Following Electromagnetic Compatibility (EMC) Testing Standards and Corrective Guidelines: Issues, Processes, and Strategy Optimization, INFINITECH will continue to explore the scope of EMC testing in depth, explain methods for evaluating EMC performance, and show how to easily build a near-field probe to assist in testing. At the same time, this paper will summarize and analyze the common problems in electromagnetic compatibility practice and their countermeasures, so as to provide readers with a comprehensive solution framework.

1. EMC test

EMC testing is to ensure that electronic equipment can operate normally in the expected electromagnetic environment without causing unacceptable electromagnetic interference to other equipment, and the equipment should also have a certain anti-interference ability. EMC testing falls into two main categories: EMI (Electromagnetic interference) and EMS (electromagnetic sensitivity or electromagnetic immunity). Below INFINITECH details the details of these test projects:

EMI (Electromagnetic Interference) test items include:

Radiation emission (RE) : Tests whether the electromagnetic energy radiated by the equipment to the surrounding space during operation exceeds the specified limit.

Conducted interference (CE) : Detects the level of electromagnetic interference transmitted by a device through conductors such as power cables and signal cables.

Harmonic current: Measures the harmonic components of equipment currents other than fundamental waves to assess the degree of pollution to the power grid.

Voltage variation and flicker: Assess the effects of voltage fluctuations and light flickering after equipment is connected to the grid, especially for sensitive loads such as lighting equipment.

EMS (Electromagnetic Sensitivity) test items include:

Electrostatic discharge (ESD) : simulates the impact of the electrostatic discharge generated by the human body or an object on the device to test the bearing capacity of the device.

Radiofrequency electromagnetic field immunity (RS) : Evaluates the stability of equipment in high-power RF fields.

Electrical Fast transient/Pulse Group Immunity (EFT/B) : Simulate the fast transient pulse group that occurs on the power line to test the shock resistance of the equipment.

Surge/lightning immunity: Simulate overvoltage surges caused by lightning or power system operation to check the effectiveness of equipment protection mechanisms.

Conducted immunity (CS) : Evaluates the resistance of equipment to interference conducted along power or signal lines.

Power frequency magnetic field immunity (PMS) : Tests the performance stability of equipment under strong power frequency magnetic fields.

Voltage drops, short outages, and Voltage Change Immunity (DIP) : Simulate the sudden drop, outage, and recovery process of grid voltage to verify that equipment can maintain normal operation.

Each test has a corresponding international or national standard (such as the IEC 61000 series), the specific test conditions, limits and methods will vary according to the type of equipment and application environment.

2, how to describe the electromagnetic compatibility performance?

Electromagnetic Compatibility (EMC) performance describes the ability of a device or system to operate in an electromagnetic environment without producing excessive electromagnetic interference (EMI) and to withstand a certain level of external electromagnetic interference without reducing its intended function. This performance is often assessed by a range of quantitative measures, one of the most commonly used units being decibels (dB), because of its ability to express a wide range of quantitative values on a logarithmic scale, which is easy to understand and compare.

The decibel (dB) is a dimensionless unit used to express the logarithm of the ratio of two quantities. In the field of electromagnetic compatibility, decibels are often used to represent the relative magnitude of power or voltage/current, especially when measuring electromagnetic interference and immunity of equipment. The decibel value (dB) can be calculated by the following formula:

Among them, the measured value is the power or voltage/current you actually measure, and the reference value is a preset standard value, and different decibel units correspond to different reference values.

For example, dBm is a power level unit with 1 milliwatt (mW) as a reference value, calculated by:

For dBmV, which is a unit commonly used in cable television (CATV) systems, voltage is measured using 1 millivolt RMS (mVrms) as a reference value. The conversion formula is:

The 20 factor here is because power is proportional to the square of the voltage (P ∝V2), so when voltage is involved, the decibel calculation is multiplied by 20 instead of 10.

dBμV is another similar unit, but the reference value is 1 microvolt (μV), which is often used to measure low-level signals, and the conversion method is similar to dBmV, except that the reference point is different.

When describing EMC performance, it may involve the conversion of multiple dB units, such as from dBm to dBμV, to accommodate different test conditions or specification requirements. These conversions help engineers assess the level of electromagnetic interference of a device or its ability to withstand specific electromagnetic interference and ensure that the product meets the appropriate EMC standards and regulatory requirements.

