Instrumentation & Measurement Magazine 23-2 - 85

rubbish. So, the metrologist who until now was almost exclusively preoccupied by the management of measuring
instruments must rise to the challenge and ensure that the
measurements made are reliable. The role has changed: the
company metrologist has become the guarantor of Veracity,
the veracity of measured data.

Bayesian Inference: a Copernican
Revolution in Metrology [6]
Although measurement uncertainties should be central to the
preoccupations of all metrologists, this is all too rarely the case.
So, what is the point of calculating uncertainties? To use them,
surely!
The NF ISO/IEC 98-4 Guide [7] offers metrology the perfect opportunity for putting them to good use: the Bayesian
approach. In this approach, the a priori concept is the basis for
estimation of the risks related to conformity checking, and this
is a tool that can serve in more ways than one.
The risk of declaring a non-compliant entity "compliant"
was summarized, in the traditional view, as the area outside
the tolerance zone (Fig. 3).
This traditional view is clearly deficient, since the simple
fact is that customer risk only exists if the entity really is noncompliant. It seems evident, therefore, that the probability of
the entity being non-compliant absolutely must be considered
when calculating risk. The risk is in fact of the coincidence of
two conditions: the measurement result being "compliant"
(probability P1) for an entity that in reality is non-compliant
(probability P2).
Probability P1 can be calculated from the measurement
uncertainty. Probability P2 can be calculated from a priori
knowledge of the production of the entity. This approach,
which combines observation (measurement) and a priori
knowledge of the reality to be measured, is known as Bayesian.
It allows us to infer from all the knowledge available (measurement, measurement uncertainty and a priori) the most
probable reality. An article in the smart-metrology.com blog [8]
explains how to use this information to obtain a more reliable
value than the measured value.

In highly simplified terms, the process is as follows:
◗◗ Take the fundamental equation of metrology (VMeasured =
VTrue + eMeasured)
◗◗ Deduce from this that there are a multitude of possible
combinations (VTrue; eMeasured) for any measured value
◗◗ Calculate the probability of each of them (P1xP2) once the
a priori and the measurement uncertainty are known
◗◗ Find the most likely combination and from it deduce the
most likely true value hiding behind the measured value
This post-processing of the measured value requires a priori knowledge of the company's procedures as well as the
measurement uncertainty. This is a novel way of using measurement uncertainty, the purpose of which is to enhance
performance. The Smart Metrologist will want to seize this
new opportunity. The skill of the metrologist of the future,
which consists in evaluating the most probable risks and values, will be much more rewarding and helpful to the company
than managing periodic calibration, so often pointless, and really only carried out to satisfy the demands arising from audits.

Dynamic Monitoring: An End to
Pointless Periodic Calibration

The longstanding strategy of "calendar-based calibration"
does not offer any guarantee of measurement reliability. This
practice, in fact, can only detect problems after they have come
into effect, whereas what we need is dynamic detection. When
it comes to risk management, it is essential to know at what
point data became unreliable, because losing control over a
procedure through unreliable data can come at a high price
when competitors prove to be more agile.
In the ultimate aim to escape periodic calibration, a priori
information is extremely useful. When one knows in advance
what one should expect to find, it is simply a matter of checking that results are continuously consistent with this a priori
knowledge. If doubts arise, it means one of two things: either the procedure has changed (this information is vital in
the quest to ensure customer satisfaction), or something in
the measurement process has altered (this information is vital if we want to know whether or not to calibrate). Statistics
offer numerous tests that
can tell us whether a sample (e.g., the measurements
for the day, the week or the
hour, depending on sampling frequency) does or
does not fit at a given confidence level with a known
parent population (a priori). These tests are exactly
what a metrologist needs
to detect an anomaly on a
measuring instrument virtually as soon as it arises,
and take whatever action
is appropriate in those
Fig. 3. Traditional view of measured value, associated uncertainty and customer risk (© IEEE, 2018, used with
permission).
circumstances.
April 2020	

