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Vaisala webinar - Common pitfalls in industrial humidity measurements

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Learn how to measure a representative condition, how to deal with the application-specific requirements, and how to manage the uncertainty.

Publicada em: Tecnologia
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Vaisala webinar - Common pitfalls in industrial humidity measurements

  1. 1. ▪ You can move and resize all the windows on your desktop for the best viewing experience ▪ You can expand the slide area to full screen ▪ Please use the Q&A window to submit any questions during the webcast ▪ From the resource list you can find useful links to learn more about the topic ▪ Click the Help icon at the bottom of your page for answers to common technical issues ▪ For the best audio quality, please make sure your computer sound is turned on and the volume is up ▪ Some networks cause slides to advance more slowly than others. If your slides are lagging, please push F5 on your keyboard to refresh the page ▪ You will receive a link to the recording few days after the webinar Welcome to the webinar: Common pitfalls in industrial humidity measurements We will begin shortly
  2. 2. 20-Nov-42
  3. 3. Common pitfalls in industrial humidity measurements 20-Nov-43 Representativity issues Temperature differences Lack of sample flow Wrong materials Instrument doesn’t meet the Application specific requirements Temperature/Pressure/Humidity Condensation problems Chemicals Uncertainty Lack of maintenance Calibration issues Lack of reference data
  4. 4. Relative humidity
  5. 5. Relative humidity and temperature 20-Nov-45 ▪ Relative humidity = Pw/Pws * 100 ▪ Depends on temperature ▪ Less temperature → More relative humidity ▪ More temperature → Less relative humidity
  6. 6. Temperature differences and relative humidity 20-Nov-46 Actual process conditions: Temperature: 60.0 DegC Relative humidity: 50.0 %RH Temperature: 25.0 DegC Measured conditions: Temperature: 58 DegC Relative humidity: 55 %RH Problem if the sensor is installed partly in the process and party outside ▪ The error is flow dependent ▪ less flow → more error
  7. 7. Temperature differences and risk of condensation 20-Nov-47 Actual process conditions: Temperature: 85.0 DegC Relative humidity: 85.0 %RH Temperature: 25.0 DegC Measured conditions: Temperature: 80 DegC Relative humidity: 100 %RH Problem: Temperature measured by the probe is not representing the process conditions
  8. 8. Solutions to Temperature difference problems 20-Nov-48 Solution 1: ▪ Improve installation Solution 2: ▪ Use a different humidity parameter
  9. 9. Dew Point Temperature
  10. 10. Dew Point temperature ▪ The dew point temperature (Td) is the temperature to which air must be cooled to become saturated with water vapor. ▪ Can be calculated based on sensor saturation ratio (%RH) and temperature. 20-Nov-410 Condensation Dew point temperature 10 °C Initial conditions 50 %RH, 21 °CCooling
  11. 11. Temperature differences resolved! 20-Nov-411 Actual process conditions: Temperature: 60.0 DegC Relative humidity: 50.0 %RH Dew point temperature: 45.7 DegC Temperature: 25.0 DegC Measured conditions: Temperature: 58 DegC Relative humidity: 55 %RH Dew point temperature: 45.7 DegC Error due to heat leakage doesn’t affect the dew point temperature!
  12. 12. How to select a right instrument for your application?
