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Temperature Sensor Training

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1 Temperature Sensor Training www.AutomationSys.Org 021-88535820-21 021-88535820-21
2 Temperature  What is temperature ? The temperature of an object can be described as that which determines the sensation of warmth or coldness felt from contact with it. www.AutomationSys.Org 021-88535820-21 021-88535820-21
Measuring temperature  Expansion  Resistance change  Thermoelectric effect  Pyrometry  Cricket www.AutomationSys.Org 021-88535820-21 021-88535820-21
4 Modern temperature scales  Fahrenheit  Celsius  Kelvin  Rankine www.AutomationSys.Org 021-88535820-21 021-88535820-21
5 Learning Objectives: Temperature Sensors  Have a basic understanding of operation principles for both an RTD and T/C and understand the benefits of using one vs the other  Know the T-well styles and how to select the most appropriate for processes  Know the main factors that affect time response
6 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouple vs. RTD Sensors – Sensor Curve Definitions – Sensor Calibration (Characterization) – Accessories www.AutomationSys.Org 021-88535820-21 021-88535820-21
7 RTD Sensors What is an RTD?  What is an RTD?  Resistance Temperature Detector  Operation depends on inherent characteristic of metal (Platinum usually): electrical resistance changes when a metal undergoes a change in temperature.  If we can measure the resistance in the metal, we know the temperature! Platinum resistance changes with temperature Rosemount’s Series 65 (High Temperature),78, 88 Rosemount’s Series 65, 68, 58 Two common types of RTD elements: Wire-wound sensing element Thin-film sensing element
8 RTD Sensors Resistance Changes are Repeatable  What is a RTD? – Resistance Temperature Detector – The resistance changes of the platinum wiring can be approximated by an ideal curve -- the EN 60751 curve (Pt100) 0 50 100 150 200 250 300 350 -200 0 200 400 600 800 o C Ohms 0 100.00 10 103.90 20 107.79 30 111.67 Resistance (Ohms) Temperature (o C) International Resistance vs. Temperature Chart: EN 60751 EN 60751
9 EN 60751 Tolerances Accuracy Temperature Resistance Grade A Grade A Grade B Grade B °C Ohms ± °C ± Ohms ± °C ± Ohms -200 18.52 0.55 0.24 1.3 0.56 -100 60.26 0.35 0.14 0.8 0.32 0 100.00 0.15 0.06 0.3 0.12 100 138.51 0.35 0.13 0.8 0.30 200 175.85 0.55 0.2 1.3 0.48 300 212.05 0.75 0.27 1.8 0.64 400 247.09 0.95 0.33 2.3 0.79 500 280.98 1.15 0.38 2.8 0.93 600 313.71 1.35 0.43 3.3 1.06
10 RTD Sensors RTDs Do Not Follow the Ideal Curve TEMPERATURE (o C) RESISTANCE (OHMS) Ideal EN 60751 Curve The EN 60751 standard describes an IDEAL Resistance vs. Temperature relationship for Pt100 385 RTDs. Every Pt100 385 RTD is slightly different - they’re not ideal! Real Sensor Curve Because RTD sensors are not ideal - they do not perfectly match the EN 60751 - there will be error introduced into the temperature measurement. This Error is the Sensor Interchangeability Error!
11 Exercise: Find the Interchangeability Error Your customer is operating a process at 100°C and is using a Platinum RTD... What is the maximum error that will be introduced into the temperature measurement from Sensor Interchangeability? +/-0.35 deg C for Class A, +/-0.8 deg C for Class B Fortunately, Sensor Interchangeability Error can be reduced or eliminated by calibration!
12 Red Red White White RTD Sensors 2, 3, and 4-wire RTDs 4-wire RTD  Why use a 2-, 3-, or 4- wire RTD?  2-wire: Lowest cost -- rarely used due to high error 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. Typically use copper wires for extension from the sensor Sensing Element (I.e. wire-wound, thin film)
13 2-wire or 4-wire RTD ?  If the sensing element is at 20°C, F What would be the temperature measured at the end of the extension wire using a 2-wire assembly F What would be the temperature measured at the end of the extension wire using a 4-wire assembly Red White 2-wire RTD 6 metres of copper extension wire, lead resistance = 0.06 ohms/metre (1 ohm = 2.5 deg C approx) Sensing Element (I.e. wire-wound, thin film) Temperature questions. Error for a 2 wire assembly 0.06 x 6 x 2 = 0.72 ohms or 1.8Deg C This means that the temperature measured at the end of the cable would be 21.8 Deg C Error for a 4 wire assembly As the lead resistances can be accounted for the temperature measured at the end of the cable would be 20.0 Deg C
14 Temperature Sensors & Accessories - Types of RTDs  Dual Element RTDs available – Rosemount 65 Series RTD Red Red White Black Red Red Green Blue Blue White Dual Element: Two 3-wire RTDs  Supports Hot Backup capability  Dual element adds only $5 over single element RTD!  Reduce the risk of a temperature point failure
15 Handheld RTD
16 Digital RTD
17 Temperature Switches
18 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouple vs. RTD Sensors – RTD Calibration (Characterization) – Accessories – Time Response
19 Temperature Sensors & Accessories - Thermocouples Process Process Temperature Temperature Hot junction – Two dissimilar metals joined at a “Hot” junction + - Cold junction MV T What is a Thermocouple? Seebeck Effect In 1821, Thomas Seebeck discovered that if two wires of dissimilar metals were joined together at both ends and one of the ends is heated,a continuous current flows through this thermoelectric circuit. If this circuit is broken, the net open circuit voltage is a function of the junction temperatures and the composition of the two metals. How do they work
20 Temperature Sensors & Accessories - Thermocouples  What is a Thermocouple? – The measured voltage is proportional to the temperature difference temperature difference between the hot and cold junction! + - MV Heat Hot junction Cold junction Voltage (mV) Temperature (o C) o C Millivolts 0 0.000 200 8.137 400 16.395 600 24.902 800 33.277 1000 41.289 Thermoelectric Voltage vs. Temperature Chart: TYPE K THERMOCOUPLE T -10 0 10 20 30 40 50 60 -50 200 450 700 950 1200
21 Temperature Sensors & Accessories - Thermocouples  Temperature range  Cost  Signal level Why would you use one type of thermocouple over another? Why would you use one type of thermocouple over another? 0 5 10 15 20 25 30 35 40 45 50 0 200 400 600 800 1000 1200 1400 1600 1800 Type R 21.0 mV at 1760°C Type J 42.3 mV at 760°C Millivolts Temperature (C) Type J Type R
22 Correct! Wrong! All thermocouple lead wire extensions MUST be with the same type of wire or the correct compensating cable! Another Hot Junction is created… not good! Temperature Sensors & Accessories - Thermocouples Cannot use copper wire for extensions! T/C wire is more expensive to run and much more care must be taken with installation!
