Liquid-in-glass thermometers

Thermomtres liquide en verre

OIM

L R

133

Edi

tion

2002

(E)

OIML R 133Edition 2002 (E)

ORGANISATION INTERNATIONALEDE MTROLOGIE LGALE

INTERNATIONAL ORGANIZATIONOF LEGAL METROLOGY

INTERNATIONALRECOMMENDATION

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Contents

Foreword ........................................................................................................................................................................... 3

1 Scope ........................................................................................................................................................................... 4

2 Application .................................................................................................................................................................. 4

3 Terminology ................................................................................................................................................................ 4

4 Description of the instrument ................................................................................................................................... 5

5 Metrological requirements ......................................................................................................................................... 6

6 Technical requirements .............................................................................................................................................. 7

7 Practical instructions ................................................................................................................................................. 8

8 Metrological controls ................................................................................................................................................. 9

References ........................................................................................................................................................................ 9

Annex A: Achievable maximum errors for thermometers (Informative) .................................................................. 10

Annex B: Methods for eliminating defects in the thermometric liquid (Informative) ............................................. 12

Annex C: Test procedure (Mandatory) ......................................................................................................................... 14

Annex D: Test report format (Mandatory for application within .............................................................................. 17the OIML Certificate System for Measuring Instruments)

Annex E: Achievable uncertainties for calibrated thermometers (Informative) ....................................................... 23

The International Organization of Legal Metrology(OIML) is a worldwide, intergovernmental organizationwhose primary aim is to harmonize the regulations andmetrological controls applied by the national metrologicalservices, or related organizations, of its Member States.

The two main categories of OIML publications are:

International Recommendations (OIML R), which aremodel regulations that establish the metrological charac-teristics required of certain measuring instruments andwhich specify methods and equipment for checking theirconformity; the OIML Member States shall implementthese Recommendations to the greatest possible extent;

International Documents (OIML D), which are inform-ative in nature and intended to improve the work of themetrological services.

OIML Draft Recommendations and Documents are devel-oped by technical committees or subcommittees which areformed by the Member States. Certain international andregional institutions also participate on a consultation basis.

Cooperative agreements are established between OIML andcertain institutions, such as ISO and IEC, with the objective

of avoiding contradictory requirements; consequently, manu-facturers and users of measuring instruments, test labor-atories, etc. may apply simultaneously OIML publicationsand those of other institutions.

International Recommendations and International Docu-ments are published in French (F) and English (E) and aresubject to periodic revision.

This publication - reference OIML R 133 Edition 2002 (E) -was developed by the OIML Technical SubcommitteeTC 11/SC 2 Contact thermometers. It was approved for finalpublication by the International Committee of LegalMetrology in 2001 and will be submitted to the InternationalConference of Legal Metrology in 2004 for formal sanction.

OIML publications may be obtained from the Organizationsheadquarters:

Bureau International de Mtrologie Lgale11, rue Turgot - 75009 Paris - FranceTelephone: 33 (0)1 48 78 12 82 and 42 85 27 11Fax: 33 (0)1 42 82 17 27E-mail: biml@oiml.orgInternet: www.oiml.org

Foreword

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OIML R 133: 2002 (E)

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1 Scope

1.1 This Recommendation specifies the metrologicaland technical requirements for general-purpose, liquid-in-glass thermometers (1) intended for laboratory use asreference or working temperature standards. Thethermometers are graduated in degrees Celsius anddivided into six accuracy classes (see 5.2.2) that applyto thermometers operating within the temperaturerange of 200 C to + 500 C.

1.2 This Recommendation covers solid-stem andenclosed-scale thermometers. In addition, such ther-mometers may be complete immersion, total immer-sion, or partial immersion thermometers. The per-formance requirements for thermometers containingmercury and organic liquids as thermometric liquidsare specifically covered in this Recommendation.Requirements for thermometers containing otherliquids such as gallium and mercury-thallium could bedeveloped by applying the same principles.

1.3 A test procedure is given to determine if thethermometers meet each specified requirement underspecified laboratory conditions. Such procedureincludes visual inspection and tests on permanency ofpigment, bulb stability, and determination of errors.

1.4 This Recommendation does not apply tomaximum registering thermometers, such as thoseused to measure body temperature.

2 Application

2.1 Liquid-in-glass thermometers are used asreference or working temperature standards inverification and calibration of thermometers and alsoin determining the conditions necessary for evaluating

the performance of other measuring instruments usedin legal metrology and industry.

2.2 Liquid-in-glass thermometers are also used inclinical laboratories for blood testing, enzyme, andother clinical analysis.

2.3 Quality control can be maintained in laboratorytemperature measurements by inter-laboratory com-parisons using liquid-in-glass thermometers.

3 Terminology

Note: For general terms in metrology and in legalmetrology, refer to the International vocabularyof basic and general terms in metrology (VIM,1993 edition) and to the International vocabularyof terms in legal metrology (VIML, 2000 edition)[1].

3.1 Stem

Tube containing the capillary through which thethermometric liquid moves with a change oftemperature.

3.2 Bulb

Reservoir for the thermometer liquid.

