What is EMC Testing? Definition & Types of Tests

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.

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:

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.