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Industrial Instrumentation

Industrial Instrumentation. “It is time to turn up the heat but first you must learn how to measure it”. Temperature Sensor.

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Industrial Instrumentation

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  1. Industrial Instrumentation

  2. “It is time to turn up the heat but first you must learn how to measure it” Temperature Sensor PEC – UET Lahore Dr. Shahid Naveed 4. November 2014 / Dr. –Ing Naveed Ramzan 2

  3. Relative Scales Fahrenheit (°F) Celsius (°C) Absolute Scales Rankine (°R) Kelvin (K) Temperature Measurement Scales

  4. Temperature Measurement Scales Imperial Fahrenheit (⁰F) / Rankine (⁰R) +/- 460 Metric Celsius (⁰C) / Kelvin (⁰K) +/- 273 212⁰F 672⁰R 373⁰K 100⁰C Fahrenheit [°F] = [°C] · 9/5 + 32 Celsius [°C] = ([°F] − 32) · 5/9 Kelvin [K] = [°C] + 273.15 Rankine [°R] = [°F] + 459.67 0⁰C 273⁰K 32⁰F 492⁰R -18⁰C 255⁰K 0⁰F 460⁰R -273⁰C 0⁰K 0⁰R -460⁰F

  5. (°F) = 9/5*(°C) +32 (°C) = 5/9*[(°F) –32] (°F) = (°R) – 459.67 (°C) = (K) – 273.15 Relationship of Temperature Measurement Scales

  6. Methods of Temperature Measurement • Mechanical Methods • Electrical Methods

  7. Methods of Temperature Measurement Expansion thermometers Filled system thermometers Electrical temperature instruments Pyrometers

  8. Methods of Temperature Measurement Expansion thermometers Filled system thermometers Electrical temperature instruments Pyrometers

  9. Expansion thermometers • Expansion of solids • Bimetallic thermometers • Expansion of liquids • Liquid in glass thermometers • Liquid in metal thermometers • Expansion of liquids • Gas thermometers

  10. Expansion thermometers Bimetallic Thermometer (Expansion of solids)

  11. Bimetallic Thermometer (Expansion of solids) Expansion Thermometers

  12. Bimetallic Thermometer (Expansion of solids) Expansion Thermometers Thermal expansion methods: Bimetallic sensors

  13. Expansion Thermometers Liquid in glass Thermometer (Expansion of liquids) Liquid in metal Thermometer (Expansion of liquids)

  14. Expansion Thermometers Gas Thermometer (Expansion of gas) • Depends on ideal gas law • Nitrogen acts like a perfect gas at extremely low temperatures • Inert and expensive • It reacts with the steel bulb temperature at 427 C

  15. Filled Thermal Systems (Filled System Thermometer, Filled Bulb Thermometer) Expansion Thermometers Spiral Type Bourdon Tube • Similar operation as the liquid in glass • Bulb • Capillary tube • Pressure element • Scale

  16. Filled Thermal System Classes (Filled System Thermometer, Filled Bulb Thermometer) Expansion Thermometers • Class l A,B – Liquid filled • Class ll A,B,C,D –Vapour filled • Class lll A,B – Gas filled • Class V A,B – Mercury Filled

  17. Filled System Thermometers • Gas filled thermometers • liquid filled thermometers • Mercury filled thermometers • Vapor pressure thermometers • Liquid inside the bulb continues to boil until the pressure in the system equals to vapor pressure of the boiling liquid. • Liquid stops boiling unless its temperature increases.

  18. Filled Thermal System Classes (Filled System Thermometer, Filled Bulb Thermometer) Expansion Thermometers • Temperature Range • Mercury: -38 F to + 1200 F • Xylene: -40 to 750 F • Alcohol: -50 F to +300 F • Ether: +70 F to +195 F

  19. Electrical Temperature Instruments • Thermocouple • Thermistor • Resistance thermometer

  20. Seebeck Effect: The generation of current in a circuit comprising of two wires of dissimilar metals in the presence of temperature difference Thermocouples When 2 dissimilar metals are joined together to form a junction, an emf is produced which is proportional to the temperature being sensed. The magnitude of emf depends on the junction temperature.

