Training - Temperature

Temperature

Level 1 - Fundamental Fundamental Training Training

Level 1 Fundamental Fundamental Traini Training ng

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Level 1 - Temperature Temperature

Contents Topics: • Wh y m eas u r e t em p er at u r e? • Tem p er at u r e t er m i n o l o g y mperatur rature e mea measure sureme ment nt tech techno nolo logy gy • Tempe • Tem p er at u r e s en s o r s • Sen s o r ac c es s o r i es • Tem p er at u r e t r an s m i t t er • Ex er c i s e

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Slide No: 3-5 6-8 9 - 13 14 - 40 41 - 52 53 - 64 65 - 67


Power Point Presentation Presentation Handou Handou ts

Temperature


Why measure temperature?

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• Because temperature affects: – – – – – –

rate of reaction viscosity state of a matter strength of m ate aterials rials quality & taste of food safety of a process

Temperature mperature is critical to the followi ng process: • Te

– – – –

Pulp & Pa Paper per Food Industry Pasteurisation Vacuum Packaging Chemical Che mical Indust ry Level 1 - Temperature Temperature

Why measure temperature? 4 Common Comm on Reasons Comm Reasons Reason s

4

• Safety – to prevent explosio n as a result of excessive temperature

• Efficiency – example: example:-- Air -Conditioning -Conditioning » accurate accurate temperat temperature ure measurem measurement ent prevent prevent the the supplier supplier from overcooling the air, which saves energy and increases efficiency

Yield • Product Quality & Yield – variation from optimu m temperature temperature result in » very little production production of the the desired desired product product » crea creati tion on of was waste te pro produ duct ct – precise temperature measurement measurement ensures efective separation separation of produ cts in

» dist distill illat atio ion n colum column n » cataly catalytic tic cracki cracking ng proces processes ses Level 1 - Temperature Temperature


Temperature


Why measure temperature? 4 Common Comm on Reasons Comm Reasons Reason s

5

Transfer • Custody Transfer – amount of material that is bought & so ld – extremely extremely impo rtant to know exact temperature temperature when determining volumetric flow rate of gas

– amount of material material contained in a specific vo lume of gas » decrea decreases ses with with risin rising g temper temperatu atures res » increa increases ses with with falling falling temp tempera eratur tures es – inaccurate temperature temperature measurement result i n » over or under-chargi under-charging ng customers customers during custody custody transfer transfer


Temperature terminology Temperature Control LLoop Temperature oop

6

• Temperature Loop Issues: – Fluid response response slowly slowly to change change in input input heat – Requires advanced advanced control strategies strategies • Feedfor Feedforward ward Control Load Disturbance TIC

Cold Water

I/P TT

Steam

Hot Water Level 1 - Temperature Temperature


Temperature


Temperature terminology Temperatu Temperatu re Measur Measur ement Scales mperature

7

BOILING POINT OF WATER

373

100°

672

212°

ICE POINT

273

0°

492

32°

0

-273°

0

AB SOLUTE ZERO

kELVIN kELVIN

Kelvin &

CELSIUS CELSIUS

-4 - 460°

RANKINE RANKINE FAHRENH FAHRENHEIT EIT

R a n k i n e a r e a a b s o l u t e s cca es a lle

°C = 5/9 (°F - 32 ) °F = 9/5 (°C) + 32 K = 273 +°C R = 460 + °F Level 1 - Temperature Temperature

Temperature terminology Temperature Measur ement Scales Temperatu Te mperature re Measur Example #1 20°C = 20 + 273

8

= 293K

20°C = 9/5*(20) +32

= 68°F

Differential Temperature °C = 5/9 °F °F = 9/5 °C K = °C °R = °F

Example: 2 points in a process differ in temperature by 100 °C. These 2 points differ by 180 °F i.e. 180 = 9/5(100) Whereas, they also differ by 100K



Temperature


Temperature Measurement Technology

9

METALS METALS chang e in VOLUME VOLUME in r espons e to change in TEMPERATURE & DISSIMILAR METAL STRIPS having different COEFFICIENT of VOLUME CHANGE. Examp xample le::

Bime Bimeta tall llic ic The Thermom rmome eter ter Thermocouple (discussed later)

Bimetallic Thermometer

The degree of deflection of 2 dissimilar dissi milar metals is proportional to the change in temperature. One end of the spiral (wounded from a long strip of material) is immersed in the process fluid and the other end attached to a pointer.



