Diapositivas Del Seminario Humedad 201
Transcript of Diapositivas Del Seminario Humedad 201
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WelcomeHumidity 201
what you need to know about humidity
#HUMIDITY201
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What business are you in?
Pha
rmaceutic
al...
Instrum
entatio.
..
Engine
ering
&...
Industrial
Man
...
Governm
ent o
r...
HVA
COther
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1. Pharmaceutical/Biotechnology/MedDevices
2. Instrumentation & Controls
3. Engineering & Architecture
4. Industrial Manufacturing
5. Government or Education
6. HVAC
7. Other
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What is your job role?
Facilitie
s
Quality
Process
Executiv
eMana..
.
Other
0% 0% 0%0%0%
A. Facilities
B. Quality
C. Process
D. Executive Management
E. Other
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How far did you travel to get here?
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Do you already use one or more?(choose up to 5)
Vais
alahum
idity
inst.
..
Vais
ala(oth
er)in
str...
Vais
alaVerite
qlog
ger
Vais
alaVerite
qmo
nit...
Vais
alaVerite
qvalid
a...
0 0 000
1. Vaisala humidity instrument
2. Vaisala (other) instrument
3. Vaisala Veriteq logger
4. Vaisala Veriteq monitoringsystem
5. Vaisala Veriteqvalidation/mapping system
Humidity 201what you need to know about humidity
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Why do we measure humidity?
Human comfort
Animal comfort
Energy efficiency
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Critical Environments
Quality Control
Product Quality
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Controlled Environments
FDA
ISO
GxP
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Industrial ProcessProcess Control
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Why do you measure humidity?(choose up to 3)
Productqualit...
Laws
®ulat
...
Hum
an/Anim
alc..
.
Energyefficie
...
Process
contro...
Research
Other
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A. Product quality
B. Laws & regulations
C. Human/Animal comfort
D. Energy efficiency
E. Process control
F. Research
G. Other
The first step towards a proper measurement is to understand the parameter you will measure.
Theory, terms & definitions
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Water Vapor Theory - H2O
- Exists in the three phases
- Which phase depends on the amount of thermal energy that is present
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American Meteorological Society GlossaryHu-mid-i-ty
Humidity
1. Generally, some measure ofthe water vapor content of air.
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Daltons Law
The total pressure of a gas is equal to the sumof the different gases partial pressures
Pt = P1 + P2 + Pn
air around us
Pt = PN2 + PO2 + Pw + Pmisc.
English chemist,meteorologist, physicist
(1766 1844)
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Practical Example of Daltons LawNitrogen..................... 77%
Oxygen ..................... 21%
Water vapor ............. 1%
Other gasses ........... 1%
1000 mbar= 770mbar+ 210mbar+ 10mbar+ 10mbar
In Denver
Pt = 840 mbar _____N2 + ____O2 + ____Pw + _____Other
Pt = Pw + Pdry
647 177 8 8
840 x 77% 840 x 21% 840 x 1% 840 x 1%
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Partial Pressure of Water Vapor (psi,mbar,hPa,inhg)
The key parameter that affects all other humidi ty
parameters
Pw
Note: The only two properties that can affect a change in Pw
adding or removing water vapor changes in system pressure
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Saturation Vapor Pressure (psi,mbar,hPa,in Hg)
Saturation Curve
On the saturation cu rve
evaporation and condensationare in equilibrium and occur atthe same rate
Pw = Pws
dewpoint = temperature
wet bulb = dry bulb
RH = 100%
Note: The only property thataffects Pws is temperature
Pws
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Temperature (C)
Pw(mbar)
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Pws Saturation Vapor Pressure
Pws - maximum vapor pressure or amount of water vapor that canexist at a given temperature. Expressed in units of pressure.
480Pws = 480 mbar
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Temperature (C)
Pw(mbar)
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Relative Humidity (%)
Relative humidity is the ratio of water vapor partial pressure present
in a gas (Pw) to the saturation vapor pressure of water at that
temperature [Pws(t)]
RH
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Relativefill=1/1100%Relative
fill
=
1/520%Relativefill=1/10
10%
Bucket Analogy
Pws = bucket size or max amount of water
Pw = amount of water in the bucket
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%RH = 100 x
%RH = 100 x =
Note: Relative humidity is strongly proportional to temperature and its measurement isvery sensitive to temperature differences.
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Temperature (C)
Pw(mbar)
Relative humidity
Pw=200Pws=480
200480
42%
PwPws (t)
(t=80)
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Temperature (C)
Pw(mbar)
Ta = 90 C Pws = mbar
Pw = mbar
RH = 100 x / = %RH
Temperature and Relative Humidity
Ta = 60 C Pws = 200 mbar
Pw = 70 mbar
RH = 100 x 70/200 = 35 %RH 700 10
70
70
%RH = 100 x Pw / Pws (t)
700
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0 10 20 30 40 50 60 70 80 90 100
Temperature (C)
Pw(mbar)
Ta = 40 C Pws = mbar
Pw = mbar
RH = 100 x / = %RH
Temperature and Relative Humidity
Ta = 60 C Pws = 200 mbar
Pw = 70 mbar
RH = 100 x 70/200 = 35 %RH70 100
70
70
%RH = 100 x Pw / Pws (t)
70
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Temperature and Relative Humidity
Rule of Thumb #1
Rule of Thumb #1*
-As temperature increases, air becomes drier (RH decreases)
-As temperature decreases, air becomes wetter (RH increases)
drier and wetter are relative terms; applies to a closed system where pressure and water vaporcontent do not change
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What about pressure and RelativeHumidity?