23 Exercise: Find the Temperature A type K thermocouple is lying on your desk. You hook up a voltmeter to the free end of the thermocouple. What voltage would the voltmeter read What’s the What’s the Temperature? Temperature? The thermostat in the room reads 20°C. o C Millivolts 0 0.000 10 0.397 20 0.798 30 1.801 Thermoelectric Voltage vs. Temperature Chart: TYPE K THERMOCOUPLE Answer 0.000mV because both junctions are at the same temperature
24 Temperature Sensors & Accessories - Rosemount T/C Offering  Type J Type J – Iron / Constantan » Black, White, » -40 to 750 °C » Least Expensive Rosemount Thermocouple Offering: Series 185 Rosemount Thermocouple Offering: Series 185  Type K Type K – Chromel / Alumel » Green, White » -40 to 1100 °C » Most Linear  Type T Type T – Copper / Constantan » Brown, White » -40 to 350 °C » Suitable for use at lower temperatures + - + - + - J K T N J K T N Colour Codes to IEC 60584 Colour Codes to IEC 60584 + -  Type N Type N – Ni-Cr-Si / Ni-Si-Mg » Pink, White » -40 to 1200 °C » Alternative to Type K but more stable at higher temperatures
25 Temperature Sensors & Accessories - Special Thermocouples  Type B Type B – Pt, 6% Rh / Pt, 30% Rh » 38 to 1800 °C  Type S Type S – Pt, 10% Rh / Pt » -50 to 1540o C  Type R Type R – Pt, 13% Rh / Pt » -50 to 1540 °C  Other T/Cs High temperature range Industrial/ laboratory standards LOW EMF output!
26 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
27 Temperature Sensors & Accessories - Thermocouples vs. RTDs Why would you use a RTD over a thermocouple? Why would you use a RTD over a thermocouple?
28 Temperature Sensors & Accessories - Thermocouples vs. RTDs  Better Stability Better Stability • T/C drift is erratic and unpredictable; RTD’s drift predictably • T/C’s cannot be recalibrated  Greater Flexibility Greater Flexibility • Special extension wires not needed • Don’t need to be careful with cold junctions Why would you use a RTD over a thermocouple? Why would you use a RTD over a thermocouple?  Better Accuracy & Repeatability Better Accuracy & Repeatability • RTD signal less susceptible to noise • Better linearity • RTD can be “matched” to transmitter (Interchangeability error eliminated) • CJC error inherent with T/C’s; RTD’s lead wire resistance errors can be eliminated
29 Temperature Sensors & Accessories - Thermocouples vs. RTDs Why would you use a thermocouple over a RTD? Why would you use a thermocouple over a RTD?
30 Temperature Sensors & Accessories - Thermocouples vs. RTDs  Applications for Higher Temperatures Applications for Higher Temperatures • Above 550°C  Lower Element Cost Lower Element Cost  Faster response time Faster response time • Especially when the hot junction is grounded to the sensor sheath  More rugged More rugged Why would you use a thermocouple over a RTD? Why would you use a thermocouple over a RTD?
31 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
32 EN 60751 Curve The EN 60751 standard (programmed into all our transmitters) describes an IDEAL Resistance vs. Temperature relationship for Pt100 385 RTDs. Temperature Sensors & Accessories - RTD Calibration TEMPERATURE (o C) RESISTANCE (OHMS) Class B Tolerance Standard EN 60751 Curve Class B Tolerance  0.8o C at -100o C  0.3o C at 0o C  0.8o C at 100o C  1.3o C at 200o C  1.8o C at 300o C  2.3o C at 400o C The goal is to find out what the real RTD curve looks like, and reprogram the transmitter to use the “real” curve! Every RTD is slightly different - they’re not ideal!