10

Expansion & Contraction of FILLED THERMAL FLUIDS Examp xample le::

Vapour pour Pre Press ssure ure Thermo hermome mete ter r

A bulb connected connected to a small bore bore capillary capillary which is connected to an indicating device. Indicating device consist of a spiral bourdon gauge attached to a pointer. The bulb is filled with a volatile liquid and the entire mechanism is gas tight and filled with gas or liquid under pressure. Basically the system converts pressure at constant volume to a mechanical movement. Level 1 - Temperature Temperature


Temperature



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Change in RESONANT FREQUENCY of crystal in respo nse t o c hange in TEMP TEMPER ERATUR ATURE E Exampl xample e:

Quart uartz z Crys Crysta tall The Thermome rmomete ters rs

Quartz crystal hermetically sealed in a stainless steel cylinder, similar to a thermocouple or RTD sheath but , larger. Quartz crystal converts temperature into a frequency. They provide good accuracy and response time with excellent stability. Hence, this technology is expensive. Level 1 - Temperature Temperature


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Collecti on o f THERMAL THERMAL RADIATION RADIATION from an object sub jected to HEAT HEAT Examp xample le::

Radia diation tion Pyrom yrome etry try

Infers temperature by collecting thermal radiation from process and focusing it on a photon detector sensor. The sensor produces and output signal as radiant energy striking it releases electrical charges.



Temperature



13

Change in RESIS RESISTANC TANCE E with respo nse to change in TEMPERATURE Ex am p l e:

Th er m i s t o r s RTD (discussed later)

Thermistors

Semi-conductors made from specific mixtures of pure oxides of nickel, manganese, copper, cobalt, and other metals sintered at very high temperature. Used with Wheatstone Bridge which amplifies small change in resistance - in a simple circuit with a battery battery and a micro-ammeter. micro-ammeter. • Stability Moderate • Linearity Poor (Logarithmic) Negative • Slope of Output Level 1 - Temperature Temperature

Temperature Temperature Sensor Sensor s RTDs

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What is an RTD ?

– Resistance Temperature Detector »

»

Operation Operation depends on inherent characteristic of metal (Platinum (Platinum usually): electrical electrical resistance to current flow changes when a metal undergoes a change in temperature. If we can measure the resistanc e in the metal, we know the temperature!

Platinum resistance changes with temperature

Wire-wound sensing element Rosemount’s Series 78, 88

Thin-film sensing element Rosemount’s Series 68, 58

Series 65

Two common types of RTD elements:



Temperature



15

How does a RTD RTD works ?

– Resistance changes are Repeatable Repeatable – The resistance resistance changes changes of the platinum platinum wiring can can be approximated approximated by by an ideal curve -- the IEC 751 751 350

) s 300 m h 250 O (

International Resistance vs. Temperature Chart: oC

0 10 20 30

Ohms 100.00 103.90 107.79 111.67

IEC 751

e 200 c n 150 a t s 100 i s e 50 R 0

-200

IEC 751

0

200

400

Temperature

600

800

(oC)

IEC 751 751 Constant Constants s are :- A = 0.00390 0.0039083, 83, B = - 5.775 5.775 x 10 -7, -12 If t>=0°C, C=0, If t<0, C = - 4.183 x 10 Example: RT = R0 [1 + At + Bt 2 + C(t-100)t 3]

= 103.90 Level 1 - Temperature Temperature


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Platinum Platinum vs other RTD RTD materials ) 0

R / 6 T

R ( e c n a t s i s e R e v i t a l e R

4

 Most linear

Nickel

5 Thermistor

Balco

 Most Repeatable

3 Platinum

2

 Positive Slope

1

0 °C -100 °F -148

 Most Stable

0 100 200 300 400 32 212 392 572 762

500 600 700 932 1112 1292

Temperature



Temperature



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Why use us e a 2-, 33-,, or 4- wir wire e RTD RTD? ? cost -- rarely used used due to high error error – 2-wire: Lowest cost from lead wire resistance

– 3-wire: Good balance of cost and performance. Good lead wire compensation.

