on the product type and its intended environment.  The figure below shows a typical application of the test.

Similarly, voltage surges are covered in IEC 61000-4-5, which spells out test procedures that are effective in predicting a product’s ability to withstand lightning surges and other sudden voltage spikes.  Voltage levels are chosen based on the product’s category and intended environment.

Your product will be subjected to a variety of transient events: power surges and ESD, as shown above, but also noise bursts, voltage dips, and magnetic pulses, among others, all identified in the IEC 61000-4 series of standards.

Your product’s application and intended environment will determine which tests to apply and at what levels.  The experts at Elite Electronic Engineering can explain the tests and guide you through the necessary steps toward verification. 

Be sure to follow the Elite Insider Newsletter in the coming months.  Those newsletters will review in detail the transient types, the standards that define and characterize them, and the tests that are performed to evaluate the immunity of your product. Continue with Part 2 and Part 3, Part 4 and Part 5.

Elite Electronic Engineering draws on 65 years of experience in testing products like yours and brings its expertise and evaluation skill to answer your questions.  We’ll see the days grow shorter this season and become more transient as they go by.  Verify that your product can also see transients go by  — Contact Elite to find out how.

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Electromagnetic Compatibility (EMC) tests require the use of specialized and costly pieces of electronic equipment.  The electronic equipment must perform the measurements accurately and efficiently.  A process used to acquire equipment at Elite Electronic Engineering, Inc. that has been successful is a collaborative effort between Elite, our customers, and the equipment manufacturers.

The process starts by identifying a need for the equipment.  The need can be identified from schedule bottlenecks, missed opportunities, operation safety concerns, or functionality.  Once the need is identified, various manufacturers of the test equipment are researched. In our research, we consider the equipment’s features, cost, warranties, and service.  Often, equipment on the market does not have the required features to meet our customer’s needs. This situation is where Elite’s personnel provide valuable insights.  Our customers and equipment manufacturers know everything about the design of their equipment.

However, Elite is in the unique position of knowing how to test our customer’s equipment and how to use the manufacturer’s test equipment.  Knowing our customer’s needs, Elite’s personnel work closely with the manufacturer to design equipment that accurately and efficiently performs the tests. This collaborative relationship has benefited everyone involved.  The EMC test industry also benefits because now the equipment Elite helped to design is available to everyone.     

Tom conducting an internal equipment training session in August.

Do you have any questions about choosing EMC Test Equipment, Lightning Testing, or other related topics? Please share your comments or questions below and this week’s expert, Tom Klouda, will get back to you as soon as possible. 

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