33 1 and 2-point Trim Reduce Sensor Interchangeability Error 0 50 100 150 200 250 300 350 400 -200 0 200 400 600 800 A 1-point trim shifts the ideal curve up or down based on the single characterized point Temperature (°C) Resistance () • Use one or two points to trim the sensor to a transmitter A 2-point trim shifts the ideal curve up or down AND changes the slope based on the two characterized points Temperature (°C) Resistance () 0 50 100 150 200 250 300 350 400 -200 0 200 400 600 800 Calibration option X8: Customer receives actual resistance values at two temperatures Calibration Option X9: Customer receives actual resistance values at one temperature One Point Trim Use with X9 Two Point Trim Use with X8
34 Callendar-Van Dusen Constants Generate True RTD Curve Ideal IEC751 curve is replaced (in the transmitter) with the REAL curve of the sensor Temperature (°C) Resistance () Customer Receives RTD-specific constants: • The V options also provides the customer with Callendar-Van Dusen Constants • These can be plugged into the transmitter to create the REAL RTD curve! Ro    99.997 0.003845 1.61027 0.172491 IEC 751 Curve REAL RTD Curve
35 V Options Provide Callendar-Van Dusen Constants » Sensor characterized over standard temperature range » Callendar-Van Dusen constants provided on sensor tag » Resistance vs. temperature table not included Ro = 99.9717  = 0.00385367  = 0.172491  = 1.61027 The V Options also provide the customer with Callendar-Van Dusen Constants When you order a sensor with a ‘V’ option, you receive the C.V.D. constants on a metal tag! You do NOT receive an R vs T table for that sensor!
36 Callendar-Van Dusen Constants Map the Real RTD Curve Rt = Ro + Ro[t-(0.01t-1)(0.01t)-(0.01t-1)(0.01t)3 ] Rt = Resistance at Temperature t (°C) Ro = Sensor-Specific Constant (Resistance at t = 0°C)  = Sensor-Specific Constant  = Sensor-Specific Constant  = Sensor-Specific Constant Using the Callendar-Van Dusen constants ELIMINATES sensor interchangeability error! Temperature (o C) Resistance () Class B Tolerance • The transmitter does not use the EN 60751 standard curve. • Instead, the C.V.D. constants are used in the equation below to create the true sensor curve EN 60751 Curve
37 Accuracy is just as Important as Repeatability  Model based control algorithm  Instrument failure – Replacement interchangeability  Process cloning There are many reasons why a customer should be concerned about accuracy in addition to repeatability: Transmitter/Sensor matching and referencing are easy ways to increase the accuracy of a temperature point measurement!
38 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
39 Sensor Accessories - Sensor Connection Heads – Rosemount/Heraeus Heads are available for » General purpose sensors » A range of IP Ratings (See Data Sheets) » Terminal block sensor, or flying lead sensor » Single or dual-element sensors » Epoxy coated aluminium,or stainless steel or plastic options available » CENELEC/BASEEFA approved version available  Used for head mounted transmitters, or sensors with Term.Blocks Typical Rosemount Connection Head (Other styles are available see Data Sheets)
40 Sensor Accessories - Extension Fittings  Extension fittings are used for a number of reasons including: – Heat dissipation from the process to the transmitter – Extend sensor through tank jacket or pipe insulation – Ease of accessibility through mounting in hard to reach areas – Disconnect sensor from process without full disassembly (Union)  Various types – to suit customer requirements 0 10 20 30 40 50 60 75 100 125 150 175 200 225 Thermow ell extension mm Temperature rise C above ambient Process Temp.= 250 °C Process Temp.= 540 °C Process Temp.= 815 °C
41 Temperature Product Training - Thermowells  What is a thermowell (T-well) ? – A unit that protects a sensor from process flow, pressure, and corrosion – Allows for sensor removal without process shutdown – Slows response time (by typically 5 times)  Why are there different material types? – To handle different corrosive environments – To handle different temperature and pressure limits
42 Temperature Product Training - Thermowells  Thermowell Failure  T-wells can fail under certain conditions  Fluid flowing around the T-well forms a turbulent wake called the Von Karman trail  The wake alternates from side to side at a specific frequency dependent on many variables  If that frequency exceeds 80% of the T-well’s natural frequency, the T-well can fail!
43  Preventing Thermowell Failure – Application acceptability can be determined by knowing the following: » Thermowell Style » Thermowell Material » Thermowell Dimensions » Fluid Velocity » Process Pressure » Fluid Density » Process Temperature » T-well failure calculations can be carried out by Rosemount Temperature Applications Groups Temperature Product Training - Thermowells Look on the back of your Sensor PDS!
44 Thermowell Design Styles: Comparison Table * Tapered Stepped Straight Process Pressure Time Response Wake Frequency 1 3 2 1 or 2 3 1 or 2 1 1 1 Drag Force 2 1 2 Rating: 1= Best Stepped Straight Tapered
45 Thermowell Mounting Styles  Threaded » Most common » Easy to remove and install  Weld in (Not available with tubular wells) » Non-removable » Used in high velocity, temperature and pressure fluids » Used in non-leak applications  Flanged » Used in corrosive environments » Used in high velocity, and high temperatures  Additional Services – various non-destuctive tests are available . . .