If double total pressure;
then 2(Pt) = 2(Pw + Pdry) = 2Pw + 2Pdry
so Pw changes proportionately to overall pressure changes
Recall Daltons Law of Partial Pressures Pt = Pw + Pdry
remember that Pws remains unchanged because T is unchanged
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Temperature (C)
Pw(mbar)
Ta = 80 C Pws = 500 mbar
Pw = 200 mbar
RH = 100 x 200/500 = 40 %RH
Pressure and Relative Humidity
Ta = 80 C Pws = mbar
Pw = mbar
RH = 100 x / = %RH
500
80
400
500400
Pt = 1000 mbar
We double the total pressure
so Pt = 2000 mbar
What happens to Pw? Pws?
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Pressure and Relative Humidity Rule of Thumb #2
Rule of Thumb #2*
-As pressure decreases, air becomes drier (RH goes down)
-As pressure increases, air becomes wetter (RH goes up)
* drier and wetter are relative terms; applies to a closed system where temperature and water vapor content do notchange
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Relative Humidity Application Example
Static discharge or product quality in a cleanroom
Product storage
Critical processing systems (capsules, powders)
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Td Dewpoint (C,F)
The temperature to which a given portion of air must be cooled at constant
pressure and constant water vapor content in order for saturation to occur
Td
The temperature at which a moist gas is saturated with respect to a plane
surface of pure liquid water
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Glass temperature above the dewpoint no condensation
Td = -10C
Beer temperature = 2C
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Glass temperature below the dewpoint condensation appears
Td = 10C
Beer temperature = 2C
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Dewpoint changes with water vapor
changes with pressure
1
log
A
P
m
TT
w
n
d
Note: Dewpoint is not a temperature dependent parameter
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Dewpoint & PressureRule of Thumb
Rule of Thumb
-As pressure increases, dewpoint temperature rises, air becomesmore moist (RH increases)
-As pressure decreases, dewpoint temperature goes lower, airbecomes drier (RH decreases)
drier and wetter are relative terms; applies to a closed system where water vapor content doesnot change
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Td/f Frostpoint (C,F)
Td/fThe temperature to which a given portion of air must be cooled at constant pressure and
constant water vapor content in order for saturation to occur
The temperature at which a moist gas is saturated with respect to a plane surface of
pure ice
Note: Td/f is a Vaisala term which means dewpoint above 32F and frost point 32F and below
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Dewpoint versus Frostpoint
Frostpoint Dewpoint
-0.10 C -0.11 C
-5.00 C -5.64 C
-10.00 C -11.23 C
-20.00 C -22.25 C
-30.00 C -33.09 C
-40.00 C -43.74 C
-50.00 C -54.24 C
-60.00 C -64.59 C
-70.00 C -74.88 C
-80.00 C -85.29 C
-90.00 C -96.37 C
AIR evaporation
ICEcondensation
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Td/f Frostpoint
Td orTd/fTd/f gives you dewpoint at 0 degrees (C) and above and frost point below 0 degrees (C)
Td gives you dewpoint across the entire range of temperatures and assumes
supercooled water below 0 degrees (C)
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Application Example - compressed air orsensitive manufacturing environments
compressor picture courtesy of Atlas Copco
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x Mixing Ratio or Humidity Ratio(g/kg, gr/lb)
xthe ratio of the mass of water vapor per unit mass of dry air towhich it is associated
Note: mixing ratio is an absolute measure, not affected bytemperature or pressure
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Application Example drying process
Mixing ratio can be used as a measure to help determine drying timewhere moisture content of a product is important like paper drying ordog biscuit drying.
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ppmv ppmw parts per million (volume/weight)
ppmv- volume of water vapor per total volume of dry gas
ppmw- mass of water vapor per total mass of dry gas
Note: ppm is an absolute measure, not affected by temperature or pressureMw is molecular mass of water ; Md is molecular mass of dry air
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ppmv and ppmw
Td/f PPMw PPMv
-40.00 14 23
-35.00 24 39
-30.00 42 67
-25.00 69 111
-20.00 113 181
-15.00 181 290-10.00 284 456
-5.00 439 706
Mw/Md = .621980
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Application Example glove box
ppm is sometimes used in dry environments where very preciseabsolute measurement is required such as in a glove box or clean room
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a Absolute Humidity (g/m3, gr/ft3, lbs/MMcf)
a- the mass of water vaporper unit volume of moist air
- the density of the water vapor
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Application Example Precision Mass
Labs where precise measurements of mass are recorded and thebuoyancy caused by the air must be considered
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Tw Wet bulb temperature (C,F)
Tw
the temperature indicated by a thermometer sheathed in a
wet cloth as air is passed over it
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Application Example evaporative cooler or swamp cooler
By comparing the wet bulb temperature to the dry bulbtemperature we can determine cooling capacity of anevaporative cooler.
