20230225 TI Electromagnetic compatibility testing methods and standards

Hello, and welcome to the TI Precision Labs video, Introducing Electromagnetic Compliance Standard Test Methods.
The details of these measurement setups and methods are covered in IEC 61000-4-X and CIS PR 11 test standards.
This document is meant to provide a short, simple overview of common tests.
Typical EMC testing includes conducted and radiated immunity and emissions, as well as a number of electrical overstress type tests.
This series on PCB design for good EMC has mainly focused on the concept of RF emissions and immunity, but there is a different Precision Labs video series focusing on electrical overstress.
Nevertheless, optimizing the PCB layout to minimize RF emissions will also generally benefit the electrical overstress This document will cover a small subset of the possible standards as an introduction to the subject.
There are many different standards and your requirement may vary depending on your local regulations and product requirements.
Let's start with a small overview of all the tests we will discuss.
Here is a list of different test standards that this video will cover.
The first three standards relate to the radiated and conducted susceptibility and emissions for the equipment under test, abbreviated EUT.
The next three standards relate to electrical overstress type testing.
Good PCB layout techniques will help to improve results for all the different test standards, but overstress tests may require additional components that protect sensitive devices from damage.
For example, TVS diodes, PTC fuses, gas discharge tubes, Schottky diodes, and RC circuits are all commonly used in protection circuits.
The overstress training series will cover these topics in detail.
This shows an example hardware setup that Texas Instruments used to look at the ADS8686S device and associated circuitry.
In general, EMC testing is done on a finished product PCB to assure robustness to electrical overstress and RF interference signals.
EMC testing also verifies that the product does not emit excessive RF so that it interferes with other products.
The IEC 61000-4-X and CISPR-11 test standards quantify the system compliance, and many products need to conform to these standards for release to market.
When doing these tests, one objective is to make sure that all the support test equipment is not impacted by the test.
For this reason, digital communications may be optically isolated, and batteries are used in place of an AC to DC supply.
Furthermore, test equipment may have some kind of filtering or decoupling to prevent the interference signal from impacting the equipment.
In this example, the product itself is isolated from the digital controller.
The IEC 61000-4-3 standard specifies the details of the radiated immunity test.
The purpose of this test is to verify the immunity of equipment under test, abbreviated EUT, to electromagnetic radiation that is generated from radio transmitters, cellular phones, and other electromagnetic sources.
The test is performed in an anechoic chamber, and the EUT is placed on a non-conductive table at 0.8 meters height.
The test distance between the EUT and the antenna is 3 meters.
The EUT is exposed and tested in an electromagnetic field with a horizontal and vertical polarity at each rating.
The RF test signal is swept from 80 megahertz to 1 gigahertz with the Yagi antenna, and from 1 gigahertz to 2.7 gigahertz with the Horn-type antenna.
The disturbance signal is 80% amplitude modulated with a 1 kilohertz sinusoidal signal.
The field strength is 10 volts per meter and 18 volts per meter for each frequency range.
The interference signal is created with an RF generator and control system, which is situated outside the anechoic chamber.
Typically, digital communications with the EUT are connected to the host PC using fully isolated fiber optic cables.
Furthermore, battery power is used as opposed to an AC-powered lab supply to avoid interference and potential disruption of the power source.

For radiated immunity, depending on the frequency range, a different type of antenna is used.
A Horn antenna is used for frequencies above 1 gigahertz.
And a Yagi antenna is used for frequencies below 1 gigahertz.
During the immunity test, the table will rotate so that the EUT is exposed to RF interference at multiple angles.
Also, the antenna orientation will be shifted by 90 degrees to change the polarization of the RF signal.
All tests are done in an anechoic chamber.
An anechoic chamber is a specifically designed room to eliminate electromagnetic reflections.
It does this by covering the interior surfaces with cone-shaped radiation absorbent material.
This slide illustrates the rotation of the antenna by 90 degrees to change the electromagnetic polarization.
The test results for radiated immunity relate to how the EUT performance is impacted by the RF interference.
The best case scenario is that under all levels and all frequencies of interference, the performance of the EUT is unaffected.
The worst case scenario is that the EUT is permanently damaged by the applied interference.
The test criteria listed assigns a letter grade to the range of different test outcomes.
Passing test criteria A indicates that the EUT had normal performance within specified limits.
The limits in this case are set by the EUT's manufacturer according to what they believe is an acceptable deviation in the product's operation from their customer's perspective.
Criteria B allows for a temporary loss of performance, but after the interference is removed, the device resumes normal operation.
For criteria C, the EUT functionality is lost without resetting the device or cycling power.
Once reset, the device resumes normal operation.
And finally, for criteria D, the EUT is permanently damaged by the applied interference.
These same criterion can be applied to many different IEC and CISPR test standards.
The test level for IEC 61000-4-3 defines the field strength for the applied interference signal.
Test level 1 is the weakest applied field strength at only 1 volt per meter, and test level 4 is the strongest field strength at 30 volts per meter.
In some cases, a non-standard test level is applied according to the customer requirements or test equipment capability.
This shows example test results where the EUT was an analog-to-digital system.
A link to the full document with all the different EMC tests is given at the bottom of the page.
Notice that two different field strengths at 10 volts per meter and 18 volts per meter were used for testing.
10 volts per meter corresponds to the IEC test level 3, but 18 volts per meter does not have a corresponding IEC test level, so it is listed as greater than 3.

