The Issues of Harsh Environments

Designing a piece of electronic hardware such that it works reliably from the get-go is a challenge, especially if it has to work outdoors or in extreme environments where temperature, humidity, vibration and radiation are the enemies of electronics.

Unfortunately, while a growing number of new electronic designs are destined to be used outdoors, the art of designing for harsh environments is not typically part of an engineering school's curriculum.  As a result, most engineers make the erroneous assumption that designing for a harsh environment is very much like designing for hospitable one but with a greater emphasis on testing and improving the design empirically, addressing the observed failure modes.  Although this approach is certainly along the recommended path, it should not be the only extra consideration; otherwise, tremendous failures could occur in deployment.

What is a Harsh Environment?

A quick definition of a harsh environment would be anywhere not "indoors," although this definition is incomplete.  Any condition of extremes relative to the human condition applies, so that includes temperature, humidity, atmosphere (including pressure), radiation and shock, whether indoors or not.  While one can easy to see that sitting outside at the south pole with minus 50 degrees winds blowing at 80% humidity easily meets the requirement, it isn't readily apparent to him that a handheld device that could be dropped five feet also meets the requirement.

A simple test is asking the question, "if this device were a human being (scaled up or down as appropriate) and subjected to the conditions of its environment -- the highest and lowest temperatures, the amount of pressure, or amount of shock, would it be expected to survive?" A cellphone operates in a harsh environment, indoors, because it can be dropped, and the amount of force it can hit a tile floor would be terminal to an appropriately scaled human being.  (It often is to the cellphone too depending on the height of the drop and the quality of its design.)

The Engineering Approach

Addressing the harsh environment begins before the design phase, in the R&D phase.  Knowing that the design includes a harsh environment, an engineer sets the research parameters and, later, the product specifications accordingly.  Paramount of concern to him are meeting the minimum and maximum storage and operating condition limits.

To maintain high-reliability for a new design, the engineering approach must:

• list the extreme storage and operating conditions
• set the design specifications accordingly
• select components that meet the specifications and reject others
• be mindful of circuit board physics, e.g. trace lengths, component mounting methods
• explore conformal coating and heating and cooling elements, as appropriate
• ensure that the fabrication drawing is consistent with the harsh environment design
• select appropriate mounting hardware, cabling and enclosure
• test the sensor inputs and software over the complete range of operating conditions

"Testing over the complete range of operating conditions" is easy to write, but could be very difficult in actual practice, owing to the exponential increase of possibilities over an increasing number of parameters and ranges.  We have found that Monte Carlo Simulation and linear programming are two very useful aids for analyzing the effects of different parameter combinations.

Post-Design & Post-Installation

No design for harsh environment is complete without a plan for follow-up during the implementation or deployment phase.  A well-designed circuit may allow additional or alternative components to allow for tweaking the final design after production.  For example, in one DataPlex design, a standard delay line circuit slowed down so much in cold temperature that an alternate delay circuit was automatically switched in, and the switch point was controlled by a variable resistance that could be easily changed in the field.

Software is Affected Too

It may not be obvious at all, but software is affected by harsh environments.  We are thinking less of the actual computing hardware that runs the software -- that is still the hardware related issues discussed above -- and more of the way the the software has been designed and tested in a warm, cozy lab.  Software that received sensor data such as values from analog to digital converters may find itself attempting to deal with extreme values that it did not encounter in the lab, and that usually leads to bugs and possible failure.

Taming Harshness

In this article, we explored the nature of harsh environments, what constitutes a quality engineering approach to design a piece of gear for those environments, and the importance of follow-up in order to make adjustments and preempt out-of-spec operation or catastrophic failures.

If you have a requirement for a harsh environment design, we invite you to consider the experience of DataPlex's staff with difficult environmental conditions and how our refined approach to R&D and engineering can mitigate certain risks for brand-new designs.  Please contact us to discuss your project.

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