3.899.5275.200 Issue 2 - 2008

© Copyright 2008

Resistance thermometers and thermocouple assembliesInstallation and maintenance manual

1.

2.

3.

4.

5.

General

Resistance thermometersassembly

Thermocouple assemblies

Receipt and handling ofmaterials

Typical faults / remedies

The PED Directive 97/23/EC is repealed and replaced by the new PED Directive 2014/68/EU with effect from 19 July 2016.

The ATEX Directive 94/9/EC is repealed and replaced by the new ATEX Directive 2014/34/EU with effect from 20 April 2016.

ATTENZIONE Lavorare in sicurezza con apparecchiature

in ghisa e vaporeWorking safely with cast iron products on steamInformazioni di sicurezza supplementari - Additional Informations for safety

Lavorare in sicurezza con prodotti in ghisa per linee vaporeI prodotti di ghisa sono comunemente presenti in molti sistemi a vapore. Se installati correttamente, in accordo alle migliori pratiche ingegneristiche, sono dispositivi totalmente sicuri. Tuttavia la ghisa, a causa delle sue proprietà meccaniche, è meno malleabile di altri materiali come la ghisa sferoidale o l’acciaio al carbonio. Di seguito sono indicate le migliori pratiche ingegneristiche necessarie per evitare i colpi d'ariete e garantire condizioni di lavoro sicure sui sistemi a vapore.

Movimentazione in sicurezzaLa ghisa è un materiale fragile: in caso di caduta accidentale il prodotto in ghisa non è più utilizzabile. Per informazioni più dettagliate consultare il manuale d'istruzioni del prodotto.Rimuovere la targhetta prima di effettuare la messa in servizio.

Working safely with cast iron products on steamCast iron products are commonly found on steam and condensate systems. If installed correctly using good steam engineering practices, it is perfectly safe. However, because of its mechanical properties, it is less forgiving compared to other materials such as SG iron or carbon steel.The following are the good engineering practi-ces required to prevent waterhammer and ensu-re safe working conditions on a steam system.

Safe HandlingCast Iron is a brittle material. If the product is dropped during installation and there is any risk of damage the product should not be used unless it is fully inspected and pressure tested by the manufacturer. Please remove label before commissioning

VaporeSteam

Flusso Flow

Esempi di esecuzioni corrette ( ) ed errate ( ) sulle linee vapore:Steam Mains - Do's and Dont's:

Flusso Flow

Prevenzione dai colpi d’ariete - Prevention of water hammerScarico condensa nelle linee vapore - Steam trapping on steam mains:

Intervalli di 30÷50 m. intervals

Pendenza - Gradient 1:100VaporeSteam

Gruppo di scaricoTrap set

Condensa - Condasate

Pendenza - Gradient 1:100

Gruppo di scaricoTrap set

Gruppo di scaricoTrap set

Condensa - CondasateCondensa - Condasate

VaporeSteam

Prevenzione delle sollecitazioni di trazionePrevention of tensile stressingEvitare il disallineamento delle tubazioni - Pipe misalignment:

Installazione dei prodotti o loro rimontaggio post-manutenzione:Installing products or re-assembling after maintenance:

Evitare l’eccessivo serraggio.Utilizzare le coppie di serraggio

raccomandate.Do not over tighten.

Use correct torque figures.

Per garantire l’uniformità del carico e dell'allineamento, i bulloni delle flange devono essere serrati in modo

graduale e in sequenza, come indicato in figura.Flange bolts should be gradually tightened across

diameters to ensure even load and alignment.

Dilatazioni termiche - Thermal expansion:Gli esempi mostrano l’uso corretto dei compensatori di dilatzione. Si consiglia di richiedere una consulenza specialistica ai tecnici dell’azienda che produce i compensatori di dilatazione.Examples showing the use of expansion bellows. It is highly recommended that expert advise is sought from the bellows manufacturer.

GuideGuides

Distanza breveShort distance

Punto di fissaggioFixing point

Movimento assialeAxial movement

Distanza media Mediumdistance

Tiranti limitatoriLimit rods

Piccolo movimento

lateraleSmall lateral

movement

Piccolo movimento lateraleSmall lateralmovement

Ampio movimento

lateraleLarge lateral

movement

Ampio movimento lateraleLarge lateralmovement

GuideGuides

GuideGuides

GuideGuides

Punto di fissaggioFixing point

Tiranti limitatoriLimit rods

Movimento assialeAxial movement

3.899.5275.2002

1 GeneralResistance Thermometers and thermocouple Assemblies, together with their accessories, aresensitive products which must be handled carefully. They contain, even if not visible from theoutside, Glass and/or Ceramic parts which are susceptible to damage. Therefore, always handlethem with due care.Never lift assemblies by one end only. They should always be supported over their full length toavoid mechanical breakage.

