Slide 1: Humidity Theory: Understanding Humidity
Humidity Theory: Understanding Humidity Jarkko Ruonala Product Manager, Industrial Instruments © Vaisala
Slide 2: Humidity calculator link
http://go.vaisala.com/humiditycalculator/5.0 © Vaisala
Slide 3: Content
Content Theory, terms and definitions Evaporation and condensation, equilibrium Vapor pressure, saturation vapor pressure relative humidity, dew point temperature, frost point temperature Other humidity variables: Wet-bulb temperature, mixing ratio Choosing the correct instrument © Vaisa
Slide 4: How does humidity affect your day?
How does humidity affect your day? © Vaisala
Slide 5: Theory, terms and definitions
Theory, terms and definitions
Slide 6: Concepts
Concepts Humidity Vapor pressure, partial pressure Evaporation, condensation, equilibrium Saturation vapor pressure Relative humidity Dew point temperature © Vaisala
Slide 7: What is humidity
What is humidity Humidity is dissolved water Humidity is in gas phase Moisture - wetness of the solid material If you can see it, it is not humidity © Vaisala
Slide 8: The water molecule
The water molecule Polarity – uneven distribution of electrical charge, causing attraction between molecules © Vaisala
Slide 9: Vapor pressure
(0 PSIA) Vapor pressure Molecules in gas phase are in constant random motion This motion exerts pressure The more molecules, higher the vapor pressure The energy of the molecules depends not only on the amount, but also temperature © Vaisala
Slide 10: Partial pressure of water
Partial pressure of water The total pressure is the sum of the partial pressures of the components in the gas (Dalton’s law) The partial pressure exerted by water vapor is called the vapor pressure Pw 500 hPa Air + 500 hPa Water = 1000 hPa (14.5 PSIA) total Ptot = P1 + P2 + P3.. = Pair + Pwater
Slide 11: Example: Water in a Closed Container
Example: Water in a Closed Container Evaporation: As a result of the random movement of molecules, some molecules have enough energy to escape through the water film Condensation: As a result of random movement of molecules, some move so slow they get trapped back in water. Equilibrium: With t
Slide 12: The Effect of Temperature
The Effect of Temperature Equilibrium Liquid phase Gas phase Notice the impact of temperature on equilibrium vapor pressure as it goes from 50 to 104 oF! © Vaisala
Slide 13: Saturation vapor pressure
Saturation vapor pressure Saturation vapor pressure is highly temperature dependent The equilibrium of water vapor in a closed container is the saturation vapor pressure in that particular temperature Condensation rate equals evaporation rate Air cannot hold any more water vapor © Vaisala
Slide 14: The humidity variables I know or use
The humidity variables I know or use: A. Relative humidity B. Vapor pressure C. Dew-point/Frost-point temperature D. Mixing ratio E. Absolute humidity F. Wet-bulb temperature G. Water content [lb/MMscf, g/Nm3] H. PPM (parts per million) © Vaisala
Slide 15: Relative Humidity
Relative Humidity The proportion of water vapor pressure (Pw) to the maximum vapor pressure in the given temperature [Pws(t)] 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 %RH = 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑎𝑎𝑎𝑎…
Slide 16: Example
1013 Example Let’s assume we have vapor pressure of 100 hPa ..And temperature 100 °C 100 RH = = ~10 % 1013 ..And temperature 60 °C 100 200 RH = = ~50 % 200 100 ..And temperature 45,8 °C 100 RH = = ~100 % 100
Slide 17: Relative humidity is by definition relative to
Relative humidity is by definition relative to A. Absolute amount of water in the air B. Temperature C. Total pressure of the system © Vaisala
Slide 18: When temperature of a gas sample is increased
When temperature of a gas sample is increased A. Relative humidity increases B. Dew point temperature decreases C. Relative humidity decreases © Vaisala
Slide 19: Dew Point Temperature
Dew Point Temperature Dew point temperature is the temperature, where the vapor pressure would equal to saturation vapor pressure This is the temperature, where the given humidity level condenses by effect of temperature Proportional to amount of water vapor © Vaisala
Slide 20: Dew point temperature only depends on
Dew point temperature only depends on A. Amount of water vapor in the air B. Vapor pressure C. Temperature © Vaisala
Slide 21: Impact of pressure
Impact of pressure Let’s assume a closed container with water vapor pressure of 10 hPa (0.145 PSIA) dew point temperature of 7 °C (44.6 °F) and total pressure of 1 bar (14.5 PSIA) When we compress the gas isothermally to 4 bars (58 PSIA), the vapor pressure increases linearly As a result, the
Slide 22: Frost Point Temperature
Frost Point Temperature Frost point temperature is the temperature, where the water vapor condenses directly to solid ice, or frost Relevant in dry conditions where saturation temperatures are well below freezing point © Vaisala
Slide 23: Frost point temperature
Frost point temperature Temperature -2°C (28.4°F) Saturation vapor pressure over ice is slighlty lower than over supercooled water Pw = 5.3 hPa Pw = 5.1 hPa = 0.08 PSIA = 0.07 PSIA Water molecules in ice form a rigid lattice Lower rate of evaporation Lower saturation vapor pressure In most
Slide 24: How much do frost point and dew point differ?
