{"id":1420,"date":"2018-05-23T11:34:29","date_gmt":"2018-05-23T10:34:29","guid":{"rendered":"https:\/\/dmunkes.de\/WP\/?p=1420"},"modified":"2018-05-23T15:36:29","modified_gmt":"2018-05-23T14:36:29","slug":"calculation-of-measurement-uncertancy","status":"publish","type":"post","link":"https:\/\/dmunkes.de\/WP\/calculation-of-measurement-uncertancy\/?lang=en","title":{"rendered":"Calculation of measurement uncertancy"},"content":{"rendered":"
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Calculation of measurement uncertancy<\/h1><\/h1><\/div>
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Ing. Buero Dieter Munkes News   \u2022   June 2, 2016<\/p>\n<\/div>

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D<\/span>uring a project to gain accreditation (EN17025) for a laboratory i need to calculate the uncertancy of a measurement system.<\/p>\n

I found that there are 2 ways to do it:<\/p>\n

A) Get a lot off samples and do some statistics.<\/p>\n

B) Get all uncertancy of influencing parameters and calculate a common result.<\/p>\n

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First create a map of influences. Ishikawa<\/a> diagram or something like a mindmap.<\/p>\n

Set in all parameters inclusive your reference. (Temperature, light, humidity…..)<\/p>\n

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Goto B)<\/p>\n

Now i see that i don\u00b4t find exact parameters for the uncertancy parameters. You may assume them. But i don\u00b4t like this.<\/p>\n

I found that my amplifier has 18ppm\/K drift, ok I know the range. But there are drift from DMS, thermovoltages at contacts….<\/p>\n

I got crazy with endless unknowns.<\/p>\n

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The way i found was: Take what you get on B) and do the remaining with A)<\/p>\n

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I my example it is a machine for testing lifetime of tooth implants. It\u00b4s a motor generating force down on an implant.<\/p>\n

In series to this is a DMS Force Bridge. For regulation the force. See the first picture.<\/p>\n

Now I put additional a reference sensor in series.<\/p>\n

The uncertancy and calibration data are known by a Dakks calibration sheet.<\/p>\n

I set the system to press with 100N down.<\/p>\n

Now i put both sensor data into a histogramm seen on the second picture.<\/p>\n

Now i calculate average and standardderivation from my internal sensor.<\/p>\n

I calculate average from my reference.<\/p>\n

I have the uncertancy from the calibrationsheet of the reference at 100N<\/p>\n

So the common uncertancy is =sqrt(  (ref uncertancy)\u00b2 +(AverageSensor-Averageref)\u00b2+(derivation internal sensor)\u00b2)<\/p>\n

As both are gauss shaped i can expand the range to cover 99% of samples by a factor around 2.7<\/p>\n

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With this i can say that the system get 99% of samples within +-0,6N at 100N force.<\/p>\n

To cover all influences you need to be sure that this influence ocure.<\/p>\n

I let the system sample overnight to get a full daily temperature cycle.<\/p>\n

 <\/p>\n

Dieter Munkes<\/p>\n

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During a project to gain accreditation (EN17025) for a laboratory i need to calculate the uncertancy of a measurement system.<\/p>\n","protected":false},"author":1,"featured_media":1561,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1420","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t