The Basics of Military EMC Testing

Military EMC testing requirements are defined by industry leaders, procurement specialists, and project leaders. The requirements have been clearly defined so that experienced EMC test engineers and test laboratories know exactly what is needed for compliance testing of systems and components, or a combination of the two. Although the onus is not on the EMC test engineers and test laboratories to make the decisions on test levels, limits, and requirements, they are still required to identify test specifications, define test procedures, as well as perform the tests. Therefore, it is important to have a basic understanding of the requirements that have been put in place for military testing standards.

MIL-STD-461 vs MIL-STD-464

When testing equipment for use in military applications, a decision needs to be made as to what military standard will be used to confirm your equipment is EMC compliant. Your options are typically between testing to MIL-STD-461 or MIL-STD-464.

There are two major differences between MIL-STD-461 and MIL-STD-464. The first thing to consider when choosing a standard is the equipment that will be tested. MIL-STD-461 is written to perform testing on components and subsystems which are installed on platforms. An example of this would be a display that is installed within the cockpit of an aircraft. MIL-STD-464 however is written to perform testing on entire platforms. So, while the display would be tested to MIL-STD-461, the aircraft itself, such as a F35 Joint Strike Fighter, would be tested to MIL-STD-464.

The other difference between the two standards is the amount of guidance that is provided to complete a test. MIL-STD-461 gives limits and test severity levels which shall be performed within a laboratory, along with clear guidance on how the testing should be performed. In the alternative, MIL-STD-464 only describes the environment where the platform under device may operate, and, therefore, the test levels that may go with it. Although it does not give instructions for testing, it does make clarifications as to how the environmental requirements relate to MIL-STD-461.

Defining The Test Approach

The test approach will be defined by the contracting/approving body. The first step in determining your requirements and test approaches is to define the test sample. Will you be testing a full vehicle or are you testing a component going inside that vehicle? As previously stated, if you are testing the full vehicle, be it a fighter jet, tank, or drone, MIL-STD-464 requirements would most likely be implemented. If you are testing a component, such as a display going on the bridge of an aircraft carrier, you would implement the requirements of MIL-STD-461. More specifically, you would test to the MIL-STD-461 version for Navy, Above Deck Equipment.

The version of the standard will be called out within the requirements of the equipment to be tested by those writing the contracts and documents. Typically, when writing the contractual requirements, those involved will select the most recent version of the standard. If the procurement of the equipment to be tested takes longer than expected and a new version of the standard is released in the meantime, the version noted within the contractual requirements shall be tested.

However, there is the occasional instance where a version of the standard may be tailored for certain requirements. For example, the United States Navy CVN-78 aircraft carrier was contracted to test to MIL-STD-461E requirements. After the contract was written and approved, but before the testing had been completed, MIL-STD-461F was released. As stated above, the initial test programs were still tested to MIL-STD-461E. However, a tailoring letter from the US Navy’s procuring activity was released stating that while the requirements of MIL-STD-461E shall be tested, laboratories were instructed to use some MIL-STD-461F updated requirements for both emissions and susceptibility testing. This led to both time and budgetary savings and was perceived to not affect test results in any way.

Full Vehicles Installed on Vehicles

There are times when a complete vehicle can be transported and even operated on another complete vehicle or system. For example, fighter jets are often installed/transported within the hull of an aircraft carrier. Does this now make the fighter jet a component or a platform? In this case, the fighter jet is a stand-alone vehicle and treated as a platform. Since the aircraft is inserted into different environments during flight and operation than when taking off, landing, or in storage on an aircraft carrier, it operates both within the confines of the carrier and on its own. Therefore, the aircraft would need to be tested to MIL-STD-464 standards.

A good rule of thumb for this type of questions is if a device can be utilized on its own without being installed within another device, vehicle or system, it should be tested to MIL-STD-464 requirements. Anything that needs support equipment to simulate loads, obtain power from another source, or is not a stand-alone piece of equipment should be tested to MIL-STD-461 requirements. There may be times where this is not always the case, but the contractual requirements, manufacturer, or approving body (if available) should help steer you in the right direction.

Summary

Understanding who defines the military EMC testing requirements can give insight to test programs, the best way to proceed with testing when a requirement is tailored, or to be more knowledgeable regarding performing testing on products. The differences within MIL-STD-461 and MIL-STD-464 should be understood by those performing testing or developing products which may undergo testing for military installations.