Failure Rate

In the "military" world of specifications, a failure rate is the degree of life expectancy of a component.

The "Failure Rate" is designated by an alphabetic letter (M, P, R & S) appearing somewhere in the military part number, (usually at the end of the part number).

       M    is the lowest rating (least reliable)

       P    is a bit better

       R    is approaching the highest

       S    is highest (most reliable)

As can be seen, the failure rates are in alphabetical order.  As we run through the alphabet, note the higher the letter, the better the failure rate.

Each succeeding letter is ten times better than the preceding letter.

   M  level means 1 out of          100       is expected to fail after 1,000 hours testing

   P   level means 1 out of       1,000       is expected to fail after 1,000 hours testing

   R   level means 1 out of     10,000       is expected to fail after 1,000 hours testing

   S   level means 1 out of   100,000       is expected to fail after 1,000 hours testing

Failure Rate may also be expressed in percent

M - 1.0% at 1,000 hours (1 out of 100 is expected to fail)

P - 0.1% at 1,000 hours (1 out of 1,000 is expected to fail)

R - 0.0l% at 1,000 hours (1 out of 10,000 is expected to fail)

S - 0.001% at 1,000 hours (1 out of 100,000 is expected to fail)

It is obvious that the better the failure rate, the higher the price.

Again, if a spec calls for an M failure rate and none is available at the time, a better failure rate (P, R, or S) may usually be substituted, BUT NOT THE REVERSE. (If the spec calls for an R failure rate, an M or P CANNOT be used.  But an S can be used)