Calibration Hanna-Mari Kaarre, 33240

Processindustriell mätteknik

Institutionen för kemiteknik

Åbo Akademi

Maj 2013

Table of Contents

Foreword.............................................................................................................................. 2

Introduction........................................................................................................................ 2

General information of calibration.............................................................................2

Calibration of instruments............................................................................................. 3

Gases used in calibration................................................................................................ 6Pure gases, including zero check gases...............................................................................6Calibration and span gases......................................................................................................7

Emission measurement instruments..........................................................................8Horiba PG-250.............................................................................................................................. 8Horiba EXSA-240CL.................................................................................................................... 9

References......................................................................................................................... 11

1

ForewordThis report is part of the course “Processindustriel mätteknik”, and the aim of

this report is to enhance students’ knowledge of calibration of exhaust devices

that are used for ship engines. The report will for example contain general

information of calibration, requirements for calibration set up by The Marine

Environment Protection Committee and descriptions of special measuring

devices.

IntroductionThe International Maritime Organization (IMO) started its work in the late 1980s

and works on preventing air pollutions from ships. [3] Depending on the location

there are today different kinds of certificates and standards that companies are

aiming for. These certificates and standards have different criteria that the

engines have to fulfil. In order to check these criteria, test runs including

different measurements are organized. Calibrations are a critical step of the

measurements, since wrongly calibrated instruments will give false results.

Therefore the calibrations must be done correctly and by professionals.

General information of calibrationCalibration is about quality assurance and reliability. Decisions made in technical

contexts are often based on some measurements. Therefore it is important to be

able to show that the measurements are trustworthy. Decisions based on

incorrect facts may lead to defective structures. Without correct measurements,

which mean traceable calibrations with a presented uncertainty, the company

risks lower quality, loosing competitiveness and in the end poor profitability. [4]

The definition of calibration is “the act of checking or adjusting (by comparison

with a standard) the accuracy of measuring instrument”. [6] Calibration is

therefore a comparison between measurements. In calibration for a instrument

measuring gas composition the standard compared with the result is a specific

gas, whose composition is known.

2

Calibration of instrumentsEvery instrument that is used for measuring an engine’s parameters must be

calibrated as often as needed in accordance with the requirements of the NOx

technical code, published by the international maritime organization. [3] The

calibration validity period varies among the different measurement instruments.

The validity period can for example be between three to twelve months; as for an

engine speed measurement instrument the valid period is three months when it

is six months for a measurement instrument for exhaust gas flow. The calibration

validity period differs also depending on if the measurements are made before

achieving a certificate or if the measurements are made when the engine already

is pre-certified. [3] These periods will be presented in the tables below. One

calibration can last up to two or three hours. [5]

The data from the calibration of the measuring instruments must be traceable to

standards recognized by the administration. A proposal must be submitted when

the calibration procedure or period differs from those given in the technical

code. The proposal must also be submitted and approved by the administration

before the test. [3]

3

NO. Measurement instrument Permissible deviation Calibration validity

period (months)

1 Engine speed ±2% of reading or ±1% of

engine’s maximum value,

whichever is larger

3

2 Torque ±2% of reading or ±1% of

engine’s maximum value,

whichever is larger

3

3 Power (where measured

directly)

±2% of reading or ±1% of

engine’s maximum value,

whichever is larger

3

4 Fuel consumption ±2% of engine’s maximum

value

6

5 Air consumption ±2% of reading or ±1% of

engine’s maximum value,

whichever is larger

6

6 Exhaust gas flow ±2,5% of reading or ±1,5% of

engine’s maximum value,

whichever is larger

6

“Permissible deviations and calibration validity periods of instruments for

engine-related parameters for measurements on a test bed” [3]

NO. Measurement instrument Permissible deviation Calibration validity

period (months)

1 Engine speed ±2% of engine’s maximum

value

12

2 Torque ±5% of engine’s maximum

value

12

3 Power (where measured

directly)

±5% of engine’s maximum

value

12

4 Fuel consumption ±4% of engine’s maximum 12

4

value

5 Air consumption ±5% of engine’s maximum

value

12

6 Exhaust gas flow ±5% of engine’s maximum

value

12

“Permissible deviations and calibration validity periods of instruments for

engine-related parameters for measurements on board a ship when the engine is

already pre-certified” [3]

Gases used in calibrationWhen using calibration gases and span and zero check gases it is important to

respect the shelf life of the gases. The expiry date, stated by the manufacturer, of

the calibration gasses and the span and zero check gases must be documented of

the person doing the calibration. [3]

Pure gases, including zero check gases

Pure gases can be used as zero check gases. The zero check gas is used for setting

the lower end of the range. “The calibration range is defined as the region

between the limits within which a quantity is measured, received or transmitted,

expressed by stating the lower and upper range values.” [2]

The following gases must be available: purified nitrogen, purified oxygen and

hydrogen-helium mixture. In the table below the required contamination limits

for these gases will be given. [3]

5

Pure gas (zero check

gas)

