Uncertainty of Measurement for Sampling

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Hello Bosses, I would like to confirm this with your comment. I get have a few years experience in plant...

Please to read the entire article.

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Posted by Ebenezer Ofori (Discussions: 1, Comments: 4)
Replied on March 4, 2018 12:00 am
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Ebenezer:

It is not so much that it must be, but some consideration of the contribution to the overall uncertainty of the measurement from sampling should be included.

Remember that in some types of testing, the uncertainty from sampling will be the single biggest contributor to the overall uncertainty of the measurement - caused by lack of homogeneity of the matrix and other things.

If I test 10 telephones for FCC Part 15, how can I determine the uncertainty associated with sampling? If I test for VOCs in soil using some mass spectrophotometric procedure, how can I determine the uncertainty associated with sampling? Two very different testing sciences and perhaps two very different considerations of sampling error.

If you conducting physical testing, it will be somewhat easier, but less straightforward than chemistry testing. Here are two aids - See Part 2 below:
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Posted by Ned Gravel (Discussions: 0, Comments: 70)
Replied on March 3, 2018 7:00 pm
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Part 2:

First, if you are doing chemistry samples, run two aliquots and subtract the variance (square of standard uncertainty) of one from the other and you will be able to identify the contribution of the standard deviation (standard uncertainty) from the sampling of the two. [A real chemist should tell you if this is OK - I am not a chemist].

Second, if you are doing electrical or physical tests, look at all the QC data you have built up over time on that type of testing and see where similar quantitative results, from similar equipments showed two different uncertainties. Again, your difference in variance will give you an idea of the contribution of sampling uncertainty. [A competent electrical and physical testing technician should be able to tell you if this is OK - it has been too long for me out of lab].

These are not perfect approaches and there may be many more, but the 2017 version of the standard does not allow us to ignore uncertainty from sampling.

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Posted by Ned Gravel (Discussions: 0, Comments: 70)
Replied on March 3, 2018 7:00 pm
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In many times Uc on sampling can be 80% of Uc
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Posted by Patrick Reposeur (Discussions: 1, Comments: 15)
Replied on March 3, 2018 7:00 pm
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An estimate can be made from scatter of test results form 3 or more samples
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Posted by Mahesh Gupta (Discussions: 0, Comments: 15)
Replied on March 6, 2018 7:00 pm
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Uncertainity in sampling also plays vital role in measurement uncertainity. In case of heterogenous of material, heterogenous test contibution either interms of standard deviation or error in sampling also shall be included in Type B of measurement unceratinity contributions.
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Posted by mariappan A.Mariappan (Discussions: 0, Comments: 2)
Replied on March 6, 2018 7:00 pm
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EURACHEM has published a good guide on Measurement uncertainty
arising from sampling; see http://www.rsc.org/images/EURACHEM1_tcm18-102815.pdf
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Posted by Martti Heinonen (Discussions: 0, Comments: 1)
Replied on March 6, 2018 7:00 pm
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Martti Heinonen, is this guidance document or is it required per any clause, sub-clause of ISO/ IEC 17025:2005. I do not think there is any specific requirement of the standard regarding Uncertainty of Measurement for Sampling.
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Posted by Muhammad Aman Mirza (Discussions: 0, Comments: 3)
Replied on March 6, 2018 7:00 pm
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Are you asking with reference to ISO/ IEC 17025? because this forum is related to this specific standard and I am surprised to read the responses.
In fact sampling is a very important part of the standard and some organizations take exception of Clause 5.7 and there is no harm if you take this benefit. If you are interested in implementing the standard in your organization, I would suggest you do calculate Uncertainty of Measurement in specific tests or Calibration. Sampling can be part of the overall uncertainty. this could include your type A uncertainty (statistics) and include your Type B uncertainties (all other). for that purpose you can take assistance from this forum or from other forums.
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Posted by Muhammad Aman Mirza (Discussions: 0, Comments: 3)
Replied on March 7, 2018 7:00 pm
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