KEVOS® MAKEOS · Quality
Instrument Calibration Check (Errors, Accuracy Class, Interpolated Correction)
From my calibration readings against a reference, is this gauge within its accuracy class, and what is the corrected value of a reading taken in service?
Calibration check of a pressure gauge, thermometer or other instrument at five points across its range: the error at each point and as a percentage of span against the accuracy class, the worst point, and the corrected (true) value of an in-service reading by linear interpolation between the two calibration points that bracket it (as the linear interpolation tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Range low end | Lowest value of the instrument range. | |
| Range high end | Highest value of the instrument range. | |
| Accuracy class (% of span) | % | Permitted error as a percentage of span. |
| Reference values and readings | ||
| Reference 1 | Reference (true) value at calibration point 1. | |
| Reading 1 | Instrument reading at point 1. | |
| Reference 2 | Reference value at point 2. | |
| Reading 2 | Reading at point 2. | |
| Reference 3 | Reference value at point 3. | |
| Reading 3 | Reading at point 3. | |
| Reference 4 | Reference value at point 4. | |
| Reading 4 | Reading at point 4. | |
| Reference 5 | Reference value at point 5. | |
| Reading 5 | Reading at point 5. | |
| In service | ||
| Reading taken in service | A reading taken in use that you want corrected. | |
Method and formulas
- Error = reading − reference; % of span = error ÷ (high − low) × 100.
- Within class if every |error| ≤ class × span ÷ 100.
- Corrected value: find the true value for the reading by linear interpolation between the bracketing calibration points (as the linear interpolation tool, finding x for a given y).
- Example: the worst error is 0.4% of span against 1%; a reading of 6 corresponds to 5.9677.
Limitations
- Rising readings only; hysteresis needs falling readings as well.
- Readings must increase with the reference for interpolation.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Record and judge a gauge calibration
- Correct readings from a gauge with a known error
- Decide whether to adjust or replace an instrument
Who it is for
- Instrument technicians
- Quality technicians
- Maintenance planners
What you get
- Error at each point and as % of span
- Worst error against the class
- Corrected value of the service reading
Interpreting the result
- If the errors are all one way, a zero or span adjustment usually brings the instrument back into class.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 121, 709–735. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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