Instrument Accuracy Checks and Calibration

  • Consider all the instruments and devices that measure something in your facility. These measurements may include temperature, weight, pressure, humidity, pH, salinity, and the list continues.
  • Each device has a purpose, and the resulting measurements are needed for monitoring and managing the equipment or product.
  • But what happens when these devices become inaccurate and fail to provide precise results?
  • Does your facility have an instrument calibration or accuracy check program with procedures to verify that the devices are precise and accurate?
  • Management should be confident that their measuring devices are reading correctly.
  • The following steps will help you establish an instrument calibration procedure, or tune-up your existing one.

Step 1: Identity the Measuring Devices/Instruments :

Develop a comprehensive list of every device in your facility that is used to measure something. This includes scales, thermometers, gauges, pH meters, and so forth. Then determine if all the listed devices are still of benefit. Those devices that are no longer of use should either be removed or marked as not being routinely checked for accuracy. Before removing any device, check with the managers, supervisors, and employees in the area to make sure it is not used. One suggestion is to place a sign on the instrument stating that it will be removed unless management is notified that it is used.

If the instruments do not have a manufacturer identification number, clearly mark each device with a unique number by attaching an asset number tag, etching the device, or using another labeling method. Identification by location (i.e., table scale) may be appropriate if there is only one of the devices; however, a numbering system is recommended, especially if any of the following circumstances apply.

  • The device is the standard used to calibrate other devices (such as a NIST-certified thermometer).
  • The device is used to monitor a critical control point (CCP).
  • Your facility has more than one of the devices. For example, table scales can be moved easily and the same one may not necessarily be returned to the same location.

As appropriate, identify the location of the instrument, such as: Receiving Office, Mixer 1, Laboratory, Packing Line 3, End of the Pasteurizer Hold Tube, and so forth.

Identify the range of use by specifying the actual temperatures, weights, etc. that will be measured by the device. For example, if a floor scale is used to weigh 500 pounds, test the accuracy at 500 pounds rather than at 20 pounds. Also identify the required or accepted range from the certified device (such as +/- 2 pounds, +/-0.50C, etc.)

Assign a procedure number for the method of certification, calibration, and accuracy checks used for each device. Documented procedures should include:

  • How to conduct the check.
  • Acceptable deviations/deviation range.
  • Corrective action if the results are not within the accepted deviation range.
  • Documentation requirements.

The instrument check/calibration procedure should include frequency of the checks for each device, such as daily, weekly, monthly, annually.

Also, specify the department or position responsible for checking the devices or for arrangements if an outside agency will be used. Finally, make sure the location of the affiliated results and corrective actions is identified in the procedure.