Shenzhen Winna Electronic Industrial Co., Ltd.

I. Basic Association between EMC and Oscilloscope

EMC mainly focuses on the electromagnetic interference immunity (EMS) of electronic devices in an electromagnetic environment and their own electromagnetic radiation (EMI). As a time - domain waveform measurement instrument, an oscilloscope can capture the instantaneous changes of voltage and current, visually presenting the characteristics of electromagnetic interference, and helping to analyze the interference source, propagation path, and impact degree.

II. Specific Application Scenarios of Oscilloscope in Observing Waveforms in EMC

EMI (Electromagnetic Radiation) Analysis

Conducted Interference Waveform Monitoring:

By using a current probe or voltage probe, measure the interference current/voltage waveforms on conductors such as the power supply lines and signal lines of equipment (such as the spike interference of a switching power supply and the pulse noise of a digital circuit), and judge the frequency, amplitude, and time - domain characteristics (such as rise time and fall time) of the interference.

Example: When a switching power supply is operating, the oscilloscope can capture periodic spike pulses. Their frequency is related to the switching frequency of the switching tube. If the spike amplitude exceeds the EMC standard, it may be necessary to optimize the filter circuit.

Indirect Analysis of Radiated Interference:

When equipment interferes through space radiation, a near - field probe (such as a magnetic field probe or an electric field probe) can be used to couple the radiated signal, and then an oscilloscope is used to observe the waveform to locate the position of the interference source (such as high - frequency traces on a PCB or chip pins).

EMS (Electromagnetic Immunity) Testing

Verification of Interference Immunity:

When applying interference signals (such as electrostatic discharge, electrical fast transient burst) to the equipment, use an oscilloscope to monitor the waveform distortion of key signals of the equipment (such as data buses and clock signals), and judge whether the equipment has functional abnormalities due to interference.

Example: Apply an electrical fast transient burst to the clock line of a microcontroller. If the oscilloscope shows that the clock waveform jitters or distorts, it may cause program operation errors, and it is necessary to strengthen the protection measures of the circuit (such as adding TVS diodes and filter capacitors).

Correlation Analysis between Signal Integrity and EMC

Signal integrity issues such as reflections and crosstalk of high - speed digital signals may cause EMI. The oscilloscope can observe the eye diagram and edge jitter of signals, and optimize the trace topology (such as impedance matching and shortening the trace length) to reduce EMI from the source.

III. Precautions for Observing EMC Waveforms with an Oscilloscope

Selection of Probes and Test Equipment

Probe Types:

Current Probe: Used to measure the interference current in conductors (such as common - mode/differential - mode current in power supply lines).

Near - Field Probe: Used in conjunction with a spectrum analyzer or oscilloscope to capture high - frequency radiated signals (note the frequency range of the probe, such as 100kHz - 1GHz).

High - Voltage Probe: If testing the interference of a high - voltage circuit, a probe with a matching withstand voltage level should be selected.

Oscilloscope Performance:

Bandwidth: It should cover the main frequency components of the interference signal (for example, when measuring a 100MHz interference, the recommended bandwidth of the oscilloscope is ≥500MHz).

Sampling Rate: It should be at least 2 - 5 times the highest frequency to avoid waveform distortion.

Storage Depth: A long storage depth can record waveforms for a long time, facilitating the capture of occasional interference events.

Test Environment and Grounding

Poor grounding can introduce additional interference noise, leading to misjudgment of waveforms. It is necessary to ensure that the ground clip of the oscilloscope is connected to the grounding plane of the equipment (such as the ground plane of the PCB or the metal housing) as close as possible to reduce the impact of the ground loop.

If testing in a laboratory environment, facilities such as a shielded room and a grounding plane can be used to reduce environmental noise interference.

Key Dimensions of Waveform Analysis

Time - Domain Characteristics: The width, amplitude, and repetition frequency of the interference pulse, and whether it is related to the working cycle of the equipment (such as the interference pulse during motor startup).

Frequency - Domain Conversion: Through the FFT function of the oscilloscope, convert the time - domain waveform into a spectrum diagram to analyze the main frequency components of the interference, which is convenient for matching filter components (such as the cut - off frequency of an LC filter).

Comparison Testing: Record the differences between the waveforms in normal operation and in the interference state to locate the interference source (for example, if the interference waveform disappears after disconnecting a certain signal line, it can be judged that this line is the interference propagation path).

IV. Limitations of Oscilloscope in EMC and Supplementary Tools

Limitations: The oscilloscope is mainly used for time - domain analysis, and its capture efficiency for wide - band, low - amplitude EMI noise (such as continuous - wave interference) is relatively low. Tools such as a spectrum analyzer (frequency - domain analysis) and an EMI test receiver (quantitative measurement in line with standards) need to be combined.

Combined Applications:

Oscilloscope + Spectrum Analyzer: Joint time - domain and frequency - domain analysis, such as using an oscilloscope to observe the time - domain characteristics of interference pulses, and at the same time using a spectrum analyzer to analyze their spectral distribution.

Oscilloscope + EMC Test Software: Some professional software can automatically record waveforms, analyze interference parameters, and generate test reports that meet EMC standards.

Summary

The oscilloscope is a basic tool for visually observing waveforms and locating interference problems in the EMC field, especially suitable for the analysis of time - domain interference characteristics and signal integrity optimization. However, in actual testing, it is necessary to combine frequency - domain analysis tools, standard test equipment, and professional methods to fully meet the requirements of EMC compliance testing and rectification.