EMI (electromagnetic interference/disturbances) are defined by the International Organization for Standardization in ISO 7637-1:2015 Preview (accessed 8/20/19) as “any electromagnetic phenomenon which can degrade the performance of a device, equipment or system, or adversely affect living or inert matter … An electromagnetic disturbance may be an electromagnetic noise, an unwanted signal or a change in the propagation medium itself.” (1)
This falls under the greater umbrella of EMC (electromagnetic compatibility) which focuses on an electrical product/equipment ability to function in its intended electrical environment/area. This type of testing can be most easily broken down by immunity and emissions testing, what you are putting out in the electrical environment and what you are taking in.
The focus on the interference or disturbances is to replicate them in a controlled environment allowing for the impact of these occurrences to be evaluated. Automotive, as opposed to other applications, presents a unique set of problems given the amount of electronic based devices and components in a small area. These disturbances or interference are also referred to as cross-talk or noise and can be transferred via both conducted and radiated methods.
Types of Disturbances/Noise
The International Electrotechnical Commission (IEC) does an excellent job at breaking out the different types of disturbances/interference. Many of these disturbances are applied/occur in the automotive sector.
- Conducted low-frequency Phenomena
- Radiated low-frequency field Phenomena
- Conducted High-frequency Phenomena
- Radiated High-frequency Phenomena
- High-altitude nuclear electromagnetic pulse (HEMP) (2)
Automotive Immunity Tests
Conducted immunity is focused on transmission of interferance or noise via direct contact. The automotive sector is unique in the amount of OEM standards, however to we are going to focus on the most common international requirements, ISO 7637-2/3, ISO 16750-2, ISO 11452-4, and ISO 10605.
Radiated immunity test subject equipment to varying levels of electric and magnetic fields in an effort to ensure no impact on the functioning of the device. The most common standards for this type of testing is ISO 11451-2 and ISO 11452-2.
ISO 7637 - Electrical Transients
ISO 7637-2:2011 - Electrical transient conduction along supply lines
ISO 7637-3:2016 - Electrical transient transmission capacitive and inductive via lines other than supply lines.
These two sections within the ISO 7637 series are the most commonly tested and referenced by associated OEM specific standards for automotive transients. Some automotive pulses, as with EFT/Microbursts, are similair to commerical requirements with some modifications to pulses to account for the automotive environment.
ISO 7637-3 Coupling Methods
- Capacitive coupling clamp (CCC)
- Direct capacitive coupling (DCC)
- Inductive coupling clamp (ICC)
ISO 16750-2 - Load Dump Pulses
ISO 16750-2:2012 - Electrical loads (for electrical and electronic equipment)
This standard provides a few different pulses including superimposed voltage and monentary dip testing, however it is most commonly referenced for it's load dump (5a) and clipped load dump (5b) waveforms. These pulses are typically test to in conjunction with the ISO 7632-2 pulses covering a wider range of automotive transients.
ISO 11452-4 - Conducted RF
ISO 11452-4:2020 - Harness excitation methods
Conducted RF testing is typically done for automotive applications to either ISO 11452-4 or OEM requirements that reference either part, or all of the standard requirements. The two methods indicated in the standard are bulk current injection (BCI) from 1 MHz to 400 MHz and tubular wave coupler (TWC) from 400 MHz to 3 GHz.
ISO 10605 - Electrostatic Discharge (ESD)
ISO 10605:2008 - Test methods for electrical distrubances from electrostatic discharge
ESD testing for automotive typically requires high voltage capabilities as with ISO 10605 which can go as high as 25 kV for air discharge testing and 15 kV for contact discharge. This standard also specifies three additional capacitence and resistance combination in addition to the 150 pF 330 Ohm typically for commerical testing:
- 330 pF / 330 Ohm
- 150 pF / 2k Ohm
- 330 pF/ 2k Ohm
ISO 11451-2:2015 - Off-vehicle radiation sources
ISO 11452-2:2019 - Absorber-lined shielded enclosure
Part 2 of ISO 11452 is focused on testing electrical components for vehicles regardless of propulsion systems, subjected to radiated fields within a absorber-lined shielded enclosure. This test is done at a one meter distance requiring both vertical and horizontal polarization above 400 MHz. Commonly used antennas include biconical, log-periodic, and horn antenna able to meet the required power levels.
