Hello, and welcome to the first installment of this new column, “Standards Practice.” I’m Karen Burnham, currently Vice President of Standards for the IEEE EMC Society. I’m hoping to use this space to do two things: educate people about standards and also use standards to educate people about electromagnetic compatibility (EMC) engineering.
I’d like to start out by discussing the wide variety of immunity standards (known in defense/aerospace as susceptibility standards) that are out there and why we need so many of them. I will focus on defense/aerospace and automotive since those are the areas I’m most familiar with. However, there are similar motivations behind medical standards, such as IEC 60601 and plenty of others. Here, I’ll be referring to MIL-STD-461 Rev G and JLR-EMC-CS from Jaguar Land Rover (JLR), both easily available. The JLR standard is broadly representative of those automotive OEMs (original equipment manufacturers, such as Ford or Toyota) impose on module suppliers.
Probably no one’s favorite is the standard Radiated Immunity test. This is exemplified by RS103 in MIL-STD-461 for defense/aerospace and JLR RI 114 for automotive. The idea behind this test is for equipment to be immune to its electromagnetic environment. Generally speaking, the main threat to a module will be the RF transmitters co-located on the same platform. Imagine a communication system on an aircraft interfering with an avionics sensor package. That class of threats should be accounted for very explicitly when a program is tailoring its radiated immunity requirements.
What’s harder to narrowly characterize is the broader array of RF transmitters in the world. While I don’t expect to have my electronics interrupted by the local AM radio transmitter, that may change if I drive up to the base of its broadcast tower. Then there are things like aircraft-tracking radar on military platforms like aircraft carriers and in civilian applications at airports. See Figure 1 to compare the levels specified by RS103 and RI 114. The transmitted threats can change significantly over time as different systems are developed, moved, or upgraded. In an example of testing evolving along with consumer technology, the automotive industry adopted radiated immunity testing such as JLR RI 115 that specifically mimics cell phone signals since passengers and drivers can be counted on to put or drop their cell phones in the most inconvenient possible places.
(a)
(b)
Figure 1: Comparing radiated susceptibility/immunity levels from (a) MIL-STD-461 and (b) JLR RI 114.
Leaving aside RS101 and 105 from MIL-STD-461 (susceptibility to magnetic fields and EMP, respectively), we can then look at the wide array of conducted immunity tests. IEC-61000-4-2 and derived standards like MIL-STD-461 CS118 and Jaguar Land Rover CI 280 are all meant to address the risk of human ESD to electronics. The JLR standard goes up to ±30 kV for certain units, while CS118 only specifies up to ±15 kV, presumably because the military has more control over how its equipment is used and can train personnel in a way you can’t with an average driver.
Continuing on, bulk current injection tests such as MIL-STD-461 CS114 and JLR RI 112 represent two threats: lower frequency ranges that are difficult to test via radiated methods due to chamber limitations but easily picked up by long cable runs and also crosstalk between conductors in those long runs.
All units must be immune to the noise carried on shared power buses, such as voltage ripple from power supplies. In MIL-STD-461, that’s covered by CS101; in the automotive world, you might look at JLR CI 210. See Figure 2 to compare the levels between the two. For a nominally 12 V system, both have max levels of 2 V (126 dBμV), but the automotive standard assumes the noise will get worse with frequency, whereas the defense standard assumes it will go down with frequency.
Figure 2: Comparing test levels for conducted immunity/susceptibility addressing low-frequency noise from power supplies.
Aside from the susceptibility requirements specifically applied only to RF systems (CS 103/104/105) or large naval vessels (CS109), the remaining MIL-STD-461 tests are largely applicable to threats such as various transients or induced currents produced by direct or nearby lightning strikes or related impulses (CS115/116/117).
The automotive folks have even more on their plate: wire-to-wire coupling when transients are induced by inductive loads switching on and off (JLR RI 130); or when there are continuous disturbances from pulse width modulated, high current modules (JLR RI 150); conducted transients resulting from loads switching on or off, particularly sudden voltage dips or a load dump (JLR CI 220), power cycling in cold start conditions (JLR CI 230); ground voltage offsets due to using chassis as current return (JLR CI 250); and immunity to transient voltage dropouts that can occur for any number of reasons, including the loosening of pins over time and potentially losing connection when going over potholes, for instance (JLR CI 265).
All of which is to say, there are a lot of different ways to disrupt a system using either radiated or conducted electromagnetic energy. Different industries have specific threats that they want to address with their EMC testing requirements based on their operating conditions and platform architecture. Keep in mind that each test represents some real-world condition, even if it’s a few steps removed or abstracted. When flowing requirements to your own EUT, give some thought to making sure that each scenario is genuinely applicable and consider making tailoring adjustments to your requirements if they don’t make sense.
References
- JLR-EMC-CS v1.0 Amendment 4, “Electromagnetic Compatibility Specification for Electrical/Electronic Components and Subsystems” 25-02-2015.
- MIL-STD-461 Rev G, “Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment” 11 December 2015.
