# Measurement Uncertainty Budget (MU) of for Ultrasonic Thickness gauge

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#### kj1027

My company is getting ready for ISO17025 accreditation as a calibration lab. We will be calibrating Ultrasonic thickness gauges as well as ultrasonic flaw detectors. Myself and another person are tasked with handling this process and I am more than confused with the measurement uncertainty portion of this.

Can anyone help with what is needed for an uncertainty budget for a digital ultrasonic thickness gauge?

I believe that the uncertainty of the cal blocks themselves, as well as the repeatability of the tech taking readings and the gauge resolution are the factors that I need to calculate individual and combined to come up with an uncertainty statement.

Can anyone help guide me with where to start and formulas or examples on how to actually do this?

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#### dwperron

Trusted Information Resource
The usual suspects on a budget like this would include at least the following.

Type B components that will need to be normalized. Use rectangular distribution unless you know otherwise:
Tolerance of the cal blocks
Calibration uncertainty of the cal blocks
Accuracy of the digital thickness gauge
Resolution of the digital thickness gauge
Any temperature or humidity component that might affect the cal blocks

Reproducibility (all techs cleared to perform this test, multiple readings)

Help can be found in many places.
The NRC of Canada offers an excellent tutorial:
An introduction to expressing uncertainty in measurement - National Research Council Canada

The NPL in England has a fine book aimed at beginners:
http://publications.npl.co.uk/npl_web/pdf/mgpg11.pdf

This document from NIST is a good start and not overly technical:
https://www.nist.gov/sites/default/...sop-29-assignment-of-uncertainty-20180131.pdf

That should get you started. Remember, this is an estimate of measurement uncertainty. Find out what the uncertainty factors are and include the ones that make a difference.

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