Simple rules – but many requirements for the military industry
It is well known that in the military industry there are extremely stringent requirements for robustness and documentation. The delivery of small quantities and expensive designs, make it tempting to use “civilian” products, but can they be used?
By Per Thåstrup Jensen
When DELTA tests products for the defence industry, the EU’s CE mark is not top priority in the requirements specification. However, the EMC Directive is very clear: Military electronic equipment is not exempt from the standard CE mark requirements.
For military products however, it is often the requirements set out by MIL-STD 461 (EMC test) and MIL-STD-810 (environment test) that dominate the requirement specification. MIL-STD-461 contains about 20 test parameters, of which 10–12 are relevant for the majority of the products (see the example in figure 1).
Figure 1. Examples of test parameters in MIL-STD-461G. Ground, Army has eight obligatory test parameters.
When industry requirements are the strictest
Because military products are normally tested and qualified in accordance with the MIL standards, it could be obvious to use the military EMC standards as the basis for the CE mark. However, this requires the aid of an EMC Notified Body, which is authorised to operate in accordance with the latest EMC Directive 2014/30/EU. The MIL standards are in fact not included with the harmonised standards for use in the EU:
And there is little possibility of the MIL standards becoming harmonised, since they are not comprehensive enough. The requirements for electromagnetic radiation in the MIL standards can be up to 10 or 20 times more stringent than the EN standards. But for transients, the requirements are low in relation to the civilian burst and surge transients at 2 kV or 4 kV (see figure 2).
Figure 2. Attenuated transient current in accordance with MIL-STD 461, test CS116. The frequency can be from 10 kHz to 100 MHz. The current Ip corresponds to a maximum 500 V transient amplitude.
The most general challenges
Expensive MIL-certified products (for example PCs) can be shown to have a weaker functional performance (less RAM and lower clock frequency) than equivalent and much cheaper civilian products. It is natural to think that the civilian product should be used, because of higher performance and low prices. Such a product is known as a Commercial-Off-The-Shelf (COTS) product. The problem is whether the civilian product can deal with the MIL environment (and pass the MIL tests).
Pack the COTS product!
A solution to the problem of robustness would be to strengthen the COTS product. If you can find an electrically and mechanically robust product, maybe it can be installed in an environment-proof and shockproof cabinet, which can absorb and protect the product against the demanding environment. A metal enclosure would improve the EMC conditions. In some applications, a “box-in-a-box” design will be able to achieve sufficiently good characteristics to be able to successfully pass the qualification test.
Approximation between the EMC requirements – STANAG 4370 and EACTP 500
Through the years, the challenge with MIL requirements has caused difficulties for the manufacturers of defence electronics. In addition to the American MIL standards, there are national standards in several countries, such as Germany (GE), Poland (PL), United Kingdom (UK), France (FR) and the USA (US) (see figure 3).
A number of Allied Environmental Conditions and Test Publications (AECTP) have been devised, which now constitute over half of the requirement factors. For EMC, the military specifications (AECTP 250) are relevant and the tests are described in the AECTP 500 documents. It is intended that NATO partners shall choose these common selected Standardisation Agreement (STANAG) requirements and test methods rather than their national provisions.
Figure 3. Share of test requirements that come from “national” specifications, such as MIL or DEF-STAN standards. IEC, EN, ETSI, ISO, RTCA and NATO STANAG are other standardisation organisations.
Choose the most widely accepted choice! It provides better access to the market
The test requirements in MIL-STD or AECTP-500 can be completely identical. But the key that opens the door to many markets can be if the manufacturers can refer to a widely accepted specification, such as AECPT-500.
To learn more about legal requirements and standards for electronic products for the military and defence industry, contact Per Thåstrup Jensen, Senior Technology Specialist at DELTA, tel.: +45 72 19 43 62, firstname.lastname@example.org.
This is a translation of a short version of an article published in Aktuel Elektronik, no. 15, 2016.