Calibration Troubleshooting Use measurement history, independent checks, process evidence, and calibration data to separate instrument problems from process drift. Contents Is the Instrument Failing, or Is the Manufacturing Process Changing? Start with the measurement trend Check the measurement system Compare measurement and process data Use controlled checks Do not assume the cause Decide what needs correction Investigation checklist Continue the investigation Is the instrument failing, or is the manufacturing process changing? A measurement trend changes over time, but the reason isn't always clear. The instrument might be changing. The manufacturing process could also be altering. Additionally, the measurement method may influence the results. Start with the measurement trend. Begin by reviewing recorded measurements. Look at results over time to find a meaningful pattern. Check for: Changes in measured values Steady movement in one direction Unexpected shifts Va...

Calibration Troubleshooting Follow a controlled review when a result sits outside tolerance. Check the method, instrument, uncertainty, acceptance rule, and product impact. Contents A Measurement Is Just Outside Tolerance. Should You Reject the Part? Record the actual result Check the tolerance boundary Find the applicable decision rule Check the measurement system Consider measurement uncertainty Separate measurement from disposition Document the decision Borderline measurement checklist Continue the investigation A Measurement Is Just Outside Tolerance. Should You Reject the Part? A measurement is slightly outside the specified tolerance. The instrument has a current calibration record. The result is near the acceptance limit. Check how the measurement was made before accepting or rejecting the part. Also, see which decision rule applies. A borderline measurement needs evidence. The display number is just one part of the decision. Record the Actual Result Sta...

Calibration Troubleshooting Investigate failed inspection results by checking instrument suitability, test points, uncertainty, setup, environment, method, and product condition. Contents Your Calibration Certificate Passed. Why Is the Part Still Failing Inspection? Calibration and inspection answer different questions Check the instrument Review the inspection method Check the specification Consider measurement uncertainty Investigate the part and process Keep the evidence together Inspection investigation checklist Continue the investigation Your Calibration Certificate Passed. Why Is the Part Still Failing Inspection? The instrument has a valid calibration certificate. The calibration result is acceptable. Yet, the part still fails inspection. This can seem contradictory when calibration and inspection are viewed as the same. They are not. Calibration checks how measurement standards match what a measuring system shows under specific conditions. Inspection chec...

Calibration Troubleshooting Two calibrated instruments can disagree because resolution, uncertainty, method, contact, environment, condition, and test points differ. Contents Two Calibrated Instruments Give Different Readings. Which One Should You Trust? Start with the Same Measurement Check whether the method was the same. Compare the instruments. Check range and resolution. Consider measurement uncertainty. Check the measurement conditions. Repeat the comparison. Do not choose the preferred number. Comparison checklist What to investigate next Two Calibrated Instruments Give Different Readings. Which One Should You Trust? Two instruments have current calibration records. You measure the same item and get different readings. It is easy to ask which instrument is correct. That is not the first question to answer. First establish whether the two measurements were actually made under comparable conditions. The instrument is only one part of the measurement system. The me...

Calibration Troubleshooting A current calibration status does not control setup, environment, method, handling, operator technique, or suitability. Review the full measurement process. Contents Your Instrument Is Calibrated. Why Can the Measurement Still Be Wrong? Contents The problem starts with a valid certificate A practical measurement problem How to investigate the result Check the instrument first Then check the measurement method Check range and capability Look at measurement uncertainty Check metrological traceability Check the environment and setup Look at the manufacturing process Your Instrument Is Calibrated. Why Can the Measurement Still Be Wrong? A calibration certificate can be valid while a measurement process still produces a result that is unsuitable for a particular decision. This situation creates a common problem in inspection and quality control. An instrument has a current calibration certificate. The operator uses it correctly according to the n...

Calibration Fundamentals Use accuracy, precision, error, correction, repeatability, reproducibility, and uncertainty correctly in measurement records and technical decisions. Contents What is accuracy in measurement? What is precision in measurement? What is measurement error? Accuracy and precision are different Four common measurement situations Why repeated measurements matter How calibration relates to accuracy and precision Measurement error and measurement uncertainty What causes measurement error? How accuracy and precision affect manufacturing inspection Accuracy, precision, and process control Accuracy vs. precision vs. error in simple terms When a measurement is reported as 20.00 mm, the number looks precise. It does not, by itself, tell you whether the measurement is close to the true or reference value, how consistently the measurement system produces results, or how much uncertainty surrounds the result. That distinction matters in dimensional inspection, ...