This is Part 5 of a series delving into the intricacies of Mil-Std-810G.
810G covers temperature in 501.5 (High Temperature) and 502.5 (Low Temperature), both of which have been covered in previous blogs. In addition, 503.5 covers Temperature Shock. Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively. Methods 520.3 will be examined in future blogs. Method 503.5 covers 13 pages of Mil-Std-810G.
Use the temperature shock test of 503.5 to determine if materiel can withstand sudden changes in the temperature of the surrounding atmosphere without experiencing physical damage or deterioration in performance.
Temperature shock effects on computers and LCDs include:
- Shattering of plastic materials
- Binding of moving parts
- Drive failure
- Cracking from differential expansion (contraction) of dissimilar materials
- Integrated Circuit (IC) bond failure
- Cracking of LCD cover glass materials
- Delamination of the LCD display
- Electronic or mechanical failures due to rapid water or frost formation
Method 203.5 includes one test procedure with four variations – essentially in the length of the test and the shock itself. It employs constant temperature at each of the extreme shock conditions because, in many instances, the thermal shock itself so outweighs the other thermal effects that the test may be performed using two constant temperatures. This is particularly the case when more severe shocks are desired, such as for evaluation of safety or initial design, and when extreme values will be used.
The tests simulate what happens when you would move equipment from one environment rapidly into a much different environment. That can be from hot to cold or from cold to hot. For hot to cold, picture moving from a warm control room to outside in the artic where the temperature might be -30 deg C or lower. Cold to hot can be as simple as moving from a cool air conditioned room to outside in Texas in the middle of summer where the temperature and humidity are both very high causing immediate condensation on the cold equipment.
As with other 810G methodologies, there are no absolute values associated with the different tests. The tests are designed to simulate performance in an intended environment. Thus, determining the climatic conditions where the equipment is to be deployed or stored is the first step. Then the test high and low points can be determined. 503.5 actually recommends using a range of temperatures that reflects the anticipated in-service environment, rather than some arbitrary extreme range.
The four test variations are:
- Procedure I-A One-way shock(s) from constant extreme temperature. Appropriate for material that is likely to be exposed only rarely to thermal shock in one direction, perform at least one shock for each appropriate condition, i.e., low to high temperature, or vice-versa.
- Procedure I-B Single cycle shock from constant extreme temperature. For materiel that is likely to be exposed to only one thermal shock cycle (one in each direction), perform one shock for each appropriate condition, i.e., low-to-high temperature, and one in the opposite direction
- Procedure I-C Multi-cycle shocks from constant extreme temperature. Appropriate for systems that may be subjected to multiple temperature shock events. A minimum of three shocks is specified.
- Procedure I-D Shocks to or from controlled ambient temperature. Essentially the same as I-C except the shock is to ambient instead of extreme hot and cold temperatures.
The tests should consider the deployed state of the equipment. Perhaps the systems are mounted in transit cases which will slow the internal temperature changes. On the other hand, a transit case may maintain an internal temperature which will suddenly change when the covers are removed.
The tests involving ambient require a single chamber. Tests to extreme high and low temperatures require two chambers where the equipment is moved from one chamber to the other. There is test equipment providing two side by side chambers with a divider between them allowing the equipment to be shuttled between the different temperatures automatically.
Chassis Plans has demonstrated experience working with customers to design rugged systems appropriate for any environment including rapid temperature changes.