  13. 13. I want to measure humidity! 20-Nov-413
  14. 14. Temperature Process conditions Pressure Relative humidity 20-Nov-416 -70 °C (-94 °F) 180 °C (356 °F) -40 °C (-40 °F) 0 °C (32 °F) 20 °C (68 °F) 100 °C (212 °F) 0 bara (0 psia) 50 bara (725 psia) 1 bara (14.5 psia) 7 bara (100 psia) 0 %RH 100 %RH 10 %RH 50 %RH Upper limit for the polymer sensor Ambient level Generic humidity application Demanding humidity application High humidity Low humidity Compressed air
  15. 15. Temperature 20-Nov-417 -70 °C (-94 °F) 180 °C (356 °F) -40 °C (-40 °F) 0 °C (32 °F) 20 °C (68 °F) 100 °C (212 °F) Generic humidity application Demanding humidity application HMP110 Humidity and temperature probe For various industrial applications Temperature range -40 … +80 °C (−40 ... +176 °F) Humidity and temperature sensors Measurement electroinics HMP5 Humidity and temperature probe For high temperatures Temperature range -70 … +180 °C (−94 ... +356 °F) Sensor head: Humidity and temperature sensors Heat resistive Probe cable 2m (or 10m) Sensor body: Measurement electroinics
  16. 16. 0 %RH 100 %RH 10 %RH 50 %RH Temperature and relative humidity 20-Nov-418 -70 °C (-94 °F) 180 °C (356 °F) -40 °C (-40 °F) 0 °C (32 °F) 20 °C (68 °F) 100 °C (212 °F) Generic humidity application Demanding humidity application ▪ Less temperature → More relative humidity ▪ More temperature → Less relative humidity
  17. 17. 0 %RH 100 %RH 10 %RH 50 %RH High temperature 20-Nov-419 -70 °C (-94 °F) 180 °C (356 °F) -40 °C (-40 °F) 0 °C (32 °F) 20 °C (68 °F) 100 °C (212 °F) Generic humidity application Demanding humidity application Boiling point • Low relative humidity-application • Consider using other humidity parameter • Dew Point temperature or mixing ratio!
  18. 18. High temperature, low humidity 20-Nov-420 -70 °C (-94 °F) 180 °C (356 °F) -40 °C (-40 °F) 0 °C (32 °F) 20 °C (68 °F) 100 °C (212 °F) Generic humidity application Demanding humidity application Boiling point HMP5 accuracy in Td:  9 °C Example application: Stable process conditions, 120 °C (248 °F) 3.7 %RH, Td 40 °C (104 °F) DMP5 accuracy:  2 °C HMP5 DMP5 DMP5 measurement performanceHMP5 measurement performance
  19. 19. 0 %RH 100 %RH 10 %RH 50 %RH High temperature – HUMICAP® vs. DRYCAP® 20-Nov-421 -70 °C (-94 °F) 180 °C (356 °F) -40 °C (-40 °F) 0 °C (32 °F) 20 °C (68 °F) 100 °C (212 °F) Generic humidity application Demanding humidity application Boiling point DMP5 HMP5 For normal and high humidity applications >10 %RH = HUMICAP® For low humidity applications <10 %RH = DRYCAP® Rule of thumb:
  20. 20. 180 °C (356 °F) -70 °C (-94 °F) 0 °C (32 °F) 100 °C (212 °F) Boiling point 350 °C (662 °F) Very High temperature 20-Nov-422 HMP5/DMP5 DMP6 Generic humidity application High temperature application Very high temperature application • Thin film polymer maximum temperature is limited to 180 °C (356 °F) • DMP6 passive cooling set will overcome this limitation.
