The metrological confirmation is the routine verification and control operation that confirms that the measuring instrument (or equipment) maintains the accuracy and uncertainty characteristics required for the measurement process over time.

 

By metrological confirmation we mean according to ISO 10012 (Measurement Mgt System): “set of interrelated or interacting elements necessary to achieve metrological confirmation and continual control of measurement processes”, and generally includes:                          

  • instrument calibration and verification;
  • any necessary adjustment and the consequent new calibration;
  • the comparison with the metrological requirements for the intended use of the equipment;
  • the labeling of successful positive metrological confirmation.

The metrological confirmation must be guaranteed through a measurement management system which essentially involves the phases of Table 1.

NORMAL PHASES PHASES IN CASE OF ADJUSTMENT PHASES IN CASE OF IMPOSSIBLE ADJUSTMENT
0. Equipment scheduling
1. Identification need for calibration
2. Equipment calibration
3. Drafting of  calibration document
4. Calibration identification
5. There are metrological requir.???
6. Compliance with metrological req. 6a. Adjustment or repair 6b. Adjustment Impossible
7. Drafting document confirms 7a. Review intervals confirm 7b. Negative verification
8. Confirmation status identification 8a. Recalibration phase (2 to 8) 8b. State of identification
9. Satisfied need 9a. Satisfied need 9b. Need not satisfied

Table 1 – Main phases of the metrological confirmation (ISO 10012)

Table 1 highlights three possible paths of metrological confirmation:

  1. the left path that normally achieves the satisfaction of the positive outcome of the metrological confirmation without any adjustment of the instrument in confirmation to phase 6;
  2. the first left path and then the middle one from phase 6a to 9a, in case of positive adjustment or repair of the instrument in confirmation and whose recalibration satisfies the confirmation: therefore, in this case, it will be necessary to reduce only the confirmation interval;
  3. the first path on the left and then the right from phase 6b to 9b, in case of negative adjustment or repair of the instrument in confirmation, which does not satisfy the result of the confirmation: therefore the instrument must be downgraded or alienated.

Metrological confirmation can usually be accomplished and fulfilled in two ways:

Comparing the Maximum Relieved Error (MRE) with the Maximum Tolerated Error (MTE), ie:

MRE <= MTE

Comparing the Max. Relieved Uncertainty (MRU) with Tolerated Uncertainty (MTU, ie:

MRU <= MTU

With reference to the previous articles, and taking into consideration the one on the Calibration, related to the evaluation of the calibration results in terms of Error and Uncertainty of a manometer, respectively equal to:

  • MRE: ±05 bar
  • MRU:   066 bar

if the maximum error and tolerated uncertainty were both 0.05 bar, then the manometer if evaluated in terms of MRE is compliant, while if evaluated in terms of MRU it is not compliant, and therefore it should follow path 2 of Table 1, or path 3; if it does not fall into it is then downgraded.


Author: Eng. Alessandro Brunelli

Book: Manuale di Strumentazione