3. Selection basis of shielding materials in electromagnetic compatibility design

In electromagnetic compatibility (EMC) design, the selection of shielding materials mainly includes the following aspects:

3.1 Frequency range of electromagnetic waves: As you mentioned, the choice of shielding materials is indeed closely related to the type (frequency) of electromagnetic waves to be shielded. High frequency electromagnetic waves (such as radio frequency and microwave) can usually be effectively shielded by high conductivity metal materials, because such materials can reflect electromagnetic waves well. Common such as copper, aluminum, steel plate, etc., they have strong reflective ability to electromagnetic waves, suitable for high frequency band shielding materials. For low-frequency electromagnetic waves, because of its long wavelength, it is easier to penetrate the metal shield, then you need to use high-permeability materials, such as iron, silicon steel sheet, etc., these materials can effectively guide the low-frequency magnetic field and convert it into heat energy consumption.

3.2 Shielding efficiency: The ideal shielding material should be able to provide sufficient shielding efficiency, that is, the degree of attenuation of electromagnetic waves. This depends on the conductivity, permeability, thickness of the material and the design of the shielding structure.

3.3 Environmental factors: The use of environment is also an important basis for the selection of shielding materials, including temperature range, humidity, chemical corrosion and other factors. For example, in humid or corrosive environments, it may be necessary to choose corrosion-resistant materials or special surface treatments.

3.4 Mechanical properties and machinability: The mechanical strength, weight, machinability and cost of the material are also factors that must be considered in practical applications. Although some metal materials have good shielding effect, they may be limited by high density, high processing difficulty or high cost.

3.5 Convenience of installation and maintenance: The material and structural design should consider the ease of installation and the possibility of later maintenance, such as the design of detachable shielding covers, shielding Windows and ventilation holes.

3.6 Regulations and standards: Different industries and regions have specific standards and requirements for EMC. When selecting shielding materials, ensure that they comply with the corresponding regulations and standards.

4. Why is it difficult for spectrum analyzer to observe transient interference such as electrostatic discharge?

The reason why the spectrum analyzer is difficult to observe transient interference such as electrostatic discharge (ESD) is mainly determined by its working principle and design characteristics: The spectrum analyzer is essentially a narrowband sweep receiver, which measures the power distribution of the signal by sequential scanning on different frequencies. This means that at any given point in time, it can only "see" a signal within a narrow range of frequencies, rather than a simultaneous view of the entire spectrum. In order to improve the signal-to-noise ratio and reduce the impact of noise, spectrum analyzers usually use longer sampling and averaging processes. This is advantageous for stable continuous signals, but for transient disturbances (such as ESD, whose duration is usually in the nanosecond range), these transient events may be completely missed or averaged out within the spectrum analyzer's sampling window, and thus cannot be effectively captured. Transient interference such as electrostatic discharge has very high peak power and very short duration, and its spectrum range can be very wide. Due to the narrow-band scanning and slow response characteristics of the spectrum analyzer, it cannot respond quickly to such a rapidly changing signal, especially over a wide frequency range. Most spectrum analyzers do not have a precise trigger mechanism for these transient events and cannot capture data at the precise moment the interference occurs, which is also an important factor that makes it difficult for them to observe transient interference.

Therefore, although a spectrum analyzer is a powerful tool for analyzing the signal spectrum, for capturing fast transient interference, it is often necessary to use other types of instruments, such as high-speed oscilloscopes or specialized transient detection devices, which have faster sampling rates and wider instantaneous bandwidth, and are better able to capture and analyze these short pulse disturbances.

5, self-made simple near field probe detailed tutorial

Making a simple near-field probe, especially an electric field probe for assisting electromagnetic interference (EMI) field diagnosis, can be done using common coaxial cables. Here is a simplified step-by-step guide for creating a basic electric field probe:

Materials required

• A section of coaxial cable (it is recommended to use a coaxial cable with sufficient shielding layer, such as RG58, RG59, etc.)

• Wire stripper

• Electrical tape or heat shrink tube

• Optional: Scissors, welding tools (if fixed connection is required)

Production procedure

1. Prepare coaxial cable: First, choose an appropriate length of coaxial cable, usually a few centimeters to tens of centimeters, the specific length according to the frequency range and application scenarios you need to detect. Shorter probes are suitable for higher frequency signal detection.

