Vaisala Oyj Class A · OMXHEX:VAIAS
Vaisala Oyj Class A — Technical Presentation (2015)
27 slides from Vaisala Oyj Class A's technical presentation, 2015
Slide 1: Relative Humidity Sensor Technology
Welcome! Relative Humidity Sensor Technology What type of sensors are in our market today? Yumi Alanoly Vaisala Application Engineer
Slide 2: Today's Agenda
Today’s Agenda 1. Mechanical Displacement Sensor Sling Psycrometer 2. Electrical Bulk Polymer Resistive Sensor Capacitive Sensor 3. Dewpoint/Frostpoint Temperature Sensor Aluminum Oxide Dewpoint Sensor Chilled Mirror 4. What else do you have to consider when choosing a sensor? Page 2 / 2
Slide 3: Mechanical
Mechanical Perhaps the oldest type of RH sensor still in use is the displacement sensor. These devices use a strain gauge or other mechanism to measure expansion or contraction of a material in proportion to changes in relative humidity. Common material: horse hair, human hair, catgut, goldbeater’s
Slide 4: Mechanical
Mechanical + Inexpensive + No power needed - 20…90% best range - Uncertainty from +/-5% up to +/-15% - Considerable hysteresis - Responds to changes in humidity very slowly Page 4 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 5: Psychrometer (wet bulb-dry bulb)
Psychrometer (wet bulb-dry bulb) Two matched thermometers over which air is drawn. One thermometer has the bulb covered by a wet ‘cloth’ or ‘wick’. This is the ‘wet-bulb’. dry bulb cloth wet bulb water Page 5 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 6: Psychrometer (wet-dry bulb)
Psychrometer (wet-dry bulb) + Simple & fundamental measurement - High uncertainty (+/- 2% to 5%) + Low price ($35 to $80 for sling) - Requires some skill to use & maintain + Can have good stability - Results usually must be calculated + Tolerates condensation without damage - Requires large air samp
Slide 7: Electrical Sensors
Electrical Sensors Bulk Polymer Resistive Capacitive – Thin Film Polymer Page 7 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 8: Resistive Humidity Sensors
Resistive Humidity Sensors Measures the electrical impedance or resistance of a hygroscopic medium such as conductive polymer, salt, or a treated substrate. The resistance changes inversely with humidity. Page 8 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 9: Resistive Humidity Sensors
Resistive Humidity Sensors - Limited range (typically 15...95 %RH) + Small and cheap - High temperature dependency + Mass production possible - Poor stability + Interchangeable/field replaceable - Sensitive to contamination - Reading altered by all substances that affect resistance; salts, hydrogen,
Slide 10: Capacitive – thin film polymer
Capacitive – thin film polymer Measures the capacitance of an electrode where a polymer acts as the dielectric portion of the capacitor The properties of the polymer/dielectric change proportionately with the change in relative humidity which results in a change of the measured capacitance Page
Slide 11: Structure of the Capacitive HUMICAP Sensor
Structure of the Capacitive HUMICAP® Sensor Upper electrode • conductive material • protects the active material of the sensor from dust, dirt and conductive particles • lets through water vapor • functions as one of the two electrodes in a capacitor Active material • active polymer film • absorbs w
Slide 12: Where to Use Vaisala HUMICAP Sensors
Where to Use Vaisala HUMICAP® Sensors Most relative humidity measurements In temperatures of -70 ...+180 °C Where humidity can range from 0...100 %RH (with some exceptions in high humidity) In processes without any high concentrations of corrosive gases and/or solvents Page 12 / 2014/ YSH/ H
Slide 13: Capacitive – thin film polymer
Capacitive – thin film polymer + wide measurement range - can be limited by distance from 0...100 %RH electronics to sensor + wide temperature range (up to - loss of relative accuracy at low 200C) end (<5%) + excellent stability - requires electronics to convert + fast response capacitance to relati
Slide 14: Dew/Frost Point Temperature