How much do frost point and dew point differ? The difference is ~10% of indication Vaisala products output Tdf, which is dew point when saturation temperature is above freezing point, and frost point when saturation temperature is below freezing point © Vaisala
Slide 25: When measuring dew point, what does not induce a change
When measuring dew point, what does not induce a change in the reading: A. Changing pressure of the gas sample B. Changing temperature of the gas sample C. Changing amount of water vapor in the gas sample © Vaisala
Slide 26: Wet-bulb temperature
Wet-bulb temperature Evaporation involves change in energy Evaporation process involves cooling effect Rate of evaporation is governed by relative humidity Wet-bulb represents the lowest achievable temperature by means of evaporation of water Dry- and wet-bulb temperatures are tabulated fo
Slide 27: Mixing ratio
Mixing ratio Gives the mass of water vapor divided by total gas mass Independent on temperature or pressure Typical applications: process control, drying Mass balance calculations Processes where pressures and temperatures vary from one stage to another Mixing ratio represents the mass f
Slide 28: Ppm (Parts Per Million)
Ppm (Parts Per Million) Vaisala products output ppm –value per dry bases Amount of water divided by amount of dry air Volumetric (ppmv) and by-weight (ppmm) numbers available Mostly used in trace humidity measurements Note – exponential relation to wet basis ppm number (amount of water div
Slide 29: Theory in practice
Theory in practice
Slide 30: Measurements under high humidity - Ceramics drying kiln
Measurements under high humidity- Case example: Ceramics drying kiln © Vaisala
Slide 31: Normal probe in high humidity application
Normal probe in high humidity application (ceramics dryer) 100.0 Probe in saturation RH [%] without warmed probe 90.0 80.0 70.0 Relative humidity [%] 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 Time [h] © Vaisala
Slide 32: Warmed Probe Technology
Warmed Probe Technology With additional T –probe; temperature elevated from ambient Without additional T-probe (heated dew point measurement) seeks to 70..80 %RH Whole probe heated above ambient Constant heating; affects the filter a must in a fuel-cell applications dew-point and T back- XHE
Slide 33: How does probe warming work?
How does probe warming work? Tambient = 14 °C (57.2°F) RHambient = 97% RH Tambient = 14 °C (57.2°F) Tsensor = 16 °C (60.8°F) RHsensor = 83 % RH at 14°C = 97 %RH Probe warming resistor Page 34 / 5/7/2018 / name / Internal use / © Vaisala
Slide 34: HMT337 warmed probe
HMT337 warmed probe 100.0 RH [%] with warmed probe 90.0 80.0 70.0 60.0 Relative humidity [%] 50.0 40.0 - Condensation problem solved 30.0 - Better quality 20.0 - Better yield 10.0 0.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 Time [h] © Vaisala
Slide 35: Practical control application in a ceramics dryer
Practical control application in a ceramics dryer © Vaisala
Slide 36: A customer case
A customer case Ceramics dryer Control variables: temperature and Control options humidity mixing ratio No control Indirect control by feed t = 130..140 °C rate x = 100 g/kg (td = 53 °C) Humidity based control RH = 5 % © Vaisala
Slide 37: Another supplier said..
Another supplier said.. Brand X distributors proposed solution: ”calibration at process temperature Another brand will provide the necessary accuracy”4 Calibration at 70 °C reference [%RH] Deviation from Brand X hysteresis 2 1.50 1.00 0.50 0 d %RH 1,5 %RH 0.00 0 50 100 0 20 40 60 80 100 -0.50 -2 -
Slide 38: Accuracy of control
Accuracy of control T = 130 °C RH = 5 % +/- 3% Brand X specified repeatability short-term: 0,5 %RH Brand X hysteresis: 1,5 %RH RH inaccuracy Brand X estimated drift in 1 year: 2 %RH multiplies in high x = 100 +/- 80 g/kg Another brand temperatures for calculated variables DMT345 specifie
Slide 39: DMT345 for high temperatures
DMT345 for high temperatures DRYCAP180S sensor High dew point measurements up to 140 °C dry-bulb Low dew-point applications (ovens and similar) up to 100 °C dry-bulb temperature Installation flange and long probe provide easy installation through insulation materials © Vaisala
Slide 40: What should be considered when measuring elevated or variable temperatures?
