What is EMC Testing? Definition & Types of Tests

what is emc testing

I. What is EMC Testing?

Electromagnetic compatibility (EMC) testing measures an electrical product’s ability to function satisfactorily in its intended electromagnetic environment without generating intolerable electromagnetic disturbances to anything in that environment. EMC differs from other safety aspects because the electromagnetic phenomena exist in the normal use environment of all electrical equipment.

Product EMC testing is performed at the design, development and production stages to ensure that all products are safe before reaching the end-user. The test evaluates the correct selection of components and the proper construction following the requirements of the relevant EMC standards. EMC type tests are usually much more stringent than routine production tests as they intend to verify a product’s safety design. Also, during EMC testing, the product sample must be energised.

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If a product doesn’t pass the EMC testing procedure, the manufacturer has two options:

  • Provide the testing laboratory with a new sample on which all relevant tests are to be performed again
  • Make all the necessary repairs and modifications on the already tested sample and have the lab repeat only the sequence of EMC tests that the sample failed.

In addition, EMC testing is required for obtaining international approvals and product certification marks for electrical products. For instance, electrical products must pass EMC testing and comply with the EMC Directive 2014/30/EU to obtain CE marking approval for the EU market.

II. Main types of EMC testing

This section focuses on the main tests for achieving EMC compliance.

Radiated Emissions (EMI) tests

Radiated emissions testing measures the electromagnetic field strength of the emissions unintentionally produced by the electrical product. These emissions are inherent to the currents and switching voltages within any digital circuit.

To perform the EMI tests, the following equipment is often needed:

  • EMI receiver, preselector and QP adapter
  • Turntable
  • RB coaxial cable
  • Attenuator
  • High pass filter
  • Broadband linearly polarised antenna
  • Open area test site and full anechoic chamber

The test procedure includes several steps, as follows:

  • Performing a preliminary measurement inside an anechoic chamber to characterise the product sample
  • Performing test and limits comparison in an open area test site with the sample placed on a remotely controlled turntable
  • Loading the specification limits and applicable correction factors to the EMI receiver
  • Maximising the readings by adjusting the turntable azimuth between 0– 360 °, the antenna height between 1– 4 meters, and antenna polarisation
  • Evaluating the emissions from the product using appropriate methods
  • Emission level = Reading Value + Ant. Factor + Cable Loss
  • Recording the output of the preliminary measurement
  • Recording the emissions levels on the frequency range in tables and spectral plots using the preliminary measurement information.

Before submitting a sample to a test lab for this type of EMC testing, manufacturers must ensure proper product design. A minor issue, such as noise on the cabling, will fail the radiated emissions test.  

Conducted Emission tests

Conducted emissions testing measures the portion of electromagnetic energy created by a product and conducted onto the power supply cord. The test aims to verify that these emissions comply with specified limits in relevant EMC standards, usually from 150 kHz to 30 MHz.

To perform the conducted emissions tests, the following equipment is often needed:

  • EMI receiver
  • AMN (artificial mains network) for the sample and any additional-peripheral equipment
  • Termination
  • Ground plane
  • Current probe
  • Coaxial cable
  • Isolation transformer
  • Filter.

The test procedure includes several steps, as follows:

  • Emission level = Reading value + Correction factor
  • Correction Factor = Cable loss + Insertion loss of LISN
  • Margin value = Emission level – Limit
  • Investigating the frequency spectrum from 0.15 MHz to 30 MHz
  • Connecting all interface ports to the appropriate peripheral units via specific cables and recording any relevant information (e.g. cables’ data)
  • Recording the emissions levels in the frequency range of 150 kHz– 30 MHz in tables and spectral plots.

Failing the conducted emissions testing is not uncommon for products with a pre-certified external AC-DC power adapter. Power supplies are often supposedly compliant, but when re-tested, they become non-compliant because of hardware changes since the initial compliance testing or flaws with the original testing.  

Keep track of your suppliers’ compliance status using the supplier portal for EU and SCIP compliance.

Flicker tests

Flicker testing is another form of emissions testing. It helps determine if the product sample produces fluctuating load in the branch circuit causing RMS voltage fluctuations with flickers. To perform this type of EMC testing, the following equipment is often needed:

  • Power source
  • Flicker meter
  • Impedance network
  • Voltage fluctuation meter.