Dew/Frost Point Temperature Capacitive – aluminum oxide dewpoint sensor Chilled mirror hygrometer Page 14 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 15: Capacitive - Aluminum Oxide
Capacitive - Aluminum Oxide (Al2O3) Capacitor which consists of aluminum and gold electrodes and an aluminum oxide insulator Responds to the partial pressure of water vapor and converted to absolute units (for Td or ppm) Page 15 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 16: Capacitive - Aluminum Oxide
Capacitive - Aluminum Oxide (Al2O3) + small - condensation or contamination on sensor + suitable for in-line site use causes significant + wide measuring range calibration shift measures dew point down - slow response time to -75...-100 °C - long stabilization time - need frequent calibration - sign
Slide 17: Condensation Hygrometer
Condensation Hygrometer Chilled Mirror NO DEW DEW detector detector light light chilled mirror chilled mirror Page 17 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 18: Condensation Hygrometer
Condensation Hygrometer + precise measurement (+/-.1C) + wide measurement range (-100..+100C) + very good long term performance + fundamental measurement - expensive - usually requires some skill/training to operate - mirror cannot tell ice or dew - contamination on mirror causes errors - requires f
Slide 19: Other technologies
Other technologies Saturated Salt Lithium Chloride This heating/cooling of the bobbin will reach equilibrium. This equilibrium temperature is directly proportional to the dewpoint Spectroscopic measures the light at a specific bandwidth where water vapor absorbs the light, based on the princi
Slide 20: Condensation
Condensation Condensation permanently shifts the readings of: Aluminum Oxides Resistive Sensors Thin Film polymers will display 100% until the condensation on the sensor fully evaporates Chilled Mirrors are not affected (unless the electronics get wet) Page 20 / 2014/ YSH/ Humidity Seminar
Slide 21: Vaisala Warmed-Probe Sensor Technology
Vaisala Warmed-Probe Sensor Technology Warmed probe • Can be selected with or without additional T probe • dewpoint output without additional T probe • RH & T output with the additional T probe • Either analog output or digital output (RS485) can be chosen • customer does the calibration by using ca
Slide 22: Vaisala Warmed-Probe Sensor Technology
Vaisala Warmed-Probe Sensor Technology Ambient: RHa, Ta , Tda Vaisala HUMICAP® sensor Heating element inside the probe Conditions inside the probe: RHs , Ts , Tda Ambient: Ta = 14 °C Humidity sensor: Ts = 16 °C RHa = 97 %RH RHs = 83 %RH Tda = 13 °C Tda = 13 °C (calculated) NOTE! The heating does not
Slide 23: Contamination
Contamination RH Sensor are all “air-breathers” and therefore cannot be protected from contamination. Cannot hermetically seal the sensor from the environment like is done with temperature sensors Particulate vs Vapor Contamination Sources of Contaminants Ultrasonic Humidifiers with impure
Slide 24: Vaisala Chemical Purge Feature
Vaisala Chemical Purge Feature For applications where the probe will be exposed to chemicals in vapor form a “chemical purge” feature will provide you better long term stability. Temp sensor is adhered to the Rh sensor Sensing element is rapidly heated to 160-180ºC, results in evaporation of che
Slide 25: Summary
Summary There are so many options in the market so start that conversation about the sensor technology with your vendors. Good place to start, what type of technology does this sensor use: • Mechanical • Electrical • Dewpoint/Frostpoint Based Page 25 / 2014/ YSH/ Humidity Seminar/ ©Vaisala
Slide 26: Vaisala Humidity Resources
Vaisala Humidity Resources On-line Humidity Calculator www.vaisala.com/humiditycalculator Humidity Conversion Formulas http://forms.vaisala.com/forms/humidity_conversion Vaisala Humidity Solution http://www.vaisala.com/en/products/humidity/Pages/default.aspx For assistance with your humidity m
Slide 27: Thank you! This concludes the webinar.
Thank you! This concludes the webinar. Follow-up email will arrive shortly with the resource links & further contact information. Page 27 / 2014/ YSH/ Humidity Seminar/ ©Vaisala