46 Fitting the Pieces Together - Tubular Assembly Sensor Head + Thermowell with integral Extension
47 Fitting the Pieces Together - Non-Tubular Assembly Sensor + Thermowell Head + Extension
48 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
49 Temperature Point Response Time  Sensor  Thermowell  Transmitter  Process Factors Affecting Temperature Point Response Time Process Transmitter Thermowell Sensor 75.4 °C
50 Sensor Time Response  Type of element – Wirewound RTD » externally or internally wound – Thin-film RTD – Thermocouple  Element packaging – Element coating, potting – Contact between element package & sheath  Sheath thickness and material Factors Affecting Sensor Response Time element sheath ceramic bore Al2O3 packing OD
51 Sensor Time Response  Type of element Thin-film has slightly faster response time than wirewound – Thermocouples do not vary significantly  Element packaging – Rosemount RTD’s are packed in magnesium oxide to provide optimum thermal conduction within the sheath – Grounded thermocouples are twice as fast as ungrounded  Sheath thickness and material – Rosemount uses 316SST and Inconel (for high temperatures) for sheath; both are very good thermal conductors Factors Affecting Sensor Response Time
52 Sensor Time Response Typical Wirewound RTD 10 - 16 s Thin-film RTD 8.0 - 12 s Ungrounded thermocouples <4 s Grounded thermocouples <2s * All results based on standard conditions: time required to reach 63.2% sensor response for water flowing at 3 ft/sec.
53 Factors Affecting Response Time of Sensors in Thermowells  Thermowell design style (thickness at tip) – Stepped is the fastest  Distance between sensor sheath and thermowell (y) – Spring loaded sensor ensures contact at the tip – Industry practice suggests using thermally conductive fill can significantly reduce time lag y Sensor Assembly Thermowell Thermally Conductive Fill
54 Time Response for Sensors in Thermowells Thermowells can slow the time response by at least a factor of 5 times
55 Factors Affecting Transmitter Repsonse Time  Time response depends on element (complexity of calculation)  2-wire RTD 440 - 760 ms  3 & 4-wire RTD 520 - 920 ms  Thermocouples 300 - 750 ms  Transmitter update time (output) every 1/2 second Process Transmitter 75.4 °C
56 Process Factors in Temperature Response Time  Velocity of the material  Thermal conductivity of the material  Density and viscosity of the material  Process time constants can be from seconds to hours: Process Water @ 3 fps t = 1 min Air at 50 fps, 40-80o C = 11 minutes Oil agitated in a bath: t = 13 minutes Oil not agitated: t = >45 minutes 75.4 °C
57 Summary: Temperature Point Response Time Sensor < 7 to 10 sec Sensor in Thermowell 60 to 120 sec Transmitter .5 to .9 sec Process Seconds to Hours • Thermowells and process material/conditions have the greatest effect on temperature point response time
58 Learning Objectives at the END: Temperature Sensors  Have a basic understanding of operation principles for both an RTD and T/C and understand the benefits of using one vs the other  Know the T-well styles and how to select the most appropriate for processes  Know the main factors that affect time response

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TemperatureTemperature Sensor Training.ppt

  • 1. 1 Temperature Sensor Training www.AutomationSys.Org 021-88535820-21 021-88535820-21
  • 2. 2 Temperature  What is temperature ? The temperature of an object can be described as that which determines the sensation of warmth or coldness felt from contact with it. www.AutomationSys.Org 021-88535820-21 021-88535820-21
  • 3. Measuring temperature  Expansion  Resistance change  Thermoelectric effect  Pyrometry  Cricket www.AutomationSys.Org 021-88535820-21 021-88535820-21
  • 4. 4 Modern temperature scales  Fahrenheit  Celsius  Kelvin  Rankine www.AutomationSys.Org 021-88535820-21 021-88535820-21
  • 5. 5 Learning Objectives: Temperature Sensors  Have a basic understanding of operation principles for both an RTD and T/C and understand the benefits of using one vs the other  Know the T-well styles and how to select the most appropriate for processes  Know the main factors that affect time response
  • 6. 6 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouple vs. RTD Sensors – Sensor Curve Definitions – Sensor Calibration (Characterization) – Accessories www.AutomationSys.Org 021-88535820-21 021-88535820-21
  • 7. 7 RTD Sensors What is an RTD?  What is an RTD?  Resistance Temperature Detector  Operation depends on inherent characteristic of metal (Platinum usually): electrical resistance changes when a metal undergoes a change in temperature.  If we can measure the resistance in the metal, we know the temperature! Platinum resistance changes with temperature Rosemount’s Series 65 (High Temperature),78, 88 Rosemount’s Series 65, 68, 58 Two common types of RTD elements: Wire-wound sensing element Thin-film sensing element
  • 8. 8 RTD Sensors Resistance Changes are Repeatable  What is a RTD? – Resistance Temperature Detector – The resistance changes of the platinum wiring can be approximated by an ideal curve -- the EN 60751 curve (Pt100) 0 50 100 150 200 250 300 350 -200 0 200 400 600 800 o C Ohms 0 100.00 10 103.90 20 107.79 30 111.67 Resistance (Ohms) Temperature (o C) International Resistance vs. Temperature Chart: EN 60751 EN 60751
  • 9. 9 EN 60751 Tolerances Accuracy Temperature Resistance Grade A Grade A Grade B Grade B °C Ohms ± °C ± Ohms ± °C ± Ohms -200 18.52 0.55 0.24 1.3 0.56 -100 60.26 0.35 0.14 0.8 0.32 0 100.00 0.15 0.06 0.3 0.12 100 138.51 0.35 0.13 0.8 0.30 200 175.85 0.55 0.2 1.3 0.48 300 212.05 0.75 0.27 1.8 0.64 400 247.09 0.95 0.33 2.3 0.79 500 280.98 1.15 0.38 2.8 0.93 600 313.71 1.35 0.43 3.3 1.06
  • 10. 10 RTD Sensors RTDs Do Not Follow the Ideal Curve TEMPERATURE (o C) RESISTANCE (OHMS) Ideal EN 60751 Curve The EN 60751 standard describes an IDEAL Resistance vs. Temperature relationship for Pt100 385 RTDs. Every Pt100 385 RTD is slightly different - they’re not ideal! Real Sensor Curve Because RTD sensors are not ideal - they do not perfectly match the EN 60751 - there will be error introduced into the temperature measurement. This Error is the Sensor Interchangeability Error!
