Limiting deviation

How should instrumentsl errors be specified?

  1. Maximum error

    2 vote(s)
    100.0%
  2. Standard deviations

    0 vote(s)
    0.0%
  3. Some combination of the above

    0 vote(s)
    0.0%
  1. Long time no post...

    I am very much disturbed after my research of measurement errors and corresponding norms, because I find so few results. There are mainly two ways to specify errors of measurement instruments. Standard deviation with its siblings and maximum error.

    I am a great fan of the old German tradition to specify maximum errors only for measurement instruments. Specifying that some piece of equipment will have an error below x for all practical purposes when operated under the specified conditions is much easier to do quantitatively than statistical deviations and errors that depend on the measurement value and environmental fluctuations. Because in most cases the errors are far from being Gaussian. So you just add add all relevant maximum errors and don't care about independence.

    But I couldn't find any norms about it. The relevant German ones don't have corresponding ISO norms. I couldn't even find a symbol for it. The German symbol is G for "Grenze" or "Fehlergrenze". I only get "uncertainties" and a number of k sigmas.

    So after so much complaining my questions:
    - Is there an international norm regarding the declaration of maximum errors.
    - What symbol do you use for "maximum error" or "limiting deviation"
    - If you have a better name for this and what do you call it? What is it called in your Physics books?
     
  2. jcsd
  3. Mech_Engineer

    Mech_Engineer 2,299
    Science Advisor
    Gold Member

    Generally speaking I would say "it depends." I've usually seen the "maximum accuracy error" specification as you've mentioned, usually defined in a +/- percentage value (example here: Honeywell Model 31 Force Transducer).

    When qualifying the performance of a complex instrument or process, it might be prudent to use more advanced statistical methods e.g. Measurement Systems Analysis (MSA): https://www.moresteam.com/toolbox/measurement-system-analysis.cfm

    Gold standard MSA books: https://www.aiag.org/source/Orders/index.cfm?search=MSA-4
     
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