Harsh Environment

What makes for a harsh environment? For a person, a harsh or inhospitable environment could be considered a set of conditions that can cause bodily harm over a period of time. The concept is much the same for electronics; for example, an electrical circuit can be easily damaged or destroyed if introduced to water or high humidity levels. Other potentially damaging conditions include extreme temperatures and temperature cycles, ingress of particulates, electrostatic discharge (ESD), electromagnetic interference (EMI), vibrations, and physical impact.

Many applications need electronics that are designed to operate in harsh environments. The downhole oil and gas industry is one such example, requiring high-reliability parts with temperature ratings which often surpass military specifications. Standards, such as NEMA ratings and the IP code (IEC 60529), exist to quantify the degree to which a product can withstand various harsh conditions.

Engineers must take into account a harsh environment prior to the design stage of development. The specific environmental conditions in which the product will be used will affect the product specifications, and must be determined beforehand.

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The IP (Ingress Protection) Code is defined by the International Electrotechnical Commission (IEC) under the IEC 60529 standard. It designates the various types and degrees of protection afforded to electrical equipment by its enclosure. The IP code itself has the form "IP XY", where X and Y are digits which denote the level of protection from particle ingress and from water, respectively. The first digit also represents the amount of protection provided to external objects from contact with parts within the enclosure. The requirements for each degree of protection are specified in the standard, as well as the procedures to test and confirm them. It is important to note that, because NEMA Enclosure Types are tested over a wider set of environmental conditions, it is not possible to obtain an equivalent NEMA Type from an IP code although the opposite (converting a NEMA Type to an IP code) may provide a good guideline. NEMA to IP code conversions should always be verified by test.

*IP69K is a German standard and not congruent with other IP standards. It should not be assumed that it meets the requirements of lower IP standards.

Similar to the IP Code (IEC 60529), the National Electrical Manufacturers Association (NEMA) provides a popular standard for protective enclosures. NEMA 250 covers a broader set of harsh conditions than the IP code and includes ratings for indoor and outdoor locations, both hazardous and nonhazardous. These conditions include ingress of water and foreign objects (e.g. dust or fibers), as well as corrosive agents and various gases and atmospheres. The table below provides a brief description of each level of protection, which NEMA specifies with a NEMA Enclosure Type Number. It is important to note that, because NEMA Enclosure Types are tested over a wider set of environmental conditions, it is not possible to obtain an equivalent NEMA Type from an IP code – although the opposite (converting a NEMA Type to an IP code) may provide a good guideline.

Often, when electronics are used in high temperature environments, some form of active or passive cooling is used to keep the components within their operating temperature range. However in some applications this is highly impractical, such as with downhole drilling operations. The downhole oil and gas industry represents one of the primary consumers of high-temperature electronic components. As oil and gas resources become scarcer, there is a growing incentive to drill ever-deeper wells. With deeper wells comes the challenge of designing equipment to withstand higher temperatures. The rate in which temperature increases with depth is defined as the geothermal gradient, and in most parts of the world is roughly 25°C per kilometer. Today, electronic components used in downhole applications must not only operate at temperatures exceeding 200°C, but also be extremely reliable; equipment failure leads to rig downtime, which is often extremely costly.

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Vibration is a potential source of the failure for many systems, and can be a major contributor to problems related to the operating environment of electronic equipment. Most electronics equipment is exposed to some amount of vibration, even if just from shipping and transportation. Portable electronics often need a degree of protection from the shock and impact of being dropped from moderate heights. In other industries, such as mil/aero and harsh industrial settings, vibration isolation and resilience can be a crucial design consideration.

Although modeling and analysis are helpful tools, testing is often necessary to ensure product reliability under harsh conditions. This is not as simple as it may seem, however. A 20-year product life is typical and expected for military qualified electronics. How can this be tested? Accelerated stress testing techniques such as HALT (Highly Accelerated Life Test) and HASS (Highly Accelerated Stress Test) offer solutions that are both practical and effective. Methods like HALT/HASS go further than mere design verification testing because they stress products beyond their specifications to determine both operational and destruct limits.

The MIL-STD-202 Test Method Standard, used by the U.S. military, specifies the testing procedure for vibration, which involves simple harmonic motion at 0.03 inches amplitude over a range of frequencies from 10 to 55Hz. Under electrical load conditions, the motion is applied for at least two hours along each axis (for a total of six hours), and the product is tested both during and after vibration.

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