– 4-wire: Theoretically the best lead wire compensation method (fully compensates); the most accurate solution. Highest cost. 4-wire RTD Typically use copper wires for Red extension from the sensor

Red Red

White White

Sensing Element (i.e. wire-wound, thin film)

Black White White

Green Green Level 1 - Temperature Temperature


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2-wire or 4-wir 4-wir e RTD RTD ? • If the sensi ng element i s at 20°C, 20°C, – What would be the temperature temperature measured at the end of the extension wire using a 2-wire assembly – What would be the temperature temperature measured at the end of the extension wire using a 4-wire assembly

Sensing Element (I.e. (I. e. wire-wound, thin film )

2-wire RTD 6 metres of copper copper extension extension Red wire, lead resistance = 0.06 ohms/metre (1 ohm = 2.5 deg C approx)

Error for a 2 wir e assembly 0.06 x 6 x 2 = 0.72 ohm s or 1.8De 1.8Deg gC This means that the temperature measured at the end of the cable woul d be 21.8 Deg Deg C

White

Error for a 4 wire assembly As t he lead l ead r esi esist stanc ances es can be accounted for the temperature measured at the end of the cable woul d be 20.0 Deg Deg C Level 1 - Temperature Temperature


Temperature



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Dual Dual Element RTDs RTDs available available

Red

Black

Red

Red Red Green

White White

Dual Element: Two 3-wire RTDs

Blue Blue

• Support Supports s Hot Backup Backup capabili capability ty • Dual element element adds only $5 over single single element element RTD » Reduce the risk of a temperature point failure

• Supports Differential Differential Temperature Temperature Measurement Measurement Level 1 - Temperature Temperature


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The IEC 751 standard curve (programmed into all our transmitters) describes an IDEAL IDEAL Resistance Resistance vs Temperature Temperature relationship f or Pt100 = 0.00385 RTDs.

) S M H O ( E C N A T S I S E R

Every RTD RT D is ly RTD is slight slightly different - they’re not ideal! ideal! v e u r C 1 5 7 C E I

Standard Standard IEC IEC 751 751 Curve Curve Class Class B B Tolerance Tolerance ± 0.8o C at -100o C ± 0.3o C at 0o C ± 0.8o C at 100o C

Class B Tolerance

TEMPERATURE ( o C)

The goal is to find out what the real RTD curve looks like, and reprogram the transmitter to use the “real” curve!

± 1.3o C at 200o C ± 1.8o C at 300o C ± 2.3o C at 400o C

(Sensor Interchangeability Error)



Temperature



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60751 Toleranc es • EN 60751 – Pt 100, α = 0.00385 Temperature °C -200 -100 0 100 200 300 400 500 600

Resistance Ohms 18.52 60.26 100.00 138.51 175.85 212.05 247.09 280.98 313.71

Accuracy Grade A Grade A Grade B Grade B ± °C ± Ohms ± °C ± Ohms 0.55 0.24 1.3 0.56 0.35 0.14 0.8 0.32 0.15 0.06 0.3 0.12 0.35 0.13 0.8 0.30 0.55 0.2 1.3 0.48 0.75 0.27 1.8 0.64 0.95 0.33 2.3 0.79 1.15 0.38 2.8 0.93 1.35 0.43 3.3 1.06


Temperature Temperature Senso Senso rs RTDs

22

Qu i z: -

Find the Interchangeability Error

Your customer is o perating a process at 100°C and is u sing a Platinu Platinu m RTD... RTD...

What is the maximum error that will be introdu ced into the temperature temperature measurement measurement from Sensor Sensor Interchangeability? Interchangeability?

+/-0.35 +/-0.3 5 deg C f or Class A, +/-0.8 +/0.8 deg C for Class B Fortunately, Sensor Sensor Interchange Interchangeability ability Error can be reduced or eliminated by Se Sensor nsor Ma Matching! tching! Level 1 - Temperature Temperature


Temperature



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What is RTD Calib Calib ratio n?

– The real RTD curve is found by by “characterizing” “characterizing” an RTD over a specific temperature range or point . » Temperature Range Characterization ⇒ Calibration certificate provided with sensor » Temperature Point Characterization ⇒ Calibration certificate provided with sensor

Customer Receives RTD-specific Resistance Data generated vs. Temperature Chart: (RTD “characterized”) oC Ohms 0.0 99.997 1.0 100.38 Temperature Bath 2.0 100.77 - One One temp temper erat atur uree 3.0 101.16 - Multi Multiple ple tempe temperat ratur ures es Level 1 - Temperature Temperature


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With a Real Real RTD, RTD, the Resistanc e vs. Temperature relationship of t he sensor is NOT NOT the same curve that is programmed into the transmitter The curve programmed into every xmtr every xmtr is the IEC 751 - th e ““Ideal” Ideal” Idea l” RTD curve

R vs. T Curv Curv e of REAL RTD RTD Resistance:

Outcome ??

