Electromagnetic Compatibility (EMC) is the ability of an electronic device to exist in an electromagnetic environment without causing interference to or being interfered with by other electronic devices within that environment. EMC is typically broken down into two categories:
- Emissions – Electromagnetic disturbances emanating from an electronic device that may cause interference/malfunction to another electronic device in the same environment. Also known as Electromagnetic Interference (EMI).
- Immunity/Susceptibility – Immunity is the ability of an electronic device to function normally in an electromagnetic environment without experiencing interference/malfunction due to the emissions emanating from another electronic device. Susceptibility is basically the opposite of immunity, in that the less a device is immune to electromagnetic interference, the more susceptible it is. Typically immunity testing is not required for consumer/commercial type products intended for sale/distribution in Australia, New Zealand, North America and Canada.
Electromagnetic Compatibility Emissions
EMC Emissions are further sub-divided into two categories:
- Radiated Emissions
- Conducted Emissions
An electromagnetic field consists of the following components:
- Electric Field (E-Field) – Usually measured in amps per meter (A/m)
- Magnetic Field (H-Field) – Usually measured in volts per meter (V/M)
These two components of an electromagnetic field are in themselves two separate fields but not totally separate phenomena. E-Fields and H-Fields move at right angles to each other.
Radiated Emissions (E-Field): Radiated emissions are electromagnetic interference (EMI) or disturbances that originate from frequencies generated internally by an electronic or electrical device. These emissions are then propagated through the air directly from the device’s chassis or from interconnected cables such as signal ports, wired ports such as telecommunication ports or power conductors. A great example is HDMI ports and the associated EMI that can radiate from these cables, we used it as a case study, the article can be found here; EMC compliance for HDMI Radiated Emissions testing (EMI). During EMC testing, radiated emissions measurements are made using a spectrum analyzer and or an EMI receiver and a suitable measuring antenna.
Radiated Emissions (H-Field): The magnetic component of the electromagnetic wave is using a spectrum analyzer and or an EMI receiver and a suitable measuring antenna. Typical magnetic field antennas include loop antennas and also include specific antennas as per CISPR 15 such as the Van Veen Loop. The Van Veen Loop antenna is essentially three loop antennae constructed together that measures the magnetic field emissions of a product in three axis (X, Y and Z).
Conducted Emissions (Both continuous and Discontinuous): Conducted emissions are electromagnetic interference (EMI) or disturbances that originate from frequencies generated internally by an electronic or electrical device. These emissions are then propagated along interconnected cables such as wired ports such as telecommunication ports or power conductors. These emissions can be either continuous (continuously emits at a given frequency) or discontinuous in nature (non-constant, occurring sporadically). During EMC testing, conducted emissions measurements are made on an EMI receiver via an ISN (impedance stabilization network) located within the test chamber. For further information about conducted emissions compliance issues and EMC fixes check out our article; Conducted EMI Emissions – Typical Problems and Common Solutions.
Electromagnetic Compatibility Immunity
EMC immunity testing can be thought of as either continuous or transient in nature. Continuous testing is applied to a product to simulate RF proximity that may occur in the real world. Transient phenomena are typically short events that involve bursts of energy.
EMC immunity testing requirements are often split based on how electromagnetic interference might couple onto a device:
- Immunity, enclosure port
- Immunity, signal ports and telecommunications ports
- Immunity, input DC power port
- Immunity, input AC power port
The test levels, types of interfering signals etc are dependent on the type of device being tested and the standard being applied.
Continuous Immunity Testing
Radiated Immunity: RF signal generators, amplifiers and antennas, are used to produce an electromagnetic field at varying frequencies. The enclosure port of the equipment under test (EUT) and associated cables are exposed to the electromagnetic field via a radiating antenna. The radiated test signal is at a specific amplitude and modulation applied for a specific time period. Most standards requiring immunity testing require this testing to be performed.
Conducted Immunity: During conducted immunity testing, an electromagnetic field is generated by an RF signal generator and amplifier. This electromagnetic field is coupled onto a products signal, data or power port via an injection device (commonly a CDN, or ‘Coupling/Decoupling Network’ is used as an injection device). This kind of conducted immunity testing is continuous in nature and is called “Radio-frequency Continuous Conducted” in many standards. Typically conducted immunity testing is applicable to AC & DC ports and signal cables longer than 3m in length.
Power-frequency Magnetic Field Immunity: A fluctuating magnetic field is produced by a magnetic coil which oscillates at the mains power frequency (50/60Hz). The EUT is placed inside this fluctuating magnetic field and exposed for enough time as to evaluate the products performance.
Transient Immunity Testing
Transient phenomena are short bursts of energy that a product under test will be exposed to for a very short amount of time. Like continuous immunity, transient immunity is applied to a products enclosure port, signal/data ports and power ports where applicable.
Electro-static Discharge (ESD): ESD pulses are applied directly to the enclosure of a device and indirectly to vertical/horizontal coupling planes in close proximity to the product under test at test levels specific to the standard being applied. For further information on the effects Electro-static Discharge and the possible ESD compliance solutions please check out out article: Electrostatic Discharge common EMC solutions.
Electrical Fast Transient (EFT) / Burst: Fast transients are a series of short pulses that are high in amplitude and repetition frequency with a short rise time. Fast transient phenomena are most often caused by high speed switching events such as interruption of inductive loads and relay contact bounce etc. Typically fast transients testing is applicable to AC & DC ports and signal cables longer than 3m in length.
Surges: Surges are a type of transient phenomena produced by high powered switching events, magnetic/inductive coupling and even lightening. Surge testing on the mains port of an EUT is applied at several phase angles of the mains supply. Typically surge testing is applicable to AC ports and sometimes also DC ports and in some EMC product standards signal cables longer than 30m in length or if the cable may run outside of a building.
Voltage Dips, Short Interruptions (VDI) and Voltage Variations: The purpose of voltage dips and short interruption testing is to simulate faults in the power network. These faults may be caused by power-cuts (blackout/brownout events) or by sudden large changes of loads. Voltage variations are typically caused by continuously varying loads connected to the power network. A voltage dip or interruption is a two-dimensional phenomenon which is characterised by the residual voltage (mains voltage after the specified dip) and duration (how long the dip in nominal voltage is applied to the product for). This test is only applicable to AC input ports of products.
Pulsed Magnetic Field: Like the power frequency magnetic field immunity testing, the product under test is placed inside a magnetic loop. Unlike power frequency magnetic field testing, rather than exposing the EUT to a continuously fluctuating magnetic field (oscillating at 50/60Hz) the EUT is exposed to a magnetic field pulse, provided by a transient generator. The magnetic pulse is high in amplitude but has a short rise time, after which the products performance is evaluated to ensure normal operation.