What should be considered when measuring elevated or variable temperatures? What is the maximum temperature at the measurement position? Is the instrument specified for accuracy in my temperature range? What is the instrument’s accuracy in terms of the engineering unit I am using? © Vaisala
Slide 41: Cooling towers and wet-bulb temperature
Cooling towers and wet-bulb temperature © Vaisala
Slide 42: Practical issues
Practical issues Temperature Maintenance Cooling water in Scaling – Reduced performance R – Make-up water A N Pumps and fans G E Control Temperature set-point Cooling water out A – Generally optimal 2..3 °C above P P the wet-bulb temperature R O – Too small approach leads to A C excessive
Slide 43: Unshielded installation with low quality sensor
Unshielded installation with low quality sensor Radiated heat 75 %RH calibration after outdoor testing +3 °C (5.4 °F) Wet-bulb temperature +2 °C (+3.6 °F) Drift of the Impossible to sensor control accurately +/- 5 %RH for optimizing approach (2..3 °C) © Vaisala
Slide 44: A good installation with a high-quality sensor
A good installation with a high-quality sensor Radiated heat +0.2 °C Wet-bulb temperature +/- 0.3 °C Drift of the RH sensor +/- 2 %RH White top surface on each plat reflects heat Black bottom surface on each plate effectively emits any absorbed heat © Vaisala
Slide 45: Theoretical low limit of beverage's temperature
In the set-up below, the theoretical low limit of beverage’s temperature is (use humidity calculator) A. 25.0 °C (77.0 °F) B. 20.1 °C (68.2 °F) C. 14.5 °C (58.1 °F) D. Don’t know, it’s gone already! T = 25 °C RH = 30 % © Vaisala
Slide 46: End of part 1
End of part 1 © Vaisala
Slide 47: Humidity measurement technologies
Humidity measurement technologies
Slide 48: History of Humidity Measurement
History of Humidity Measurement © Vaisala
Slide 49: Comparison of traditional technologies
Comparison of traditional technologies Mechanical Psychrometer Chilled mirror Resistive Range 10 % 15 % -95 .. -20 °C Tf 5 % minimum Range max 100 % 100 % < 100 °C Td 100 % Accuracy typ. +/- 5% +/-2..5 % ~1 %RH +/- 5 % Hysteresis Very high None None High Stability Very poor Poor Very good Poor Maint
Slide 50: Performance
Performance Chilled mirror hygrometer HMP7 Relative Humidity and Temperature Laboratory reference etc. probe with capacitive HUMICAP sensor Field instrument for indudustrial use Requires maintenance No regular maintenance need Accuracy: +/- 0.1 °C in dew point Accuracy: +/- 0.8 %RH a
Slide 51: Radio sonde
Radio sonde Measurements in atmosphere up to 30 km above sea level with 5 m/s vertical speed RH range 0..100 %RH Rapid changes up and down Temperature +60..-90 °C Cloud layer © Vaisala
Slide 52: Vaisala innovation: Capacitive thin-film polymer sensor
Vaisala innovation: Capacitive thin-film polymer sensor Vaisala founded by prof. Vilho Väisälä in 1940’s Humicap invented in 1973 For radiosonde application Current de facto technology Later on productized for industrial applications [Name] 5/7/2018 © Vaisala 6
Slide 53: Vaisala HUMICAP
Vaisala HUMICAP® The sensor capacitance responds directly to changes in relative humidity Operating range: Relative humidity 0..100 %RH Temperature -40..+180 °C Withstands chemicals Withstands wetting Fast response time Low hysteresis © Vaisala
Slide 54: Theory of operation
Theory of operation Overlap © Vaisala
Slide 55: HUMICAP sensor is sensitive to changes in
HUMICAP sensor is sensitive to changes in A. Dew point temperature B. Vapor pressure C. Relative humidity © Vaisala
Slide 56: HUMICAP vs DRYCAP
HUMICAP® vs DRYCAP ® Capacitive humidity sensors are sensitive to relative humidity as the primary physical variable HUMICAP® withstands continuous high humidity and immersion 0..100 %RH DRYCAP ® is optimized for low humidity measurements, generally for < 10 or 5 %RH In general, when frost p
Slide 57: HUMICAP sensor types
HUMICAP ® sensor types HUMICAP180 HUMICAP180R Composite temperature sensor HUMICAP180L2 for chemical purge HUMICAP180V C for Composite Humicap180RC Humicap180C HUMICAP R2 and R2C Humicap180VC © Vaisala
Slide 58: Which sensor should I use?
