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Standards and Calibration
Standards and calibration are used to manage the measurement systems to reduce and control measurement errors.
When to use
Most measurement systems require periodic calibration. The characteristics of the measurement equipment will determine the appropriate interval. These calibrations should be done using standards that are traceable back to international or national measurement standards.
Metrology is the science of measurement systems. The metrology department in an organization is normally responsible for maintaining the accuracy and precision of the measurement systems. This will include the creation of a calibration schedule and process for each measurement system and the conduct of Gage R&R studies.
The calibration process requires a measurement standard. This measurement standard is a physical object, system or experiment that has a known true value. The value of this object, system or experiment is traceable to a recognized international of national standard. That means the item was measured by a national laboratory and the exact value was determined.
Within the calibration process, the measurement system measures this object, system, or experiment and the measurement system results are compared to the known true value. If the measurement system results differ from the true value, the measurement system is adjusted until the results match the true value. For systems prone to precision error, multiple measurements are done and the average of those measurements is compared to the true value.
Calibrating with traceable standards builds trust and confidence in the measurement system. The standards ensure that a common unit of measure is being used and that data from one system can be correlated with data from another system. Reviewing the five types of measurement errors and how to address them:
- Accuracy errors are addressed by calibrating the measurement system to remove bias.
- Precision errors are quantified using a Gage R&R Study. Based upon the magnitude of error, the measurement system is improved or a different system is selected.
- Stability errors are addressed by monitoring and maintaining the measurement systems with regular maintenance and calibration. Another popular technique is the routine use of a golden standard by the operator to identify if the system has changed.
- Linearity errors are inherent in the design of the measurement system. If these exist, a different measurement system that is linear in the normal range of measurements should be selected.
- Discrimination errors are inherent in the design of the measurement system. If the discrimination is not acceptable, a different measurement should be selected.
Hints & tips
- Check with your Metrology department to establish an effective calibration plan.
- Check with your Metrology department before starting a Gage R&R Study. They may have done one that you can leverage.
- Companies with a large Metrology department will acquire their own traceable standards for doing calibration in-house. Those without a large Metrology department will often send the measurement systems to a laboratory that does calibration using traceable standards.
- The right answer to measurement error problems varies depending upon the type of problem. Sort out your errors so that you don’t waste time and money fixing the wrong thing.
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