Green coffee -- Procedure for calibration of moisture meters -- Routine method

This International Standard specifies a procedure for adjustment and subsequent calibration of moisture meters for green coffee beans with reference samples (RSs). The RSs are green coffee beans of various moisture contents, determined by a standard method (ISO 6673). NOTE This method of determining the loss in mass can be considered, by convention, as a method for determining the water content and can be used as such by agreement between the interested parties. This International Standard is applicable to green coffee as beans.

Café vert -- Mode opératoire d'étalonnage des humidimètres -- Méthode de routine

General Information

Status
Published
Publication Date
20-May-2012
Technical Committee
Drafting Committee
Current Stage
6060 - International Standard published
Start Date
15-May-2012
Completion Date
21-May-2012
Ref Project

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ISO 24115:2012 - Green coffee -- Procedure for calibration of moisture meters -- Routine method
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INTERNATIONAL ISO
STANDARD 24115
First edition
2012-06-01
Green coffee — Procedure for calibration
of moisture meters — Routine method
Café vert — Mode opératoire d’étalonnage des humidimètres —
Méthode de routine
Reference number
ISO 24115:2012(E)
ISO 2012
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ISO 24115:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s

member body in the country of the requester.
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Published in Switzerland
ii © ISO 2012 – All rights reserved
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ISO 24115:2012(E)
Contents Page

Foreword ............................................................................................................................................................................iv

1 Scope ...................................................................................................................................................................... 1

2 Normative references ......................................................................................................................................... 1

3 Terms and definitions ......................................................................................................................................... 1

4 Principle ................................................................................................................................................................. 1

5 Equipment and material ..................................................................................................................................... 1

6 Procedure .............................................................................................................................................................. 2

6.1 Test conditions ..................................................................................................................................................... 2

6.2 Alignment of instrument deviation ................................................................................................................. 2

6.3 Calibration of moisture meter .......................................................................................................................... 2

6.4 Temperature correction ..................................................................................................................................... 3

6.5 Calculation of uncertainty ................................................................................................................................. 4

6.6 Calibration curves for indirect reading equipment .................................................................................... 5

7 Expression of results ......................................................................................................................................... 5

Annex A (normative) Reference sample preparation and determination of moisture content as a mass

fraction loss .......................................................................................................................................................... 6

Annex B (informative) Example for moisture determination of samples to serve as reference ................... 9

Annex C (informative) Results of interlaboratory tests .......................................................................................... 11

Annex D (informative) Examples for separate steps of the procedure ..............................................................12

Bibliography .....................................................................................................................................................................16

© ISO 2012 – All rights reserved iii
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ISO 24115:2012(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International

Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 24115 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 15, Coffee.

iv © ISO 2012 – All rights reserved
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INTERNATIONAL STANDARD ISO 24115:2012(E)
Green coffee — Procedure for calibration of moisture meters —
Routine method
1 Scope

This International Standard specifies a procedure for adjustment and subsequent calibration of moisture meters

for green coffee beans with reference samples (RSs).

The RSs are green coffee beans of various moisture contents, determined by a standard method (ISO 6673).

NOTE This method of determining the loss in mass can be considered, by convention, as a method for determining

the water content and can be used as such by agreement between the interested parties.

This International Standard is applicable to green coffee as beans.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced document

(including any amendments) applies.
ISO 3509, Coffee and coffee products — Vocabulary
ISO 6673:2003, Green coffee — Determination of loss in mass at 105 °C

ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 3509, ISO/IEC Guide 99, and the

following apply.
3.1
reference sample

sample of green coffee beans, sufficiently homogeneous and stable with reference to specified properties,

which has been established to be fit for its intended use in measurement or in examination of nominal properties

NOTE See Annex A.
4 Principle

From green coffee beans, a set of samples with different moisture contents is prepared, to be taken as reference

samples (RS). Their individual moisture content (or mass fraction loss) values are obtained by the respective

determinations of loss in mass by applying ISO 6673.