Which sensor should I use? HUMICAP180R HUMICAP R2 R for Robust General purpose General purpose Latest generation, like Humicap180R but with improved corrosion HUMICAP180 resistance Previous generation Faster response time under low temperatures HUMICAP180V For applications wher
Slide 59: HUMICAP robustness
HUMICAP® robustness © Vaisala
Slide 60: Sensor purge
Sensor purge Sensor purge Saturated Ethylene Glycol test 16 Regeneration of the 14 Deviation from reference [%RH] sensing element by 12 brief heating 10 8 Evaporates volatile 6 contaminants from the 4 active polymer 2 0 0 5 10 15 20 25 30 -2 Exposure in days [Name] 5/7/2018 © Vaisala 14
Slide 61: HUMICAP stability
HUMICAP® stability 2 Three Humicap180R sensors in 1.5 outdoor test 1 At 75 %RH 0.5 Drift [%RH] Drift less than 1 %RH over full 0 At 0 %RH range -0.5 -1 1000 days test -1.5 -2 0 200 400 600 800 1000 1200 Time [days] Three sensors in outdoor test located in Southern Finland © Vaisala
Slide 62: Full Temperature Range Linearity
Full Temperature Range Linearity Calibration at 70 °C 3.5 Deviation from reference [%RH] 2.5 1.5 0.5 -0.5 0 10 20 30 40 50 60 70 80 90 -1.5 -2.5 -3.5 Reference %RH © Vaisala
Slide 63: Response time
Response time The response time of the sensor is ~15 s in room temperature and still air. Diffusion – temperature Gas exchange – flow Temperature – thermal mass Choice of filter affects to the thermal mass, gas exchange and response time Diffusion time multiplies by factor of ~2 for every 10
Slide 64: End of part 2
End of part 2 © Vaisala
Slide 65: Calibration and traceability
Calibration and traceability © Vaisala
Slide 66: Why knowing calibration, uncertainty and traceability is important?
Why knowing calibration, measurement uncertainty and traceability is important? Uncertainty is numerical quality of a measurement, with respect to the international measurement system Traceability means the documented path from the instrument to the international measurement system Measurements
Slide 67: I take care of calibrations by
I take care of calibrations by A. Not applicable B. My equipment is not calibrated C. Own calibration laboratory D. Third-party calibration laboratory E. Field-checks F. Other © Vaisala
Slide 68: Traceability and calibration
Traceability and calibration © Vaisala
Slide 69: Traceability
Traceability “Property of a SI measurement result BIPM Primary whereby the result can be reference National related to a reference Secondary laboratories through a documented reference Accredited laboratories unbroken chain of Reference standards Working standards calibrations, each End users contri
Slide 70: International System of Units: SI
International System of Units: SI Système international d’unités SI base units Length 1 metre Mass 1 kilogram Time 1 second Electric current 1 Ampere Temperature 1 Kelvin Amount of substance 1 mole Luminous intensity 1 candela Measurement standard, in which all traceable measurements can be traced [
Slide 71: Traceability of Vaisala RH instrument
Simplified example: Traceability of Vaisala RH instrument SI units National laboratory NIST MIKES MIKES Accredited Accredited laboratory laboratory Primary standard Triple-point cell of Pressure primary Vaisala SPRT reference water standard Measurement Standards Working standard Laboratory PRT refer
Slide 72: What is calibration?
What is calibration? Calibration means comparing the instrument reading with a reference (a calibration standard) Quality of calibration is defined by the following The competence of the laboratory The management system of the laboratory By definition, every measurement has The methods use
Slide 73: What is adjustment?
What is adjustment? Linear adjustment Adjustment is correcting the (offset and gain) instrument to minimize deviation from the calibration reference Gain Normal service procedure is calibration (”as-found”) and adjustment + calibration (”as-left”) This is sometimes called Offset ”Calibration”
Slide 74: Types of adjustment: Offset
Types of adjustment: Offset Offset © Vaisala
Slide 75: Types of adjustment: Linear adjustment
Types of adjustment: Linear adjustment Gain Offset © Vaisala
Slide 76: Multi-point correction
Multi-point correction Necessary when sensor is non- linear and further linearization is Gain Gain Offset Offset required Gain Offset Gain Offset © Vaisala
Slide 77: Things to ask
Things to ask What does your quality system require? What does your application require? [Name] 5/7/2018 © Vaisala 13
Slide 78: Quality Management System
Quality Management System ISO9001: Quality Management Systems – Requirements ISO9001 clause 7.6: Control of measurement and monitoring equipment ISO10012:2003: Measurement management systems - Requirements for measurement processes and measuring equipment ISO17025:2005: General requirements
Slide 79: How often to calibrate?
