22. Calibration – Measurement Uncertainty Setup
For measurement uncertainty setup, the following process flow will be the general guideline to establish the model for respective calibration’s measurement uncertainty based on environment, master gauges and other variation factors.
Measurement Uncertainty Modelling Process Flow
Before measuring the uncertainty mode, the following things shall be considered
- Measurement Uncertainty Inputs:
- Mean and standard deviations from experimental data (type A) and expert evaluation (type B).
- Specification limits from gauge manufacturer
- Certified tolerance for acceptance
- Published datasheet
- Reasonable source for uncertainty.
- Measurement Uncertainty Inputs:
- Evaluate standard uncertainty from both type A and type B evaluation.
- After completing the listing of uncertainty sources, combine all possible sources with a mathematical formula to express the relation for uncertainty to measurement result. Type A and Type B standard uncertainty shall also be calculated before coming to the next step.
- After completing the listing of uncertainty sources, combine all possible sources with a mathematical formula to express the relation for uncertainty to measurement result. Type A and Type B standard uncertainty shall also be calculated before coming to the next step.
- Calculating Sensitive Coefficient:
- When y = f (x1 , x2 , x3)
- Then y’s uncertainty is actually contributed by uncertainties from x1 (u1), x2 (u2) and x3 (u3).
- if x1, x2, x3 is related, then
- uc = u1 + u2 + u3
- if x1, x2, x3 is independent completely, then
- uc² = u1² + u2² + u3²
- When calculating the uncertainty individually, refer to the mathematical and take partial derivative from y to calculate.
- u1 = δy / δx1
- u2 = δy / δx2
- u3 = δy / δx3
- When y = f (x1 , x2 , x3)
- Evaluate standard uncertainty from both type A and type B evaluation.
- Calculating Combined Standard Uncertainty and Extended Uncertainty:
The following process flow are the detailed example of how to setup the measurement uncertainty:
In conclusion, measurement uncertainty shall be the evaluation method for all calibration laboratories. There is no finite measurement from laboratories, uncertainties from gauges, environment, appraisers and other factors shall be considered before presenting calibration results.