Contamination limits/purity %

Purified nitrogen

Contamination ≤ 1 ppmC,

≤ 1 ppm CO,

≤ 400 ppm CO2,

≤ 0.1 ppm NO

Purified oxygen Purity > 99.5% volume O2

Hydrogen-helium

mixture

40 ± 2% H 2, balance He

Contamination ≤ 1 ppmC,

≤ 400 ppm CO2

Purified synthetic air

Contamination ≤ 1 ppmC,

≤ 1 ppm CO,

≤ 400 ppm CO2,

≤ 0.1 ppm NO

Oxygen content 18% - 21% volume

[3]

Calibration and span gases

The span gases are used for setting up the top end of the calibration range. Some

mixtures of the gases with the following chemical composition should be

available:

- CO and purified nitrogen

- NOx and purified nitrogen (NO2 should not be more than 5% of the NO

content)

- O2 and purified nitrogen

- CO2 and purified nitrogen

- CH 4 and purified synthetic air, or C3H8 and purified synthetic air. [3]

In addition to these mixtures other gas mixtures can also be used. The only

requirement in that case is that the gases do not react with each other. The

concentration of calibration and span gases should be specified in the unit

volume per cent or volume ppm. The real concentration of a calibration and span

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gas should not vary more than 2 % from the nominal value. This means that the

known accuracy of the primary gases, which are used in the blending, should be

at least 1%. The accuracy must also be traceable to national or international gas

standards. Gases used for calibration and span can be diluted with purified N 2 or

purified synthetic air to achieve the required concentration. The dilution will

then be operated with precision blending devices, in other words gas dividers.

For each calibration using a blending device the verification must be made

between 15 and 50 % of full scale. Alternatively the blending device can be

tested with an instrument that naturally is linear, for example using NO gas with

a Chemiluminescence Detector (CLD). [3]

When putting up the span values for the instrument the span gases must be

directly connected to the instrument. The blending devices must be checked at

the used settings, so if the settings are being changed the device should be

checked again. The measured concentration of the device must be compared to

the nominal value. The difference in each point should not be more or less than

1% of the nominal value. A gas analyser cannot be linearized with the same gas

divider twice. [3]

Gases that are checking the interference of oxygen contain propane or methane.

The amount of hydrocarbons in propane and methane should be 350 ppmC ± 75

ppmC. The concentration can be checked by chromatographic analysis of total

hydrocarbons and impurities or by dynamic bleeding. The dominant diluent

should be nitrogen and the rest will consist of oxygen. [3]

A system leakage test should always be done during a test run. That can be done

with a flow meter or with zero and span gases. In the leakage test done with zero

and span gases concentrations will be compared. At the beginning of the

sampling line there will be a concentration step change when zero gas will be

changed to span gas. After a while the current concentration will be compared to

the concentration at the beginning. If the concentration now is lower than the

concentration at the beginning it means that there is a leakage or calibration

problem. [3]

7

Emission measurement instruments

Horiba PG-250

Horiba PG-250 is a portable instrument used for measuring NOx, NO, CO2, O2 and

SO2. The Horiba PG-250 meets the ISO 8178 standard, which is “an international

standard designed for a number of non-road engine applications.” [1]

The ISO 8178 is used in many countries in the European Union, USA and Japan

for emission certification and/or type approval. [1] Horiba PG-250 meets also

the IMO NOx code measurement standards. [5] FINAS Accredited Laboratory,

which follows the EN ISO/IEC 17025 standard guarantee the quality of the

Horiba PG-250.

Horiba PG-250. [5]

Horiba EXSA-240CL

Horiba EXSA-240CL is a portable emission measurement system of NOx, NO and

O2. As the Horiba PG-250 this instrument also meets the ISO 8178 and IMO NOx

code measurement standards. The quality of this device is also guaranteed by

FINAS. The Horiba EXSA-240CL measures NOx with a chemiluminescent

detector and an electro-chemical sensor measures O2. Both NOx and O2 are

measured on a wet basis. [5]

8

Horiba EXSA-240CL

For all these measurement instruments the calibration requirements set by IMO

are valid. The calibration must in other words be done according to these

requirements and be done by a certified organization.

9

References[1] DieselNet; Emission Tet Cycles ISO 8178,

http://www.dieselnet.com/standards/cycles/iso8178.php, (26.5.2013)

[2] Calibration Principles, http://www.isa.org/Template.cfm?

Section=Find_Books1&template=Ecommerce/

FileDisplay.cfm&ProductID=7577&file=ACFBA59.pdf, (26.5.2013)

[3] International Maritime Organization (2009); Revised Marpol Annex VI,

Regulations for the prevention of air pollution from ships and NOx Technical Code

2008, (26.5.2013)

[4] Swedac; Kalibrering, http://www.swedac.se/sv/Omraden/Kalibrering/,

(20.5.2013)

[5] T. Sundell 19.1.2011; WFI Technical service emission measurement systems,

(21.5.2013)

[6] The free dictionary by farlex, http://www.thefreedictionary.com , (20.5.2013)

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