1. They include a ‘calibration interval tolerance’. I smiled at first when I heard this but it’s true, the calibration interval has a tolerance limit.   An example is a calibration interval of 1 year +/- 2  months.

2. An instrument that is being kept for a longer period and is calibrated only every time it is used, or before it will be used for measuring. 

3. Some instruments have no calibration due date at all, considering that this kind of instrument is calibrated before use in everyday operation.

4. There are calibration intervals based on the number of times the instrument is used. For example, we will only calibrate an instrument after it is used 500 times.

As you can see, there is no one exact solution that fits all, it all depends on the user. The important thing is we have a procedure to follow that is properly planned with justifications or proper documents as evidence why we choose such a method.

You can tweak or add additional details or criteria to suit your needs.  You can gather most methods from reference guides and combine each of them. It is up to you how you can create the best calibration interval analysis program for you.

Conclusion

Determining the calibration interval is one of the main requirements when it comes to instrument maintenance and quality control. And as per my exposure to different users, this is one of the most asked topics.

In establishing a Calibration interval, there are 2 main steps that we need to follow, first is to establish the Initial Interval, the second is to determine the Final or Fixed Calibration Interval as we progress. Whether we choose the initial interval as the fixed interval or establish a new fixed interval is ok, the important thing is we need to have data to justify our decisions. There should be a method that we follow in order to implement this. I call the method in this post, the ‘Floating Interval Method’.

In this article, I have presented:

1. What is a calibration Interval?
2. Why Do We Need to Determine Calibration Frequencies of Instruments
3. How to Determine Calibration Interval of Instruments

a. 4 Major Objectives For the Implementation of Calibration Interval Analysis
b. How to Establish the Initial Calibration Interval
c. How to Determine the Fixed Calibration Interval

> Example of Calibration Interval Calculation of Pressure Test Gauge – Method Implementation Procedure

4. References Guides that We can Use to Perform Other Methods of Analysis
5. Some Techniques that I observe others are doing in relation to calibration Interval