2 Resistance Thermometer AssembliesWe supply complete Resistance Thermometer assemblies ready for immediate use. These shouldbe installed, in the medium whose temperature is to be measured, to such a depth that the heattransfer along the assembly, taking heat away from the source, is kept to a minimum (i. e. immersionof the order of 6 to 15 times the diameter of the assembly Pocket or Thermowell). However, in thecase of installations where only a small depth of immersion is possible, at least 1 to 1-1/2times thelength of the resistance element winding should be immersed.In pipes of small diameter this can often only be achieved by installing the assembly at an angle orbend. In all cases the unit should always be directed against the fluid flow.Assemblies will always be subjected to wear which will depend upon the field conditions and theirhandling.

2.1 Connecting LeadsI Connecting leads linking the Resistance Thermometer Assembly to the measuring instrumentshould be installed in accordance with the National Standards for electric cables relative to thecountry where the equipment is in use.NOTE: Copper leads only are required.Special care should be taken on installation to minimise contact resistance (acid free soldering orsimilar) as the voltage present in resistance thermometer circuits is considerably smaller thannormal line voltage and therefore will not penetrate any oxide layers at bad connection points.Poor contacts and insulation faults will simulate temperatures above or below the true value. Also,leads should not be run near to power lines.In some cases where highly sensitive instruments are in use it will probably be necessary to utilisescreened and twisted connecting leads in order to avoid pick- up.

2.2 MaintenanceAll assemblies should be checked at regular intervals to assess the level of erosion, corrosion orother possible damage to the protecting tube, i. e. Pocket or Thermowell.It is recommended that the entire installation be checked periodically by short-circuiting the resistancethermometer and bringing into the system a standard resistance of known value (hence simulatinga known temperature). Thus the entire circuit is easily checked for correct functioning.In general, no other maintenance checks are required.

3.899.5275.200 3

3 Thermocouple AssembliesWe supply complete Thermocouple Assemblies ready for immediate use.These should be installed, in the medium whose temperature is to be measured, to such a depththat the heat transfer along the assembly, taking heat away from the source, is kept to a minimum(i. e. immersion of the order of 6 to 15 times the diameter of the assembly Pocket or Thermowell).If the assembly has a Ceramic outer protecting tube, this should be protected against impact withother solids in order to avoid mechanical breakage and/or excessive mechanical stresses.For all assemblies, vertical installation is to be preferred, especially for long assemblies, in order toavoid sagging of the metal or ceramic protecting tubes.Flame contact should be avoided in all cases.Ceramic protecting tubes should always be heated up slowly, preferably being installed with thetemperature source cold so that both are heated up together. if this is not possible then ceramicprotecting tubes must be pre-heated before installation in order to avoid damage by thermal shock.Connection Head temperatures should never exceed 200°C.Both the Thermocouple Wires and the Protecting Tubes, i. e. Pocket or Thermowell, will be subjectedto wear etc. which will depend upon the field conditions and the handling of assemblies.

3.1 Compensating / Connecting LeadsCompensating Leads / Connecting Leads between the Thermocouple Assembly and the measuringinstrument should be installed according to the National Standards for electric cables relative tothe country where the equipment is in use.At all times the insulation resistance to earth should be at least 1 MOhm.If Compensating Leads are used they must correspond to the type of Thermocouple in use.Correct polarity for connections should be observed at all times in order to avoid “read-out” errors.All connections must be clean and metal bright.Cable runs should preferably not be near to other electric cables in order to avoid induction problems.Where such difficulties are likely to arise, screened and twisted cable should be used.

3.2 MaintenanceAll thermocouples should be checked at regular intervals to assess levels of erosion, corrosion orother possible damage to the protecting tube.In order to do this, it is usually necessary to withdraw the thermocouple from service and in suchcases extreme care should be taken when handling assemblies having ceramic protecting tubesas they are very fragile, especially when hot. Such assemblies should be withdrawn slowly andshould be replaced equally slowly in order to avoid thermal shock problems.Base metal thermocouples will tend to deteriorate at high temperatures with the result that theirelectrical resistance will increase. Therefore, it may be necessary to check the instrument systemexternal circuit resistance from time to time to ensure all is well.The thermo-electric characteristics of thermocouples will also change due to contamination.Therefore, they should be checked periodically and replaced as necessary.Care should be taken to ensure that compensating leads are properly connected and that there areno faulty contacts or oxide layers forming on the contacts/terminals.Cable runs should also be examined along their entire lengths from time to time to check that noinsulation defects are forming and that dampness is not affecting the insulation.The insulation resistance between conductors and earth should at all times be higher than 1 MOhm.