3.3 Contraction chamber

Enlargement of the capillary that is located below themain scale or between the main scale and auxiliaryscale and that serves to reduce the length of thethermometer or to prevent contraction of the liquidcolumn into the bulb.

Liquid-in-glass thermometers

(1) Applies only to the French text.

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3.4 Expansion chamber

Enlargement at the upper end of the capillary toprovide protection against possible bulb distension orbreakage as a result of excessive liquid and gaspressures when a thermometer is exposed to atemperature greater than its working range.

3.5 Main scale

Scale graduated in appropriate units, covering theworking temperature range of the thermometer.

3.6 Auxiliary scale

Short, optional scale, either at the lower end or theupper of the thermometer, that contains a referencepoint, usually the ice point (0 C).

3.7 Reference point

Temperature usually at a physical phase transition,such as the ice point or triple point of water, at which athermometer is checked for changes in bulb volumeand for separation of the liquid in the capillary.

3.8 Measuring (working) temperature range

Set of values of temperature for which the error of thethermometer is intended to lie within specified limits.

3.9 Maximum permissible errors (MPEs)

Extreme values of an error permitted by specifications,regulations, etc. for a given liquid-in-glass thermo-meter.

3.10 Accuracy class

Class of liquid-in-glass thermometers that meet certainmetrological requirements intended to keep errorswithin specified limits.

4 Description of the instrument

Note: For more details concerning the design,construction, use and testing of liquid-in-glassthermometers, see references [2] and [3].

4.1 Principal features of a liquid-in-glassthermometer

4.1.1 A liquid-in-glass thermometer consists of a bulb,stem, thermometric liquid, and an inert gas above theliquid column. These and other features of a solid-stemthermometer and of an enclosed-scale thermometerare shown in Figure 1, a) and b) respectively.

4.1.2 A thermometer may have one or two enlarge-ments in the capillary. One enlargement is theexpansion chamber located at the top of the thermo-meter. Its purpose is to reduce the pressure build-up ingas filled thermometers and to accommodate excessiveliquid when the thermometer is exposed to atemperature greater than its working range.

4.1.3 Another enlargement is the contraction cham-ber. This chamber is usually below the main scale orbetween the main scale and the auxiliary scale. Itspurpose is to reduce the length of capillary; however, itslocation with respect to the scale should be such that itallows the thermometer to perform properly.

Figure 1 Principle features of liquid-in-glass thermometers:a) solid stem thermometer, b) enclosed scale termometer.

Protective glass sheath

Main scale

Auxiliary scale

Bulba b

Stem

Expansion chamber

Contraction chamber

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4.1.4 It may not be necessary for a thermometer tohave a contraction chamber or expansion chamber. Ifan expansion chamber is not present, then a length ofcapillary of uniform cross section located between theupper end of the main scale and the upper end of thethermometer may serve the same purpose.

4.2 Types of liquid-in-glass thermometers

4.2.1 A solid-stem thermometer consists of a tubular,thick-walled capillary tube with a bulb fused to thebottom and the top fused closed. The scale is markedon the surface by an appropriate method to establish apermanent scale.

4.2.2 An enclosed-scale thermometer consists of asmall tube with capillary attached to a scale in a fixedrelationship. The bottom of the tube is fused to a bulb,and the top is fused closed. The scale and capillary tubeare enclosed in a protective glass sheath. A sleeve ofmetal, or other suitable material, is attached to the topor a glass finish is provided.

4.3 Immersion

Note: The liquid-in-glass thermometers addressed inthis Recommendation are supported vertically.

4.3.1 A complete-immersion thermometer is designedto indicate temperature correctly when the entirethermometer is exposed to the temperature beingmeasured. This requires the thermometer to beimmersed in a clear liquid in a container having ameans to observe its scale. The reading of thethermometer may be influenced by the hydrostaticpressure exerted on the bulb which depends on theliquid in which it is immersed and the depth of itsimmersion. Hence, such parameters may need to betaken into account.

4.3.2 A partial-immersion thermometer is designed toindicate temperature correctly when the bulb and aspecified part of the stem are exposed to thetemperature being measured. The remainder of thestem (emergent stem) is exposed to temperatures thatare variable and different from the medium beingmeasured. For measurements of greatest accuracy, thetemperature of the emergent stem of the thermometershould be specified. If the actual temperature of theemergent stem is different from the specifiedtemperature, it is usually necessary to apply an

emergent stem correction. For this purpose, theaverage temperature of the emergent stem can bemeasured using a faden thermometer (i.e. a thermo-meter with an extended bulb, see references [2] and[3]). A partial-immersion thermometer should haveeither a marked immersion line or a physical indicationof the immersion depth.

4.3.3 A total-immersion thermometer is designed toindicate temperature correctly when the bulb and theportion of the thermometer stem containing thethermometric liquid are exposed to the temperaturebeing measured. It is necessary, however, for themeniscus of the thermometric liquid in the stem of thethermometer to be above the level of the medium beingmeasured in order to be read properly (usually, one ortwo scale divisions). An error may occur when thethermometric liquid in the emergent stem is above andat a different temperature than the medium beingmeasured. Such errors can be compensated for byapplying an emergent-stem correction.