These RSs with assigned moisture values are used for calibration of moisture meters.

5 Equipment and material

5.1 Green coffee as beans, in a quantity sufficient to prepare n reference samples, RSi, i = 1 … n (the

minimum is 5), with moisture mass fraction ranges between 8,5 % and 13,5 %, prepared according to A.1.

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ISO 24115:2012(E)

5.2 Thermometer, range between 0 °C to 120 °C, scale division 0,1 °C, provided the moisture meter does

not display the sample temperature.

5.3 Moisture meter, equipped with all the accessories specified by the manufacturer. It shall include a

channel for green coffee, which will be the subject of calibration.
5.4 Balance, capable of being read to the nearest 0,1 g.
5.5 Equipment necessary for determinations according to ISO 6673.
6 Procedure
6.1 Test conditions

The procedure shall be carried out at ambient temperature and at a relative humidity from 40 % to 70 %.

Prior to the test, allow conditioning of the green coffee bean RSs to ambient temperature.

6.2 Alignment of instrument deviation

6.2.1 Before adjustment, verify the equipment in accordance with the manufacturer’s instructions.

NOTE The verification is necessary to ensure the electronic gauging.

6.2.2 For moisture meters with direct reading, select green coffee beans channel.

6.2.3 For each RSi, obtain the difference between the reference sample moisture mass fraction, w ,

RSi

determined according to ISO 6673, and the moisture meter reading, w , where i is the reference sample number

assigned. Record them as Δw = w - w in the column headed “Difference” of Table 1.

i RSi ri

6.2.4 Calculate the average of the differences, Δw , and adjust the moisture meter bias according to the

manufacturer’s operation manual.
Table 1 — Input values to obtain the bias for moisture meter adjustment
Moisture mass
Reference Equipment reading
fraction of Difference
sample on sample
reference sample
RSi, i = 1 … n w w Δw = w - w
RSi ri i RSi ri
RS1
RS2
...
RS(n - 1)
RSn
The moisture content (or mass fraction loss), w , is obtained using ISO 6673.
RSi
6.3 Calibration of moisture meter
6.3.1 For calibration, use the moisture meter after adjustment (6.2).
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ISO 24115:2012(E)

6.3.2 Take the oven moisture values of the RSs, obtained according to A.2, and insert the figures into the

appropriate w cells in Table 2.
RSi

6.3.3 Take a test portion from RS1 in accordance with the equipment manufacturer’s instructions or the

equipment capacity, and pour it into the moisture meter. Record the reading from the equipment in the cell

matching the first row, RS1, and column, w , of Table 2; this cell corresponds to w .

ri,1 r1,1

Provided the equipment requires a defined test portion quantity, use the balance specified in 5.4.

6.3.4 Repeat the the procedure specified in 6.3.3 with the same test portion twice and record the readings in

the subsequent cells which correspond to w , and w for RS1.
r1,2 r1,3
At least three determinations shall be performed.

6.3.5 Calculate the arithmetic average of the RS1 readings, w , w , and w , and record it in the

r1,1 r1,2 r1,3
corresponding cell of column w , i = 1 … n; j = 1,2,3 of Table 2.
r,ij

6.3.6 Calculate the experimental standard deviation, s , of w , w , and w and insert it into the

1 r1,1 r1,2 r1,3
corresponding cell of column s of Table 2.

6.3.7 Measure the temperature of the test portion RS1 and record it in the corresponding cell of column

T of Table 2.

6.3.8 Repeat the procedure as specified in 6.3.3 to 6.3.7 with the other reference samples, RS2 to RSn and

their test portions.

