Desert Humvee High TemperatureThis is Part 3 of a series delving into the intricacies of Mil-Std-810G.   810G covers temperature in 501.5 (High Temperature), 502.5 (Low Temperature) and 503.5 (Temperature Shock). Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 502.5 and 520.3 will be examined in future blogs.  Method 501.5 covers 12 pages of Mil-Std-810G.   High temperature effects on computers and LCDs include:

  • Exceeding the published high temperature limits for the components such as processors and chip sets causing damage
  • Exceeding operating limits on components inside the power supply such as transformers
  • Intermittent operation as the processors automatically slows down in a protective mode
  • Intermittent operation as power supply modules shut down in a protective mode
  • Reduced component life
  • The screen on LCDs can turn black at elevated temperatures
  • Glue creep or failure

  With a few exceptions, the Methods for temperature do not place absolute limits on the devices to be tested.  There is no specification delineating a maximum temperature of 50 deg C, for example.  Thus, a manufacturer stating their device has been tested per Mil-Std-810G for operation between 0 and 50 deg C has written their own test method.   The limitations for 501.5 specify the Method is appropriate for short term (months as opposed to years), even distributions of heat throughout the test item.  For the purposes of testing, time is allowed for the test item to stabilize in temperature.   Within 501.5 are three procedures:

  • Procedure I – Storage
  • Procedure II – Operation
  • Procedure III – Tactical Standby to Operational

  In general, companies will publish both storage and operating temperature specifications but rarely, if ever, tactical standby to operational for computers or LCDs. The term “tactical” is used to identify materiel that is not in storage, but is in a standby operational configuration, and as such is subjected to extended non-operational conditions immediately prior to operation.   Humidity is usually not a factor in high temperature testing.  However, climatic conditions should be considered. Identify the appropriate climatic conditions for the geographic areas in which the materiel will be operated and stored. There are two climatic categories where high temperatures are typically encountered: Hot Dry and Basic Hot.   Basic Hot is applicable to many parts of the world, extending outward from the hot dry category of the southwestern United States, northwestern Mexico, central and western Australia, Saharan Africa, South America, southern Spain, and southwest and south central Asia.  The ambient air temperature is specified at 30-43 deg C (86 to 110 deg F) and induced at 30-63 deg C (86 to 145 deg F).  Induced temperature is a result of heat loading from sun exposure, for example.  Humidity ranges from 5% at 63 deg C (induced) to 44% at 31 deg C (induced).    As can be seen, the target area is hot and dry!   Hot Dry covers Southwest and south central Asia, southwestern United States, Saharan Africa, central and western Australia, and northwestern Mexico.  The ambient temperature is specified at 32 to 49 deg C (90 to 120 deg F) and induced at 33 to 71 deg C (91 to 160 deg F).  Humidity ranges from 1% to 7%.  Really hot and really dry.   Cyclic temperature exposure should be considered.  Generally, 7 cycles is sufficient for Procedure I – Storage and 3 cycles for Procedure II – Operation.   A situation to be aware of and which needs careful attention and control is run-away chamber temperature during testing.  A high power computer may generate more heat than the chamber can cool resulting in unanticipated high temperatures beyond the scope of the testing.   Chassis Plans rugged military grade computers are designed to function in high temperature environments for high power systems.  Included are multiple high velocity fans, optimized air flow paths, and Chassis Plans’ proprietary SysCool®  Intelligent Fan Controller.