An electrical and electronic product usually emits unwanted electromagnetic energy (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 evaluates 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. An emission 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 emission measurement tests.

What is the Emission measurement test for EMC? What are the different types?

EMC emission measurement test is a type of EMC testing that measures the amount of electromagnetic radiation emitted by an electronic device or system. This test is performed by using EMC measuring instruments such as spectrum analyzer/EMI receiver and other supporting equipment. This test is performed as per EMC emission measurement standards that specify the EMI emission limit for products, measurement procedures, test setup, and so on. The EMC emission measurement test ensures that the product does not emit more than a specified level of EMI that is prescribed in the related EMC emission standard and does not cause interference with other electronic devices or systems. 

There are two main types of EMC emission testing: Conducted emissions (CE) and radiated emissions (RE) measurement tests.

Conducted emissions (CE) measurement: 

Conducted EMI is unwanted electromagnetic emissions (EMI), i.e., noise currents generated at radio frequencies from electrical & electronic devices while working that propagate through the power cord or power line and may affect the other connected devices on the same line.

The conducted emission measurement test measures the levels of conducted EMI emitted by the product while working. The CE measurement test is performed as per EMC emission standards, such as CISPR 11, CISPR 32, EN55022, EN55011, etc. These EMC standards specify the EMI emission limits for products, measurement procedures, test setup, and other related information to conduct a CE measurement test. 

The CE measurement test ensures that the product does not emit more than the conducted EMI emission limit specified in the EMC emission standards (i.e., compliant with EMC emission standards) and does not cause interference with other connected devices or systems on the same line. 

Conducted emission measurement test setup for LED/CFL lamps 

All conducted emission measurement tests are usually performed inside a screened room. The CE measurement test is performed by using a line impedance stabilization network (LISN), an EMI receiver/spectrum analyzer (measures EMI level), and other supporting equipment. This test is performed at a frequency range of 150 kHz to 30 MHz, and the readings are displayed/measured in the voltage (dBμV) versus frequency. During this test, the EUT is in the normal operating state.  

The purpose of LISN is to do the following things.

• To filter out noise from the AC main and supply pure AC power to the EUT.
• To couple/direct the EUT-generated emissions to the EMI receiver to measure the emission.
• To provide stable line impedance between the AC main and EUT in the frequency range of 150 kHz to 30 MHz to avoid power signal reflections.

Radiated emission (RE) measurement test: 

Radiated EMI is the unintentional electromagnetic energy emission (in the form of electromagnetic wave (EM wave) from an electrical and electronic product that propagates via air and may affect the performance of or damage the other nearby electronic devices. 

The radiated emission (RE) measurement test measures the amount of electromagnetic radiation emitted by a working device/product. The CE measurement test is performed as per EMC emissions standards, such as CISPR 11, CISPR 32, EN55022, EN55011, etc. These EMC standards specify the EMI emission limits for products, measurement procedures, test setup, and other related information to conduct a RE measurement test. The RE measurement test ensures that the product does not emit more than the radiated EMI emission limit specified in the EMC emission standards (i.e., compliant with EMC emission standards) and does not cause interference with other nearby electronic devices or systems. 

The RE measurements can be performed either in a specialized test chamber (e.g., an anechoic chamber) or on OATS (open area test site), between the frequency range from 30-MHz and (up to) 6-GHz. The radiated electromagnetic energy is measured in electric field strength (dBμV/m) versus frequency. The RE measurements are performed by a spectrum analyzer or an EMI receiver with a suitable EMC antenna. A typical RE measurement setup is shown below.

Typical Radiated emission measurement test setup

The EUT is positioned on a EUT turntable, and the antenna is positioned at a distance of 3m/10m/30m as per EMC standards requirement. Usually, the antenna height is in the range of 1 m to 4m for both vertical and horizontal polarization. The antenna may be any type, such as a monopole, dipole, biconical, log-periodic, horn, loop, etc. 

The electromagnetic energy emitted by the EUT is received by the antenna. The antenna converts the received EM energy into an electrical signal. The electrical signal is fed to the measuring equipment (e.g., Spectrum analyzer) for EMI measurements. During this test, the EUT is in the normal operating state.  

Note: In addition to CE and RE measurement, harmonics, flicker, and clicks are also measured for a product.

Click here to view the list of EMC Testing companies that provide EMC Emission testing services.