IMMUNITY
Immunity is the ability of equipment to keep operating as required when exposed to electromagnetic disturbances.
Immunity tests apply specified disturbances and monitor the equipment against defined performance criteria. The required levels depend on the product and environment; they are not simply the same as its emissions limits.
Common tests include conducted RF immunity, radiated RF immunity, electrostatic discharge (ESD), electrical fast transients (EFT), magnetic field immunity, voltage dips and interruptions, and surges.
Filtering, grounding, shielding and appropriate protection components can improve immunity. The right approach depends on how the disturbance reaches the affected circuit.
Conducted immunity
Conducted RF immunity considers disturbances coupled onto external power, signal and control cables. Testing applies a defined RF disturbance and checks whether the equipment continues to perform as required.
IEC 61000-4-6 describes a common test method for immunity to conducted disturbances induced by radio-frequency fields. The applicable product standard determines the test conditions and performance criteria.
A suitable filter or ferrite can help reduce a cable-borne disturbance. Choose it for the affected interface, frequency range and installation.
Example: Noise on your power lines is finding its way into your product and causing it to operate unexpectedly - just like for Conducted Emission, our range of power line filters is a great place to start!
When selected correctly, the right filter will help to stop unwanted noise getting in to your product.
RADIATED IMMUNITY
Radiated Immunity ensures that electronic devices and systems can continue to operate correctly and safely in the presence of emissions from other devices and systems.
Radiated Immunity testing involves exposing the product to a range of electromagnetic disturbances through the air and measuring its ability to continue to operate correctly.
Radiated Immunity tests are quite similar to Radiated Emissions tests - the main difference is that power is injected through an antenna instead of being measured - so many of the steps taken to improve a product's emissions can also be used to improve its resilience.
Click here to explore our range of products designed to help you with Radiated Immunity problems.
Example: Your product is going into a harsh environment and is struggling to continue to operate correctly in the presence of high levels of electromagnetic noise from other nearby devices - adding EMC gasket to your enclosure can help improve the robustness of your product in the presence of EMI by sealing gaps and filtering out unwanted noise.
Click here to see an example of one of our EMC gasket materials.
ESD
Electrostatic Discharge (ESD) is a sudden and
momentary flow of electric current between two differently charged objects when
brought close together or when the charge is discharged through an electronic device
or system.
ESD can cause interference to the operation of a device or system and in extreme cases can cause catastrophic failures.
We stock a number of different products to help reduce the effects of ESD on your product.
Example: ESD pulses at an accessible connector make a device behave erratically. Suitable protection components can help clamp the disturbance, but their voltage, capacitance and layout must suit the interface. High-speed signal lines need particular care.
Electrical fast transients (EFT)
EFT consists of short, repetitive bursts of fast electrical disturbances, often associated with switching events and inductive loads.
Testing applies a defined burst to relevant connections and monitors the equipment. Filtering, bonding and suitable protection components can help, depending on the coupling path.
Example: Transients are making it through the power lines and into your product - Varistors on the power lines may help to reduce the effect of the transients by limiting the voltage that is able to make it through the rest of the product.
Magnetic field immunity
Power-frequency magnetic fields can affect sensitive circuits and components. Testing exposes equipment to a defined field, usually generated by a test coil, while its performance is monitored.
The material and mitigation needed depend strongly on frequency. A sheet intended for RF noise absorption should not automatically be selected for a 50/60 Hz magnetic-field problem.
Ask us about the field frequency, affected circuit and available space before choosing a material.
Example: A mains-frequency field affects a sensitive sensor. Moving or reorienting the sensor, reducing loop area, or using suitable magnetic shielding may help. Select a material for the actual field frequency and verify the result.
Voltage dips and interruptions
Supply faults and changes in load can cause temporary reductions or losses of voltage. Testing checks how the equipment behaves during and after these events.
Applicable standards define the test conditions and performance criteria. IEC 61000-4-11 is one commonly used test method for equipment within its scope.
Possible remedies include suitable power-supply hold-up, energy storage or controlled recovery. The solution depends on the required interruption duration and equipment load.
Example: A short power interruption resets a controller. Check the power-supply hold-up time and the controller's undervoltage behaviour. Additional energy storage or a different supply may be needed; an ordinary EMC filter does not replace a hold-up or backup-power solution.
SURGES
Mains surge is a type of electromagnetic interference (EMI) that can cause malfunctions, degrade performance, or even lead to catastrophic failure in electronic devices and systems.
Mains surges are commonly caused by voltage spikes or bursts that are generated by switching events or inductive load changes.
Click here to explore our range of products designed to help you with Surge immunity.
Example - A surge event has caused a catastrophic failure of your product - adding varistors to power lines can help to reduce the effect of any surges on the lines.
Putting it into practice
Immunity concerns the equipment's response to incoming disturbances. Identify the test, the affected function and the entry path before selecting a fix.
Choose filtering, shielding or protection that suits the circuit, then repeat the relevant test and check normal operation. The acceptable response is determined by the applicable performance criteria.
STILL UNSURE?
We have tried our best to provide as much information as we can to help you find the right fix for your EMC issues — if you need further help, contact us using the button below.