Transmitter Input: 138.8

138.8

212°F Process Temperature

The Transmitter Translates 138.8 138.8 into 213.4°F Using t he IEC 751 751

NOT match RTD curve. Transmitter curve does NOT match Transmitter reading does NOT equal NOT equal process temperature. If we could tell the transmitter the shape of th e “ Re Real” al” RT RTD D curve, we could eliminate the interchangeability interchangeability error! Level 1 - Temperature Temperature


Temperature



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Sensor Sensor Matchin Matchin g - eliminates sensor sensor interchangea interchangeability bility error Pt100 Pt100 a385 a385 Temp Temp vs Resistance Resistance e c n a t s i s e R

Tag R o = 99.9717 α = 0.00385367 β = 0.172491 δ = 1.61027

real sensor curve standard IEC 751 curve sensor matched curve in tx

Outcome ??

Temperature

A fourth order equation can be programmed into Smart Transmitters to follow non-ideal sensor curvature; simply enter four constants using 275. Transmitter curve is perfectly matched to “ideal” RTD curve Transmitter reading equals process temperature Level 1 - Temperature Temperature


26

Sensor Sensor Matchin Matchin g - Mapping the Real RTD Curve • The trans transmitt mitter er does ddo oes nno ott use use transmitt trans es not the IEC 751 standard curve. • Inst Instead, ead, Callendar ndar-Van -Van Inste ad, the Calle v e u r ) C Dusen Duse n constants const ants can be used in used ( 5 1 7 e C the equation below to create E c I n a the true sensor curve. t s i s • Or, Or , the act actual ual IE IEC C 75 7511 e R Class B constants A,B, and C can be Tolerance used in the IEC 751 equation equation if if Temperature ( C) known. o

Rt = Ro + Roα[t-δ(0.01t-1)(0.01t)- β(0.01t-1)(0.01t) 3] 4th Order Callendar-Van Dusen Dusen Equation Equation

R t R o α δ β

= Resistance at Temperature t (°C) = Sensor-Specific Constant (Resistance at t = 0°C) = Sensor-Specific Constant = Sensor-Specific Constant = Sensor-Specific Constant (If (If t >=0°C, then β = 0) Level 1 - Temperature Temperature


Temperature



27

Sensor Trimming

– Data from the the resistance resistance vs. temp. temp. chart chart can be used to reduce sensor interchangeability error – Use one or or two points points to trim the the sensor to a transmitter transmitter

400

) ( e c n a t s i s e R

350 300

One Point Point Tri m Use with X9 (or X8)

400 350

250 200 150

A 1-point trim trim shifts the ideal curve up or down based on the single characterized point

100 50

) ( 300 e c 250 n a 200 t s 150 i s e 100 R

0

200

400

600

A 2-point trim shifts the ideal curve curve up or down AND changes the slope based on the two characterized points

50

0 -200

Two Point Trim Use with X8

0

800

-200

0

Temperature (°C)

200

400

600

800

Temperature (°C)


Temperature Temperature Sensor Sensor s Thermocouples

28

What What is a Thermocoup Thermocoup le ? – Two

dissimilar metals joined at a “Hot” junction – The wires are connected to an instrument (voltmeter) that measures the potential created by the temperature difference between the two ends. Process Temperature

Hot junction

DT

+ MV

Cold junction

“40 millivolts!,” millivolts!,” Tommy Seebeck yelled in a heated debate.

The junction of two dissimilar metals creates creates a small vo ltage output propo rtional to temperature! Level 1 - Temperature Temperature


Temperature



29

How does a Thermocoupl Thermocoupl e work ? – The measured voltage is proportional proportional to the temperature difference between the hot and cold junction! (T 2 - T1) =ΔT. Hot junction

+

Measurement Junction Heat

T

MV

T2

0 10 20 30

Reference Junction

T1

-

Thermoelectric Voltage vs. Temperature Chart: oC

Cold junction

80

) V 60 m ( e g 40 a t l o V 20

Millivolts

0.000 0.591 1.192 1.801

IEC 584

0 -500

TYPE E THERMOCOUPLE

-20

0

500

1000

Temperature (oC) Level 1 - Temperature Temperature


30

Hot-Junction Configurations

– Grounded • improv improved ed the therma rmall cond conduc uctiv tivity ity • quic quicke kest st resp respon onse se time times s • susce suscepti ptibl ble e to elec electri trica call noise noise – Ungrounded • sligh slightly tly slower slower respo response nse time time • not not susce suscepti ptible ble to ele electr ctrica icall noise

