EMC Compliance and EN 61000-4-6: What Medical Device Manufacturers Should Know About RF Conducted Immunity
Electromagnetic compatibility (EMC) testing is an important step before putting medical devices on the market. The various standards that fall under this testing are mainly designed to ensure equipment continues to operate when in the presence of other electromagnetic phenomena.
We’ll discuss EN 61000-4-6: RF Conducted Immunity, including the main purpose of the standard, what equipment doesn’t apply, and the basic classes and test elements used to ensure medical devices meet the standard.
What is Standard EN 61000-4-6: RF Conducted Immunity?
EN 61000-4-6, also known as IEC 61000-4-6, is an immunity testing standard for conducted disturbances created by radio frequency fields that range between 9kHz and 80 MHz. The standard defines how to test electronic and electrical equipment to make sure it can withstand electromagnetic interference (EMI) from radio frequency (RF) transmitters, because this interference can cause malfunction or complete working failure.
What is Excluded from EN 61000-4-6?
Equipment is excluded from this standard if it doesn’t have at least one conducting cable or wire. This could look like a signal line, earth connection, or mains supply.
These cables and wires can interact with disturbing RF fields. The wires and cables can act like antennas and pick up EMI from RF transmitters. Tests are also not required in the 9kHz – 150 kHz range because this frequency is not normally used by RF transmitters.
Where Can Disturbances Come From?
Disturbances can come from transmitting radio systems whose fields cause disturbances in lines. Systems can include mobile phones, wireless phones, radio, and television. They can also come from motor drivers, power converters, or other electronics that create low-frequency interference currents.
Assumptions with EN 61000-4-6
Standard EN 61000-4-6 comes with a few assumptions about how electromagnetic fields affect electrical equipment. The assumptions are stated to make the testing procedure more straightforward and manageable.
The standard assumes that the dimensions of the equipment are small compared to the wavelengths from the interfering waves, so the equipment can be used as a point source. The cables, therefore, can be modeled as passive receiving antennas for the equipment.
The whole length of cables installed to the equipment is also assumed to be potentially affected by electromagnetic field disturbances. The cable systems are assumed to be in “resonant mode,” which means they are particularly susceptible to certain EMI frequencies.
Testing for EN 61000-4-6
To test and see how conducted disturbing signals will affect the equipment, the signal is injected into the cabling using coupling/decoupling networks (CDN).
A CDN is a device that connects an electromagnetic disturbance source to equipment under test (EUT) and then decouples the EUT from the source. The coupling transfers the energy of the disturbance source to the EUT while minimizing loss. The decoupling isolates the EUT from the disturbance source so that it doesn’t affect other equipment connected to the EUT.
During the test, any cables that stem from the EUT need to be supported at a 30 mm height from the reference ground plane. This is because the ground can act as an antenna and pick up interference, skewing the results of the testing process.
When testing, equipment will be subject to EMI that they may expect to experience in a normal operating environment from radio frequency (RF) transmitters. The setup includes generating the electric and magnetic fields (E and H) using an RF transmitter, antenna, and coupling network. The RF transmitter stars by generating the signal, which travels to the EUT through the antenna. The coupling network couples the signal to the cables and connectors on the EUT.
It’s important to note that the CDN tests one cable at a time, which isn’t consistent with real-life scenarios. However, this is done to better isolate and troubleshoot problems.
Coupling Devices for EN 61000-4-6
There are a few different types of coupling devices that can be used to test for RF disturbances. The most preferred is the coupling/decoupling network (CDN) devices because they provide a repeatable and consistent way to inject electromagnetic disturbances into EUTs while protecting auxiliary equipment (AE) that is not being tested from the disturbances.
However, testing can also be done using direct injection devices, clamp injection devices, and decoupling networks.
Test Levels and Classes for IEC 61000-4-6
Four different levels may be tested in EN 61000-4-6. The level will be chosen based on the electromagnetic environment where the EUT will normally be used.
The higher the test level and class, the higher the tested electromotive forces (EMF) and decibels relative to 1 microvolt (dBuV). The classes are as follows:
Class 1
At this level, there may be radio stations or television stations greater than 1 km away. This would be a low-level electromagnetic radiation environment. Low-power transceivers are normally at this level.
Class 2
Typical commercial environments are generally categorized as Class 2. Electromagnetic radiation in this environment is moderate, and low-power portable transceivers with a <1W rating can be in use. However, there are restrictions regarding use when in close proximity to equipment.
Class 3
Most industrial environments fall under class 3, where equipment may be subject to severe electromagnetic radiation. In these environments portable transceivers rated 2W or more are used fairly close to equipment, but still not within 1 meter. There may also be nearby industrial, scientific, and medical equipment (ISM) and high-powered broadcast transmitters close to the equipment.
Class X
For environments that don’t fall into one of these categories, Class X can be used as an open immunity test level.
For more information on class levels, testing conditions, and other specific details, refer to Academy of EMC.
What Medical Device Manufacturers Should Consider When Looking for EN 61000-4-6 Compliant PSUs
Medical devices that are looking to test for EMC compliance will need to ensure their entire device operates per the necessary standards, including IEC 61000-4-6. Because the regulations apply to entire devices and not individual components, RAM Manufacturers’ PC-based power supply units for medical devices are not specifically tested on these EMC standards. However, we do meet the standards, eliminating one component to check off your list when you’re going to market.
Our downloadable data sheets include information on which standards our power supply units meet. If you have any other questions about compliance or other standards, please contact us today.
RAM Technologies’ power supplies are 60601-1 3.2 certified and meet 60601-1-2 EMC standards. When you’re designing your medical device and need help with a PSU, contact us for details.
More Resources:
Downloadable Guide to IEC 60601-1
EMC Compliance and EN 61000-4-3: RF Susceptibility
EMC Compliance and EN61000-4-4: EFT Level 3
EMC Compliance Testing for Medical Devices