IEEE Instrumentation & Measurement Magazine	85


http://smart-metrology.com

Instrumentation & Measurement Magazine 23-2

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 23-2

No label
Instrumentation & Measurement Magazine 23-2 - No label
Instrumentation & Measurement Magazine 23-2 - Cover2
Instrumentation & Measurement Magazine 23-2 - 1
Instrumentation & Measurement Magazine 23-2 - 2
Instrumentation & Measurement Magazine 23-2 - 3
Instrumentation & Measurement Magazine 23-2 - 4
Instrumentation & Measurement Magazine 23-2 - 5
Instrumentation & Measurement Magazine 23-2 - 6
Instrumentation & Measurement Magazine 23-2 - 7
Instrumentation & Measurement Magazine 23-2 - 8
Instrumentation & Measurement Magazine 23-2 - 9
Instrumentation & Measurement Magazine 23-2 - 10
Instrumentation & Measurement Magazine 23-2 - 11
Instrumentation & Measurement Magazine 23-2 - 12
Instrumentation & Measurement Magazine 23-2 - 13
Instrumentation & Measurement Magazine 23-2 - 14
Instrumentation & Measurement Magazine 23-2 - 15
Instrumentation & Measurement Magazine 23-2 - 16
Instrumentation & Measurement Magazine 23-2 - 17
Instrumentation & Measurement Magazine 23-2 - 18
Instrumentation & Measurement Magazine 23-2 - 19
Instrumentation & Measurement Magazine 23-2 - 20
Instrumentation & Measurement Magazine 23-2 - 21
Instrumentation & Measurement Magazine 23-2 - 22
Instrumentation & Measurement Magazine 23-2 - 23
Instrumentation & Measurement Magazine 23-2 - 24
Instrumentation & Measurement Magazine 23-2 - 25
Instrumentation & Measurement Magazine 23-2 - 26
Instrumentation & Measurement Magazine 23-2 - 27
Instrumentation & Measurement Magazine 23-2 - 28
Instrumentation & Measurement Magazine 23-2 - 29
Instrumentation & Measurement Magazine 23-2 - 30
Instrumentation & Measurement Magazine 23-2 - 31
Instrumentation & Measurement Magazine 23-2 - 32
Instrumentation & Measurement Magazine 23-2 - 33
Instrumentation & Measurement Magazine 23-2 - 34
Instrumentation & Measurement Magazine 23-2 - 35
Instrumentation & Measurement Magazine 23-2 - 36
Instrumentation & Measurement Magazine 23-2 - 37
Instrumentation & Measurement Magazine 23-2 - 38
Instrumentation & Measurement Magazine 23-2 - 39
Instrumentation & Measurement Magazine 23-2 - 40
Instrumentation & Measurement Magazine 23-2 - 41
Instrumentation & Measurement Magazine 23-2 - 42
Instrumentation & Measurement Magazine 23-2 - 43
Instrumentation & Measurement Magazine 23-2 - 44
Instrumentation & Measurement Magazine 23-2 - 45
Instrumentation & Measurement Magazine 23-2 - 46
Instrumentation & Measurement Magazine 23-2 - 47
Instrumentation & Measurement Magazine 23-2 - 48
Instrumentation & Measurement Magazine 23-2 - 49
Instrumentation & Measurement Magazine 23-2 - 50
Instrumentation & Measurement Magazine 23-2 - 51
Instrumentation & Measurement Magazine 23-2 - 52
Instrumentation & Measurement Magazine 23-2 - 53
Instrumentation & Measurement Magazine 23-2 - 54
Instrumentation & Measurement Magazine 23-2 - 55
Instrumentation & Measurement Magazine 23-2 - 56
Instrumentation & Measurement Magazine 23-2 - 57
Instrumentation & Measurement Magazine 23-2 - 58
Instrumentation & Measurement Magazine 23-2 - 59
Instrumentation & Measurement Magazine 23-2 - 60
Instrumentation & Measurement Magazine 23-2 - 61
Instrumentation & Measurement Magazine 23-2 - 62
Instrumentation & Measurement Magazine 23-2 - 63
Instrumentation & Measurement Magazine 23-2 - 64
