Date: Fri, 8 Oct 1999 14:44:45 -0700
From: Jan Johansen <[email protected]>
To: Greg Gogates <[email protected]>
Subject: Uncertainty and Proficiency Testing
Dear ISO-25er’s,
We recently received the results of a proficiency test back. The test was for a 5 * digit multimeter. This test was accomplished NAPT(National Association for Proficiency Testing). They handled everything in a professional manner We passed with flying colors. However after reviewing the data from all other participants, I have some observations that I think bears some discussion.
In order to make this as easy as possible I will only deal with one data point, the 10VDC on the 20VDC range. I am going to list the values from the labs that were within +/- .0001 VDC of agreeing with my reading and their stated uncertainties.
Lab Value Uncert
1 9.9985 9e-005
2 9.9985 .00098
3 9.9984 .0018
4 9.9984 .00043
5 9.9983 .0001
6 9.9984 .00013
7 9.9983 .0009
8 9.9985 .0006
9 9.9983 .0001
10 9.9984 .0003
Reported Nominal Value for the test was 9.99839 +/- 8.8 e-005
As you can see the results are quite varied. Here are the observations.
1. The measuring instrument is a 5 * DMM. The best resolution on the 20 VDC range is .0001. How can the nominal value be reported to .00001? It is my contention that a value should never be reported past the maximum resolution of the readout.
2. The definition of uncertainty say’s ‘ … the result of a measurement , that characterizes that characterizes the dispersion of the values that could reasonable be attributed to the measurand.’
3. The device providing the measurand is the 5 * DMM. The one year specification for the DMM is +/- .0015% Rdg + 3 counts or +/- 0.0018 VDC.
4. It doesn’t matter who’s calibrator you use (Fluke, Wavetek), the majority of the uncertainty is in the DMM since it is the unit providing the measurand. Since a specification is a valid Type B uncertainty, it appears that most of the labs did not include it and only reported the uncertainty of their standards, NOT the measurement uncertainty.
5. We could have connected the DMM to our 10 V in-house reference, but it would not have improved our uncertainty by much, because of what is providing the measurement.
I would like to know if I am all wet or am I right. I am uncertain that even this forum will have consensus but it seems to be a good place to air this kind of information.
Thank you
Jan Johansen
JJ Electronics
[email protected]
From: Jan Johansen <[email protected]>
To: Greg Gogates <[email protected]>
Subject: Uncertainty and Proficiency Testing
Dear ISO-25er’s,
We recently received the results of a proficiency test back. The test was for a 5 * digit multimeter. This test was accomplished NAPT(National Association for Proficiency Testing). They handled everything in a professional manner We passed with flying colors. However after reviewing the data from all other participants, I have some observations that I think bears some discussion.
In order to make this as easy as possible I will only deal with one data point, the 10VDC on the 20VDC range. I am going to list the values from the labs that were within +/- .0001 VDC of agreeing with my reading and their stated uncertainties.
Lab Value Uncert
1 9.9985 9e-005
2 9.9985 .00098
3 9.9984 .0018
4 9.9984 .00043
5 9.9983 .0001
6 9.9984 .00013
7 9.9983 .0009
8 9.9985 .0006
9 9.9983 .0001
10 9.9984 .0003
Reported Nominal Value for the test was 9.99839 +/- 8.8 e-005
As you can see the results are quite varied. Here are the observations.
1. The measuring instrument is a 5 * DMM. The best resolution on the 20 VDC range is .0001. How can the nominal value be reported to .00001? It is my contention that a value should never be reported past the maximum resolution of the readout.
2. The definition of uncertainty say’s ‘ … the result of a measurement , that characterizes that characterizes the dispersion of the values that could reasonable be attributed to the measurand.’
3. The device providing the measurand is the 5 * DMM. The one year specification for the DMM is +/- .0015% Rdg + 3 counts or +/- 0.0018 VDC.
4. It doesn’t matter who’s calibrator you use (Fluke, Wavetek), the majority of the uncertainty is in the DMM since it is the unit providing the measurand. Since a specification is a valid Type B uncertainty, it appears that most of the labs did not include it and only reported the uncertainty of their standards, NOT the measurement uncertainty.
5. We could have connected the DMM to our 10 V in-house reference, but it would not have improved our uncertainty by much, because of what is providing the measurement.
I would like to know if I am all wet or am I right. I am uncertain that even this forum will have consensus but it seems to be a good place to air this kind of information.
Thank you
Jan Johansen
JJ Electronics
[email protected]