We are currently using a set of 6 thermoelements only for temperature measurements during testing of medical devices. So far each thermoelement is calibrated once a year. Since the calibration of the thermoelements is quite expensive, we only have a limited number of these. The problem is, that the temperature tests we are doing usually has to be performed at more locations than we have thermoelements. We solve this by repeating the tests after the the thermoelements have been placed at the different locations.
I would like to change this by the following:
- Buy a set of thermoelements from one production batch (lets say 20) that come with a batch certificate from the manufacturer, stating compliance with the corresponding accuracy class. This would be an ISO certificate only, not an accredited calibration certificate.
- Calibrate a sample of this set by an accredited calibration lab (maybe retain this one as a reference).
- Add a safety margin to the uncertainty of the calibrated sample and apply this extended uncertainty to the whole set (that even already has the ISO certificate for compliance with +-0,5K, but better safe than sorry). Lets say I use type T thermoelements and the calibrated sample complies with +-0,5K (type T, class I), I could maybe add another +-0,5K resulting in an uncertainty of +-1,0K for the whole set.
- After a given use time (lets say a year), dispose the set of thermoelements and start at again with a new set.
I would like to not perform in-house calibration, because I fear that the requirements for this would outweigh the benefits.
This would lead to less calibration costs (1 vs. 6 times). The costs for an accredtited calibration of one single thermoelements are approximately the same as for buying 10 new ones. So we still safe money here. And we could use more thermoelements (20 vs. 6) in order to save time and efforts during testing. Addtionally it would also be OK to perform tests, were we lose a thermoelement (e.g. due to having to cement it to the device under test). Currently sacrifying a thermoelement is not an option.
My concern is, that the accreditation body will give me a non-conformity, since not each single one of the thermoelements is metrologically traceable (only the one that has been calibratied by an accredited calibration lab). I tried to get some information from the accr. body, but unfortunately they are a little reserved, saying they cannot really say if this is OK or not, unless they have seen this during an official audit :-(
What do you think?
I would like to change this by the following:
- Buy a set of thermoelements from one production batch (lets say 20) that come with a batch certificate from the manufacturer, stating compliance with the corresponding accuracy class. This would be an ISO certificate only, not an accredited calibration certificate.
- Calibrate a sample of this set by an accredited calibration lab (maybe retain this one as a reference).
- Add a safety margin to the uncertainty of the calibrated sample and apply this extended uncertainty to the whole set (that even already has the ISO certificate for compliance with +-0,5K, but better safe than sorry). Lets say I use type T thermoelements and the calibrated sample complies with +-0,5K (type T, class I), I could maybe add another +-0,5K resulting in an uncertainty of +-1,0K for the whole set.
- After a given use time (lets say a year), dispose the set of thermoelements and start at again with a new set.
I would like to not perform in-house calibration, because I fear that the requirements for this would outweigh the benefits.
This would lead to less calibration costs (1 vs. 6 times). The costs for an accredtited calibration of one single thermoelements are approximately the same as for buying 10 new ones. So we still safe money here. And we could use more thermoelements (20 vs. 6) in order to save time and efforts during testing. Addtionally it would also be OK to perform tests, were we lose a thermoelement (e.g. due to having to cement it to the device under test). Currently sacrifying a thermoelement is not an option.
My concern is, that the accreditation body will give me a non-conformity, since not each single one of the thermoelements is metrologically traceable (only the one that has been calibratied by an accredited calibration lab). I tried to get some information from the accr. body, but unfortunately they are a little reserved, saying they cannot really say if this is OK or not, unless they have seen this during an official audit :-(
What do you think?