5 Metrological requirements

5.1 General

The scale of a thermometer shall be graduated andmarked in degrees Celsius (C) and traceable to na-tional and international standards and in accordancewith the International Temperature Scale of 1990 (ITS-90).

5.2 Accuracy class

5.2.1 Thermometers of all immersion types shall beassigned an accuracy class based on their maximumpermissible error.

5.2.2 The following accuracy classes shall apply:

Accuracy class Maximum permissible error (MPE) (C)

A 0.1B 0.2C 0.5D 1.0E 2.0F 5.0

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5.2.3 The manufacturer shall specify the measuringtemperature range over which the accuracy classapplies. The measuring temperature range specifiedshall be defined by the extreme values of the markedscale on the thermometer and shall be extended by aspecified number of graduated divisions necessary toenable verification of the accuracy class of thethermometer. On the basis of experience, theachievable maximum errors over specified measuringtemperature ranges for some thermometric liquidsused in liquid-in-glass thermometers are listed inAnnex A.

5.2.4 The temperature scale for a specific accuracyclass of thermometers shall have a scale interval equalto the absolute value of the maximum permissibleerror. Smaller scale intervals shall be permittedprovided that no more than 14 scale marks percentimeter are included.

Note: The temperature scale should be marked so thatits resolution, or readability, is such that anobserver can estimate a reading to at least one-half of one scale division without the aid of anoptical device other than eyeglasses normallyused for correcting vision.

5.3 Auxiliary scale

The maximum permissible error of an auxiliary scale,if included, shall be the same as that for the main scaleof the thermometer.

6 Technical requirements

6.1 The thermometric liquid used in a thermometershall be appropriate for its indicated measuring range.Mercury may be used for temperature measurementfrom 38 C to + 500 C, and an organic liquid may beused for temperatures from 200 C to + 200 C. Theorganic liquid may include a dye to aid in reading thethermometer if the dye is insensitive to light and doesnot stain the glass.

Note: Since the organic liquid adheres to the capillarysurface, adequate time is necessary for the liquidto drain, especially when used at low tem-peratures.

6.2 A dry inert gas, such as nitrogen, shall beintroduced in the capillary above the mercury columnat sufficient pressure to retard mercury vaporization athigher temperatures and to prevent the oxidation of themercury column.

6.3 The capillary shall not have observabledimensional irregularities in diameter or containextraneous material, such as small glass chips.

6.4 The scale spacing shall either be uniform forthermometers filled with mercury or other liquid witha constant coefficient of expansion over the measuringrange, or shall vary over the length of the scale in orderto accommodate the nonlinear coefficient of the liquid.The scale marks indicating intervals shall be clear,straight, uniform in length and width, and indelible.Solid stem thermometers should be provided with anopaque white or yellow enamel strip to facilitatedetection of the capillary and reading of level of themeniscus.

6.5 The values and sequence of temperature markedon the scale shall be clear and legible and in the properorder. Enclosed-scale thermometers shall be providedwith a mark to verify the correct position of the stripbearing the scale with regard to the capillary. For atube with the capillary having a prismatic crosssection, no distortion shall exist when viewing theliquid column over its full length from a fixed position.

6.6 The scale shall be placed on the thermometeraccording to the following criteria with the lengthsspecified being minimum values and greater valuesbeing acceptable (see Figure 2).

6.6.1 A 13 mm length of unchanged capillary betweenthe bulb and the immersion line or lowest scale markwhen the scale mark value is less than or equal to100 C, and a 30 mm length when the lowest scale markvalue is greater than 100 C.

6.6.2 A 5 mm length of unchanged capillary betweenthe contraction chamber and the auxiliary scale markbelow, if an auxiliary scale is present. This does notapply to the expansion chamber.

6.6.3 A 10 mm length of unchanged capillary betweenthe contraction chamber, other than the bulb, and theimmersion line or scale mark located above when thescale mark value is less than or equal to 100 C and a30 mm length when the scale mark value is greaterthan 100 C.

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6.6.4 A 10 mm length of unchanged capillary abovethe highest scale mark when an expansion chamberexists at the upper end of the thermometer, and a30 mm length for a thermometer without an expansionchamber.

6.7 The auxiliary scale, when included, shall have aminimum of ten scale divisions, five above and fivebelow the reference point.

6.8 The bulb of the thermometer shall be free of gas.If gas is present, the gas shall be removable (see AnnexB).

6.9 The liquid in the capillary shall be united. Ifseparation has occurred, it shall be possible to reunitethe liquid (see Annex B).

6.10 The markings indicating the thermometer scaleshall be permanent and the lines shall be uniform andnot wider than one fifth of the scale spacing.

Note: Markings may be applied by etching and thenfilled with a pigment, silk screening, or baked-in.

6.11 The bulb and stem of the thermometer shall bemade of an appropriate thermometric glass for thespecified measuring temperature range and for therequired stability of readings.

Note: The glass should be stabilized by heat treatment,in order that it can endure expected temperatureand mechanical stress and shock. It should notinclude defects likely to impair its readability.The bulb should not be greater in diameter thanthe stem except in special cases. See reference[4].

