In the last Back-to-Basics blog, I covered Compression and Tension Force Calibration. As I continue to cover basic concepts for beginners, this blog will cover the differences between calibration and verification. What is a Calibration? Let me start by stating that there are several definitions of calibration across multiple standards. My favorite definitions are below. […]
Guide for Understanding Uncertainties on a Morehouse ASTM E74 Calibration Certificate Reporting the Expanded Uncertainty on an ASTM E74 Calibration Certificate 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 […]
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 […]
Specifying a Tolerance, the Difference Between Percentage of Indicated Value vs % of Full-Scale Output - Intro In looking at various equipment, it seems the force equipment in the test and measurement industry specifically specifies tolerances as a percent of full scale. When determining accuracy or tolerance, several crane scales, tension links, and hand-held force […]
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 in the metrology community. We are hoping to simplify […]
The Importance of Considering Reproducibility in the Measurement Process Uncertainty - Intro 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). […]
Why a 4:1 TUR is Not Enough: The Importance of Analyzing the Probability of False Accept Risk Figure 1 Graph Showing Method 5 Acceptance Limits Several organizations and publications reference the use of a 4:1 Test Uncertainty Ratio (TUR). Some standards even reference a TUR requirement greater than or equal to 4:1. The question to […]
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 […]
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 over time this ensures that there will be some instability in the system. Some […]
Cosine Error Should be Considered in any Torque Measurement Process ISO/IEC 17025 When Calculating Torque Measurement Error Cosine Error should be considered A ‘vector’ is known as a quantity that is defined by its size and direction. Every time the effect of a known force is evaluated on a static or dynamic system, all applied, […]
Guidance on Uncertainty Budgets for Force Measuring Devices Part 4. Calculating Uncertainty for ISO 376 Uncertainty Analysis ISO 376 Uncertainty Analysis Introduction: All calibration laboratories accredited to ISO/IEC 17025 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 […]
Guidance on Uncertainty Budgets for Force Measuring Devices Part 3. Calculating Uncertainty for Force Measuring Devices for Measurement or Calculating Uncertainty for Force Measuring Devices 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 […]
