A.6. Thermal Tests
Thermals tests check to see whether the system can stand up to the temperature and humidity conditions it will experience in both operating and nonoperating modes. The testers place the system in a thermal chamber and run it through a series of temperature and humidity cycles as shown in Figure A.1. (Temperature is shown on the Y-axis in Centigrade scale, humidity is shown in percentages above the temperature graph, and durations of the dwells [flat lines] and transitions [sloped lines] in hours are show on the X-axis.) Often, active and heat-producing components such as CPUs and power supplies are instrumented with thermal sensors to check, over the course of the test, whether these components exceed their maximum operating temperatures. These tests are sometimes referred to as "four corners" tests, because graphs of maximum and minimum temperatures and humidity under operating and non-operating conditions produce a rectangle or parallelogram with four corners.
Another type of thermal test involves thermal shocks, where temperatures are changed rapidly. For example, consider the circuitry in a satellite, where ambient temperatures and humidity will go from the balmy launch pad to frigid and desiccated upper atmosphere and then outer space in a period of minutes.