6.12 Each thermometer shall be marked or labeledpermanently with the indication C or C next to thescale, the manufacturers trade name or mark, serialnumber, and accuracy class. For partial immersionthermometers, the immersion depth shall be eithermarked by a line or by another physical indication. Theimmersion depth shall also be labeled on thethermometer. For accuracy classes A and B, themanufacturer shall specify the emergent stemreference temperature for partial immersion thermo-meters.

7 Practical instructions

7.1 When selecting a thermometer for a particularapplication, the range of temperature and maximumpermissible error required for the measurementsshould be determined. In particular, the ambientconditions under which the thermometer is usedshould be considered.

7.2 If the thermometer is to be used at partialimmersion, it should be determined whether thetemperature of the emergent stem will be close to thevalue specified for its use. Otherwise, appropriatecorrections need to be calculated and applied (see 4.3.2and references [2] and [3]).

7.3 If the thermometer has to fit into a specialapparatus or other equipment, its proper length anddiameter should be selected according to whether atotal-immersion or a partial-immersion thermometer isrequired.

Figure 2 Capillary clearances (minimum values)

13 mm 5 mm 10 mm

30 mm

10 mm (Scale mark value above is less than or equal to 100 C)30 mm (Scale mark value above is greater than 100 C)

13 mm (Lowest scale mark value is less than or equal to 100 C)30 mm (Lowest scale mark value is greater than 100 C)

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7.4 Organic thermometric liquids are highly volatilehaving low surface tension, and, therefore, distillationof the thermometric liquid and separation of the liquidcolumn may occur. Special care should be taken in thestorage, preparation, and use of such thermometers.

8 Metrological controls

8.1 Type evaluation

8.1.1 The manufacturer shall submit for evaluation tothe national responsible body, a representative sampleof the thermometer type, along with appropriate andcomplete instructions for thermometer. Test data mayalso be provided that demonstrates that thethermometer type meets the performance require-ments according to this Recommendation.

8.1.2 The national responsible (or authorized) bodyshall carry out visual inspection and performance testsor may accept the manufacturers test data that canassist in determining whether a thermometersperformance meets the requirements of thisRecommendation. The performance tests shall becarried out in a laboratory at ambient temperaturewithin 23 C 3 C and with a temperature stabilityduring the testing period of 1 C. The procedures foran overall test of thermometers, including metrologicaland technical requirements, are given in Annex C.

8.1.3 Visual inspection includes the following:

capillary of uniform diameter and free of extraneousmaterial (6.3 and C.1.1);

scale spacing uniform or varying according to theexpansion coefficient of the thermometric liquid (6.4and C.1.2);

scale marks clear, straight, and uniform (6.4 andC.1.3);

temperature values on the scale in proper sequenceand placement (6.5 and C.1.4);

scale on thermometer in correct location (6.6 andC.1.5);

marking of auxiliary scale, if included (6.7 andC.1.4);

bulb free of gas (6.8, B.2 and C.1.6); liquid completely united in the capillary (6.9, B.3 and

C.1.7); labeling (6.12).

8.1.4 Performance tests include the following:

permanency of scale marks (6.10 and C.2); bulb stability (6.11 and C.3);

errors of thermometer scale (5.2 and C.4); errors of the auxiliary scale or reference point, if

included (5.3 and C.4.5).

8.1.5 The report on the thermometers visualinspection and performance tests carried out duringtype evaluation shall contain at least the items ofinformation according to the format provided in AnnexD. A specific format may be developed according tonational preference for national use. The manufacturershall be provided specific comments for each testfailure.

8.2 Initial and subsequent verification

8.2.1 The visual inspection and performance testsspecified in 8.1.3 and 8.1.4, except for the first pointunder 8.1.4, shall be carried out during initial orsubsequent verification.

8.2.2 The period of validity of initial or subsequentverifications shall be specified by the nationalresponsible body.

8.3 Certificates may be issued for a thermometerthat successfully passes type evaluation and initial andsubsequent verification tests.

8.4 Liquid-in-glass thermometers may be used assecondary and reference standards when calibrated.Uncertainties that may be achieved for calibratedthermometers over specified temperature ranges arelisted in Annex E only as a guide.

References

[1] International vocabulary of basic and generalterms in metrology, (VIM, 1993 edition) andInternational vocabulary of terms in legalmetrology, (VIML, 2000 edition)

[2] ISO 386:1977 Liquid-in-glass laboratorythermometers - Principles of design, constructionand use, International Organization forStandardization

[3] Wise, J. A., Liquid-in-Glass ThermometerCalibration Service, NIST Special Publication250-23 (1998), National Institute of Standardsand Technology, Gaithersburg, MD 20899, USA

[4] ISO 4795:1996 Glass for thermometer bulbs,International Organization for Standardization

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A.1 The achievable maximum errors for liquid-in-glass thermometers, as given in Tables 1 and 2, list themeasuring temperature ranges and thermometricliquids for which experience has indicated the accuracyclasses are currently achievable.

Note: The values are valid when determined undercontrolled laboratory conditions (see C.4).

