EMC & EMI Emissions Measured

Do you have an electronic device that is being manufactured? Did you know your product needs to be tested for electromagnetic compatibility? This article will explain what happens with this process.

All electronic devices and electric equipment make use of electromagnetic waves produced by electrically charged particles in motion. This electromagnetic radiation travels through the air, empty space, and other substances.

The full range of wavelengths and particles called photons forms the ‘electromagnetic spectrum’.

Regulatory compliances require that electronics undergo electromagnetic testing, a critical step when bringing a new product to the market.

What is EMC and EMI Testing?

Generally speaking, electromagnetic testing should only be performed by a recognised EMC testing body. The testing is grouped into two categories, emissions testing, and immunity testing.

– Emissions Testing

The purpose of emissions testing is to ensure that emissions from the device being tested are below the limits relevant for that type of device.

Basically it measures the amount of electromagnetic ‘noise’ generated during normal operation of the device.

The tests can provide reasonable assurance that the device will not emit harmful interference while operating within its normal operating environment.

– Immunity Testing

The purpose of immunity testing is to ensure that the device will operate as intended within its expected operating environment and how it reacts when exposed to disturbances such as electromagnetic noise from other devices or equipment.

Regulatory compliance requires both types of testing. The most common applications for electromagnetic testing are:

– Medical devices where devices must work together in close proximity without performance being compromised by interference or electromagnetic noise.

– Military or Aerospace devices to meet standards for avionics equipment and other goods.

– Consumer products such as cellular phones, satellite TV dishes, laptops, and microwave ovens to avoid harmful interference in real-world conditions.

What is the Difference Between EMC and EMI Testing?

Both types of testing are vital for electronic product development and companies across the world are required to comply with EMC/EMI limits finalised by standard bodies before launching products to the market for consumer use.

EMC (Electromagnetic Compatibility) and EMI (Electromagnetic Interference) testing are essential to verify the electromagnetic levels mentioned for any manufactured device.

Designers need to consider the specific military or industrial standards required for products under development.

How to Measure EMC and EMI Emissions

An electromagnetic field consists of two components:

– Electric Field or E-Field measured in V/M (volts per metre)
– Magnetic Field or H-field measured in A/m (amps per metre)

These two fields move at right angles to each other.

Emissions are subdivided into Radiated and Conducted Emissions

Radiated Emissions Testing

This test measures the electromagnetic field strength of emissions unintentionally generated by a product, how large they are, and if they comply with emissions limits set for the particular product.

Radiated emissions measurements are done by using a spectrum analyser and/or EMI receiver as well as a suitable measuring antenna.

The frequency band of interest will be scanned in a test lab to detect emissions that are close to the limits. A process called ‘maximisation’ is used to focus on these emissions and quantify the amplitude of their field strength.

Two primary test sites used for this purpose are:

– Open Area Test Sites (OATS)
– Semi Anechoic Chambers

Conducted Emissions Testing

As a device creates electromagnetic energy, a certain amount is conducted into the power supply cord. Test labs measure these emissions to verify that they comply with the specified limits.

A typical conducted emissions test involves one or more LISNs placed between the power source and an EUT (Equipment Under Test) that filter and isolate unwanted RF signals.

LISNs help to minimise external noise, allowing the lab to only measure noise from the EUT device.

Passing EMC/EMI testing will depend on several factors such as a good understanding of the process involved, the skill of the designers, and proper preparation. The estimated failure rate for first-time passes is 50%.

An EMC design review before designing a product or sending a device to an EMC test lab can help check your product against industry-standard best practices and issues that could increase the chances of first-time pass failure.

If you would like to know more about the EMC standards and product testing or need EMC testing done, then look no further than Compliance Engineering.

We are the definitive source for all of your Electromagnetic Compatibility (EMC) requirements. Please call us today on + 61 3 9763 3079 or contact us here.