  • 11. 11 Exercise: Find the Interchangeability Error Your customer is operating a process at 100°C and is using a Platinum RTD... What is the maximum error that will be introduced into the temperature measurement from Sensor Interchangeability? +/-0.35 deg C for Class A, +/-0.8 deg C for Class B Fortunately, Sensor Interchangeability Error can be reduced or eliminated by calibration!
  • 12. 12 Red Red White White RTD Sensors 2, 3, and 4-wire RTDs 4-wire RTD  Why use a 2-, 3-, or 4- wire RTD?  2-wire: Lowest cost -- rarely used due to high error 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. Typically use copper wires for extension from the sensor Sensing Element (I.e. wire-wound, thin film)
  • 13. 13 2-wire or 4-wire RTD ?  If the sensing element is at 20°C, F What would be the temperature measured at the end of the extension wire using a 2-wire assembly F What would be the temperature measured at the end of the extension wire using a 4-wire assembly Red White 2-wire RTD 6 metres of copper extension wire, lead resistance = 0.06 ohms/metre (1 ohm = 2.5 deg C approx) Sensing Element (I.e. wire-wound, thin film) Temperature questions. Error for a 2 wire assembly 0.06 x 6 x 2 = 0.72 ohms or 1.8Deg C This means that the temperature measured at the end of the cable would be 21.8 Deg C Error for a 4 wire assembly As the lead resistances can be accounted for the temperature measured at the end of the cable would be 20.0 Deg C
  • 14. 14 Temperature Sensors & Accessories - Types of RTDs  Dual Element RTDs available – Rosemount 65 Series RTD Red Red White Black Red Red Green Blue Blue White Dual Element: Two 3-wire RTDs  Supports Hot Backup capability  Dual element adds only $5 over single element RTD!  Reduce the risk of a temperature point failure
  • 18. 18 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouple vs. RTD Sensors – RTD Calibration (Characterization) – Accessories – Time Response
  • 19. 19 Temperature Sensors & Accessories - Thermocouples Process Process Temperature Temperature Hot junction – Two dissimilar metals joined at a “Hot” junction + - Cold junction MV T What is a Thermocouple? Seebeck Effect In 1821, Thomas Seebeck discovered that if two wires of dissimilar metals were joined together at both ends and one of the ends is heated,a continuous current flows through this thermoelectric circuit. If this circuit is broken, the net open circuit voltage is a function of the junction temperatures and the composition of the two metals. How do they work
  • 20. 20 Temperature Sensors & Accessories - Thermocouples  What is a Thermocouple? – The measured voltage is proportional to the temperature difference temperature difference between the hot and cold junction! + - MV Heat Hot junction Cold junction Voltage (mV) Temperature (o C) o C Millivolts 0 0.000 200 8.137 400 16.395 600 24.902 800 33.277 1000 41.289 Thermoelectric Voltage vs. Temperature Chart: TYPE K THERMOCOUPLE T -10 0 10 20 30 40 50 60 -50 200 450 700 950 1200
  • 21. 21 Temperature Sensors & Accessories - Thermocouples  Temperature range  Cost  Signal level Why would you use one type of thermocouple over another? Why would you use one type of thermocouple over another? 0 5 10 15 20 25 30 35 40 45 50 0 200 400 600 800 1000 1200 1400 1600 1800 Type R 21.0 mV at 1760°C Type J 42.3 mV at 760°C Millivolts Temperature (C) Type J Type R
  • 22. 22 Correct! Wrong! All thermocouple lead wire extensions MUST be with the same type of wire or the correct compensating cable! Another Hot Junction is created… not good! Temperature Sensors & Accessories - Thermocouples Cannot use copper wire for extensions! T/C wire is more expensive to run and much more care must be taken with installation!
  • 23. 23 Exercise: Find the Temperature A type K thermocouple is lying on your desk. You hook up a voltmeter to the free end of the thermocouple. What voltage would the voltmeter read What’s the What’s the Temperature? Temperature? The thermostat in the room reads 20°C. o C Millivolts 0 0.000 10 0.397 20 0.798 30 1.801 Thermoelectric Voltage vs. Temperature Chart: TYPE K THERMOCOUPLE Answer 0.000mV because both junctions are at the same temperature
  • 24. 24 Temperature Sensors & Accessories - Rosemount T/C Offering  Type J Type J – Iron / Constantan » Black, White, » -40 to 750 °C » Least Expensive Rosemount Thermocouple Offering: Series 185 Rosemount Thermocouple Offering: Series 185  Type K Type K – Chromel / Alumel » Green, White » -40 to 1100 °C » Most Linear  Type T Type T – Copper / Constantan » Brown, White » -40 to 350 °C » Suitable for use at lower temperatures + - + - + - J K T N J K T N Colour Codes to IEC 60584 Colour Codes to IEC 60584 + -  Type N Type N – Ni-Cr-Si / Ni-Si-Mg » Pink, White » -40 to 1200 °C » Alternative to Type K but more stable at higher temperatures
  • 25. 25 Temperature Sensors & Accessories - Special Thermocouples  Type B Type B – Pt, 6% Rh / Pt, 30% Rh » 38 to 1800 °C  Type S Type S – Pt, 10% Rh / Pt » -50 to 1540o C  Type R Type R – Pt, 13% Rh / Pt » -50 to 1540 °C  Other T/Cs High temperature range Industrial/ laboratory standards LOW EMF output!
