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 Conducted Immunity
This type of electrical occurrence for automobiles are fairly common place, given the complexity and numerous electrical components in a compact space. Often times in vehicles, as opposed to other electrical equipment, connections and components are often switched or disconnected. This leads to unique challenges and testing criteria for automobiles or vehicles that have propulsion systems.
Some of the most common international conducted immunity-based standard include ISO 7637, ISO 10605, and SAE J1113. These standards form the backbone of much of the testing for conducted immunity with vehicles. However, as with the rest of EMC testing in this industry, manufacturer-based standards play a large role often referencing these international standards.
Common times of conducted immunity testing for automotive applications include load dump, electrical fast transients (EFT) and microbursts. The unique manufacturer standards require that test generators offer a large degree of flexibility. Below is and example of Waveform Pulse 5 of ISO 16750-2/ISO 7637-2(2004). This information was gathered from LD200N user manual, which can be accessed by click here.(3)
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 series of standards by the International Organization for Standardization is often viewed as the “baseline” for automotive testing. With that being said, often times both other international standards as well as manufacturer-based standards reference it. It is broken out into 5 different 5 standards
- ISO 7637-1- Definitions and general considerations
- ISO 7637-2
- ISO 7637-3 - Electrical transient transmission by capacitive and inductive coupling via lines other than supply lines
- ISO 7637-4 - Electrical transient conduction along shielded high voltage supply lines only
- ISO 7637-5 - Enhanced definitions and verification methods for harmonization of pulse generators according to ISO 7637
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?
EAutomotive 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.”