Is it correct to combining all sources of uncertainty of the calibration of equipments and glassware in the budget uncertainty of a test method for wastewater, for example, Chemical Oxygen Demand?
Dear Maria Del Carmen Espinosa Lloréns
IMHO:
When You use gauges You should put into your budget just final standard uncertainty. With equipment You have two ways:
1. Put to budget only MPE (Maximum Permissible Error) or
2. Put sources in the case when You are expert.
Regards
Dear Marcin:
Many thanks!
I referred to equipment and glassware used to measure in the test methods.
Both items have been calibrated in the Cuban National Metrology Institute whose certificates uncertainty is issued.
My question is associated whether it is appropriate to consider in the diagram cause-effect (or Ishikawa), calibration as a primary source (combining all secondary sources of this), and not as secondary sources separately from each other sources uncertainty of the test.
Could you comment about this?
Thanks in advance
Ma. del C.
Dear Maria,
yes, I think you should take into account all considered uncertainty source. if you have your Ishikawa diagram, you can use all the factors into uncertainty budget. You can start to decide for each factors whether they are type A and type B uncertainty.
Usually, the calibration uncertainty is not the most contributed uncertainty source. Commonly the most contributors are e.g. procedure, instrument error, environment. But, yes we should take into account calibration uncertainty.
After all, according to GUM, all uncertainty sources have to sum of squared to get the combined uncertainty.
As per ISO GUM, first you must write down your measurement model. This measurement model shall include what sources of uncertainty influence your measurement result, and how they influence the meausurement result. So it's not just a matter of taking squared sum of everything, rather you really need to consider how each source of uncertainty actually affects the measurement.
Conference Paper Uncertainty in 3D Micro Measurement with Focus Variation Microscopy
Dear Maria,
in addition to what others have said, I'd like to stress the remark made by Jean-Luc to consider the whole measurement process. Especially with wastewater the handling of the sample (e.g. storage conditions, manner of transportation (if any)) may be a source of error,therefor it is vital to have, and follow, a clear protocol encompassing sample collection until final analysis.
best regards
Francois
Dear Maria,
Based on GUM, all sources of uncertainty must be combined using the partial derivatives of the mathematical model of your measurand. The uncertainty sources from the calibration of equipments and glassware must be negligible when compared to other sources. However, if you have a large temperature variation in your laboratory during the test, you must consider the uncertainty of uncertainty: calibration certificate and expansion of the liquid due to the temperature.
Best regards,
Elcio Oliveira
Thank you very much to all colleagues who sent a tip or comment
Ma. del C.
Correctly. It will nazyvatsya method is Precision. (ISO/IEC 5725)
Dear colleagues:
First of all, many thanks for your valuable comments.
I would like to share with you the uncertainty documentation related to the test methods which our lab are using in wastewater characterization, in order you could understand with precision, the specific question I had published. But in this moment, I have all documents in Spanish. Who can understand my native language in order to publish the document written in that way?
Waiting for your answer
Ma. del C.
Dear Maria,
I am from Brazil. Portuguese and Spanish are next. (Estoy estudiando Español.)
Best regards
Gracias por su respuesta.
¿Me podría dar una dirección de correo electrónico para enviarle el documento por esa vía?
Gracias de antemano.
Ma. del C.
Estimada Maria,
Mi correo electrónico és: [email protected]
Muchas gracias.
Muchas gracias.
Paso a enviarle el documento y el comentario específico de lo que necesitaba consejo.
Un saludo desde Cuba
Yes. There is such a thing as "traceability". That is, the result is related to the standard (true value) through the documented unbroken chain of calibrations, each contributing to the measurement uncertainty.
- Badges
- Science topic
- Similar topics
- Solid State Physics
- Devices