  • 26. 26 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
  • 27. 27 Temperature Sensors & Accessories - Thermocouples vs. RTDs Why would you use a RTD over a thermocouple? Why would you use a RTD over a thermocouple?
  • 28. 28 Temperature Sensors & Accessories - Thermocouples vs. RTDs  Better Stability Better Stability • T/C drift is erratic and unpredictable; RTD’s drift predictably • T/C’s cannot be recalibrated  Greater Flexibility Greater Flexibility • Special extension wires not needed • Don’t need to be careful with cold junctions Why would you use a RTD over a thermocouple? Why would you use a RTD over a thermocouple?  Better Accuracy & Repeatability Better Accuracy & Repeatability • RTD signal less susceptible to noise • Better linearity • RTD can be “matched” to transmitter (Interchangeability error eliminated) • CJC error inherent with T/C’s; RTD’s lead wire resistance errors can be eliminated
  • 29. 29 Temperature Sensors & Accessories - Thermocouples vs. RTDs Why would you use a thermocouple over a RTD? Why would you use a thermocouple over a RTD?
  • 30. 30 Temperature Sensors & Accessories - Thermocouples vs. RTDs  Applications for Higher Temperatures Applications for Higher Temperatures • Above 550°C  Lower Element Cost Lower Element Cost  Faster response time Faster response time • Especially when the hot junction is grounded to the sensor sheath  More rugged More rugged Why would you use a thermocouple over a RTD? Why would you use a thermocouple over a RTD?
  • 31. 31 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
  • 32. 32 EN 60751 Curve The EN 60751 standard (programmed into all our transmitters) describes an IDEAL Resistance vs. Temperature relationship for Pt100 385 RTDs. Temperature Sensors & Accessories - RTD Calibration TEMPERATURE (o C) RESISTANCE (OHMS) Class B Tolerance Standard EN 60751 Curve Class B Tolerance  0.8o C at -100o C  0.3o C at 0o C  0.8o C at 100o C  1.3o C at 200o C  1.8o C at 300o C  2.3o C at 400o C The goal is to find out what the real RTD curve looks like, and reprogram the transmitter to use the “real” curve! Every RTD is slightly different - they’re not ideal!
  • 33. 33 1 and 2-point Trim Reduce Sensor Interchangeability Error 0 50 100 150 200 250 300 350 400 -200 0 200 400 600 800 A 1-point trim shifts the ideal curve up or down based on the single characterized point Temperature (°C) Resistance () • Use one or two points to trim the sensor to a transmitter A 2-point trim shifts the ideal curve up or down AND changes the slope based on the two characterized points Temperature (°C) Resistance () 0 50 100 150 200 250 300 350 400 -200 0 200 400 600 800 Calibration option X8: Customer receives actual resistance values at two temperatures Calibration Option X9: Customer receives actual resistance values at one temperature One Point Trim Use with X9 Two Point Trim Use with X8
  • 34. 34 Callendar-Van Dusen Constants Generate True RTD Curve Ideal IEC751 curve is replaced (in the transmitter) with the REAL curve of the sensor Temperature (°C) Resistance () Customer Receives RTD-specific constants: • The V options also provides the customer with Callendar-Van Dusen Constants • These can be plugged into the transmitter to create the REAL RTD curve! Ro    99.997 0.003845 1.61027 0.172491 IEC 751 Curve REAL RTD Curve
  • 35. 35 V Options Provide Callendar-Van Dusen Constants » Sensor characterized over standard temperature range » Callendar-Van Dusen constants provided on sensor tag » Resistance vs. temperature table not included Ro = 99.9717  = 0.00385367  = 0.172491  = 1.61027 The V Options also provide the customer with Callendar-Van Dusen Constants When you order a sensor with a ‘V’ option, you receive the C.V.D. constants on a metal tag! You do NOT receive an R vs T table for that sensor!
  • 36. 36 Callendar-Van Dusen Constants Map the Real RTD Curve Rt = Ro + Ro[t-(0.01t-1)(0.01t)-(0.01t-1)(0.01t)3 ] Rt = Resistance at Temperature t (°C) Ro = Sensor-Specific Constant (Resistance at t = 0°C)  = Sensor-Specific Constant  = Sensor-Specific Constant  = Sensor-Specific Constant Using the Callendar-Van Dusen constants ELIMINATES sensor interchangeability error! Temperature (o C) Resistance () Class B Tolerance • The transmitter does not use the EN 60751 standard curve. • Instead, the C.V.D. constants are used in the equation below to create the true sensor curve EN 60751 Curve
  • 37. 37 Accuracy is just as Important as Repeatability  Model based control algorithm  Instrument failure – Replacement interchangeability  Process cloning There are many reasons why a customer should be concerned about accuracy in addition to repeatability: Transmitter/Sensor matching and referencing are easy ways to increase the accuracy of a temperature point measurement!
