Conducted Emission

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Conducted emissions refer to electromagnetic disturbances that are transmitted through conducting wires or cables connected to an electrical or electronic device. These emissions can propagate along power lines, signal lines (such as data cables), and any other conductive paths that are connected to the device.

Here's a detailed breakdown of conducted emissions:

Sources:

Conducted emissions originate from various sources within electronic equipment:

1. Power Supplies: Switching power supplies and transformers can generate conducted emissions due to switching transients and harmonics.

2. Electronic Circuits: Digital circuits, especially those with fast switching speeds, can produce conducted emissions through power and signal lines.

3. Motors and Drives: Electric motors and motor drives can introduce conducted emissions into power lines due to switching frequencies and power modulation.

4. Cables and Connectors: Poorly shielded or improperly grounded cables can act as antennas, radiating conducted emissions.
    

Frequency Range:

Conducted emissions typically cover a wide frequency range, often from a few kilohertz (kHz) up to several hundred megahertz (MHz), depending on the nature of the emitting device and the frequency of the signals or power being processed.

• Low Frequency Range (LF): Typically below 150 kHz, includes power line harmonics and switching noise from power supplies.

• Radio Frequency Range (RF): Spans from 150 kHz to several hundred MHz, encompassing emissions from digital circuits, clock signals, and other high-frequency components.

Measurement and Testing:

Conducted emissions are typically measured using specialized equipment such as spectrum analyzers and conducted emission measurement receivers. Testing is conducted with the device under test (DUT) connected to a standardized test setup that simulates real-world operating conditions. Measurements are taken across specified frequency ranges to ensure compliance with applicable EMC standards.

Test Setup
 

 

Test Instrument

Below are the some Major Test equipment, required for Conducted Emission Testing

1. EMI Receiver

2. Line Impedance Stabilization Network (LISN)

3. Pulse Limiter

4. RF Cables

Test Parameters

1. Frequency Range: 9kHz to 30MHz (depends on the Product standard)

2. Detector: Quasi-Peak, Average

Test Procedure

1. Setup EUT (Equipment Under Test) at the designated place, 0.8m high on the insulated table.

2. Table must be kept on the Ground Reference plane and at a distance of 0.4m from the Vertical coupling plane.

3. EUT should be energised through LISN with the rated Voltage and current and to be set in the highest configuration to achieve max level of emission from it.

4. RF cable should be connected between LISN and EMI Receiver.

5. Set the desired frequency range, limit lines and other parameters in EMI Receiver to receive the EMI signal from the EUT.

6. Select the peaks closure to limit line and measure the Q-Peak and Average values for final measurement.

7. Repeat step 5 & 6 for every individual line and neutral.

8. Capture the data like emission level in dbµV, Limit at that particular frequency, calculate the margin to mention in the final report. 

9. There are different limit lines as per different product standards.

Most of the standards refers to the below limits lines based on the end use of the product. 

Conducted Emission limits_Class A

Frequency Range (MHz)	Quasi Peak (dbμV)	Average (dbμV)
0.15 - 0.5	79	66
0.5 - 30	73	60

Conducted Emission limits_Class B

Frequency Range (MHz)	Quasi Peak (dbμV)	Average (dbμV)
0.15 - 0.5	66-56	56-46
0.5 - 5.0	56	46
5.0 - 30	60	50

 

Electromagnetic Emissions from the DUT should be less than the limits mentioned above. 

Conducted Emission Spectrum with both the Class A and Class B limits. 

In summary, conducted emission testing ensures that devices meet regulatory EMC limits, contributing to reliable and interference-free operation across electrical and electronic systems.