Hi,
does anyone know which confidence intervall (95%?, 99%?) was used for old Fluke specifications as listed in the Fluke 5440B or 5450A manual?
And why did they say one has to add the uncertainty of the cal standard algebraically (old manuals)? In newer specifications (8508A for example) they RSS the cal standard uncertainty together with the measurement uncertainty.
Best
Philipp
Even if I don't know, I wouldn't bother to check. Surely it is 99%. No sane person would warrant a multi-function calibrator at 95%. Here is the reason (IMO good reading):
" ...
For a standard resistor, whose value is specified at a
95% confidence level to be within limits centered
about the nominal value for the resistor, we
could expect to have to re-trim 5% of the
standards before they could be shipped.
Specifying a complex instrument at the true 95%
confidence level for each point would be a
manufacturing disaster. For example, each
Fluke Model 5520A Multiproduct Calibrator is
tested at 552 points on the production line prior
to shipment. If each of the points has a 95%
probability of being found in tolerance, there
would only be a 0.95552(raised to the 552) = 0.00000000051%
chance of finding all the points within the
specification limits if the points are independent!
Even if we estimate 100 independent points
(about 2 per range for each function), we would
still have only a 0.95100(raised to the 100) = 0.6% chance of being
able to ship the product.
...
"
[Edit: Added two exponents lost in copy from pdf-file]
Source:
download.flukecal.com/pub/literature/msc04.pdf HAVING CONFIDENCE IN SPECIFICATIONS
David Deaver
Fluke Corporation
PO Box 9090
Everett, WA 98206
425-446-6434
David.Deaver@Fluke.com
-o-
Of course it is a bit different if not all points are independent, the box has ACAL or ... But the point is clear: The more output/measurement types/ranges, the more likely it is that one or more test points break the interval. So you want a "wide" interval to at least be sure most of your boxes are within spec for the calibration period.