Calculators and decision tools
Calibration intervals, pass or fail decisions with guard bands, and uncertainty budgets. Try them with your own numbers.
Budget, decision, interval
Try them with your own numbers. Everything runs in your browser, and nothing you type is sent anywhere.
| Source | Value ± | Distribution | c | u (share) | Remove |
|---|
Value is the stated uncertainty for Normal (k = 2), the standard deviation for Normal (k = 1), and the half-width ± a for Rectangular, Triangular and U-shaped. c is the sensitivity coefficient, usually 1.
- Combined standard uncertainty
- Expanded uncertainty U
- Largest contributor
Example: a Pt100 checked at 100 °C. A class A Pt100 is allowed ±(0.15 + 0.002|t|), which is ±0.35 °C at 100 °C. U is assumed to be at k = 2 (about 95 %). A guard band of 1 × U is the simple default, and 0 means no guard band.
- Deviation from nominal
- Accept if reading is within
- Reject if reading is outside
- Tolerance to uncertainty (T / U)
- Chance the true value is within tolerance
The chance figure assumes a normal distribution with no prior knowledge about the item (see JCGM 106). The undetermined zones are the same ones shown in the section above, here on both sides of the nominal value.
- Drift rate
- Fit quality (R²)
- Calibrations used
Fits a straight line to the absolute as-found errors and projects when it reaches the decision limit. It is a screening estimate, not a replacement for your lab's interval policy (for example ILAC G24 methods) or engineering judgment. Use a period for decimals.
How long can an instrument go?
Five past calibrations of a type K thermocouple used near 900 °C show a steady drift. Set how much error you can tolerate and the chart works out when the next calibration is really due, with a safety margin built in.
Suggested interval, with a 20% guard band under the limit.
Example data, invented to show the idea. A class 2 type K thermocouple at 900 °C is allowed about ±6.75 °C.
Pass, fail, or undetermined?
A temperature reading is never an exact number. When its uncertainty crosses a tolerance limit, a plain pass or fail can be wrong. A guard band keeps you from accepting, or rejecting, something you can't be sure about.
- Pass
- The value plus U is still inside the limit. Accept.
- Undetermined, pass side
- The value is inside the limit, but the value plus U goes over. A guard band of U does not accept it.
- Undetermined, fail side
- The value is over the limit, but the value minus U is back inside. It is not rejected outright.
- Fail
- The value minus U is already over the limit. Reject.
Example: a thermometer check where the error limit is 1.0 °C, with a guard band equal to U, the simplest rule. Real decision rules come from your standard or contract, and the wording varies, for example conditional pass and conditional fail. Example values.