  21. 21. Operation principle of a passive cooling set Hot side 300 °CCool side 20 °C Cooling set dissipates heat away from the sensor, allowing direct installation into high-temperature processes such as baking ovens Removable cooling fins 2020-11-0423 Sensor temperature 120 °C
  22. 22. 180 °C (356 °F) -70 °C (-94 °F) 0 °C (32 °F) 100 °C (212 °F) Boiling point 350 °C (662 °F) Extreme temperatures 20-Nov-424 HMP5/DMP5 DMP6 Sampling system 800 °C (1500 °F) 20 °C (68 °F) 1000 °C (1900 °F) or more
  23. 23. Pressure 20-Nov-425 0 bara (0 psia) 50 bara (725 psia) 1 bara (14.5 psia) 7 bara (100 psia) Ambient level Compressed air Generic humidity application Demanding humidity application HMP3 General purpose Humidity and temperature probe HMP7 Humidity and temperature probe for high humidities Generic sensor head: • Designed for atmospheric pressures. • Not designed for pressure applications • 0.5 bar (7 psi) variation is acceptable Pressure tight sensor head: • Vapor and pressure proof construction • Mimimum pressure: full vacuum • Maximum pressure depends on sensor construction, from 10 bar up to 100 bar
  24. 24. Pressure and relative humidity 20-Nov-426 0 bara (0 psia) 50 bara (725 psia) 1 bara (14.5 psia) 7 bara (100 psia) Ambient level Compressed air Generic humidity application Demanding humidity application 0 %RH 100 %RH 10 %RH 50 %RH ▪ Less presure → Less relative humidity ▪ More pressure → more relative humidity
  25. 25. Compressed air 20-Nov-427 0 bara (0 psia) 50 bara (725 psia) 1 bara (14.5 psia) 7 bara (100 psia) Ambient level Compressed air Generic humidity application Demanding humidity application 0 %RH 100 %RH 10 %RH 50 %RH Quality requirement: ISO8573-1:2010 CLASS 2: Vapor pressure Dew Point temperature ≤ -40°C Low humidity application • DRYCAP-application DM70 Handheld dewpoint meter DMT143 Dew Point transmitter
  26. 26. Pitfalls in compressed air application 20-Nov-428 ▪ Wrong installation location ▪ Improper flow not giving real picture ▪ Leaks in the system ▪ Wrong piping materials
  27. 27. High humidity 20-Nov-429 Generic humidity application Demanding humidity application 0 %RH 100 %RH 10 %RH 50 %RH HMP3 General purpose Humidity and temperature probe HMP7 Humidity and temperature probe for high humidities HUMICAP + PT100: • Replaceable humidity sensor • No protection against condensation or chemicals Composite sensor: • Humidity and temperature sensor attached to each other • Temperature sensor can be used for warming the humidity sensor
  28. 28. HMP7 – Ultimate solution for condensing environments! ▪ Prevents condensation from occurring on the sensor even in a 100% RH environment ▪ Entire probe is warmed typically 5 degrees above dewpoint temperature ▪ Separate temperature probe TMP1 for calculating RH if needed 30 HUMICAP® PT100/sensor heater Filter Probe body Probe heating element VIM Product training - Humicap Technology2019-04-08
  29. 29. Warmed probe – How it works 31 HUMICAP® PT100/sensor heater Filter Probe body Probe heating element Conditions inside the probe: RHs , Ts , Tda Ambient: RHa, Ta , Tda Ambient: Ta = 14 °C RHa = 97 %RH Tda = 13 °C Humidity sensor: Ts = 16 °C RHs = 83 %RH Tda = 13 °C (calculated) • NOTE! The heating does not affect dew point! • The ambient temperature is measured with separate T-probe! VIM Product training - Humicap Technology2019-04-08
  30. 30. Comparison of warmed and non-warmed sensor heads in high humidity Weather 60.0 70.0 80.0 90.0 100.0 16:47 23:13 05:56 12:37 19:19 02:05 08:47 Time (hh:mm) Humidityreading(%RH) -3 -2 -1 0 1 2 3 4 5 6 7 Temperature(°C) Temperature Warmed sensor head Normal sensor head Delay of > 1.5 h Humidity readings One day and night VIM Product training - Humicap Technology32 2019-04-08
  31. 31. Low humidity 20-Nov-433 Generic humidity application Demanding humidity application 0 %RH 100 %RH 10 %RH 50 %RH DRYCAP® HUMICAP® For normal and high humidity applications >10 %RH = HUMICAP® For low humidity applications <10 %RH = DRYCAP® Rule of thumb:
  32. 32. Chemicals
  33. 33. Problem with cleaning agents 20-Nov-435 Assumption: Sensor drifted due to cleaning chemicals Calibration result: Sensor is within tolerance