A.2 Table 1 provides a listing of the achievablemaximum errors for total immersion liquid-in-glassthermometers filled with either mercury or an organicliquid.

A.3 Table 2 provides a listing of the achievablemaximum errors for partial immersion liquid-in-glassthermometers filled with either mercury or an organicliquid.

Annex A

Achievable maximum errors for thermometers

(Informative)

Accuracy Temperature range in C

class 200 38 0 + 50 + 100 + 200 + 300 + 360

(MPE)ato to to to to to to to

38b 0 + 50 + 100 + 200 + 300 + 360 + 500

A Mc M M ( 0.1)

B M M M M ( 0.2)

C M M M M M ( 0.5)

D M M M M M ( 1.0)

E Od M/O M/O M/O M/O M M ( 2.0)

F O M/O M/O M/O M/O M M M ( 5.0)

Table 1 Achievable maximum errors for total immersion thermometers

a MPE means maximum permissible error in C.b 38.8 C is the freezing point of mercury. c M symbolizes a mercury filled thermometer.d O symbolizes an organic liquid filled thermometer.

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Accuracy Temperature range in C

class 200 38 0 + 50 + 100 + 200 + 300 + 360

(MPE)ato to to to to to to to

38b 0 + 50 + 100 + 200 + 300 + 360 + 500

A ( 0.1)

B Mc M ( 0.2)

C M M M M ( 0.5)

D M M M M M ( 1.0)

E M M M M M M ( 2.0)

F Od M/O M/O M/O M/O M M M ( 5.0)

Table 2 Achievable maximum errors for partial immersion thermometers

a MPE means maximum permissible error in C.b 38.8 C is the freezing point of mercury. c M symbolizes a mercury filled thermometer.d O symbolizes an organic liquid filled thermometer.

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B.1 This Annex provides examples of methods bywhich defects in the thermometric liquid in the bulband capillary of the thermometer may be eliminated,namely, removing trapped gas and reuniting separatedliquid. Other equivalent methods may also be effective.

B.2 By visual inspection, examine the bulb of thethermometer to determine the presence of any trappedgas that will appear as a circle on the inner surface ofthe bulb glass. If gas is present, remove it by thefollowing or equivalent method.

Note: This method is applicable only for mercury filledthermometers. This inspection may be carriedout with the aid of a low-power microscope ormagnifier.

B.2.1 Immerse only the lower half of the bulb intopowdered carbon dioxide (dry ice) or a mixture ofpowdered dry ice and alcohol.

Note: Do not immerse the bulb for too long a period oftime because the mercury could freeze and thenbreak the bulb if the lower portion of themercury in the bulb thaws before the mercury atthe top.

B.2.2 When the mercury has come down into thelower part of the cone, which joins the bulb to the stem,remove the thermometer from the dry ice. Hold it inthe inverted position, and then tap it once against theside of your hand to introduce a large gas bubble in thebulb. Tap and rotate the thermometer against yourhand, to cause the large gas bubble to come in contactwith all of the inner surface of the bulb, thus removingsmaller gas bubbles that are present.

B.2.3 Examine the thermometer again under themicroscope to ensure that all small gas bubbles havebeen removed. When only the large gas bubble ispresent and at the top of the bulb, place the lower halfof the bulb back into the dry ice and bring all of themercury into the cone or top of the bulb. Remove thethermometer from the dry ice. While in an uprightposition, swing the thermometer in a circle or slightly

tap the bulb on a soft surface, such as a rubber stopper.Either of these two methods will force the large bubbleout and reunite the mercury column.

B.3 Use one of the following or an equivalentmethod as appropriate to reunite a separated liquidcolumn.

B.3.1 For a mercury filled thermometer, use dry ice tocause all of the mercury to descend into the bulb orlower. Remove the thermometer from the dry ice andtap it on a soft object, such as a rubber stopper, tobreak away the separated mercury from the wall of thebulb or cone. Allow the thermometer to come to roomtemperature, and the mercury column will then bereunited.

B.3.2 For a mercury filled thermometer with anexpansion chamber and a separation in the upperportion of the liquid column, heat the thermometerbulb to allow the separated portion and the top of themercury column to reunite into the expansion chamberand, thereby, cause the gap between separated portionsto become very thin when the mercury gets into thelarger diameter of the expansion chamber. Break awaythe mercury from the wall of the chamber by tappingthe thermometer against your hand. Then slightly tapthe thermometer on a soft surface to force the mercurydown to the bottom of the expansion chamber where itcan be picked up by the top of the mercury column asthe thermometer is heated again.

Note: When using this method (which is not applicableif it requires the thermometer to be heated above260 C), do not heat the thermometer with aconcentrated heat source, such as a flame.Preferably, heat the thermometer with a liquidthat has a boiling point and flash point above thehighest graduation on the thermometer. If thebulb is heated, then the thermometer should bestored for a period of at least 72 hours beforecarrying out any of the performance tests.

B.3.3 For a mercury filled thermometer with acontraction chamber, either cool or heat the

Annex B

Methods for eliminating defects in the thermometric liquid

(Informative)

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thermometer, as appropriate, to bring the separationinto the contraction chamber. After this small portionof mercury is in the chamber, slightly tap thethermometer to force the mercury from the wall andinto the form of a drop. Either tap, heat, or cool thethermometer to reunite the drop of mercury with themain column.