How often to calibrate? Calibration interval is subject to the operating conditions Humidity/temperature Chemical contaminants As-found certificates help in determining suitable calibration interval [Name] 5/7/2018 © Vaisala 15
Slide 80: What options do I have for calibration?
What options do I have for calibration? Field calibration Reference instrument Portable calibrator Laboratory calibration Quality of In-house calibration: Service • Competences • Management system • Methods Factory service • Equipment and the references [Name] 5/7/2018 © Vaisala 16
Slide 81: Calibration interval is defined by
Calibration interval is defined by A. The manufacturer of the instrument B. The quality policy C. Calibration laboratory’s recommendation © Vaisala
Slide 82: Options for calibration: Field Calibration
Options for calibration: Field Calibration © Vaisala
Slide 83: Single point or multi-point
Single point or multi-point Single-point Multi-point When stable condition When relative humidity When not close to changing on wide range extremes of When measuring close to measurement range extremes of the measurement range [Name] 5/7/2018 © Vaisala 19
Slide 84: Field calibration references
Field calibration references Handheld Humidity Single-point HMK15 Salt generator calibrator Multi-point Multi-point [Name] 5/7/2018 © Vaisala 20
Slide 85: HMK15 salt calibrator
HMK15 salt calibrator Intrinsic reference based on known property of saturated salt solutions generating known relative humidity levels Uncertainty 1.2..2 %RH Batch traceable Salt Equilibrium RH at 20 °C Applicable standards: LiCl 11.3 %RH ASTM E104-85 DIN 5008 MgCl 33.1 %RH JIS Z8806 NaCl 75.
Slide 86: HMK15 salt calibrator
HMK15 salt calibrator A reference instrument can be used as a reference for additional accuracy or traceability reasons Common mistakes: Insufficient stabilization time Temperature gradients Adjustment in too narrow RH range [Name] 5/7/2018 © Vaisala 22
Slide 87: Options for calibration: Laboratory
Options for calibration: Laboratory calibration © Vaisala
Slide 88: Laboratory calibration
Laboratory calibration Reduces uncertainty components from calibration Constant and controlled environment Multi-point calibration possible For wide-span applications and validating linearity Special calibrations RH calibrations under different temperatures Accredited calibrations © Va
Slide 89: Accredited calibration?
Accredited calibration? Accredited calibration laboratory is running a Quality Measurement System in compliance to ISO/IEC 17025, ANSI/NCSL Z540 or other standard Management system Technical requirements • Professionally made and validated uncertainty calculations • Verified traceability to in
Slide 90: What Type of Calibration Do I Need?
What Type of Calibration Do I Need? Does your company’s Quality Management Standards (QMS) require an 1SO17025 Accredited Calibration? No Yes 1 don’t know ‘Will you need to defend or demonstrate proper calibration procedures to <— Yes assure the quality of test results? Accredited Calibration No Do
Slide 91: Which option works best for you?
Which option works best for you? • QMS requirements • Number of points needed • Humidity Field calibration range Factory calibration Own staff or sourced • Temperature Highest quality references In-house laboratory range Calibration + Adjustment Manage your own lab, training, standards
Slide 92: Case example
Case example © Vaisala
Slide 93: Case example: spot-check calibration: In spec or not?
Case example: ”spot-check” calibration: In spec or not? Field calibration (spot check) of a wall-mount RH/T transmitter Device under test (DUT): Temperature [°C]: 22.1 (71.8°F) Relative Humidity [%RH]: 57.6 Reference instrument: Temperature [°C]: 21.87 (71.37°F) Relative Humidity [%RH]:
Slide 94: Should it be adjusted?
DUT Reference Temp [°C/°F] 22.1 / 71.8 21.87 / 71.37 RH [%RH] 57.6 55.10 Should it be adjusted? A.Yes B.No © Vaisala
Slide 95: Steps of uncertainty estimation
Steps of uncertainty estimation Recognize the relevant uncertainty components Estimate the standard uncertainty of each component Express the model equation Calculate the sensitivity coefficients Calculate the expanded uncertainty © Vaisala
Slide 96: Uncertainty components of temperature calibration
Uncertainty components of temperature calibration What are the uncertainty components? Related to the reference? Calibration correction Calibration uncertainty Stability Resolution Related to the device under test? Resolution Related to the set-up? Humidity spatial distribution
Slide 97: Source of information: Datasheet
Source of information: Datasheet © Vaisala
Slide 98: Uncertainty of temperature?
