Understanding EMI, EMC, EMC testing, and EMC standards

An electrical and electronic product usually emits some amount of unwanted electromagnetic energy (called electromagnetic interference (EMI)) during its operation. The EMI of a product may affect the performance of or sometimes damage the nearby electronic device(s).

Electromagnetic Compatibility (EMC) is the capability/ability of an electrical & electronic product to withstand a specified degree of electromagnetic disturbance (EMI) from the nearby electronic device(s) and not emit more than a specified amount of electromagnetic interference (EMI). An electrical and electronic product can get into to market when it meets the requirements of EMC emission and immunity standards. The EMC emission measurement standards ensure the product does not emit more than a specified level of EMI. The EMC emission measurement standards specify the EMI emission limit for products and EMI emission measurement procedures. The EMC immunity standards ensure that the product can withstand EMI from nearby devices and operate properly. The EMC immunity standards specify the test procedure, test setup, test levels, and so on.  

EMC testing is the process of evaluating whether the product meets the requirements of EMC emission and immunity standards. When a product meets the requirements of these EMC standards, the product is said to be EMC compatible/EMC certified product (i.e., withstand EMI from nearby devices & operate properly, and not emit more than a specified level of EMI) and can sell in the market. EMC testing typically involves two types of tests: emissions measurement test and immunity test. Emissions measurement test is used to measure the amount of EMI emitted by a device, while immunity testing is used to measure the device's ability to withstand EMI from external sources.  This article discusses the EMC immunity tests.

What is Immunity testing for EMC? What are the different types of EMC Immunity tests?

EMC immunity test is a type of EMC testing that measures the ability of an electrical & electronic device to withstand electromagnetic interference (EMI). In EMC immunity testing, the product is subjected to different types of electromagnetic phenomena such as conducted EMI, radiated EMI, ESD, and more. The immunity test ensures that the product can withstand a specified degree of EMI from other devices while working in the intended real-time environment. This means that the product can function properly even when exposed to electromagnetic interference from other devices in its intended operating environment.

Types of EMC immunity tests:

Because there is a wide range of potential EMI exist in real-world electrical & electronic system such as conducted EMI, radiated EMI, ESD, EFT, and more, a product is subjected to multiple types of immunity testing to ensure the product can withstand EMI. The types of EMC immunity tests include:

• Conducted immunity test  
• Radiated immunity test (RI test)
• Magnetic field testing
• Electrostatic discharge (ESD) testing
• Electrical Fast Transient (EFT) test
• Surge test
• Voltage dip test

The EMC immunity tests are conducted as per EMC immunity standards in a lap environment to check whether the product complies with the related EMC immunity standard.  Let’s discuss the EMC immunity tests one by one.  

Conducted immunity test:  This test is performed to determine the ability of a device/product to withstand the conducted EMI. Conducted EMI is unwanted electromagnetic emissions (EMI) from devices while working that propagate through the power cord or power line and may affect the other connected devices on the same line. Therefore, it is necessary to test the ability of the device to withstand the conducted EMI.

Fig: Typical conducted immunity test setup 

In the conducted immunity testing, the equipment under test (EUT) is subjected to conducted EMI test signals to test the immunity of the EUT against the conducted EMI. Typically, the test setup of this test consists of a EUT, a signal generator, an amplifier, an injection device (e.g., CDN, EM clamp, BCI probes, and direct voltage equipment injection), and other auxiliary equipment.  During the conducted immunity test, the RF signal generator generates test signals (voltage/current). Then the injection device (e.g., CDN) injects the test signals into the connecting cable of the EUT for evaluating the withstanding ability of the EUT. If the EUT withstands the applied test signal and operates properly, the EUT is considered to pass the test, otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand the conducted EMI from other electromagnetic sources, such as power lines & other electronic devices that the device will encounter while in normal real-time usage. 

The conducted immunity test is conducted as per international EMC standards, such as IEC 61000-4-6 (an EMC standard by the International Electrotechnical Commission).  The EMC standards for the conducted immunity test specify the test procedure, test setup, test levels, frequency range, and so on. 

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Radiated immunity test (RI test): This test is conducted to determine the ability of a device/product to withstand radiated EMI. Radiated EMIs are the unwanted electromagnetic interference that is generated by electrical & electronic devices while working and propagates through the air, which may affect the other electronic equipment nearby. Therefore, it is necessary to test the ability of the device to withstand the radiated EMI.