B.3.4 For a mercury filled thermometer that has asmall drop of mercury in the expansion chamber and isgraduated beyond 200 C, invert the thermometer andplace it in an oil bath having a temperature of 200 C to300 C causing the mercury drop to distill andcondense inside the capillary within the main scale andoutside of the bath medium. Then remove thethermometer from the oil bath and allow it to cool.Return the thermometer to its upright position, andplace the bulb, including the lower portion of the stem,in the oil bath causing the mercury column to rise in

the capillary that is within the main scale, thus pickingup the condensed mercury.

B.3.5 For an organic-liquid filled thermometer, reunitethe separated liquid either (a) by forcing the separatedportion and the top of the organic liquid column intothe expansion chamber as described in B.3.2 or (b) bydispersing the separated liquid (because the capillary islarge) by tapping the thermometer against the side ofyour hand and then holding the thermometer uprightcausing the dispersed liquid to flow down the capillary,thus joining the main column. Heat the top of anorganic liquid filled thermometer before using it sincea clear organic liquid can condense in the expansionchamber.

B.3.6 Use centrifugal force to reunite the separatedliquid by placing the thermometer in a centrifuge withthe bulb oriented outward.

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C.1 Visual inspection

C.1.1 Examine the entire capillary of the thermometerto determine that it is uniform without any observabledeformity or irregularities and free of extraneousforeign material.

Note: Objects such as glass chips, which may get intothe capillary during manufacturing, can movewithin the capillary and thereby hold the liquidor trap gas which can cause the thermometerreadings to be erratic. This inspection may becarried out with the aid of a low-powermicroscope or magnifier.

C.1.2 Using a length measuring device, ensure that thescale graduations of the thermometer are uniformlyspaced with no appreciable variations from one end ofthe scale to the other. This applies to thermometerswith thermometric liquids of constant expansion overthe temperature scale (6.4). Owing to of the non-uniform expansion of an organic fluid, organic-liquidfilled thermometers may show a more significantvariation in the scale spacing than mercury filledthermometers.

C.1.3 Using a length measuring device, examine thescale marks of the thermometer. These marks shall beclear with sharp edges, straight, uniform, and of theproper length. They shall not be wider than one fifth ofthe scale spacing (i.e. the distance between the centerof the scale marks). For an enclosed-scale thermo-meter, check the correct position of the strip bearingthe scale. For a prismatic cross-section capillarythermometer, check the capillary for possible distortionby viewing the liquid column over its full length from afixed position.

C.1.4 Examine the numbers and sequence on thescale(s) of the thermometer. The numbers shall be clearand legible and in the proper sequence and shallcorrespond to the correct line on the scale. If anauxiliary scale is included, check its conformity with6.7.

C.1.5 Using a length measuring device, check theminimum distances related to the scale specified in 6.6to within 1 mm. The distances shall not be smallerbut may be greater than those specified.

C.1.6 Examine the bulb of the thermometer fortrapped gas. If present, remove the gas using themethod given in B.2 or an equivalent method.

C.1.7 Determine whether the thermometric liquid iscontinuous. If not, reunite the liquid using one of themethods given B.3 or an equivalent method.

C.2 Permanency of scale markings

C.2.1 Expose a portion of the scale to a temperature ofapproximately 260 C or its specified maximumtemperature, whichever is lower, for about 3 hours.After that time, remove the thermometer, allow it tocool, and compare the heated portion of the scale withthe portion that was not heated.

C.2.2 The thermometer shall pass this test if thepigment does not appear to be loosened, burned out,chalked, or faded.

C.3 Bulb stability

C.3.1 Immerse the entire bulb of the thermometer intoa bath or furnace at a temperature equal to thespecified maximum temperature of its working range.After the thermometer has reached temperatureequilibrium, as evidenced by observing the levelchanges of the thermometric fluid, remove the

Annex C

Test procedure

(Mandatory)

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thermometer from the bath or furnace and let it coolslowly in air to a temperature of 20 C above ambienttemperature or 50 C, whichever is lower. Place thethermometer in a reference bath, such as an ice bath,and record its indicated temperature within 1 hour.

C.3.2 Place the thermometer bulb back in the heatedbath or furnace (C.3.1). After a period of 24 hours,remove the thermometer and allow it to cool in thesame manner as described in C.3.1. Place thethermometer in the reference bath (C.3.1) and recordthe indicated temperature.

C.3.3 The difference between the temperaturemeasured in C.3.2 and that measured in C.3.1 shall bewithin 70 % of the maximum permissible error of thethermometer.

C.4 Errors over the working temperature range

C.4.1 A reference thermometer and a closed-top,constant-temperature bath shall be used to test aliquid-in-glass thermometer to determine whether itsindications are within the maximum permissible errorspecified in 5.2.2. Measurements shall be made at leastat the extreme values of the working temperature rangefor the accuracy class specified by the manufacturerand at one or more temperature values in between theextreme values. Measurements shall also be made at areference point if provided. If the thermometer has anauxiliary scale, one value on the auxiliary scale shall bechecked.