Instrumentation & Measurement Magazine 23-2 - 65
Instrumentation & Measurement Magazine 23-2 - 66
Instrumentation & Measurement Magazine 23-2 - 67
Instrumentation & Measurement Magazine 23-2 - 68
Instrumentation & Measurement Magazine 23-2 - 69
Instrumentation & Measurement Magazine 23-2 - 70
Instrumentation & Measurement Magazine 23-2 - 71
Instrumentation & Measurement Magazine 23-2 - 72
Instrumentation & Measurement Magazine 23-2 - 73
Instrumentation & Measurement Magazine 23-2 - 74
Instrumentation & Measurement Magazine 23-2 - 75
Instrumentation & Measurement Magazine 23-2 - 76
Instrumentation & Measurement Magazine 23-2 - 77
Instrumentation & Measurement Magazine 23-2 - 78
Instrumentation & Measurement Magazine 23-2 - 79
Instrumentation & Measurement Magazine 23-2 - 80
Instrumentation & Measurement Magazine 23-2 - 81
Instrumentation & Measurement Magazine 23-2 - 82
Instrumentation & Measurement Magazine 23-2 - 83
Instrumentation & Measurement Magazine 23-2 - 84
Instrumentation & Measurement Magazine 23-2 - 85
Instrumentation & Measurement Magazine 23-2 - 86
Instrumentation & Measurement Magazine 23-2 - 87
Instrumentation & Measurement Magazine 23-2 - 88
Instrumentation & Measurement Magazine 23-2 - 89
Instrumentation & Measurement Magazine 23-2 - 90
Instrumentation & Measurement Magazine 23-2 - 91
Instrumentation & Measurement Magazine 23-2 - 92
Instrumentation & Measurement Magazine 23-2 - 93
Instrumentation & Measurement Magazine 23-2 - 94
Instrumentation & Measurement Magazine 23-2 - 95
Instrumentation & Measurement Magazine 23-2 - 96
Instrumentation & Measurement Magazine 23-2 - 97
Instrumentation & Measurement Magazine 23-2 - 98
Instrumentation & Measurement Magazine 23-2 - 99
Instrumentation & Measurement Magazine 23-2 - 100
Instrumentation & Measurement Magazine 23-2 - 101
Instrumentation & Measurement Magazine 23-2 - 102
Instrumentation & Measurement Magazine 23-2 - 103
Instrumentation & Measurement Magazine 23-2 - 104
Instrumentation & Measurement Magazine 23-2 - 105
Instrumentation & Measurement Magazine 23-2 - 106
Instrumentation & Measurement Magazine 23-2 - 107
Instrumentation & Measurement Magazine 23-2 - 108
Instrumentation & Measurement Magazine 23-2 - 109
Instrumentation & Measurement Magazine 23-2 - 110
Instrumentation & Measurement Magazine 23-2 - 111
Instrumentation & Measurement Magazine 23-2 - 112
Instrumentation & Measurement Magazine 23-2 - 113
Instrumentation & Measurement Magazine 23-2 - 114
Instrumentation & Measurement Magazine 23-2 - 115
Instrumentation & Measurement Magazine 23-2 - 116
Instrumentation & Measurement Magazine 23-2 - 117
Instrumentation & Measurement Magazine 23-2 - 118
Instrumentation & Measurement Magazine 23-2 - 119
Instrumentation & Measurement Magazine 23-2 - 120
Instrumentation & Measurement Magazine 23-2 - Cover3
Instrumentation & Measurement Magazine 23-2 - Cover4
https://www.nxtbook.com/allen/iamm/24-6
https://www.nxtbook.com/allen/iamm/24-5
https://www.nxtbook.com/allen/iamm/24-4
https://www.nxtbook.com/allen/iamm/24-3
https://www.nxtbook.com/allen/iamm/24-2
https://www.nxtbook.com/allen/iamm/24-1
https://www.nxtbook.com/allen/iamm/23-9
https://www.nxtbook.com/allen/iamm/23-8
https://www.nxtbook.com/allen/iamm/23-6
https://www.nxtbook.com/allen/iamm/23-5
https://www.nxtbook.com/allen/iamm/23-2
https://www.nxtbook.com/allen/iamm/23-3
https://www.nxtbook.com/allen/iamm/23-4
https://www.nxtbookmedia.com