Single Grounded

Dual Grounded

Single Ungrounded



Temperature



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Hot-Junction Configurations

– Unisolated • juncti junction ons s at the the same same tempe temperat rature ure • both both junc junctio tions ns will will typic typicall ally y fail fail at the same time

Dual Ungrounded, Un-isolated

– Isolated • juncti junctions ons may/m may/may ay not not be be at the same temperature • increa increase sed d relia reliabil bility ity for each each junction • failu failure re of of one one junc junctio tion n does does not not affect the other

Dual Ungrounded, Isolated Level 1 - Temperature Temperature


32

Why is Cold Junc tion Compensation Compensation needed? needed? – Reference – Reference Junction must be kept constant .

» 2 Methods Methods used to accomp lished this : • Place Reference Junction in Ice Bath Iron +

Measure T2 = 100 + 10°C

Δ T = 110°C

ICE BATH

Constantan

_ 5.812 mV

Reference °C T1 = 0°C 0 2

NOT NOT Practical !

Volt Meter

-100 -0 MILLIVOLTS -4.632 0.000 -4.550 -0.995

+0

100

0.000 1.019

5.268 5.376

6

-4.876

-0.301

0.303

5.594

10

-5.036

-0.501

0.507

5.812

14

-5.194

-0.699

0.711

6.031



Temperature



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What What is Cold Junct ion Compensation Compensation

– Electronic Circuitry – Electronic » passing current current through

a Thermistor

Transmitter

Iron Constantan

Connection Head

Δ T = 80°C

4.186 mV

+

Measure T2 = 110°C

Example: Amb ien t Temp = 30°C

Common Practise Practise !

1.536 mV

_ Reference Junction

= 5.722 mV » 110°C

Extension Wires °C -100 -0 MILLIVOLTS 0 -4.632 0.000 10 -5.036 -0.501

+0

100

0.000 0.507

5.268 5.812

30

-5.801

-1.481

1.536

6.907

60

-6.821

-2.892

3.115

8.560

80

-7.402

-3.785

4.186

9.667



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Types Types of Thermocoupl e )Type

J – Iron / Constantan Constantan • White, Red • 0 to 760 °C • Least Expensive

+ )

Type K – Chromel »

Yellow, Red 0 to 1150 °C

»

Most Linear

»

+ -

/ Alumel + -

)

Type T – Copper

/ Constantan » » »

Blue, Red -180 to 371 °C Highly resistant to corrosion from moisture



Temperature



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Other Types – High temperature range – Industrial/ laboratory standards – LOW EMF output! (Not very sensitive) – Expensive!

)

)

– Pt, »

Type B – Pt, »

Type R

)

13% Rh / Pt -50 to 1540 °C

Type S – Pt,

6% Rh / Pt, 30% Rh 38 to 1800 °C

»

10% Rh / Pt -50 to 1540o C



36

Why use one type over another ? )

Temperature range

)

Cost

Type J 80

Type E

Type R

70 60 s t 50 l o v 40 i l l i M 30

Type J

Type K

Type T

20 10

)

Signal level

)

Linearity of the range

Temperature (C)

0 0

250

500

750

1000

1250



Temperature



37

Al l ther t hermo moco co uple up le lead l ead wir w ir e extens ext ensio io ns MUST be with the same type of wire!

Correct! Wrong!

Another Hot Junction is created… not good!

Cannot use copper wire for extensions! T/C wire is more more expensive to run and much harder to install!


Temperature Temperature Sensor Sensor s Comparison

38

Why choos e RTD RTD over Thermoco Thermoco uple ? Better Accuracy & Repeatability

– RTD signal less susceptible to noise – RTD – Better – Better linearity – RTD – RTD can be “matched” to transmitter (Interchangeability error eliminated) – CJC – CJC error inherent with T/C’s; RTD’s lead wire resistance errors can be eliminated Better Stability

– T/C – T/C drift is erratic and unpredictable; RTD’s drift predictably – T/C’s – T/C’s cannot be re-calibrated Greater Flexibility

– Special extension wires not needed – Special – Don’t – Don’t need to be careful with cold junctions Level 1 - Temperature Temperature


Temperature



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Why choos e thermocoupl e over RTD RTD ? Ap pl ic ati on s for f or Hig her Temp erat ur es

