Cal specs when Lab environment is out of tolerance.

[tarzan271]

I would like to see how labs are handling device under test (DUT) calibration specs when your environment goes out of tolerance or outside the DUT spec range.

For example, a manufacturer spec'd a DUT measurement to ±3% between 20-30 deg C and ±5% between 5-50 deg C. If your lab temp is 18 or 19 deg C, do you use the ±3% or ±5% tolerance? What if your lab temp is 17 deg C?

In my opinion, we should always use the ±3% tolerance regardless of the lab environment. The only thing that should be adjusted when a lab is outside the 23±5 deg C range are the standards tolerances to make sure the TUR is still met as per the calibration procedure.

What is your opinion and does anyone know how auditors would view this situation? i.e NCSLI, ISO, and other international bodies.

[sbdata2009]

CYA, and use the worst case + or - 5%

[briansalomon]

If your environment is outside the DUT tepmerature range for the +/- 3% tolerance the +/- 5% tolerance applies until the temperature exceeds that range.

Using the tighter tolerance would not increase the risk of incorrectly finding the DUT in tolerance it simply isn't the correct tolerance to apply if the environment is in fact outside the range the mfr specified for the +/- 3% tolerance.

If the DUT is in tolerance for the temperature range it is calibrated in, I don't see a limited cal here. I would call the DUT in-tolerance.

In my experience most accrediting body auditors are knowledgeable, reasonable people. They are likely to ask why you would not simply apply the tolerance the manufacturer has cited.