Uncertainty of temperature? Reference: Vaisala HM70 handheld Accuracy: 0.1 °C Calibration correction: -0.01 °C Calibration uncertainty: 0.1 °C Stability: 0.05 °C Resolution: 0.01 °C Set-up and DUT? RH/T sensor Temperature spatial: 0.5 °C location Temperature temporal: 0.1 °C Temp
Slide 99: Model equation and uncertainty
Model equation and uncertainty Correction = Reference value – Indication of DUT Uncertainty = Uncertainty of the reference + Uncertainty of the DUT Uncertainties sum up quadratically Distribution of the uncertainty varies. Different shapes of distribution are scaled to normal distribution eq
Slide 100: Uncertainty budget for temperature
Uncertainty budget for temperature © Vaisala
Slide 101: Do we need to adjust for temperature?
Do we need to adjust for temperature? Influence on total calibration uncertainty 24 0.350 23.5 0.300 0.250 23 0.200 22.5 0.150 0.100 22 0.050 0.000 21.5 21 20.5 20 Ref T [°C] DUT T [°C] © Vaisala
Slide 102: Uncertainty of Relative Humidity calibration
Uncertainty of Relative Humidity calibration Reference: Vaisala HM70 handheld Accuracy: 1.0 %RH Calibration correction: -0.6 %RH Calibration uncertainty: 0.6 %RH Resolution: 0.1 %RH Long-term stability: 1.0 %RH Set-up and DUT? Temperature equilibrium: 0.6 °C RH difference spatial/t
Slide 103: RH sensitivity coefficient for temperature
RH sensitivity coefficient for temperature Relative Humidity has non-linear dependency on temperature The magnitude of the dependency differs with the RH and temperature condition Sensitivity coefficient tells how the uncertainty in a variable is reflected to the uncertainty of another variabl
Slide 104: Uncertainty budget for Relative Humidity
Uncertainty budget for Relative Humidity © Vaisala
Slide 105: Should we adjust for Relative Humidity?
Should we adjust for Relative Humidity? Chart Title Influence on total calibration uncertainty 60 0.700 0.600 58 0.500 56 0.400 54 0.300 52 0.200 0.100 50 0.000 Reference Uncetainty in Specified Calibration Microclimate RH Ref resolution DUT 48 drift temperatures accuracy uncertainty stabilization r
Slide 106: What uncertainty to expect with RH calibration?
What uncertainty to expect with RH calibration? Field check: +/- 2..5 %RH HMK15: +/- 1.2..2 %RH NIST: Hybrid humidity generator: +/- 1 % Vaisala factory calibration: +/- 0.6.. 1.0 % © Vaisala
Slide 107: End of part 3
End of part 3 © Vaisala
Slide 108: Dew point in compressed air
Dew point in compressed air © Vaisala
Slide 109: Compressed Air
Compressed Air Compressed air is often called the fourth utility in industry, right behind water, electricity and natural gas Where is it measured? Energy storage: Instrument air for tools, robots, pneumatic actuators.. Trains: brakes, couplings, pneumatic doors.. Vortex cooling Conveyor m
Slide 110: Why Measure Dew Point?
Why Measure Dew Point? Dryer performance monitoring Condition monitoring Dryer switching endpoint Time controlled vs dew point demand controlled Efficiency Compressed air quality at point of use Quality assurrance 5/7/2018 © Vaisala 3
Slide 111: When Dew Point, When Relative Humidity?
When Dew Point, When Relative Humidity? When RH is ~5 %RH ±2 °C Td = ±1 %RH ±5.6°F Td = ±1 %RH When RH is ~1 %RH ±2 °C Td = ±0.2 %RH ±5.6°F Td = ±0.2 %RH © Vaisala
Slide 112: How dew point sensor works?
