I've been having discussions with other calibration professionals and can't get a concensus.
According to ISO/IEC 17025:2017, Clause 7.8.4.1a: Calibration certificates shall include...the measurement uncertainty of the measurement result presented in the same unit as that of the measurand or in a term relative to the measurand (e.g., percent).
Basically, what this particular clause is saying is that your uncertainty units should be the same as the measuring units. If you're measuring ºC then your uncertainty must also be in ºC; if you're measuring psi then your uncertainty must also be in psi.
This isn't a problem when you're calibrating, say, a pressure gauge. If your gauge is in psi, you apply a pressure in psi, read off the pressure in psi, and calculate the uncertainty in psi.
The problem crops up when you're calibrating pressure transmitters. You apply a pressure in psi and read off the output in milliamps. What do you do? Do you calculate the uncertainty in psi or in mA?
For me, the answer was obvious. 17025 says the uncertainty units must be the same as the measurand units, so the uncertainty must be in psi. I've found, however, that quite a number of calibration laboratories are giving uncertainties in milliamps! To me, this was a violation. So I was surprised to learn that they've been accredited! They passed!
So, my question is, how can this be? If you violate any clause in ISO, you're given a non-compliance notice. Why are these laboratories passing if they are not following this particular clause?
Note: same issue for temperature transmitters, flow transmitters, any type of transmitter that outputs a signal in different units from the measurand.
Calculating Uncertainty for Transmitters
Re: Calculating Uncertainty for Transmitters
