Recommendations for Setting & Adjusting Instrument Calibration Intervals

The importance of calibration in the maintenance of an instrument used for taking measurements is well understood by all who use this equipment. These highly sensitive instruments come with an assigned measurement tolerance and a recommendation on the calibration interval from the manufacturer, and it’s clear that failure to follow those recommendations can lead to a host of issues, including inaccurate measurements.

Although the manufacturer establishes a calibration interval based on their own data and usage when designing the unit, setting instrument calibration intervals intervals according your own specific needs can be more complicated.

Follow these recommendations

Manufacturers set recommended intervals using data from three sources — similar products, individual components within the instrument and su-bassemblies in existing mature products.

However, once you’ve purchased and begun to use the instrument, outside factors can affect its performance and should be considered when assessing calibration intervals for your own operation. Three key factors are:

1. Conditions: Typical operating conditions, such as temperature, vibration, frequency of use and other variables, can play a role in calibration intervals.

2. Your unique application: The manufacturer cannot know the specific situation in which you’ll use the measuring instrument. For example, it could be that you only need that instrument on a few occasions throughout the year, and your interval will be much longer.

3. Added features: Does your instrument feature any circuitry or firmware that monitors the state of the instrument? At a minimum, it might provide feedback that allows you to assess the instrument and determine whether it is possible to extend your calibration interval. Other instruments have built-in features which allow it to self adjust based on use and conditions, which can dramatically lower the amount of maintenance needed.

Assessing data and making adjustments to the calibration interval

To accurately assess the calibration interval, you'll need two years of calibration history. This creates a clear picture of how the instrument will react over an extended period of use. Setting instrument calibration intervals with less than two years of data isn't ideal, as the data will not provide a sufficient history of the instrument's performance.

For instruments with a sufficient data history, also look at how many days have passed since the instrument's last calibration was completed. You will see a pattern emerge for the time elapsed between repairs and adjustments. This will also make decisions for setting instrument calibration intervals much easier.

Once you’ve confirmed that sufficient data exists, proceed with a statistical analysis. Binary logistic regression, hypothesis testing on proportions and data fitting are the most common methods used. The idea here is to create a model that helps predict future behavior. This further increases the importance of having a large enough sample size.

MATsolutions provides calibration and repair services for a variety of equipment by numerous manufacturers, and we’re available to answer any questions you may have about proper calibrations for your equipment. Contact us today to learn more about how we can meet your needs.