• Abov Above e 1100 1100°F °F Lower Element Cost

• Cost is the the same when when consideri considering ng temperatu temperature re point performance requirements Faster Fa ster response t ime

• Insignifica Insignificant nt compared compared to response response time for for T-Well and process Perceived as more rugged

• Rosemount Rosemount constru construction ction techniqu techniques es produce produce extremely rugged RTD



RA NGE

-200 to 500º C 500 to 1100º C >1100º C

40

OFFER RTD Thermocouple Type K

Special Thermocouple R, S or B



Temperature


Senso Senso r accessori es Extension Fittings

41

• Extension fitti ngs are used for a number of reasons : – Heat Heat dissipation from the process to th e transmitter

Transmitter Housing Temperature Temperature Rise vs.Extension Length for a test Installation 60

– Extend sensor sensor thro ugh tank jac ket or pi pe i ns ul ation ati on

– Ease Ease of accessibility throu gh mountin g in h ard to reach areas areas

– Disconnect sensor from process without fu ll disassembly (Union) (Union)

– Two types of Assembly • Coup Couplin ling g and and nipp nipple le ass assem embly bly • Union Union and and nip nipple ple asse assemb mbly ly

C ° 50 t . n p i e m b 40 e T m A g 30 n e i v s o u b 20 o A H e s i 10 R

815°C Oven Temp. 540°C Oven Temp. 250°C Oven Temp.

0 3

4

5

6

7

8

9

Extension Length, Inches


Sensor Sensor accessories Extension Fittings

42

Example Example of Appli cation )

Example #1

Lets say:

– 4 inch extension 32°C + 30°C

Temp Limit of Transmitter is 70°C Amb. Temp is 32°C

62°C Ceiling )

Example #2

– 6 inch extension 32°C + 20°C 52°C Ceiling

Transmitter Housing Temperature Temperature Rise vs.Extension Length for a test Installation 60 C ° 50 t . n p i e m b 40 e T m g A 30 n e i v s o u b 20 o A H e s i 10 R

815°C Oven Temp.

0 3

4

5

6

7

8

Extension Length, Inches Level 1 - Temperature Temperature


9

Temperature


Senso Senso r accessories Thermowells

43

What is a thermowell (T-well) ?

– A unit that that protects protects a sensor sensor from process flow, pressure, vibrations, and corrosion – Allows for sensor removal removal without without process shutdown – Slows response response time (by 5 times) times) Why are there different material types ? – To

handle different corrosive environments

– To

handle different temperature and pressure limits Level 1 - Temperature Temperature

Sensor Sensor accessories Thermowells

44

Thermowell Thermowell Design Design Styles - Comparison Table Rating: 1= Best

Process Pressure

Time Response

Wake Frequency

Price

Drag Force

Tapered

1

2

1 or 2

3

2

Stepped

1

1

3

1

1

1

3

1 or 2

1

2

Straight



Temperature



45

Thermowell Thermowell Mounting Styles Styles

• Thre Thread aded ed – Most common – Easy to remove and install • Wel Welded – Non-removable – Used in high velocity, temperature and pressure fluids

– Used in non-leak applications • Flan Flange ged d – Used in corrosive environments – Used in high velocity, and high temperatures Level 1 - Temperature Temperature


46

What What is t hermowell analysis ?

– A method used to determine determine if a thermowell thermowell is physically physically capable of withstanding the process conditions. – It includes includes wake frequency, frequency, resonance resonance,, or Murdock Murdock calculations. – Stress calculation calculations. s. – Pressure calculations calculations Pipe Standoff What we do not want is damage to the customer’s Plant

Sensor Thermowell

PROCESS FLOW




Temperature


47

Thermowell Thermowell Failures Failures

– T-wells can can fail under under certain conditions conditions – Fluid flowing flowing around the T-well forms a turbulent wake called the Von Karman trail – The wake alternates alternates from side to side at a specific frequency dependent on many variables – If that frequency frequency exceeds 80% of the the Twell’s natural frequency, the T-well can fail!



48

Stress Failur Failur e

• T-wells can fail under stress conditions • Fluid flowing past the T-well creates a stress on the thermowell where it is attached to the pipe • This can cause the thermowell to snap off! STRESS

FLOW



Temperature



49

Static Pressure Failure

• T-wells can can fail due to excess process pressure • Excess process pressure can cause cause the thermowell to collapse!