Note: Before this test is conducted, the thermometershould remain at room temperature for at leastthree days to allow the bulb to stabilize.

C.4.2 Use a reference thermometer with a validcalibration and an uncertainty value over the requiredmeasuring temperature range of no larger than one-fourth the absolute value of the maximum permissibleerrors of the thermometer being tested.

Note: The reference thermometer may be a calibratedindustrial platinum resistance thermometer withan appropriate resistance measuring instrument,a digital thermometer, a thermistor with a digitalvoltmeter and constant current source, orpreferably another liquid-in-glass thermometer.

C.4.3 Use a closed-top, constant-temperature bathhaving a uniform and regulated temperaturethroughout the medium and having a volume largeenough and of sufficient depth to accommodate thenumber and types of thermometers being tested.Regulate the bath temperature to within 0.01 C suchthat the temperature variation within the usableportion of the bath shall be within 0.05 C.

Note: Manufacturers of constant-temperature bathsshould be consulted about the appropriate oilsand salts available. The following media shouldbe considered for use in the bath over theindicated temperature range:

200 C liquid nitrogen 150 C to 50 C methyl pentane 50 C to 0 C ethanol+ 5 C to + 95 C water+ 95 C to + 200 C oil+ 200 C to + 500 C molten salt

C.4.4 At liquid nitrogen temperature (approximately 200 C), check the error by immersing the referencethermometer and thermometer to be tested in a Dewarflask containing liquid nitrogen. Within approximatelytwo to three minutes after the reference thermometerindicates that the bath is in a steady temperature state,read the two thermometers, one immediately after theother. The difference between the two readings shallnot exceed the maximum permissible error for thethermometer under test.

C.4.5 In the temperature range from 110 C to+ 500 C, check the errors by using closed-top constanttemperature baths as described in C.4.3. Place thethermometer to be tested in the bath with the referencethermometer. If the thermometer under test is a total-immersion thermometer, immerse it in the bath so thatthe meniscus is within 10 mm above the surface of theliquid. If the thermometer under test is a partial-immersion thermometer, immerse it to the immersionline or to the specified depth. At subsequent highertemperature points, immerse the total-immersionthermometer further into the liquid so that themeniscus is always within 10 mm above the surface ofthe liquid and keep a partial-immersion thermometerin the initial position throughout the entire test. Whentesting an organic-liquid filled thermometer, allowadequate time for the liquid to drain down the capillaryfor temperature below room temperature. Withinapproximately two to three minutes after the referencethermometer indicates a stable bath temperature, readit and the thermometer being tested simultaneously.

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The differences between the two readings shall notexceed the maximum permissible error for thethermometer under test.

C.4.6 At the ice point (0 C) temperature, check theerror by immersing the thermometer to be tested in anice bath. Prepare an ice bath by adding crushed ice tocooled distilled water to form a slush. As the ice melts,it may be necessary to drain off some of the water andadd more crushed ice. For a total-immersionthermometer, place it in the bath so that the meniscusis about two scale divisions above the surface of the iceor remove the totally immersed thermometer quicklyfrom the bath for reading; for a partial-immersion

thermometer, immerse it to its immersion line or to thespecified depth. With the thermometer at the properdepth, pack ice around it and wait at least 1 to 2minutes for the thermometer to reach equilibrium.Before reading, tap the thermometer lightly toeliminate the possibility of the mercury being stuck inthe column. The difference in indication of thethermometer under test and 0 C shall be within themaximum permissible error for the thermometerunder test.

Note: This test also applies to checking the errors of anauxiliary scale, if included. The ice should bemade using laboratory grade water that may bedistilled, de-ionized, or filtered.

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Annex D

Test Report Format

(Mandatory for application within the OIML Certificate System for Measuring Instruments)

This Test report format presents, in a standardized way, the results of the various tests and examinations to which apattern (or type) of a liquid-in-glass thermometer shall be submitted when being considered for approval. Thesetests are listed in Annex C to this Recommendation.

In the case of the application of this Recommendation: to the OIML Certificate System for Measuring Instruments, use of this Test report format is mandatory. in national regulations (and in other cases), use of this Test report format is informative. However, in this case:

it is strongly recommended that all metrology services or laboratories evaluating patterns (or types) ofliquid-in-glass thermometers according to national regulations based on this Recommendation should usethis Test report format directly, or after translation into a language other than English or French;

it is even more strongly recommended that this Test report format is used directly in English or French, orin both languages, whenever test results may be transmitted by the country performing these tests to theapproval authorities of another country, for example under bi- or multi-lateral cooperation agreements.

A test report intended for use in the OIML Certificate System or for other purposes shall include the followinginformation.

Report No.: ................................................................................................

OIML Recommendation No.:...................................................................

Edition (year): ...........................................................................................

D.1 Name and address of the testing laboratory(ies)

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.2 Location at which tests were performed if other than that indicated in D.1

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

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D.3 Name and address of the manufacturer

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.4 Name and address of applicant if other than the manufacturer

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.5 Identification of the type tested:

trade name .........................................................................................................

type number .......................................................................................................

serial number .....................................................................................................

accuracy class ....................................................................................................

scale interval ......................................................................................................

measuring temperature range ..........................................................................

immersion type ..................................................................................................