  21. Typical Industrial Thermocouple Assembly

  22. TCs are identified by a single letter type and grouped according to their temperature range Base Metals – up to 1000 °C Type J, Type E, Type T, Type K Noble Metals – up to 2000 °C Type R, Type S, Type B Refractory Metals – up to 2600 °C Type C, Type D, Type G Thermocouple Types

  23. Metal Combinations Chromel = Nickel-chromium Alumel = Nickel-aluminum Constantan = Copper-nickel

  24. Thermocouple Tables Voltage to Temperature Conversion 1.445 mV equal to temperature ……………………………………..

  25. Thermocouple Callibration Charts Voltage to Temperature Conversion

  26. Thermistors • Thermistor, a word formed by combining thermal with resistor, is a temperature-sensitive resistor fabricated from semiconducting materials. • The resistance of thermistors decreases proportionally with increases in temperature. • The operating range can be -200°C to + 1000°C

  27. Thermistors • The thermistors can be in the shape of a rod, bead or disc. • Manufactured from oxides of nickel, manganese, iron, cobalt, magnesium, titanium and other metals.

  28. Thermistors • The word that best describes the thermistors is “sensitive”

  29. Thermistor Charts Resistance to Temperature Conversion

  30. Advantages: Small sizes and fast response Low cost Suitability for narrow spans Disadvantages: More susceptible to permanent decalibration at high temperatures. Use is limited to a few hundred degrees Celsius. Respond quickly to temperature changes, thus, especially susceptible to self-heating errors. Very fragile Thermistors

  31. Electrical Resistance Change (RTD) Resistance Temperature Detector- RTD The industry standard is the platinum wire RTD (Pt100) whose base resistance is exactly 100.00 ohms at 0.0 °C. RTD (Resistance Temperature Detector) is a temperature sensitive resistor. It is a positive temperature coefficient device, which means that the resistance increases with temperature. The resistive property of the metal is called its resistivity.

  32. Electrical Resistance Change (RTD) Platinum Wire RTDs (PRTs) PRTs have established themselves as the de-facto industry standard for temperature measurement, and for many reasons: • linear temperature sensors • Resistance vs temperature characteristics are stable and reproducible • linear positive temperature coefficient (-200 to 800 °C) • very accurate and suitable for use as a secondary standard

  33. Electrical Resistance Change (RTD) Platinum Scale ( 0 to 100 °C )

  34. Electrical Resistance Change (RTD) International Practical scale for Temperature (0 to 650. 30 °C)

  35. Electrical Resistance Change (RTD) International Practical scale for Temperature (Below 0 °C)

  36. Electrical Resistance Change (RTD) International Practical scale for Temperature

  37. 10 ohms Copper RTD - .00427 coefficients 100 ohms Platinum RTD - .00385 coefficients (new IEC) 100 ohms Platinum RTD - .00392 coefficients (old) 120 ohms Nickel RTD - .00672 coefficient 604 ohms Nickel-Iron RTD - .00518 coefficients Electrical Resistance Change (RTD) Other RTDs All base resistances are specified at a temperature of 0 degrees C A Pt1000 will have a base resistance of 1000 ohms at 0 deg. C

  38. RTDs with a bridge circuit Only practical if the RTD lead wires are short. In many applications the RTD is located far from the conditioning circuit adding extra resistance because the length of the copper lead wire. Cu = 0.0302 Ω per ft. How much error will 100 ft length of Cu lead wire introduce? Most RTD’s have an extra wire to compensate for the length of lead wire.

  39. Radiation pyrometers Radiation Pyrometer

  40. Optical pyrometers (600 to 3000 °C) Radiation Pyrometer • basic principle of using the human eye to match the brightness of the hot object to the brightness of a calibrated lamp filament inside the instrument • Compare incident radiation to internal filament radiation

  41. Data Required to Provide Measurement of Process Temperature

  42. Data Required to Provide Measurement of Process Temperature

  43. Data Required to Provide Measurement of Process Temperature

  44. Data Required to Provide Measurement of Process Temperature

  45. Criteria for Selecting a Suitable Temperature Measuring Instrument

  46. Summary of Temperature Sensor Characteristics

  47. Summary of Temperature Sensor Characteristics

  48. Assignment • Advantages and disadvantages of all temperature measuring instruments • Calibration of thermometers • Bimetallic thermometers • Liquid in glass thermometers • Thermocouples thermometers • Filled system thermometers • Resistance thermometers (RTD) • Radiation pyrometers • Optical pyrometers

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