Downloaded from https://www.everyspec.com AMCP 706.1M fects such as nonreversibility, interactions, is preferable. The final choice of an ap- and aging must be accounted for. proach depends on what is to be accom- plished with the test and is influenced Elaborate environmental test facilities are strongly by factors such as time, cost, skills, , not always required. Simply heating Indi- and instrumentation. vidual circuit components near a soldering iron may in some cases be more informs- Combined environment testing has two tive than testing the entire circuit or assembly significant advantages over single environ- in an oven. And, In the absence of certain ment testing:
capabilities, an improvised test may be better than none at all. For example, me1•.d'al 1. The ability to Investigate the combined shock may be simulated by dropping the effects of multiple conditions; i.e., combined Items from a priscribed height, testing, in most cases, more closely approxi- mates the real environment. When facilities do not exist for generating combined environments, combined environ- 2. Several conditions usually can be ment effects must be simulated by using applied simultaneou y in a shorter time than single environments In sequence. If the in sequence, due to savings In set-up time.
severity levels of the environments are not Therefore, combined testing often saves set deliberately to damage the equipment, money. The major disadvantage of this ap- the order of application is determined by proach is that the initial equipment cost for whatever is most convenient, When tests combined testing is higher. cause damage, the order of environments must be considered carefully, First, apply In qualification and acceptance testing, those conditions least likely to damage the combined environments are preferable, The specimen.
For the mechanical part, humidity increased confidence derived from the know- and salt spray tests thus logically would be ledge that synergistic effects are accounted applied, before vibration or a mechanical for frequently permits the use of smaller load test. An electronic part usually would safety factors. be tested by applying vibration before high temperature. Such test sequencing allows When testing to relate cause and effect, the maximum amount of information to be combined environment testing is used as an obtained before damage occurs, extension of single environment testing.
During the development phase, initial testing Ordering of environments for items com- usually is applied to determine the effects posed of both mechanical and electrical parts of single environments. Combined environ. , is not as clear-cut. The same basic criterion rnents are employed after single environment still applies, and the ability to repair the Item effects have been determined and conbined can greatly influence the ordering, effects become of interest.
Single environ- mcnt testing also may be preferable in long If both single and combined environmental duration tests due to the impractimality of conditions can be generated, it does not committing combined environmental test necessarily follow that the combined testing facilities fot long periods of time. Ile-; 'f." .