How dew point sensor works? All capacitive and resistive solid state sensors are based on equilibration of humidity between the surroundings and the sensor Similar operation with humidity sensors When relative humidity and temperature are known, the dew point temperature can be calculated © Va
Slide 113: Vaisala dew point technology
Vaisala dew point technology DRYCAP sensor is optimized for sensitivity in low humidity ranges by a special engineered polymer Sensor purge function always included Unique auto-calibration function Sensor responds to very small changes in relative humidity Sensitivity combined with robustn
Slide 114: Vaisala DRYCAP Auto-calibration technology
Vaisala DRYCAP® Auto-calibration technology 1. Auto-calibration start: Sensor Sensor warmed temperature RH value decreases when T increases Sensor 2. Sensor starts to cool down after humidity short warming. time RH reading starts to increase. 1. 2. 5. 6. 3. 3. RH and T values logged during humidity
Slide 115: DRYCAP sensor for low humidity
DRYCAP sensor for low humidity Tolerates wetting, recovers perfectly Tolerates contaminants: Compressor oils, volatile organics Fast response time No drifting – recommended calibration interval 2 years Small hysteresis ISO9001 calibrated at factory © Vaisala
Slide 116: Compressed Air Systems
Compressed Air Systems Basics: The air contains water as water vapor. The water may cause problems in the compressed air system – condensation and corrosion in the distribution system and quality problems at the point of use Challenge: Energy efficient control of dryers requires measurement with com
Slide 117: Compressed Air: Regenerating Drying
Compressed Air REGENERATING DRYING © Vaisala 10
Slide 118: Compressed Air: Drying Regenerating
Compressed Air DRYING REGENERATING © Vaisala 11
Slide 119: Analyzing correct operation of the dryer by dew point measurement
Analyzing correct operation of the dryer by dew point measurement 10 10 Dew point temperature [°C] 0 0 Dew point temperature [°C] -10 -10 Input -20 -20 Input Output Output -30 -30 -40 -40 -50 -50 Dryer operates normally Dryer is loaded too early Regeneration cycles Air leak into the dryer
Slide 120: Desiccant dryer condition monitoring
Desiccant dryer condition monitoring 10 10 0 0 Dew point temperature [°C] Dew point temperature [°C] Input Input -10 -10 Output Output -20 -20 -30 -30 -40 -40 -50 -50 Dryer does not work Regenerated dryer does not work Regeneration does not work Insufficient cooling time Severely contamina
Slide 121: Process Pressure vs. Ambient
Process Pressure vs. Ambient Measurement process at pressure Measurement at ambient pressure + typically true specified dew point + line pressure fluctuation has no effect Value that user wants to know e.g. in dryers + easy to remove instrument for service + no sampling system needed
Slide 122: Sampling Cells
Sampling Cells DMT242SC • G3/8”, G1/4” ISO (inlet, outlet) • G1/2” for probe DMT242SC2 • Like above, but with 1/4” swagelok fittings DSC74C • For pressurized air, quick connector and leak screw • Pressurized measurement DSC74C • For measurement in atmospheric pressure • Fixed leak screw 3 ..1 0 bar
Slide 123: Portable Dewpoint Vaisala DSS70A
Portable Dewpoint Vaisala DSS70A 5/7/2018 © Vaisala 16
Slide 124: Requirements for Accurate Switchpoint Control?
Requirements for Accurate Switchpoint Control? Stability at -10°C / 14°F frost point Stability at -40°C/-40°F frost point © Vaisala
Slide 125: Dew point error at constant temperature
Dew point error at constant temperature Overshoot 15 10 5 Vaisala DRYCAP180U: DMT152 Dew point error, °C Sensor B Sensor C 0 Sensor D Vaisala DRYCAP180D: DMT143 Sensor F -5 Sensor G Sensor H -10 -15 -76 -66 -56 -46 -36 -26 Reference dew point, °C Undershoot 5/7/2018 © Vaisala 18
Slide 126: Temperature dependency at -50°C dew point level
Temperature dependency at -50°C / -58 °F dew point level 15 10 Vaisala DRYCAP180U: DMT152 5 Sensor B Dew point error, °C Sensor C 0 Sensor D Sensor E Sensor F -5 Vaisala DRYCAP180D: DMT143 Sensor H -10 Sensor I Sensor J Sensor K -15 -20 -10 0 10 20 30 40 50 Temperature of environment, °C MIKKA 5/7/2
Slide 127: Repeatability
Repeatability 2.00 Vaisala Vaisala Ultra DryDRYCAP180U: 1.50 DMT152 Sensor B Michell Ultra Dry 1.00 Sensor C GE Pana- metrics Dew point error, °C 0.50 Sensor D Cosa Xentaur 0.00 Sensor E Alpha Moisture -0.50 Sensor F TEKHNE -1.00 Vaisala Vaisala StandardDRYCAP180M: Dry -1.50 DMT143 Michell Standard
Slide 128: Short-term stability
Short-term stability -44 Vaisala DRYCAP180U: DMT152 -46 Sensor B -48 Sensor C -50 Sensor D -52 Sensor E -54 Vaisala DRYCAP180M: DMT143 -56 Sensor G -58 Sensor H -60 0 12 24 36 48 60 72 84 time, h 5/7/2018 © Vaisala 21
Slide 129: End of part 4
End of part 4 © Vaisala
Slide 130: Installation and Good Measurement Practices
Installation and Good Measurement Practices © Vaisala
Slide 131: How do you decide what instrument to purchase?