Automotive Emissions Tests
Emissions tests for vechiles are mainly done with two standards, CISPR 25 with on-board recievers and CISPR 12 that have off-board recievers. We will focus heavily on CISPR 25 with CISPR 12 being mentioned briefly after the more recent updates to CISPR 25.
CISPR 25:2016 - Limits and methods of measurement for the protection of on-board recievers.
CISPR 25 includes both conducted and radiated emissions components while also providing both component level and vechile level testing.
Automotive Radiated Immunity
Radiated immunity testing for many applications, including automotive, require shielded enclosures or chambers for testing. This testing allows for electrical apparatuses/equipment susceptibility, which can impact functionality, to be tested with the emissions of surrounding devices.
Given the vast amount of electronics and electronics-based components in vehicles today, this type of testing has become increasingly important.
There are a variety of methods of testing for radiated immunity. However, the majority of testing can be simplified down to a signal generator, amplifier, antenna, and most often a way to measure the electrical field. This type of testing is creating an electrical field, with that being said, a shielded enclosure is required. Given the signal generator and amplifier, these systems can also be used in conducted RF testing.
Electrostatic Discharge (ESD)
ESD is a commonly occurring phenomena that effects a variety of applications, including automotive based ones. Vehicle based testing often requires testing to 30kV and requires specific resistance and capacitance networks required for waves shaping. The most common testing networks include 150pF/2kOhm, 330pF/2kOhm, and 330pF/330Ohm. These networks are most often interchangeable and are categorized based upon resistance/capacitance values.
ISO 10605 Covers Discharges (3):
- ESD in assembly
- ESD caused by service staff
- ESD caused by occupants
Results/Impacts of Testing
Results for automotive based testing are often broken down by a variety of different criteria. These are most often based upon the ability for the equipment under test (EUT) to function. Some common criteria include complete and permanent deterioration of function. To determine these, it’s necessary to refer to the associated testing standard and categorize accordingly.
There are 5 main classifications for all testing standards, these including automotive based standards. (5)
- (1) International Standards- ISO, IEC/CISPR, etc.
- (2) Regional Standards - EN, ASEAN, etc
- (3) National Standards. - JIS, BS, ANCI etc
- (4) Industrial Standards - JEITA, SEMI, etc
- (5) Form Standards - Bluetooth, USB, HDMI, etc
This automotive based standard titled “Road vehicles — Test methods for electrical disturbances from electrostatic discharge” is one of the mainly referenced and tested to automotive electrostatic discharge (ESD) international standards. This standard, as mentioned early clearly defines discharges into three main categories. The International Organization for Standardization states “This International Standard is based in part on IEC 61000-4-2 and describes vehicle-specific requirements.”(4).
Each manufacturer-based standard has the potential to provide unique testing requirements for EMC (both conducted and radiated testing). These unique testing requirements, often time exclusive to a particular brand, make testing to these standards especially challenging. As previvoulsy mentioned, these automotive standards often refer to common international standards within the industry including ISO 7637, SAE J1113 and many others.
Common Immunity Testy System
There are a variety of test systems for both immunity and emissions testing available. The below video walks through a little about the EM Test automotive conducted immunity test equipment and how they function.
What is Automotive/Vehicle EMI?
Vehicle EMI (electromagnetic interference) or disturbances are defined by the International Organization for Standardization in ISO 7637-1:2015 Preview (accessed 8/20/19) as “any electromagnetic phenomenon which can degrade the performance of a device, equipment or system, or adversely affect living or inert matter … An electromagnetic disturbance may be an electromagnetic noise, an unwanted signal or a change in the propagation medium itself.” (1)
Why test for EMI & Electrical disturbances?
The reasons behind testing for EMI or disturbances can most easily be categorized as:
- Testing for quality control/functionality
- Testing to ensure compliance for a particular standard/methodology
What is Automotive EMC?
Automotive EMC is the ability for electronic equipment/apparatuses to function in its anticipated electrical environment, associated in some way with a vehicle or machine.
What is the purpose of Component level Automotive testing?
Teseq Automotive Electrical Disturbances “The purpose of component level testing is due to the interoperability of these components and the tendency for all electronic subassemblies to cause noise on the battery lines and wiring harness. Testing subassemblies for both emissions and immunity ensures compatibility when these assemblies are built into the final production vehicle.”