50

Checking Checking For Thermowell Thermowell Suitabilit y

– Thermowell Thermowell calculations calculations can be be carried out provided we have information on the following: • • • • • • • • • •

Thermowell Style Thermowell Material Thermowell Thermowell Dimensions Dimensions Fluid Velocity or Flow Rate Process Pressure Process Temperature Fluid Density

Look on the back of your Sensor PDS!

Fluid Viscosit Viscosit y Various Various Process Pipe Dimensions Dimensions T-well T-well calculations can be carried out by Rosemount Tempera Temperature ture Applications Groups Level 1 - Temperature Temperature


Temperature



51

Why do we need need all all th is inf ormation? ??

1. To calcul ate the natur natural al frequ frequency ency 2. To calcu calculate late the wake frequ frequency ency 3. To calculate the fluid velocity 4. To calculate the stress on th e T/W T/Well ell 5. To calculate the maximu maximu m pressure


Senso Senso r accessori es Thermowells

52

What can we do if the Thermowell Thermowell fails??? • What – We can redesign redesign the Thermowell Thermowell by:» Changing the style of Thermowell. » Changing the length of the Thermowell. » Changing the diameter of the Thermowell. » Changing the Thermowell material. » If all else fails, we can use a velocity collar. Flange Velocity Collar Thermowell

Pipe Standoff

Process Pipe PROCESS FLOW Level 1 - Temperature Temperature


Temperature


Temperature Temperature transm itter What does a Transmitter do & Why use Transmitter? What Transmit ter? Transmit

53

Transmitter Transmitter converts temperature temperature sensor’s s ignal from r esistance or voltage into into a common digital or analog analog 4-20 4-20 mA mA control signal 4-20 mA Signal = 12 mA

IEC 751 Resistance Signal = 138.5

(Range: 0-200°C)

“ Sma Smart” rt” Tra Transmitters nsmitters also relay a digital signal

100 °C Copper Wire (RTD only)

Ranged: 0 - 200°C

Control System

100 °C

– Converts a noise susceptible signal to a standard, more robust robust 4-20 mA signal – Provides local indication of temperature temperature measurement – Smart Smart transmitter provides ⇒ remote communication & diagnostics ⇒

improved accuracy & stability

⇒

reduced plant inventory Level 1 - Temperature Temperature

Temperature Temperature transm itter Wire Direct Dire ct vvs. s. Transmitt Transmit ter Transmit Direct er

54

The alternative alternative to using a transmitter Controller

Example 8 Temp. Temp. Measur Measur ement Point s

PLC GW

PLC

I/O Interface I/O Terminations

(1) “Spur”: Length of T/C wire run from process to Junction Box

(2) “Trunk”: Length of Bundled cable from Junction Box to Marshalling Panel

2

Junction Box

1 Marshalling

IS (Exi) Barriers

Turbine



Temperature


Temperature Temperature transm itter Tra Transmit nsmit ter Mounti M ounti ng Styles Transmi nsmi tter Mounting

55

4 main transmitter mounting styles

 Head-Mount

 Rail-Mount

 Rack-Mount

 Field-Mount



56

Field Mount Control Room

Field 4-20 mA Signal

Control System

4-20 mA Signal

RTD or T/C

Remote-Mounted Field Mount Xmtr

Ω or mV

Integral-Mounted Field Mount Xmtr

signal

To terminate sensor

Sensor connection head

Process Pipe

RTD or T/C Terminate Sensor Level 1 - Temperature Temperature


Temperature


Temperature Temperature transm itter Tra Transmit nsmit ter Mounti M ounti ng Styles Transmi nsmi tter Mounting Head Head Mou nt Control Room

57

To house transmitter only

Field 4-20 mA

Control System

4-20 mA

Remote-Mounted Head Mount Xmtr

Junction Box

To terminate sensor

Integral-Mounted Head Mount Xmtr Ω or mV

Connection head

T/C or RTD


Process Pipe T/C or RTD

To house transmitter & terminate sensor



58

Rail Rail & Rack Rack Mount - Remote-Mounting Configurations Control Room 4-20 mA Control System

Rail Mount

Field To terminate sensor

Ω or mV


Rack Mount: Accepts multiple multiple inputs

Ω or mV

Process Pipe T/C or RTD

T/C or RTD



Temperature


Temperature Temperature transm itter Factors Affecting Re Factors Response sponse Respons spons e Time Time Time

