My purpose here is to present and help you understand the calibration interval analysis procedure that you can implement if it suits your needs.
A disclaimer should be noted. These are my implementation based on my understanding and experience, it may be different from your situation so a proper review should be given. It is your responsibility as the user to evaluate the effectiveness of this method if you implement and take responsibility for the consequences of the decisions taken as a result of using this method.
Now let us start…
I will present here a modified method based on the principle of a control chart and a calendar-time method as per ILAC G24 (OIML D 10:2007). I will call this method the ‘Floating Interval Method’ because it can increase or decrease in a given condition.
To establish a fixed interval, below is the calibration interval analysis procedure:
1. Gather historical records of the instrument using its calibration report for the past 2 years or more.
2. Choose at least 3 readings that are mostly used, for example, the min, middle, and max to determine stability or drift.
3. Use excel to summarize the readings.
4. Using the specifications and the calibration results, create a chart with control limits (a control chart)-see below the table using excel (there are many tutorials about control chart in Google that you can follow).
5. Understand and analyze the trend.
> Based on the trend, you can decide whether to increase or decrease the calibration interval based on the Implementation Rule that you created for the Floating Interval Method. (See below presentation)
a. Implementation Rule #1: 100% Increased on the next calibration interval after the 2 years if results are within 80% – Max 24 months interval
b. Implementation Rule #2: 50% reduced on the next calibration interval every time As-Found results are within warning interval or OUT-OF-TOLERANCE (and adding back the 50% after passing on the next recalibration) –see the flow below second scenario.
6. Determine the final interval.
