ConsultGLP

At the recent Eurachem/PUC ISO 17025 training course in Nicosia, Cyprus on 20-21 February 2020, I had learnt something new from Dr Stephen Ellison’s presentation.

There is a measurement uncertainty package in the R Language, named “metRology”.  You can download this library when you are in the R environment.

For example, if we were asked to evaluate the uncertainty of the following expression:

expr = A + 2xB + 3xC + D/2

where A = 1, B = 3, C=2, D=11.  The sensitive coefficients, c’s, from the above expression are thus 1, 2, 3 and ½ for A, B, C and D, respectively.

Assuming the standard uncertainties of these parameters are constant at 1/10^th of their values, the following steps demonstrate how the combined standard uncertainty can be evaluated.

> library(“metRology”)

Attaching package: ‘metRology’

The following objects are masked from ‘package:base’:

    cbind, rbind

> expr<-expression(A+B*2+C*3+D/2)

> x=list(A=1,B=3,C=2,D=11)

> u=lapply(x,function(x) x/10)

> u

$A

[1] 0.1

$B

[1] 0.3

$C

[1] 0.2

$D

[1] 1.1

>

> u.expr<-uncert(expr,x,u,method=”NUM”)

> u.expr

Uncertainty evaluation

Call:

  uncert.expression(obj = expr, x = x, u = u, method = “NUM”)

Expression: a + b * 2 + C * 3 + D/2

Evaluation method:  NUM

Uncertainty budget:

     x    u      c     u.c

A   1   0.1   1.0   0.10

B   3   0.3   2.0   0.60

C   2   0.2   3.0   0.60

D  11  1.1   0.5  0.55

   y:  18.5

u(y):  1.01612