59

Thermowell 

Sensor



Thermowell



Transmitter



Process Sensor

75.4 °C

Process Transmitter


Temperature Temperature transm itter Factors Affecting Re Factors Response sponse Respons spons e Time Time Time  Type

60

of element

– Thin-film has slightly faster response response time than wirewound – Thermocouples do not vary significantly

Element  Element

packaging

– Rosemount RTD’s are packed in magnesium oxide to to provide optimum thermal conduction within the sheath – Grounded thermocouples are twice as fast as as ungrounded OD

Sheath  Sheath

thi ckness and material – Rosemount uses 316SST 316SST and Inconel Inconel (for high temperature temperatures) s) for sheath; both are very good thermal conductors

ceramic sheath bore

element

Magnesium Oxide Packing Level 1 - Temperature Temperature


Temperature


Temperature Temperature transm itter Factors Affecting Re Factors Response sponse Respons spons e Time Time Time  Thermowell Thermowell

61

design style (thickness (thickness at at tip)

– Stepped is the fastest fastest  Contact

between between sensor sheath sheath and thermowell (x and y) – Spring loaded sensor ensures contact at the tip tip (x=0) – Industry practice suggests suggests using thermally conductive fill can significantly reduce time lag

Tapered Tapered thermow thermowell ell = 26 seconds seconds

x

y

Stepped Stepped thermow thermowell ell = 22 seconds seconds Industry data shows stepped t-well with fill = 11 seconds

Thermowell Thermally Conductive Fill

Sensor Assembly Level 1 - Temperature Temperature

Temperature Temperature transm itter Factors Affecting Re Factors Response sponse Respons spons e Time Time Time 

Time response depends on element (complexity of calculation) – 2-wire RTD – 3 & 4-wire RTD – Thermocouples



62

440 - 760 ms 520 - 920 ms 300 - 750 ms

Transmi Transmi tter update time (output) every 1/2 second

Transmitter 75.4 °C

Process Level 1 - Temperature Temperature


Temperature



63



Veloci Veloci ty of the material



Thermal Thermal condu ctivi ty of t he material material



Densit Densit y and viscosi ty of t he material material



Process time constants can can be from seconds to hours:

75.4 °C

Water @ 3 fps t = 1 min Air at 50 fps, 40-80 oC = 11 minutes Oil agitated in a bath: t = 13 minutes Oil not agitated: t = >45 minutes

Process



Sensor Sensor in Thermowell Transmitter Process

64

< 7 to 10 sec 60 to 120 sec .5 to .9 sec Seconds to Hours

• Thermow Thermowells ells and process process materia material/co l/condit nditions ions have have the greatest effect on temperature point response time



Temperature


Exercise

65

A 4-20 mA transmitter is is spanned 50 to 150°C. Express the span in in the following units:

1.

[

] to

[

] °F

2.

[

] to

[

]K

3.

What What is the the tem tempe pera ratu ture re readi reading ng if the the abov above e transmitter outputs 10 mA?

[

°C]

4.

An old old diff differ eren enti tial al tem tempe pera ratu ture re ind indic icat ator or wit with h a scale of 0 - 100°F is reading reading 60°F. What What is that reading in °C?

[

°C]

5.

An Pt 100 100 RTD RTD has has the the foll follow owin ing g C.V C.V.D .D cons consta tant nts s R0 =100.00Ω, α = 0.003842, δ =1.415, β = 0.11. If the temperature being measured is 30°C, Ω] What will be the resistance value? [


Exercise

66

Identify the characteristics for RTD & Thermocouple & indicate them by entering a “R” or a “T” respectively.

6.

High accuracy.

[

]

7.

Can handle wider temperature range.

[

]

8.

CJC is not required.

[

]

9.

Can be matched to transmitter.

[

]

10.

Faster response time.

[

]

Identify which the the sensor or thermowell thermowell design that provide faster faster response time.

11.

A. B.

Thin-film RTD Wire Wounded RTD

[

]



Temperature


Exercise

67

12.

A. B.

Thin-film RTD Wire Wounded RTD

[

]

13.

A. B. C.

Straight Thermoell Tapered Th Thermowell Stepped Thermowell

[

]

14.

A. B.

Grounded Thermocouple Un-grounded Thermocouple

[

]

15. 15.

Whic Which h Therm Thermow owel elll moun mounti ting ng styl style e can be be used used in high velocity and high temperature corrosive environment.

[

]

A. B. C.

Threaded Welded Flanged



Training - Temperature

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