D.6 Summary of the visual inspection

D.6.1 Capillary of uniform diameter and free of foreign material:

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

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D.6.2 Scale spacing of a uniform width (or adapted to the expansion of the thermometric liquid):

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.6.3 Scale marks clear, straight, and uniform:

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.6.4 Temperature values on the scale are in correct sequence and placement:

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.6.5 Scale placed on the thermometer as specified in 6.6 (and 6.7 if an auxiliary scale is included):

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

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D.6.6 Gas in the thermometer bulb: yes n no nGas successively removed: yes n no n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.6.7 Liquid separated: yes n no nLiquid successfully reunited: yes n no n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.6.8 Labeling of the thermometer:

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.7 Summary of performance tests

D.7.1 Permanency of scale markings:

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

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D.7.2 Bulb stability test:

Reference temperature: ....................... Temperature indication of thermometer under test: ....................... Difference: .......................

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.7.3 Errors of the thermometer:

Testing laboratory ambient temperature:before the test: .......................after the test: .......................

Reference thermometer:type: .......................uncertainty: .......................date of last calibration: .......................accuracy class specified by the manufacturer (if applicable): .......................measuring temperature range: .......................

For a partial-immersion thermometer under test:emergent stem reference temperature: .......................measured emergent stem temperature: .......................correction .......................

Note: For partial-immersion thermometers of accuracy classes A and B, emergent stem temperature correctionsmay be required. In such cases, spaces shall be provided in the following table to record the emergent stemreference temperature, the measured emergent stem temperature and the corrected measured temperaturevalue.

pass n fail n

Temperature indication in C

Reference thermometer Thermometer under test Difference (error)

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Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.7.4 Errors of the auxiliary scale, if included, and/or reference point:

Reference temperature: .......................

Temperature indication of thermometer under test: .......................

Difference: .......................

pass n fail n

Comments:

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

................................................................................................................................................................................................

D.8 A brief statement of conclusions as to whether the thermometer tested meets therequirements of this Recommendation:

D.9 Person(s) responsible for the testing:

Signature(s) and title(s): .........................................................................

Date: .........................................................................................................

23

Annex E

Achievable uncertainties for calibrated thermometers

(Informative)

E.1 Liquid-in-glass thermometers may be used as secondary or reference standards.

E.2 Table 3 provides a listing of the achievable expanded uncertainties (k = 2) in calibration for total immersion,liquid-in-glass thermometers.

E.3 Table 4 provides a listing of the achievable expanded uncertainties (k = 2) in calibration for partial immersion,liquid-in-glass thermometers.

Note: The values given in Tables 3 and 4 are achievable under laboratory conditions and using a closed-top,constant temperature bath.

Table 3 Achievable expanded uncertainties (k = 2) in calibration for total immersion thermometers

a MPE means maximum permissible error in C.

b 38.8 C is the freezing point of mercury.

c Indicates an organic liquid filled thermometer; otherwise, the uncertainty values apply to mercury filledthermometers.

Accuracy Temperature range in C within specified limits

class 200 100 38b 10 10 10 10 10 10

(MPE)ato to to to to to to to to

+ 50 + 50 + 100 + 50 + 100 + 200 + 300 + 400 + 500

A 0.02 0.02 0.02( 0.1)

B 0.03 0.03 0.03 0.06 ( 0.2)

C 0.05 0.05 0.05 0.1 0.1 ( 0.5)

D 0.1 0.1 0.1 0.2 0.2( 1.0)

E 1.5c 0.2 0.2 0.2 0.5 0.5 1.0 ( 2.0) 1.5c 1.5c 1.5c 2.0c

F 3.0c 3.0c 0.5 0.5 0.5 1.0 1.0 2.0 3.0 ( 5.0) 3.0c 3.0c 3.0c 3.0c

OIML R 133: 2002 (E)

Table 4 Achievable expanded uncertainties (k = 2) in calibration for partial immersion thermometers

a MPE means maximum permissible errors in C.

b 38.8 C is the freezing point of mercury.

c Indicates an organic liquid filled thermometer; otherwise, the uncertainty values apply to mercury filledthermometers.

Accuracy Temperature range in C within specified limits

class 200 100 38b 10 10 10 10 10 10

(MPE)ato to to to to to to to to

+ 50 + 50 + 100 + 50 + 100 + 200 + 300 + 400 + 500

A ( 0.1)

B 0.05 0.05 ( 0.2)

C 0.1 0.1 0.1 0.2 ( 0.5)

D 0.2 0.2 0.2 0.3 0.5 ( 1.0)

E 0.5 0.5 0.5 1.0 1.0 2.0 ( 2.0)

F 4.0c 4.0c 1.0 1.0 1.0 2.0 2.0 3.0 4.0 ( 5.0) 4.0c 4.0c 4.0c 4.0c

Printed in France GRANDE IMPRIMERIE DE TROYES

OIML R 133: 2002 (E)