How do you decide what instrument to purchase? (choose top 3 in order) A. Referral from a colleague B. Web research C. Magazines D. Vendor websites E. Vendor salesperson © Vaisala
Slide 132: Follow the Manufacturer's Instructions
Follow the Manufacturer's Instructions Read the Manual Use the Technical Support Use the Application Engineers Use the Sales Engineers © Vaisala
Slide 133: Proper installation
Follow the Manufacturer's Instructions Proper installation Must be mounted in area where air or gas is representative of the process or environment Air should flow around or past the sensor – good air flow is an advantage; it ensures that the probe and ambient air are at the same temperature & e
Slide 134: Probe installation
Follow the Manufacturer's Instructions Probe installation horizontal is preferred; bend in the cable allow for temperature and pressure fittings use insulation and sample line heating ensure representative sample of air with flow preferred to be sealed to be insulated © Vaisala
Slide 135: Ensure a proper calibration
Ensure a proper calibration Is the calibration within the recommended interval? Is it traceable? Is there a valid certificate available? Does the calibration comply with your requirements? © Vaisala
Slide 136: Keep records
Keep records Record of calibration Record of adjustments Record of repairs Out of tolerance results Record of any damage to the instrument © Vaisala
Slide 137: Spot-check performance
Spot-check performance Check at intervals between calibrations Check before and after any event that may stress the instrument Transportation Packaging or shipping Check against one or, even better, two other instruments © Vaisala
Slide 138: Be knowledgeable about the parameter
Be knowledgeable about the parameter a x ppm Td Tw h RH Know what parameter you are measuring and be aware of the potential effects of the environment around the point of measure. sensor type gas effect – CO2, pure hydrogen, other high concentrations of gas temperature & pressure effect is
Slide 139: Be knowledgeable about the parameter
Be knowledgeable about the parameter Polymer & organic sensors measure RH 1200 1000 Saturation Curve Pw 800 Pw (mbar) %RH = 100 x P ws (t) 600 400 200 0 0 10 20 30 40 50 60 70 80 90 100 Temperature (°C) temperature – temperature - temperature - temperature Note: at 20°C a temperature difference of j
Slide 140: Be knowledgeable about the parameter
Be knowledgeable about the parameter How is the parameter determined? Is it measured directly or calculated? Does the calculation require pressure input? Is the calculation dependent on temperature? Dew point or Frost point? (for example) Pressure dew point or atmospheric dewpoint? Mixin
Slide 141: Be aware of potential external factors
Be aware of potential external factors • Do not introduce external factors that will affect the measurement – direct sunlight – body heat and humidity – non-representative sources of heat – stagnant and/or non representative air samples – temperature leakage © Vaisala
Slide 142: Be aware of potential external factors
Be aware of potential external factors © Vaisala
Slide 143: Anomalous Sources of Heat or Cold
Be aware of potential external factors Anomalous Sources of Heat or Cold 77F 50F © Vaisala
Slide 144: Temperature Leakage
Be aware of potential external factors Temperature Leakage • If the temperature of the process is considerably higher than that of the environment, the whole probe and preferably a part of the cable must be in the process [adds 3.2% error] 80°C / 176°F 70 %RH 22°C / 72°F 78°/172° © Vaisala
Slide 145: Temperature leakage
Be aware of potential external factors Temperature leakage – Less critical, but enough difference where you want the whole portion of the metal probe inside the process and the cable sealed. 22°C 28°C 72°F 82°F © Vaisala
Slide 146: Temperature leakage
Be aware of potential external factors Temperature leakage – Very large differences require heavy insulation 180C/356F 85%RH © Vaisala
Slide 147: Temperature
Be aware of potential external factors Temperature – From room to high temperature high humidity chamber Testing chamber 70°F ambient temp 104ºF 60% RH Td = 87ºF What is the dew point? You must PRE-HEAT the probe!! © Vaisala
Slide 148: Water Vapor Pressure
Be aware of potential external factors Water Vapor Pressure Testing chamber 80°F @ 35%RH 120ºF What is Td? 50F Td = -76ºF What is ppmv? 12,000 ppmv ppmv=11 What is the ppmv? © Vaisala
Slide 149: Summary – Good Measurement Practice 7 Points
Summary – Good Measurement Practice 7 Points 1. Choose the correct instrument 2. Follow the manufacturers instructions 3. Ensure a proper calibration 4. Keep records 5. ‘Spot-check’ performance 6. Be knowledgeable about the parameter 7. Be aware of potential external factors © Vaisala
Slide 150: Was this Measurement Practice section beneficial?
Was this Measurement Practice section beneficial? A. Very beneficial B. Somewhat beneficial C. Neutral D. Minimally beneficial E. Not at all beneficial © Vaisala
Slide 151: End of part 5
End of part 5 © Vaisala