Measurement Accuracy Requires a Calibration Program

When you use a measurement instrument, you assume it is giving you an accurate measurement.

• However, that is not always the case. Even normal use and wear of the device can affect its measurements.

• Combine normal wear and tear with the realities of a manufacturing environment (such as oil, metal or plastic chips, and the chance that the gage or instrument may be dropped or jolted) and you start to realize the importance of a good calibration system.

A formal measurement device management program including a rigorous calibration program is required to ensure measurement accuracy.

Components of a good measurement device management program include:

• Instrument inventory lists

• Assessment of testing needs

• Calibration procedures including the use of contracted calibration services if needed

• Records of device maintenance history, calibration records, and traceability documentation

• Management of calibration standards

• Identification of training requirements & related resources

• System audit requirements

Calibration Systems

• ISO 10012-1 (titled, "Quality Assurance Requirements for Measuring Equipment, Part 1, Metrological Confirmation System for Measuring Equipment) and ANSI/NCSL Z540-1 define the requirements for the establishment and maintenance of a calibration system designed to control the accuracy of measuring and test equipment and measurement standards.

• A Calibration Record should include:

  • Description of the device

  • Characterization and condition of the measuring instrument

  • Date of calibration

  • Calibration procedure

  • Environmental conditions during calibration

  • Measurement and results supported by data

  • Identification of any failures

  • A traceability statement

  • A statement of the estimated uncertainty

• It is important to have written procedures for calibration procedures. Steps to check the calibration of a device include:

  • Define the temperature and relative humidity requirements.

  • Visually examine the device for damage and wear.

  • Clean the measuring surfaces being careful not to damage them.

  • Check the device using the appropriate standards. If the device has a variable scale, check the low, mid-point, and high-end of the range.

If checks indicate the measuring device is not accurate, remove the device from service.

• Initiate action to adjust and recalibrate if possible.

  • Document the results of the calibration.

  • Attach the appropriate calibration sticker to the instrument.

• If the device cannot be fixed, tag it with an "inactive" sticker and destroy it if that is appropriate.

If checks indicate the measuring device is accurate, attach the appropriate calibration sticker and return the device to service.