Uncertainty of Measurement for Calibration Laboratory?

A

amanbhai

#1
It maybe a simple question!
We are a calibration lab and working for ISO/ IEC 17025:2005.
Now question is: Do we need to calculate the uncertainty of measurement for each new calibration equipment (we calibrate for our customer) or we can calculate it once and mention it for each same equipment we calibrate e.g. thermometer.

Any feedbaks are appriciated!
 
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qusys

Trusted Information Resource
#2
Re: Uncertainty of measurement for Calibration lab?

It maybe a simple question!
We are a calibration lab and working for ISO/ IEC 17025:2005.
Now question is: Do we need to calculate the uncertainty of measurement for each new calibration equipment (we calibrate for our customer) or we can calculate it once and mention it for each same equipment we calibrate e.g. thermometer.

Any feedbaks are appriciated!
It should be done for each equipment to be calibrated, since its characteristic
 
A

amanbhai

#3
But sometimes it is very difficult to calculate a single thermometer since it takes a lot of time in repeatability and reproduceability.
 
D

dv8shane

#4
But sometimes it is very difficult to calculate a single thermometer since it takes a lot of time in repeatability and reproduceability.
In my opinion if the UUT contributors are more than 5% of system uncertainty, you should calibrate each type individually with a separate uncertainty budget. You could categorize several models i.e. Fluke 3.5 digit thermometers under 1 budget if the proofs show that they biggest contributors are the repeatability and resolution of 0.1 degrees you could possibly then express the uncertainty as +/- X least significant digit(s) for the category. This helps to cut down on development time and internal costs.
 

BradM

Staff member
Admin
#5
Good posts on these already.

I have seen the spectrum, from someone calculating it once and posting as Best Measurement Capability (changed only when standards are calibrated); to estimating every calibration that is performed.

I think it depends on how stable your processes are, and how significant the variance is each time you verify it, and your customer requirements (if applicable).

Personally, I think the data should explain your answer. If you have enough history from... say.. every day it the data demonstrates stability, then extend to every week.
 
Last edited:
M

matwelli

#6
But sometimes it is very difficult to calculate a single thermometer since it takes a lot of time in repeatability and reproduceability.
but without this data....you have not truly checked the calibre of the device under test.

LIG thermometers need bore uniformity and hysteresis of the glass checked
Fully supported PRT's need hysteresis checked
Thermocouples need estimations for inhomogenity

what sort of thermometers are you calibrating ? we may be able to sugest a method that speeds up teh process and allows an easy way to estimate the uncertainty each time

if you wanted to do a "blanket" or "type test" uncertainty, the number would be quite large as you would have to allow for worst case on alot of contributions to the budget.
 
C

chriswhitehead

#8
ARRRRR!! I've spent two weeks of my own time gleaning as much information I can about the dreaded uncertainty measurements and lots of practising. I can now get a figure for my certificates that looks like the correct figure but how can I be sure its right.

Any courses in the UK?
Any other sites for more practise examples?
 

adamt

Involved In Discussions
#9
I feel your pain as I was in the same boat years ago. The problem is there is different ways to come up with an uncertainty for a UUT. My best suggestion is to try to think of anything that would affect the measurement and write it out, add it together and expect if you missed something your auditor will have you include it in your budget. Make sure you look at the new ILAC-p14/2010 there are some new requirements that you may have to include in your calculations. Hope this helps
 
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