For all the immunity tests here, the device passed criterion A. This means that the EUT continued to operate under the presence of the interference signal within some predetermined limits.
Technically, this means the device may show some impact from the RF interference, but the impact was minimal and inside the limits set by the EUT manufacturer.
Also, the test was done over a range of frequencies and with different antenna polarization.
The CISPR-11 test standard defines the maximum allowed radiated emissions for different types of test equipment.
The test setup looks very similar to the radiated immunity setup, but the antenna receives RF signals radiated from the EUT rather than transmitting them.
The RF pickup from the antenna is then measured by a spectrum analyzer, which is external to the anechoic chamber.
As with the radiated immunity setup, the antenna will be rotated 90 degrees to measure the different polarity of the RF emissions.
Furthermore, the table will be rotated to check if RF emissions are stronger in different physical orientations.
This slide shows the test chamber used for radiated emissions testing.
Generally, the same chamber and antenna are used for this test as was used for the radiated immunity test.
The difference is the antenna is connected to a spectrum analyzer here as opposed to a signal generator that was used in the immunity test.
Again, the product is placed on a non-conductive rotating table at a defined distance from the antenna.
This slide shows the maximum RF emissions defined by CISPR-11. Class B is used for residential buildings, and class A is for all other types of uses.
Residential requirements are more restrictive.
The example covered in this presentation will use the class A limits as it is a type of test equipment and is not used in residential environments.
Notice that there are two sets of limits depending on how close the measurement antenna is to the EUT.
Also notice that the limit is less restrictive at higher frequencies.
The objective of the emissions test is to make sure that all emissions stay below the specified limit.
This slide shows the measured radiated emissions for our example system.
In these two example measurements, the antenna polarization was adjusted, and the clock rate was adjusted.
Both examples pass here, but the margin for the 50 megahertz clock is fairly low.
To thoroughly test a product, it may be important to test the product in many different modes of operation and to physically orient the product differently.
For test results that don't pass compliance or have very low margin, it may be necessary to do a new PCB revision and apply the principles discussed in other videos in this series.

 

The IEC 61000-4-6 standard specifies the details about the conducted immunity test.
The test is to verify the EUT immunity to conducted electromagnetic disturbances introduced to the EMC board input terminals.
The test signal is generated from an RF signal generator, and an RF power amplifier is used to amplify the test signal to the specified level.
The test signal is injected to the EMC board input with an injection probe.
Spectrum analyzer number one is used to monitor the output of the power amplifier, and spectrum analyzer number two is used to monitor and verify the injected signal with a monitoring probe.
The frequency is swept from 150 kilohertz to 80 megahertz with a disturbance signal of 80% amplitude that is modulated with 1 kilohertz sinusoidal signal.
The two field strength levels applied are 3 volts per meter and 10 volts per meter.
This slide shows the conducted immunity test setup and the test results for our example test.
For the test results, note that the field strength applied is the standard field strength corresponding to levels 2 and 3 according to IEC 61000-4-6. The test criterion is also defined by the IEC specification as discussed previously.
Passing criterion A indicates that normal operation within specified limits was observed when the conducted immunity signal was applied.
Notice in this example that the system passed criterion A for both levels.
The picture shows the different elements involved in the physical setup.
Note that ferrite beads are used on the power supply and USB cable to minimize the impact the EMC test signal has on the computer and power supply.
Again, one of the goals of EMC testing is to test only the EUT and to attempt to minimize the impact of the EMC signals on test equipment.
Electrical fast transients, abbreviated EFT, is an overstressed robustness test that emulates real-world transient events such as relay and motor switching.
These transients are often introduced on AC power lines but can couple into sensitive signal connections if they run near switching sources.
The EFT signal is coupled into the input lines capacitively.
The IEC 61000-4-4 standard specifies the details about the EFT in terms of test signals and the requirements.
The EFT signal is a series of rapid high-voltage test pulses ranging from 250 volts to 2 kilovolts.
The pulses are sent in groups of 75 fast pulses that are repeated every 300 milliseconds.
The total test time for each test is approximately one minute.
Note that a special EFT signal generator is used to create the rapid high-voltage pulses.
Passing EFT and other overstressed type tests normally involves adding overstressed protection devices at the input and output connections of the EUT.
The ADC Precision Lab series on electrical overstress covers these kinds of protections in detail.
Common circuits include the usage of TVS diodes, Schottky diodes, PTC fuses, gas discharge tubes, and simple RC circuits.
Tight layout methods near the PC board entry helps to minimize parasitic inductance and improves the effectiveness of these circuits.
It is not unusual to cause permanent damage to the EUT during the EFT tests, so it's a good idea to bring multiple copies of the EUT when doing a series of EMC tests.
This slide shows a closer look at the EFT signal.
For both signals shown, the pulse groups are repeated every 300 milliseconds.
The top EFT signal has a 5 kilohertz pulse frequency for a pulse group length of 15 milliseconds.
The bottom signal has 100 kilohertz pulse frequency for a pulse group length of 0.75 milliseconds.
The actual shape and width of the EFT pulse is shown at the bottom of the page.
For our example EFT test, test levels 2, 3, and 4 were used, which corresponds to plus or minus 1 kilovolt, 2 kilovolts, and 4 kilovolts according to the IEC 61000 4-4 test standard.
Notice in the example test results that for some cases, criterion A passed, and for others, criterion B passed.
Criterion A indicates that the EUT had normal performance within specified limits, and criteria B allows for temporary loss of performance, but after the interference is removed, the device returns to normal operation.
Thus, devices that pass criterion B did not pass criterion A. In other words, for the EUT that passed criterion B, there was a temporary loss of performance, but after the EFT was complete, the equipment resumed normal operation.
The electrostatic discharge test, or ESD, is another example of an electrical overstress test.
This test simulates the impact of direct contact and air discharge types of ESD events.
The contact discharge test is the most aggressive test.
In this case, the tip of the ESD gun is placed on conductive screws on the input terminal blocks of the EUT.
Air discharge tests are run three different ways.
Direct air gap discharge, indirect discharge to a horizontal coupling plane, abbreviated HCP, and indirect discharge to a vertical coupling plane, abbreviated VCP.
In the air gap discharge test, the tip of the ESD gun is placed near insulating surfaces of the input terminal blocks of the EUT.
Using the good PCB layout principles discussed in this series can help make the equipment more robust against ESD.
Also, using input protection circuitry, such as Schottky and TVS diodes, is important in protecting against ESD.
The TI Precision Labs video series on electrical overstress covers protection circuits in detail.
This slide shows a picture of the horizontal and vertical coupling planes used in ESD testing.
The photograph on the right illustrates direct contact discharge on a screw terminal connection.
The physical dimension of the coupling planes, as well as the distance to the EUT, are defined in the IEC specification.
The surge test is meant to simulate high energy surges caused by switching of power systems from load changes and short circuit faults, as well as lightning strikes.