6.3.9 Determine a correction term, C , to compensate for an estimated systematic effect of moisture for each

w moisture reading by applying Formula (1)
Cw=−w i = 1 … n j = 1,2,3 (1)
rRiiSrij
NOTE For an example, see Table D.2.
Table 2 — Input values to obtain the calibration of moisture meter
Sample Standard Reference
Reference Equipment readings on RSs Moisture meter
temperature deviation of sample
sample and corresponding mean correction
°C reading moisture
C =−w w
RSi T w w w w s w
i ri,1 ri,2 ri,3 i RSi
ri RSi rij
rij,
RS1
RS2
...
RS(n - 1)
RSn

The moisture content (or mass fraction loss), w , is obtained using ISO 6673; see A.2.

RSi
6.4 Temperature correction

6.4.1 Calculate the moisture reading correction term, C , due to bean temperature (if not automatically done

by the instrument itself) based on equipment manufacturer instructions; otherwise follow steps 6.4.2 to 6.4.5.

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ISO 24115:2012(E)

NOTE Some manufacturers provide an automatic temperature correction programme with their instruments.

6.4.2 Determine the moisture content of the RSs with the moisture meter at a given temperature.

6.4.3 Increase the temperature of the samples by about 5 °C to 10 °C and determine the new values at the

moisture meter.

6.4.4 For each RS, take the difference in moisture readings at test temperatures, and the difference of

temperatures, and calculate the respective ratio
ξ = (2)

6.4.5 Calculate the arithmetic mean of the ratios, ξ , to obtain the resulting moisture reading correction term

C due to bean temperature.
CT=−ξ T (3)
T refs
NOTE For an example, see Table D.4.
6.5 Calculation of uncertainty
[1]
This approach is based on that set out in ISO/IEC Guide 98-3:2008.

When reporting the result of a measurement of a physical quantity, it is obligatory that some quantitative

indication of the quality of the result be given so that those who use it can assess its reliability. Without such

an indication, measurement results cannot be compared, either among themselves or with reference values

given in a specification or standard.

It is therefore necessary that there is a readily implemented, easily understood, and generally accepted

procedure for characterizing the quality of a result of a measurement, that is, for evaluating and expressing its

uncertainty.
The components of moisture measurement uncertainty are:
a) U : uncertainty of the (assigned) value of the reference sample;
RSi

b) s /√j: uncertainty type A given by the moisture meter readings obtained from the experimental standard

deviation s using reference material i, with j = 3 repetitions (see 6.3.6);
c) u : uncertainty type B due to moisture meter accuracy;
d) u : uncertainty type B due to moisture meter resolution;
e) u : uncertainty type B due to the temperature (see 6.4 and D.4).
BTi

Calculate the expanded uncertainty of the moisture meter, U , for each moisture point i using Formula (4):

 
U  s
RSiri 22 2
Uk= + ++uu +u (4)
 
mi   Ba Br BTi
 
 
[1]

where k is the coverage factor; generally k = 2 for a probability of 95 %, according to ISO/IEC Guide 98-3:2008.

For each individual case, it is necessary to check every possible source of uncertainty.

1) In most cases, regressions are linear, however, it can prove necessary to apply another type, e.g. quadratic,

regression.
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ISO 24115:2012(E)
6.6 Calibration curves for indirect reading equipment

If the equipment does not give a measurement result directly in moisture content, but as a dimensionless value,

generate a calibration curve by comparing the equipment readings for each sample with the moisture of the RSs.

For a graphic calibration, plot the n values of the reading means, w , on the abscissa against the n values

r,ij

of sample moisture content, w on the ordinate, with i = 1 ... n for the samples and j = 1, 2, 3 for the replicate

RSi
readings to obtain the calibration curve.

The calibration curve relates the equipment readings to moisture content (or mass fraction loss) of the

reference samples.
For calculation, a linear regression is suitable in most cases.
7 Expression of results

The moisture content of a sample, w , determined using a moisture meter which has been calibrated with

the method described in this International Standard, shall be expressed as
ww=+CC+ ±U (5)
HO rr T m
where
w is the moisture content meter reading;
C is the correction for the moistu
...

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