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While there is a fair amount of redundancy, recognizing the subtle differences between the different versions of and its derivative standards is important as it will impact the cost of the testing as well as the degree of difficulty in complying. Updated in as B and again in as C, changes included an expanded scope as well as modifications to the limits originally defined in the A-version.
Test methods are defined in D. Similar to D, this document was published with an application guide which gives an historical perspective on the reasons for the various tests and helps to clarify the methods used in this testing.
The E version of this standard combined both into one document. Some general pieces of information will be helpful in navigating the military standards.
The military and aerospace world uses the term susceptibility, rather than immunity used in the commercial world. In addition, recognizing the following abbreviations will be helpful:.
This standard provides an interesting read from a historical perspective because it specifies the requirements for some of the antennas that should be used for the testing. Table I of this standard categorizes the different types of equipment that might be tested.
The table below lists most of the tests covered by this standard, and which tests apply to which types of equipment.
The table below shows the most commonly performed tests of MIL-STDA, but is not a comprehensive list of all tests covered by this standard. Although this standard is not often used anymore, it can still be called out when a part that was originally qualified more than 25 years ago is replaced with new hardware. The rationale behind this is that if it worked for hardware that was previously qualified, it will work for the replacement hardware.
One of the most important aspects of this standard that one should be aware of is the extremely stringent limit for CE01 and CE03, conducted emissions on power leads. Although both curves specify 20 dBuA 10 uA of current from MHz, the A-version is more stringent at lower frequencies where low-order harmonics of switched mode power supplies SMPSs are likely to reside. This would clearly impact the front-end filter design of a SMPS.
Another was the addition of the CE07 test, which specifies limits for the magnitude of power bus sag seen on an input power bus due to turn-on and the back EMF surge as a result of turn-off.
One can also see the increase in bandwidth in a number of the tests, most notably RS03 up to 40 GHz. Notable among the changes made were a much more clear delineation between types of equipment being tested — each equipment type has its own part.
Other than the notices which amended , this was the first major update to since its initial publication in So drastic a change was D that it changed all the test designators. This allowed one to easily recognize that the new standard was being specified for a given program.
This change was implemented for all test setups, but the most significant impact it had was on the CE measurement. Conducted emissions on power leads had previously been performed using a clamp-on current probe and the measurement was taken in terms of dB above one microamp.
The current probe technique is still used for CE However, CE changes this measurement to one more similar to the commercial test method; namely, a voltage measurement taken off a coaxial port on the LISN. Another change that was made to D version which was a significant improvement was specifying minimum sweep time requirements for both emissions and susceptibility testing. Especially on susceptibility testing, this was a glaring hole in the previous standards.
By defining minimum requirements for sweep times and also giving test labs the latitude to perform a step and dwell routine , the standards greatly reduced the possibility that susceptibility problems could be missed during testing.
Better definition in the standard also helped to ensure greater repeatability from lab to lab. Next was the addition of making a pre-test calibration part of the test procedure. When testing to the previous standards, one could go through an entire test suite with a faulty cable and never know it. This cable could adversely affect the results for one or many tests, depending on how often it was used. Performing a pre-test calibration is an excellent check to ensure that cables and connectors are in good condition, the correct transducer factors have been entered with the correct signs!
Finally was the abolition of narrowband and broadband measurements. Instead, it specified a single emission limit that should be used and specified the measurement bandwidth of the receiver. This was given as a function of frequency. This change was also a significant step in the direction of the commercial standards and eliminated what had been a controversial and ambiguous part of the previous standards. Significant changes made are as follows:.
One aspect of EMI testing for MIL-STD that has become much more prevalent in the past 15 years or so, has been tailoring of a given test standard to better reflect the anticipated environment that will be seen on a specific platform. While tailoring is more prevalent in the aerospace community, it may be seen in military procurement as well. The requirement may have been relaxed in some areas and, more important, it may have made more stringent in others. Technical Notes Regarding Tailoring One aspect of EMI testing for MIL-STD that has become much more prevalent in the past 15 years or so, has been tailoring of a given test standard to better reflect the anticipated environment that will be seen on a specific platform.
Not reviewing the requirements carefully can result in a serious underbid of procurement. Ask an Expert. While subtle changes were made from the D-version, the most radical change was integrating the limits and test methods into one document.
Conducted susceptibility, power and interconnecting control leads, 50 kHz to MHz. Conducted susceptibility, damped sine transients, pins and terminals, 10 kHz to MHz.
Radiated susceptibility, magnetic and electric fields, spikes and power frequencies. Conducted susceptibility, bulk cable injection, damped sine transients, cables and power leads, 10 kHz to MHz.
MIL-STD-461 – Revisions A – D
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