In the door or out in the field
Let's say I ship 1M items per year to an automotive assembly line. Since I 100% test the electronics, I get 5 rejects from the line per year at plug in, turn on(5 PPM, yeah?)
So, the vehicles go out and get beat up by the end user. Over the two year warranty period, I get 5,000 warranty claims for replacement. (5,000 PPM, right?). But wait, during the 2 year period, I've fielded 2M parts, so 2,500PPM, ok? Maybe not.
I tend to view PPM as an assembly line reject measure. Fielded returns (warranty) fall into a reliability calculation for me, mean time to failure or mean time between failures, failure rate, etc. Obviously, line side rejects will be much lower than defective product in the field after 2 years of wear and tear.
Where do I measure PPM?
Let's say I ship 1M items per year to an automotive assembly line. Since I 100% test the electronics, I get 5 rejects from the line per year at plug in, turn on(5 PPM, yeah?)
So, the vehicles go out and get beat up by the end user. Over the two year warranty period, I get 5,000 warranty claims for replacement. (5,000 PPM, right?). But wait, during the 2 year period, I've fielded 2M parts, so 2,500PPM, ok? Maybe not.
I tend to view PPM as an assembly line reject measure. Fielded returns (warranty) fall into a reliability calculation for me, mean time to failure or mean time between failures, failure rate, etc. Obviously, line side rejects will be much lower than defective product in the field after 2 years of wear and tear.
Where do I measure PPM?