3.899.5275.2004

4 Recepit and HandlingOn receipt of assemblies and/or immediately prior to installation, we recommend the followingchecks be made:

4.1 For Resistance Thermometers1 Using an ohm-meter or resistance bridge, check that the thermometer winding circuit is in order,

i. e., resistance reading at ambient temperature will be of the order of 110 ohms, i.e., includingelement lead resistance.

2 Check insulation to earth is in order, i.e., take reading between one terminal and assemblysheath/outer casing. A thermometer can usually be considered satisfactory if insulation resistancereadings of 100 Mohms is achieved (test voltage, max. 100 volts at ambient temperature).

4.2 For Thermocouples1 Providing the thermocouple has an insulated, i.e., unearthed, hot junction, check the insulation

to earth as described in (2) above for Resistance Thermometers.2 Warm the hot junction end of the assembly and with the thermocouple connected to a millivolt

meter, check polarity of connections.

3.899.5275.200 5

5 Malfunzionamenti tipici / rimediPossible Cause RemedyFault

Electr ical /Magnet ic p ick-upa l o n g c o n n e c t i n g l e a d s t oinstrument

(a) Ensure all compensatingleads/wiring between sensorassemblyand instrument are screened withwire braidingor metal foil.(b) Screening should be groundedat one point only.(c) If magnetic pick-up is theproblem ensure the connectingcable cores are twisted/inert winedalong their length.

S igna l f rom Sensorbreaks down

Insulation to earth break-down C h e c k t h e t h e r m o c o u p l e /thermometer insulation to earth asdampness may have penetratedthe seal. This can sometimes becured by drying out in an oven andresealing, Alternatively, replacethe measuring inset. Check if tem-perature is too high for rating ofthermometer

Assembly may be installed in theshadow of other equipment

Select a di f ferent point forinstallation

Response time too long

Depth of immersion may be toolow

Immersion depth should be > 6 to15 times the diameter of theAssembly Pocket or Thermowell

Thermowell or Pocket may be toolarge in bore diameter and /oroutside diameter

Use smallest, technically safe,outside diameter for Pocket orthermowell.Inset O D. should haveminimum clearance in Pocket/Thermoweil bore. If clearance islarge, consideration should be givento filling bore with contact agent,i.e. oils, silicon grease for example

Remove assembly from processand clean. Also, consider changingpoint of installation to safeguardagainst recurrence

Pocket or Thermowell may havebecome coated with processdeposits

Vibration Check that spring loading of insetis operating correctly i.e. that inseti s ‘ b o t t o m e d ’ i n P o c k e t /Thermowell Consider shorterassembly Consider re-sitingassembly

Thermometer s ignalperiodically interrupted

3.899.5275.2006

Possible Cause RemedyFault

Wrong select ion of Pocket/T h e r m o w e l l m a t e r i a l f o rapplication

Check the process medium andthe Thermowell/Pocket materialfor compatibility

B a d l y c o r r o d e dThermowell or Pocket

Thermocouple wires may be verysmall in diameter, hence having anelectrical resistance too high forinstrument

Either change thermocouple andwiring to ensure lower resistancevalues or change instrument toone having higher input resistancecapability

Thermocouple readsincorrectly although wirecombination correct

Cold junction compensation maybe faulty

Check cold junction compensationat instrument. Instructions usuallyavailable in instrument manual

Thermocouple outputf l u c t u a t e s b u t i sotherwise correct

Suspect chemical influences onthe sensor, especially if runningtemperature is high

Oxygen , Su lphu r , S i l i con ,Hydrocarbons etc., all change thechemical structure of the sensormaterials. Examine sensor atregular intervals and determinewhether to change at set intervalsto avoid problem or considerchanged design of assembly-purge type etc.

Temperature indicatorchanges gradually overperiod of days or months

Parasitic EMF’s P o s s i b l y d u e t o w r o n gthermocouple materials, poorelectrical contacts or connections

Temperature indicationdeviates widely fromtable values

Cable res is tance h igh andno compensated

If connection system is 2-wire,consider changing to wires ofgreatercross-section.Alternatively change to 3 or 4 wireconnection system. The latter mayrequire change of instrument

R e s i s t a n c eThermometer readshigh although sensorknown to be correct

3.899.5275.200 7

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3.899.5275.200 Issue 2 - 2008.05

RIPARAZIONIIn caso di necessità, prendere contatto con la nostra Filiale o Agenzia più vicina, o direttamente con la Spirax-Sarco S.r.l.Ufficio resi - Via per Cinisello, 18 - 20834 Nova Milanese (MB) - Tel.: 0362 49 17.1 - Fax: 0362 49 17 307

PERDITA DI GARANZIAL'accertata inosservanza parziale o totale delle presenti norme comporta la perdita di ogni diritto relativo alla garanzia.

Spirax-Sarco S.r.l. - Via per Cinisello, 18 - 20834 Nova Milanese (MB) - Tel.: 0362 49 17.1 - Fax: 0362 49 17 307