  • 38. 38 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
  • 39. 39 Sensor Accessories - Sensor Connection Heads – Rosemount/Heraeus Heads are available for » General purpose sensors » A range of IP Ratings (See Data Sheets) » Terminal block sensor, or flying lead sensor » Single or dual-element sensors » Epoxy coated aluminium,or stainless steel or plastic options available » CENELEC/BASEEFA approved version available  Used for head mounted transmitters, or sensors with Term.Blocks Typical Rosemount Connection Head (Other styles are available see Data Sheets)
  • 40. 40 Sensor Accessories - Extension Fittings  Extension fittings are used for a number of reasons including: – Heat dissipation from the process to the transmitter – Extend sensor through tank jacket or pipe insulation – Ease of accessibility through mounting in hard to reach areas – Disconnect sensor from process without full disassembly (Union)  Various types – to suit customer requirements 0 10 20 30 40 50 60 75 100 125 150 175 200 225 Thermow ell extension mm Temperature rise C above ambient Process Temp.= 250 °C Process Temp.= 540 °C Process Temp.= 815 °C
  • 41. 41 Temperature Product Training - Thermowells  What is a thermowell (T-well) ? – A unit that protects a sensor from process flow, pressure, and corrosion – Allows for sensor removal without process shutdown – Slows response time (by typically 5 times)  Why are there different material types? – To handle different corrosive environments – To handle different temperature and pressure limits
  • 42. 42 Temperature Product Training - Thermowells  Thermowell Failure  T-wells can fail under certain conditions  Fluid flowing around the T-well forms a turbulent wake called the Von Karman trail  The wake alternates from side to side at a specific frequency dependent on many variables  If that frequency exceeds 80% of the T-well’s natural frequency, the T-well can fail!
  • 43. 43  Preventing Thermowell Failure – Application acceptability can be determined by knowing the following: » Thermowell Style » Thermowell Material » Thermowell Dimensions » Fluid Velocity » Process Pressure » Fluid Density » Process Temperature » T-well failure calculations can be carried out by Rosemount Temperature Applications Groups Temperature Product Training - Thermowells Look on the back of your Sensor PDS!
  • 44. 44 Thermowell Design Styles: Comparison Table * Tapered Stepped Straight Process Pressure Time Response Wake Frequency 1 3 2 1 or 2 3 1 or 2 1 1 1 Drag Force 2 1 2 Rating: 1= Best Stepped Straight Tapered
  • 45. 45 Thermowell Mounting Styles  Threaded » Most common » Easy to remove and install  Weld in (Not available with tubular wells) » Non-removable » Used in high velocity, temperature and pressure fluids » Used in non-leak applications  Flanged » Used in corrosive environments » Used in high velocity, and high temperatures  Additional Services – various non-destuctive tests are available . . .
  • 46. 46 Fitting the Pieces Together - Tubular Assembly Sensor Head + Thermowell with integral Extension
  • 47. 47 Fitting the Pieces Together - Non-Tubular Assembly Sensor + Thermowell Head + Extension
  • 48. 48 AGENDA  Temperature Sensors and Accessories – RTD Sensors, Rosemount Offering – Thermocouple Sensors, Rosemount Offering – Thermocouples vs. RTDs – RTD Calibration (Characterization) – Accessories – Time Response
  • 49. 49 Temperature Point Response Time  Sensor  Thermowell  Transmitter  Process Factors Affecting Temperature Point Response Time Process Transmitter Thermowell Sensor 75.4 °C
  • 50. 50 Sensor Time Response  Type of element – Wirewound RTD » externally or internally wound – Thin-film RTD – Thermocouple  Element packaging – Element coating, potting – Contact between element package & sheath  Sheath thickness and material Factors Affecting Sensor Response Time element sheath ceramic bore Al2O3 packing OD
  • 51. 51 Sensor Time Response  Type of element Thin-film has slightly faster response time than wirewound – Thermocouples do not vary significantly  Element packaging – Rosemount RTD’s are packed in magnesium oxide to provide optimum thermal conduction within the sheath – Grounded thermocouples are twice as fast as ungrounded  Sheath thickness and material – Rosemount uses 316SST and Inconel (for high temperatures) for sheath; both are very good thermal conductors Factors Affecting Sensor Response Time
  • 52. 52 Sensor Time Response Typical Wirewound RTD 10 - 16 s Thin-film RTD 8.0 - 12 s Ungrounded thermocouples <4 s Grounded thermocouples <2s * All results based on standard conditions: time required to reach 63.2% sensor response for water flowing at 3 ft/sec.