  34. 34. Chemical purge ▪ Especially for high concentrations of cleaning agents/chemicals ▪ Working principle ▪ The sensor is rapidly heated to +160..180 °C. This procedure evaporates the interfering chemicals ▪ Starts with heating stage, continues with settling and when the temperature of the sensor is decreased the transmitter returns to normal mode ▪ Function freezes the output values for about 6 minutes. 36 HUMICAP® PT100/sensor heater Filter Probe body VIM Product training - Humicap Technology2019-04-08
  35. 35. Chemical purge and ethyl acetate HUMICAP® PT100/sensor heater Filter Probe body Probe heating element Ethyl a ce ta te (a pr.700ppm) 4-7.10.97 55 60 65 70 75 Interval 120min Interval 720min
  36. 36. Chemical purge and isopropanol HUMICAP® PT100/sensor heater Filter Probe body Probe heating element Webinar 2018-12-04, Condensing enviroments Chemical purge after 35 days exposure to Isopropanol (saturated)
  37. 37. Chemical tolerance Long term exposure comparison ▪ Green: drift less than 3 %RH, probe tolerates long-term exposures. ▪ Orange: Drift more than 3 %RH but less than 10 %RH, not recommended. ▪ Red: Drift more than 10 %RH, not recommended. Conclusion: ▪ Sensor technology matters! ▪ Chemical purge improves the long term stability 20-Nov-439 Chemical / probe VAISALA HMP7 Brand X Brand Y Acetic acid (HAc), 355 days, 800 ppm > 3 %rh > 3 %rh >10 %rh Methyl Ethyl Ketone (MEK), 355 days, 3000 ppm > 3 %rh > 3 %rh >10 %rh Isopropanol (IPA), 126 days, 50000 ppm < 3 %rh > 3 %rh < 3 %rh Toluene, 229 days, 2000 ppm < 3 %rh < 3 %rh < 3 %rh Hydrochloric Acid (HCl), 16 days, 300 ppm > 3 %rh after 16 days Broken after 1.5 days Broken after 7.5 days Sulfur Dioxide (SO2), 89 days, 200 ppm < 3 % > 3 %rh > 3 %rh
  38. 38. How to deal with the uncertainty?
  39. 39. Which plan is worse? No calibration plan ▪ Tolerable in some extent ▪ Requires good quality instruments DRYCAP® thin film polymer sensor stability (over 11 years!) in a compressed air line Bad calibration plan Periodical maintenance calibration, but lacking one or more elements: ▪ Traceability ▪ On-site reference ▪ Representativity Leads into: ▪ Delusion of control ▪ Misinterpretations 20-Nov-441
  40. 40. Bad calibration plan example 1: Temperature differences in process ▪ Sensor is installed partly inside the process. ▪ Good flow → error caused by the temperature difference is small. 20-Nov-442 Actual process conditions: Temperature: 60.0 DegC Relative humidity: 50.0 %RH Temperature: 25.0 DegC Measured conditions: Temperature: 59.8 DegC Relative humidity: 50.5 %RH Flow: 3 m/s (10 fps)
  41. 41. Bad calibration plan example 1: Temperature differences in calibration ▪ Calibration made with a humidity calibrator ▪ Sensor is installed partly inside the chamber → temperature leak is stronger than in the process ▪ Bad calibration ▪ Both, the process and calibration procedure can be improved! 20-Nov-443 Reference probe: Temperature: 60.0 DegC Relative humidity: 50.0 %RH Temperature: 25.0 DegC Probe under test: Temperature: 58.0 DegC Relative humidity: 55 %RH Air circulation & Conditioning Humidity calibrator 60 C, 50 %RH
  42. 42. Bad calibration plan example 2: Lack of reference data 20-Nov-444 Instrument is calibratied periodically Calibration result: Pass -3 -2 -1 0 1 2 3 Drift(%RH) Time Sensor drift Drift at 0 %RH Drift at 75 %RH ? ? ? ? Solution: Supplement the reference data with spot checks!
  43. 43. Summary 20-Nov-445 • Installation location and calibration • Avoid condensation if possible. If not possible, use a warmed probe Take into account temperature differences • It withstands the process conditions: Temperature, pressure, humidity and chemicals • It has the best performance under the condition you want to measure: HUMICAP® or DRYCAP® Select the right measuring instrument • Keep the traceability intact with periodically calibrated instruments • Supplement your reference data with spot checks.Compare the readings
  44. 44. 4-Nov-2046 Insight PC software Indigo product family

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