Reference calibration tools (traceable to NIST) that are not used in production

[snoopy2017]

Hi everyone,

I have a question regarding calibration under ISO 13485:2016. For reference calibration tools (traceable to NIST) that are not used in production, how often should we calibrate them?They are used to calibrate production tools but then are put away and locked up. These reference tools are traceable to NIST but do not have an expiry date. How would a manufacturer determine the calibration expiry date for these tools? I would appreciate any advice. Thanks.

 

[itsbiodiversity]

If the tools are used to calibrate the production tools their status would be even MORE important than the production tools. The items may have no calibration due date because no due date was requested at the time they were calibrated. Calibration labs do not determine the calibration due date - it is not allowed. If a customer has not requested a due date it is usually left blank on both the certificate and the cal sticker. You must determine (based on risk, cost, and likelihood the item would drift out of tolerance to a point that it affects the work being completed just to name a few) how often the items should be calibrated. If you have control charting of the standards and they are used infrequently you may extend the dates. If you are very concerned you should shorten the interval.

If you'd like to provide some more details I would be glad to explain further or offer some guidance if necessary.

 

[snoopy2017]

Thanks so much for the helpful response. Could you explain what you mean by control charting of standards? Also, should we document our rationale for a specific calibration interval somewhere for the reference tool?

Thank you.

 

[itsbiodiversity]

A control chart procedure is used for controlling bias and long-term variability. The procedure is designed to be implemented in real time after a baseline and control limits for the check standard of interest have been established from the database of check standard values. A separate control chart is required for each check standard.

If the check standard value exceeds one of the control limits set by your company, the process is judged to be out of control and the current calibration run is rejected. The best strategy in this situation is to repeat the calibration to see if the failure was a chance occurrence. Check standard values that remain in control, especially over a period of time, provide confidence that no new biases have been introduced into the measurement process and that the long-term variability of the process has not changed.

Out-of-control signals, particularly if they recur, can be symptomatic of one of the following conditions:
Change or damage to the reference standard(s)
Change or damage to the check standard
Change in the long-term variability of the calibration process


So to put it simply - you would control chart either your calibration data for each calibration event in different ranges (depending what type of instrument you are dealing with) or control chart internal checks (for an easy example - checking master caliper with calibrated gage blocks every month or according to a PREDEFINED schedule). As long as the data remains within your PREDEFINED control limits (either the OEM tolerance, 1/4 the tolerance of the gages your standard calibrates, etc.) you can justify lengthening the calibration interval. If the standard deviation of the control chart data is high it may be in your interest to either shorten the interval or leave the interval as is.

 

[itsbiodiversity]

Thanks so much for the helpful response. Could you explain what you mean by control charting of standards? Also, should we document our rationale for a specific calibration interval somewhere for the reference tool?

Thank you.

I apologize I left off one part - it is always a good practice to document the rationale for your calibration interval. It will, minimally, show that you did analyze the interval and you didn't just "wing" it.

A simple example of this justification for a gage block set could be as follows:

The gage block set calibration interval has been adjusted from one year to three years based on 6 consecutive calibration events with each meeting calibration requirements.

Or

The gage block set calibration interval has been adjusted from one year to three years due to the type of items currently calibrated using the gage blocks as a standard. The blocks are a Grade 0 and are only used to calibrate calipers with a resolution of 0.001".

If anyone else out there disagrees please feel free to chime in.