  • 53. 53 Factors Affecting Response Time of Sensors in Thermowells  Thermowell design style (thickness at tip) – Stepped is the fastest  Distance between sensor sheath and thermowell (y) – Spring loaded sensor ensures contact at the tip – Industry practice suggests using thermally conductive fill can significantly reduce time lag y Sensor Assembly Thermowell Thermally Conductive Fill
  • 54. 54 Time Response for Sensors in Thermowells Thermowells can slow the time response by at least a factor of 5 times
  • 55. 55 Factors Affecting Transmitter Repsonse Time  Time response depends on element (complexity of calculation)  2-wire RTD 440 - 760 ms  3 & 4-wire RTD 520 - 920 ms  Thermocouples 300 - 750 ms  Transmitter update time (output) every 1/2 second Process Transmitter 75.4 °C
  • 56. 56 Process Factors in Temperature Response Time  Velocity of the material  Thermal conductivity of the material  Density and viscosity of the material  Process time constants can be from seconds to hours: Process Water @ 3 fps t = 1 min Air at 50 fps, 40-80o C = 11 minutes Oil agitated in a bath: t = 13 minutes Oil not agitated: t = >45 minutes 75.4 °C
  • 57. 57 Summary: Temperature Point Response Time Sensor < 7 to 10 sec Sensor in Thermowell 60 to 120 sec Transmitter .5 to .9 sec Process Seconds to Hours • Thermowells and process material/conditions have the greatest effect on temperature point response time
  • 58. 58 Learning Objectives at the END: Temperature Sensors  Have a basic understanding of operation principles for both an RTD and T/C and understand the benefits of using one vs the other  Know the T-well styles and how to select the most appropriate for processes  Know the main factors that affect time response

Editor's Notes

  • #2: We can describe the temperature of an object as that which determines the sensation of warmth or coldness felt from contact with it. (The hotness or coldness of an object.) or THE PROPERTY OF A SYSTEM THAT DETERMINES WHETHER IT IS IN THERMAL EQUILIBRIUM WITH OTHER SYSTEMS.
  • #3: Temperature can be measured in a variety of ways. Some of the more common methods are:- Expansion of a gas, liquid, or other material such as mercury. Change in resistance of metals. (Sir Humphrey Davey) Platinum resistance thermometers - Sir William Siemen Thermoelectric effect. (Thomas Seebeck) Pyrometer. -- Measures the amount of emitted radiation (usually infra-red). (Max Planck) Bimetallic. -- Unequal expansion of two different metals welded together. A not very common method is, The Cricket Thermometer -- Count the number of chirps a cricket makes in 15 seconds, add 40, and the result is the temperature in Deg.F.
  • #4: Hook (1664) -- Every degree represented an equal volume equivalent to 1/500th part of the volume of the thermometer liquid.(Red dye in alcohol). The first meteorological records used this scale. Fahrenheit (1724) -- Based on three fixed points, Mixture of ice, pure water, and ammonium chloride or sea salt (0 Deg F), a mixture of ice, and pure water (32Deg.F), and the temperature of the human body (96 Deg.F). Centigrade (Anders Celsius 1742) --Based on two points. Boiling point of water (0), and the melting point of ice (100). This was later changed to 0 Deg C for the melting point of ice, and 100 Deg C for the boiling point of water. Celsius -- The centigrade scale has now been dropped in favour of the Celsius scale which is defined as the triple point of water (0.01 Deg) and the boiling point of water at standard atmospheric pressure (99.975 Deg.C.). Kelvin -- The temperature at which the pressure of an ideal gas is zero is defined as 0 K, and the triple point of water is set at 273.16 K. Rankine -- The temperature at which the pressure of an ideal gas is zero is defined as 0 K, and 1 Deg R is equivalent to 1 Deg F (0 Deg C = 491.67 Deg. R.
  • #7: Have one of the experienced sales people answer this.
  • #8: Have one of the experienced sales people answer this.
  • #11: ANSWER = +/-0.35°C for a Class A, or +/-0.8°C for a Class B This means that if a Class B sensor which is at the minimum value is replaced with one of the maximum value, the temperature would appear to have increase by 1.6°C (EN 60751 tolerances)
  • #12: Find the error in a 2-wire: 18 A.W.G. copper wire, Resistance = 6.385 Ohms/ 1000 ft -Assuming a length of 20 ft (6 meters), this adds 0.33°C error to the measurement. If the gage wire is higher (e.g. 22), the error shoots up to 0.84°C!
  • #13: Error for a 2-wire assembly: 0.06 x 6 x 2 = 0.72 ohms which is equivalent to 1.8°C. This means that the temperature measured at the end of the cable would be 21.8°C. Error for 4-wire assembl y: As the lead resistances can be measured, the temperature measured at the end of the cable would be 20.0°C
  • #21: Ask: 1. Which is the lowest cost? (Types J,and K) 2. Which covers the highest temperature? (Type K)
  • #23: Answer: 0mV How? 1. A thermocouple does not measure temperature, it measures temperature difference between the two junctions. 2. Since both junctions are at the same temperature, the output, which is the difference in temperature between the two junctions must be 0mV
  • #24: What are the most commonly sold types of T/C’s? (Type J and K)
  • #27: It is also more probable for poisoning to occur in a thermocouple than in an RTD simply due to the amount of metal in the Thermocouple. In an RTD, the sensor metal itself is limited to a very small region. In a T/C, the sensor metal runs from the tip of the T-well, and the entire distance to the transmitter.
  • #44: Process Pressure: Is dependent on the thickness of the T-well wall only, and for most (“normal”) cases, the thicknesses of the T-wells we offer are identical. Time Response: Obvious. Stepped are the best: Less material to heat up due to smaller diameter. Wake Frequency: Stepped are the worst. They Have the lowest natural frequency and cause the highest wake frequency. ** Key equation: Wake frequency/Natural < 0.8 Price: From the V.1 Sensor PDS: Stepped and straight t-well are the same price, tapered are more expensive Drag Force: Stepped is best due to smallest diameter tip. Less area, less force. With the other two, it’s dependent on other things. Sometimes one will be better, sometime the other will be better. *****NOTE: (From Khoi’s friend): Top three t-wells (All threaded): Stepped, straight and then tapered (57.1% of t-wells sold). 84% of t-wells sold are threaded