Fig: Radiated immunity test setup

In the radiated immunity testing, the EUT is subjected to radiated EMI test signals to test the immunity of the EUT against the radiated EMI. Typically, the test setup of this test consists of a EUT, RF signal generator, power amplifier, antenna, and other supporting equipment. During the radiated immunity test, the RF signal generator generates test signals that are amplified and applied to an antenna that transmits EM waves (simulates the radiated EMI) to the EUT. The antenna creates the required electric field strength (V/m) over a wide range of frequencies to test the immunity or ability of the EUT. If the EUT withstands the applied electric field strength (V/m) and operates properly, the EUT is considered to pass the test; otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand the radiated EMI from other electromagnetic sources, such as power lines & other electronic devices that the device will encounter while in normal real-time usage. 

The radiated immunity test is conducted as per international EMC standards, such as IEC 61000-4-3 (an EMC standard by the International Electrotechnical Commission).  The EMC standards for the RI test specify the test procedure, test setup, test levels, and so on. For most of commercial products, RI tests are mandatory from frequency 80 MHz up to 1 GHz.

Magnetic field testing:  This test is performed to determine the ability of a device/product to withstand the power frequency (50/60 Hz) magnetic field. The power frequency magnetic field is produced by power lines, transformers, motors, and other electrical devices that operate at 50 or 60 Hz (depending on the country); this magnetic field can induce unwanted currents in nearby conductors/devices. In the electrical system, the power-frequency magnetic fields may be present continuously or for a short period. The continuous or steady power line frequency magnetic field created is because of normal operating conditions (i.e., due to the normal AC flow through the conductors). The short duration Magnetic field is because of fault occurrence or initial power turn-on of electronic equipment.  Since the magnetic field of a device/conductor can affect the performance of the nearby device(s), it is necessary to test the ability of the device to withstand the power frequency magnetic field.

Fig: Magnetic field test setup

In the magnetic field testing, the EUT is subjected to the power-frequency (60/50 Hz) magnetic field generated by a magnetic field generator to test the immunity of the EUT against the magnetic field. During the test, the generator supplies and controls the current flow through a loop antenna, thereby establishing the required power-frequency magnetic field for conducting both continuous and short-duration magnetic field immunity EMC tests.  If the EUT withstands the applied magnetic field and operates properly, the EUT is considered to pass the test; otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand both continuous and short-duration magnetic fields from other electromagnetic sources, such as power lines & other electrical devices that the product will encounter while in normal real-time usage.  

The magnetic field testing is conducted as per international EMC standards such as IEC 61000 4-8. The EMC standards for magnetic field immunity testing describe the range of test levels, test equipment used, test setup, test procedure, and so on.

Electrostatic discharge (ESD) testing: This test is performed to determine the ability of a device/product to withstand electrostatic discharge (ESD). ESD is a phenomenon that occurs when two objects with different electrical potentials come into contact/very close to each other, causing sudden and momentary electric current flows between the two objects. For example, ESD can occur when the person handling printed circuit boards or troubleshooting electronic devices without using an electrostatic wrist strap. ESD may cause damage to electronic equipment/components, ICs, LCDs, memory, etc. Therefore, it is necessary to test the ability of the device to withstand ESD.

Fig: ESD immunity test setup

In the ESD immunity testing, the EUT is subjected to ESD test pulses to test the immunity of the EUT against the ESD. This test is done by using the ESD simulator. The ESD simulator is an instrument used to generate the ESD test pulses. The ESD generator can apply test pulses directly (through contacts) and indirectly (over the air) to the EUT. This generator can generate test pulses with 8kv for air discharge and 4kv for contact discharge. Typically, the EUT is subjected to at least 10 ESD test pulses with each polarity, at a minimum of four test points on the enclosure of the device or part of the device where people can touch it. If the EUT withstands the applied ESD test pulses and operates properly, the EUT is considered to pass the test; otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand ESD that the product will encounter while in normal real-time usage.   

Electrostatic discharge (ESD) testing is conducted as per international EMC standards such as IEC/EN 61000 4-2. The EMC standards for ESD describe the typical discharge current waveform, range of test levels, test equipment used, test setup, test procedure, and so on.  

