- #1
mwcmwc
- 2
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Hi Everyone,
Brand new user here. Decided I want to say hi by posting a question.
So an interesting discussion popped up at work today...regarding measurement accuracy.
Test instruments such as DMM or oscope will have accuracy spec usually in the form of:
X=(reading)*(somepercentage)+offset
where X is the accuracy error calculated for that reading. As X increases, accuracy decreases.
The discussion came about when we decided to use these error calculations for a series of measurements with defined tolerances/limits that would be used to do a pass/fail test for a group of boards. There are engineers that are questioning the test instruments ability to do these measurements, so it came down to these two options:
1.) Use nominal value as the reading variable. Argument for is if design is solid, the board should always have nominal.
2.) Use nominal + high tolerance as the reading variable. Essentially, this will use the high limit as the reading value, thus presenting a more conservative calculation with higher instrument accuracy. Argument for this is, play it safe. We do not want to have bad design slip out on to the field.
To me it more or less boils down to a yield vs. design. Doing 1 will pass more boards than 2, yet 2 is the more conservative approach.
Finally coming to me question, what would you do and why? Personally, I'd pick 2, just seems like the right engineering thing to do.
Regards,
mwc
Brand new user here. Decided I want to say hi by posting a question.
So an interesting discussion popped up at work today...regarding measurement accuracy.
Test instruments such as DMM or oscope will have accuracy spec usually in the form of:
X=(reading)*(somepercentage)+offset
where X is the accuracy error calculated for that reading. As X increases, accuracy decreases.
The discussion came about when we decided to use these error calculations for a series of measurements with defined tolerances/limits that would be used to do a pass/fail test for a group of boards. There are engineers that are questioning the test instruments ability to do these measurements, so it came down to these two options:
1.) Use nominal value as the reading variable. Argument for is if design is solid, the board should always have nominal.
2.) Use nominal + high tolerance as the reading variable. Essentially, this will use the high limit as the reading value, thus presenting a more conservative calculation with higher instrument accuracy. Argument for this is, play it safe. We do not want to have bad design slip out on to the field.
To me it more or less boils down to a yield vs. design. Doing 1 will pass more boards than 2, yet 2 is the more conservative approach.
Finally coming to me question, what would you do and why? Personally, I'd pick 2, just seems like the right engineering thing to do.
Regards,
mwc