Category: Measurement Uncertainty

Measurement Uncertainty

In the last Back-to-Basics blog, I covered Calibration versus Verification. As I continue to cover basic concepts for beginners, this blog will define measurement uncertainty and examine why it is important. What is Measurement Uncertainty? What measurement uncertainty is not is an error. It is imperative to understand the difference between these two terms as […]

Ultimate Guide for Understanding Uncertainties on a Morehouse ASTM E74 Calibration Certificate

Reporting the Expanded Uncertainty of the measurement is a requirement of ISO/IEC 17025 and likely always will be. However, if you look at several different certificates of calibration, their Expanded Uncertainty reported, contributors and reporting methods will vary greatly. Some include a blanket statement of uncertainty, while others simply ignore significant contributions required by several […]

Load cell calibration: What does “Traceable to NIST” really mean?

Load cells have various applications across several fields, from verifying the correct amount of stamping press force to testing rocket thrust stands. They are so common that almost everyone owns several in some shape or form, whether they realize it or not. Load cells are found in your car, bathroom scale, and almost any digital […]

How to Calculate the Resolution of a Load Cell

Per Section 4.14 of JCGM 200:2012, Resolution is the “smallest change in a quantity being measured that causes a perceptible change in the corresponding indication.” Over the years, this simple definition has become a topic of confusion amongst the metrology community. We are hoping to simplify how to calculate the resolution of the Unit Under […]

The Importance of Considering Reproducibility in the Measurement Process Uncertainty

Most people in the metrology community will agree that a calibration laboratory's ability to reproduce measurement results belongs in an uncertainty budget. Several Accreditation Bodies require reproducibility to be at least considered as part of a calibration laboratory's Calibration and Measurement Capability (CMC). The question on Reproducibility is, does it only apply to my equipment, […]

How to Calculate the Uncertainty of a Deadweight Primary Standard Machine

Figure 1: Morehouse 1,000 lbf automated deadweight machine Deadweight Force Machines or Primary Force Standard (CMCs as low as 0.001 % of applied force) – a deadweight force applied directly without intervening mechanisms such as levers, hydraulic multipliers, or the like, whose mass has been determined by comparison with reference standards traceable to the International […]

Load Cell Stability – How It Can Kill Your Uncertainty Budget

Load cells are a combination of metal, strain gauges, adhesive, and more.  Like humans, every measuring instrument is subject to aging.  Load cells age from mechanical stress or fatigue and overtime this ensures that there will be some instability in the system. This cannot be prevented, but it can be detected and corrected by setting […]

Guidance on Uncertainty Budgets for Force Measuring Devices Part 4. Calculating Uncertainty for Force Proving Instruments Calibrated to ISO 376

How to Calculate CMC for Devices Calibrated in Accordance with the ISO 376 Standard Introduction: All calibration laboratories accredited by A2LA are required to submit uncertainty calculations for the Calibration and Measurement Capability uncertainty claims included in the scope of accreditation. The assumptions made for the determination of the uncertainty budgets, if any, must be […]

Guidance on Uncertainty Budgets for Force Measuring Devices Part 3. Calculating Uncertainty for Force Measuring Devices for Measurement or Verification of Force Using Non-Linearity

Background: Currently, there are discrepancies regarding what is acceptable for a force calibration uncertainty budget.  A common mistake is to include too many lines from the load cell specification sheet. For example, if a load cell is used to make ascending measurements only, the effect of the uncertainty contribution for hysteresis should not be included […]

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