2. Peel the cable: Use wire strippers to carefully peel the outer insulation of the coaxial cable to expose the inner shield (braided mesh or foil). Ensure the integrity of the shielding layer to avoid damage.

3. Separate the shield: Separate the shield from the internal insulation a short distance (about a few millimeters) to expose the core conductor. For braided mesh shielding, it can be gently folded back, and for cables with foil layers and braided mesh, it may be necessary to carefully peel or cut the foil layer.

4. Trim the shield: As needed, you can trim the end of the shield to make it flat or form a specific shape (such as a tip or ring), which helps focus the sensitive area of the probe.

5. Protection and retention: Use electrical tape or heat shrink tubes to cover the connection between the exposed shield and the core conductor to prevent short circuits and ensure the mechanical stability of the probe.

6. Finished: You have now made a simple near-field probe. The probe's shield (or part of it) serves as a ground reference, while the core conductor is used to sense the electric field. When in use, the probe is close to the electronic device under test or the circuit board, and the probe is connected through the oscilloscope or other measuring equipment to help diagnose the source of electromagnetic interference.

Precautions for use

• This simple probe is sensitive to detecting high frequency signals, but may not be suitable for low frequency applications.

• When used in an environment without shielding measures, the probe may pick up electromagnetic wave signals from other sources in the environment, affecting diagnostic accuracy.

• In consideration of safety and accuracy, ensure that the equipment under test has been correctly powered off or appropriate safety measures have been taken before use.

This simple probe is suitable for initial field diagnostics and teaching demonstrations, but in professional EMC LABS, more sophisticated commercial near-field probes may be used that are more optimized in design to provide greater accuracy and stability.

6, electromagnetic compatibility common problems and solutions

6.1 Excessive electromagnetic radiation

Description of the problem: The electromagnetic radiation generated by the device exceeds the specified limit, which may interfere with the normal operation of the surrounding electronic equipment.

Solution:

• Optimize the PCB layout, reduce the loop area, reasonable wiring, to avoid the formation of large loops.

• Add shielding measures, using metal housings or shields to isolate radiation sources.

• Filters are added to the input and output of the power supply to suppress conductive noise.

• The use of appropriate absorbing materials, such as ferrite magnetic rings, absorbing materials, etc., to absorb radiation energy.

6.2 System Faults Caused by Electrostatic Discharge (ESD)

Problem Description: The transient high voltage generated by electrostatic discharge may damage electronic components or cause system misoperation.

Solution:

• ESD protection circuit of input/output port is added during design, such as TVS diode, Zener diode, etc.

• Improve device grounding design to ensure a good grounding path.

• Antistatic materials are used to make the housing to reduce static accumulation.

• Use an ESD wrist strap and ESD clothes to prevent ESD damage.

6.3 Communication errors caused by insufficient radiation immunity

Problem Description: The device does not work stably in an environment with strong electromagnetic radiation, which may result in communication errors or data loss.

Solution:

• Strengthen the shielding of the equipment to ensure that the internal circuit is not affected by external radiation.

• Optimize the circuit design and improve the filtering and decoupling capability of the circuit.

• Add filters and buffer circuits to protect sensitive circuits from external interference.

• Differential signal transmission is adopted to enhance the anti-interference ability of the signal.

6.4 Conducted Interference

Problem Description: The electromagnetic interference conducted by the device affects other devices through power cables and signal cables.

Solution:

• Install a power line filter to suppress conducted noise.

• Optimize power and ground design to reduce common-mode and differential mode interference.

• Isolation transformers or photoelectric isolators are used to isolate interference paths.

6.5 Lightning strike and Surge protection

Description of the problem: During thunderstorms or power grid anomalies, surge voltages can damage electronic equipment.

Solution:

• Install a surge protector (SPD) at the power inlet.

• Add transient voltage suppressor (TVS) to protect critical circuits.

• A well-designed grounding system ensures effective discharge of inrush current.

Through the above methods, common problems in electromagnetic compatibility can be effectively solved to ensure the stable and reliable operation of electronic equipment in a complex electromagnetic environment.