 

IEC 61000-4-5 specifies the two types of combination wave generators, abbreviated CWG.
The 10 microsecond, 700 microsecond CWG is specifically used to test the ports of symmetrical telecommunications lines.
The 1.2 microsecond slash 50 microsecond CWG is used for all other cases.
These waveforms are shown on the next page.
The EUT is subject to five positive and five negative surges at each rating.
The surge is repeated at least once per minute.
A coupling and decoupling network, abbreviated CDN, is required for the surge test.
The IEC 61000-4-5 specification defines the impedance and capacitance used in the coupling network in the different cases.
In this example, the EUT was tested with the surge through a coupling slash decoupling network, CDN 1117, with a 0.5 microfarad capacitor and a twisted cable.
This slide shows the test result table and the surge waveform shape.
Notice that the source impedance in the coupling network can be adjusted to make the test more aggressive.
In this example, the 2-ohm source impedance corresponds to a 500-amp surge when a 1 kilovolt pulse is applied.
As compared to the EFT transient, the duration of the surge pulse is much longer.
That is, it lasts hundreds of microseconds, as opposed to nanoseconds.
As with the other tests, the criterion and test levels are defined by the IEC specification.
The test level corresponds to the test voltage, and the criterion defines the operational behavior during the test.
This slide shows the physical setup for surge testing.
In the picture, you can see the coupling network, surge generator, EUT, and other support circuitry.
The oscilloscope monitors the surge waveform during the test for confirmation.
That concludes this video.
Thank you for watching.
Please try the quiz to check your understanding of this video's content.
Question 1, true or false, the pulse duration for surge is longer than the pulse used for EFT, and surge emulates a lightning strike.
The correct answer is A, true.
Question 2, true or false, TVS diodes, Schottky diodes, and guest discharge tubes are used to minimize the effects of radiated emissions.
The correct answer is B, false.
These devices are used for overstress tests such as EFT and surge.
Question 3, why is it a common practice in EMC testing to use batteries for power, fiber optic communications, and ferrite beads on cables?
The correct answer is B. This helps protect the test equipment from damage and performance impact.
One common objective in EMC testing is to make sure that the overstress and interference signals do not damage or impact the performance of the support and measurement circuitry.
Question 4, true or false, the radiated emissions and radiated immunity test can use the same anechoic chamber and antenna.
The main difference is that the immunity test requires a signal generator, and the emissions test requires a spectrum analyzer.
The correct answer is A, true.
Through the principle of reciprocity, an antenna that works well as a transmitter will work equally well as a receiver.
That's all for today's video.
Thanks for watching.