EMC Compliance and EN 61000-4-3: What Manufacturers Should Know About RF Susceptibility
Electromagnetic interference isn’t only a problem coming from the medical device itself. It’s also an issue that medical equipment has to withstand to operate properly. EN 61000-4-3, also known as IEC 61000-4-3, is one of many electromagnetic compatibility (EMC) standards that devices have to go through before going on the market. We’ll go through what radiofrequency (RF) susceptibility can mean for your device, test and class levels, and what’s included in the testing environment.
EN 61000-4-3 RF Susceptibility
EN 61000-4-3, also known as IEC 61000-4-3, is a test standard that measures how well electronic and electrical equipment can resist radio wave interference. Suppose medical devices are around a lot of radio signals from things like Wi-Fi routers, cell phones, or microwave ovens. In that case, they need to be able to handle a certain level of radiated radio frequency interference (RF) from them. Failure to handle these interferences can lead to serious patient injuries.
Testing for Standard IEC 61000-4-3
To confirm immunity against radiofrequency emissions, tests are conducted in a shielded anechoic chamber. These chambers are built to block the entrance or exit of any electromagnetic waves. This is done to focus the test and to prevent interference from with other devices outside the chamber, due to the high field strength of the RF signals.
The antenna that generates RF signals and the equipment under test (EUT) are generally 3 meters apart, but the testing area should be set up in a way that resembles how the EUT will be used in real life.
The table or support that holds the EUT should be made out of non-conductive, non-metal material that is between 0.05 and 0.15m in height for equipment that stands on the floor, and 0.8m in height for tabletop equipment. A material like polystyrene is recommended, because wood can become reflective around higher frequencies, meaning the frequency can bounce off the surface instead of being absorbed.
While the 3-meter length is the standard, the EUT should be evaluated using manufacturer wiring and connectors. If the required wiring length is under 3 meters, use that length for testing. If it’s over, a minimum of 1 meter of cable needs to be exposed to the field, and excess cables can be bundled in 30-40 centimeter lengths.
Performing the test correctly requires the following equipment:
- Anechoic chamber: The chamber needs to be large enough to fit the EUT and create a uniform field around it. It may need to include additional absorbers to reduce reflections if it is not fully lined with them.
- EMI filters: These are optional, but if used, should not cause any extra resonance effects.
- RF signal generator: The signal generator needs to produce an amplitude-modulated signal in the right frequency band for the test.
- Power amplifier: The antenna can emit the right field strength with the power amplifier, which needs to have distortion products 6dB below fundamental frequency at minimum.
- Field generating antenna: The antenna system needs to be linearly polarized (oscillate in a single plan) and should meet the frequency requirements for the test. Antennas may be bi-conical (broadband & omnidirectional), log-periodic (broadband & directional), or horn (narrowband & directional).
- Isotropic field sensor: An isotropic field sensor can measure the electric field strength of an electromagnetic wave in all directions. The sensor you use needs to withstand the field strength being measured. It’s recommended that the sensor has a fiber optic link to an indicator that is outside the chamber. A fiber optic link will be immune to EMI interference.
- Equipment for Power Level Recording: There also needs to be equipment available that logs the required power levels to generate the right field strength for the test.
Test Levels for EN 61000-4-3
Each frequency range comes with its own test level and should be evaluated under the standard. Testing can be done for general-purpose RF immunity, as well as for mobile communication and other devices at higher frequencies.
For general purpose, RF immunity should be tested between the 80MHz and 1000MHz frequency range without any gaps, meaning the testing should be applied continuously across the range.
For higher-frequency devices, tests don’t have to be performed continuously. These tests apply to the 800MHz to 960 MHz and 1.4 GHz to 6.0 GHz frequency ranges. Some countries have set operating bands, so the test may only consist of those bands.
Volts Per Meter (V/m) Standards Per Level
RAM Technologies’ power supply units are suitable for medical devices at test level 3, which includes tolerance to radiated electromagnetic fields at a strength of 10 volts per meter (V/m). The field strength tested at each level is as follows:
- Level 1: 1 V/m
- Level 2: 3 V/m
- Level 3: 10 V/m
- Level 4: 30 V/m
- Level X: Special (this level is open for other products that may not be applicable under these standards)
What test levels and frequency bands are evaluated will depend on the electromagnetic radiation environment the EUT is exposed to post-installation. These environments are further divided into 5 classes (including class X, which is open like the test level):
- Class 1 is for low-level radiation environments. This might look like low-power transmitters and receivers.
- Class 2 is for common commercial environments. Low-power portable transceivers (1W rating) might be used, but not without certain restrictions regarding how close they can be to equipment.
- Class 3 is for normal industrial environments and settings where there may be severe electromagnetic radiation. Portable transceivers with 2W ratings or more may be closer to equipment, but still at 1m away or greater.
- Class 4 is similar to Class 3, but portable transceivers can be closer to the equipment – within 1 meter. There may also be interference coming from other sources within 1m of the equipment.
What to know about EMC Compliance and PSUSs for Your Medical Device
While our power supplies don’t need to be individually tested to meet EMC compliance, we understand that your medical device as a whole will need to be compliant. Because our PSUs meet the standards, using one of our products in your equipment means one less factor to worry about. Please reach out if you have any questions about our power supply units or about the other standards our PSUs meet.
You can find also additional EMC information on our downloadable data sheets, available on each power supply page.