Electrical Fast Transient (EFT) test: This test is conducted to determine the ability of a device/product to withstand Electrical Fast Transient (EFT). The EFTs are generally high-frequency pulses caused by sparking (arcing), which can affect the equipment's performance or can cause equipment failure. The EFT issues occur due to the events such as relay contact bounce, interruption of inductive loads, fluorescent lights, when AC/DC connection is made or broken,  equipment powered down, circuit breakers operation, and so on.  EFT issues are also occurring in electric automotive systems, ethernets, and data lines.  Therefore, it is necessary to test the ability of the device to withstand the EFT.

Fig: EFT immunity test setup

In the EFT immunity testing, the EUT is subjected to EFT or burst test pulses to test the immunity of the EUT against the EFT. The EFT testing is performed with the help of an EFT/Burst generator and CDNs (Coupling decoupling networks) or a capacitive clamp. In this test, the EFT or burst generator simulates/generates the EFT (burst) interference test signals (i.e., series of fast rise time and short duration pulses, typically 5ns by 50ns). Then the EFT test signals are transmitted/applied to the EUT via the CDN or a capacitive clamp.   If the EUT withstands the applied EFT test pulses and operates properly, the EUT is considered to pass the test; otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand EFT that the product will encounter while in normal real-time usage. 

 Electrical Fast Transient (EFT) testing is conducted as per international EMC standards such as IEC 61000 4-4. The EMC standards for EFT describe the range of test levels, test equipment used, test setup, test procedure, and so on.  

Surge testing: This test is performed to determine the ability of a device/product to withstand the surge. Surge is a transient overvoltage (short-time overvoltage) in an AC power system that occurs due to the events such as load switching, capacitor bank switching, device faults, and lightning discharges. Usually, the duration of the surge is in the several µs to ms range. The surge waveform nature can be oscillatory or impulsive with the rising wavefront typically on the order of 0.5 μs to 10 μs. The surge voltage level typically is in KV, which can severely damage electrical/ electronic devices. Therefore, it is necessary to test the ability of the device to withstand the surges. 

Fig: Surge immunity test setup

In surge immunity testing, under laboratory conditions, the EUT is subjected to standard surge voltage and surge current to test the immunity of the EUT against the surge. The surge testing is performed with the help of a surge generator and coupling and decoupling networks. In this test, the surge generator simulates/generates a standard surge voltage waveform with the pulse shape 1.2 / 50 µs and a surge current with the standard pulse shape 8 / 20 µs. Then, the surge voltage/current is transmitted into a port of the EUT via the coupling network. If the EUT withstands the applied surge test voltage/current and operates properly, the EUT is considered to pass the test; otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand the surge that the product will encounter while in normal real-time usage.

The surge testing is conducted as per international EMC standards such as IEC 61000 4-5. The EMC standards for surge immunity testing describe the range of test levels, test equipment used, test setup, test procedure, and so on.  

Voltage dip test:  This test is performed to determine the ability of a device/product to withstand voltage dip. The voltage dip is the short duration temporary voltage magnitude drop in the main supply voltage of the electrical distribution system or supply system. The common causes of voltage dip are faults in the connected equipment, various faults in transmission and distribution networks, high inrush current, and load switching. The voltage dip can affect the performance of electrical & electronic and other sensitive equipment connected to the electrical network.  Therefore, it is necessary to test devices to work against the voltage dip phenomenon.

Fig: Typical voltage dip test setup

In the voltage dip test, the EUT is subjected to voltage dip (test levels of 30%, 60%, and >95% below the rated voltage) for a short duration, typically 10ms, 100ms, and 5000ms. Usually, five dips are performed at a rate of one dip per minute for each test level. The voltage dip testing is performed with the help of a signal generator, controller, connecting cables, and supply system. If the EUT withstands the voltage dip and operates properly, the EUT is considered to pass the test; otherwise, the EUT is considered as failed. This immunity test ensures that the product can withstand the voltage dip phenomenon that the product will encounter while in normal real-time usage. 

The voltage dip testing is conducted as per international EMC standards such as IEC 61000 4-11. The EMC standards for voltage dip testing describe the range of test levels, test equipment used, test setup, test procedure, and so on.