The test procedure includes as follows:

  • Determining acceptable values and relative voltage change characteristics
  • Measuring the RMS voltage fluctuations on the ac mains caused by the sample
  • Evaluating the flicker severity using appropriate methods and recording the output
  • Measuring the relative voltage changes and determining if the total accuracy is better than ±8%.

Radiated RF electromagnetic immunity tests

The radiated RF electromagnetic immunity test measures the performance of the product’s immunity to radiated RF electromagnetic field disturbances for simulating the interference of transmitted electromagnetic waves. This test required the following equipment:

  • Signal generator
  • RF power amplifier
  • Function generator
  • Biconical antenna and log-periodic antenna
  • Millivoltmeter
  • Isotropic “E” field probe
  • Dual directional coupler
  • Power amplifier
  • Field sensor
  • Anechoic chamber or semi-anechoic chamber
  • Absorbers
  • RF coaxial cable
  • CCD and a monitor for CCD.

During the test, the product sample is subjected to a field of 3V/m, and amplitude modulated 80% by a 1-kHz sinusoidal signal. And the radiated field is applied in vertical and horizontal polarisation using appropriate antennas. The test is performed in an anechoic or semi-anechoic chamber.

Electrostatic discharge immunity tests

This form of EMC testing evaluates the performance of the immunity to electrostatic discharges at the enclosure, accessible ports and other similar areas of the product sample. The following equipment must be provided to perform electrostatic discharge immunity testing:

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  • ESD simulator
  • Oscilloscope
  • Horizontal coupling plane
  • Vertical coupling plane
  • Discharge electrode
  • Discharge return cable
  • Bleeder resistors
  • Insulating support.

The test procedure includes three main steps. First, applying potentials of ±2 kV, ±4 kV, ±8 kV, and ±15 kV (or others specified in the relevant EMC standards) near each applicable test point (air discharges are applied to insulating surfaces). Secondly, applying potentials of ±2 kV, ±4 kV, ±6 kV, and ±8 kV (or others specified in the relevant standards) to each applicable test point (contact discharges are applied to conductive surfaces and coupling planes). Lastly, performing indirect discharge using the direct contact ESD test tip. In this regard, potentials of ±2 kV, ±4 kV, ±6 kV, and ±8 kV (or other specified in safety standards) are applied to the centre of the vertical edge of the coupling plane at a distance of 0.1m from the outer casing of the product sample to each applicable test point.

Surge immunity test

Surge immunity testing evaluates the performance of the equipment’s immunity to surge disturbances. Three pieces of equipment are needed to perform this test – surge wave generator, coupling/decoupling network and reference ground plane.  

The test procedure includes several steps:

  • Applying test voltages in a synchronised way to the voltage phase at zero-crossing and peak value of the A.C. voltage wave (both, positive and negative).
  • Applying the surge to the equipment’s power supply terminals via the capacitive coupling decoupling network.
  • Testing at least five positive and five negative discharges at selected points of the power supply (0°, 90°, 180°, and 270° of the sine wave).

Magnetic field immunity test

This form of EMC testing measures the performance of the immunity of an electrical product to magnetic field disturbances. The test requires the use of the following equipment:

  • Test generator
  • Magnetic field probe and tester
  • Decoupling network
  • Square coil or another inductive coil
  • Back filter.

During the test, the equipment is subjected to a continuous magnetic field by use of an induction coil. Afterwards, the induction coil is rotated by 90° to expose the product to the test field with different orientations. Three orthogonal planes are tested. Lastly, the dwell time at each frequency is measured and should be at least equal to the time the product needs to respond.

Electrical fast transient (EFT) immunity test

This test helps evaluate the performance of the product’s immunity to electrical fast transient disturbances. The equipment needed for the test is as follows:

  • Burst generator
  • Coupling decoupling network
  • Reference ground plane, capacitive clamp
  • Interconnection cable
  • 33 nF capacitor probe for direct injection.

During the test, an EFT test signal is applied to the neutral and ground lines of the product sample’s mains input at a distance of 1 meter from the sample. The test signal voltage is applied for 1 minute to each line in negative and positive polarities. The same test signal is also applied to the signal lines connected to the product unit.

Harmonic tests

Harmonic testing measures the harmonic current requirements of an electrical product. By limiting the harmonic current requirements, the harmonic load on local power supplies is decreased, which helps avoid specific electrical product hazards (e.g. overheating) and increases efficiency.

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