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h Enthalpy (kj/kg; btu/lb)
h Measure of the total energy in a
moist gas
heat content
sum of the latent heat + sensibleheat
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Application Example - HVAC
Enthalpy is a useful measurement for determining HVACequipment size and efficiency
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Psychrometric Terms
relative humidity RH [%RH]
partial pressure of water vapor Pw [mbar; in.Hg]
saturation pressure Pws [mbar; in.Hg]
dewpoint/frost point Td/f [C; F]
absolute humidity a [g/m3; gr/ft3]
mixing ratio/humidity ratio x [g/kg; gr/lb]
wet bulb temperature Tw [C; F]
ppmv
ppmw
enthalpy h [kJ/kg; Btu/lb]
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Summary
1. Daltons Law of Partial Pressures Pw2. Saturation Vapor Pressure Pws only changes with
temperature
3. Other terms pressure and temperature effects
4. Rule of Thumb #1 temperature and RH
5. Rule of Thumb #2 pressure and RH
6. Dewpoint only pressure and water vapor content affect it
7. Absolute parameters versus relative parameters
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End of Section 1
Humidity Theory, Terms & Defini tions
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Humidity SensorTechnology
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Brief History of the Hygrometer1450 - Nicolas Cryfts determines humidity by using a scale
1480 Leonardo DaVinci reproduced the concept andrecorded it in the Codex Atlanticus
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Brief History of the Hygrometer
1625 Santorrio Santorre invented the first strain typehygrometer
1783 Horace Benedict de Saussere invented the hairhygrometer
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Brief History of the Hygrometer1657 Grand Duke Ferdinand deMedici invented the first condensationhygrometer
1801 John Dalton re-invented thecondensation hygrometer anddeveloped Law of PartialPressures
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Brief History of the Hygrometer
1853 August Bravais invented the whirling psychrometer
1973 Vaisala patented the HUMICAP thin film polymercapacitive sensor
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MechanicalExploit the expansion and contraction of organic materials with changesin humidity; changes are amplified through the use of levers that move aneedle or pointer.
horse hair, human hair, catgut, goldbeaters skin, textile, or plastic
hair element
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Mechanical
hair element
+ inexpensive
+ no power needed
- 2090% best range
- Uncertainty from +/-5% up to +/-15%
- calibrated with a wet rag to 100%;no dry end calibration
- considerable hysteresis
- responds to changes in humidityvery slowly
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Psychrometer (wet bulb-dry bulb)Two matched thermometers over which air is drawn. One thermometerhas the bulb covered by a wet cloth or wick. This is the wet-bulb.
wet bulb
dry bulb
water
cloth
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Psychrometer (wet-dry bulb)
+ simple & fundamental measurement
+ low price ($35 to $80 for sling)
+ can have good stability
+ tolerates condensation withoutdamage
- High uncertainty (+/- 2% to 5%)
- requires some skill to use & maintain
- results usually must be calculated
- requires large air sample
- sample will be humidified (altered) bywater that is evaporating
- accuracy affected bycontaminated/dirty wick
1
23
4
HYGROMETER
1 2
3
4
5
6
7
8
ENCLOSUREHYGROMETRICTABLES
fan motor heat introduc ed
turbulancethick wickcontaminated wickwick qualityporous(ceramic) sleevenon-sealed thermometersnon-identical thermometerspoor resolution instrumentslow acc uracy instruments
poor water q uality
water temperature changes affect depressionwater container material non-plastictwo-wire system ca uses errorstables, accurac y of reading
5
678
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Condensation Hygrometer
Chilled Mirror
l ightdetector
chilled mirror
NO D EW DEW
lightdetector
chilled mirror
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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 frequent maintenance
- complex in construction
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Electrical Sensors
Resistive
Capacitive thin film polymer
Capacitive aluminum oxide
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Resistive Humidity Sensors
Measures the electrical impedance or resistance of a hygroscopicmedium such as conductive polymer, salt, or a treated substrate.
The resistance changes inversely w ith
humidity.
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Resistive Humidity Sensors
+ small and cheap
+ mass production possible
+ Interchangeable/fieldreplaceable
- limited range (typically 15...95 %RH)
- high temperature dependency
- poor stability
- sensitive to contamination, condensation
- reading altered by all substances thataffect resistance; salts, hydrogen,oxidizing agents, other chemicals
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Capacitive - Aluminum Oxide (Al2O3)
capacitor which consists of aluminum and gold electrodes and analuminum oxide insulator
responds to the partial pressure of water vapor and converted toabsolute units (for Td or ppm)
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Capacitive - Aluminum Oxide (Al2O3)
+ small
+ suitable for in-line site use
+ wide measuring rangemeasures dew point downto -75...-100 C
- condensation orcontamination on sensorcauses significantcalibration shift
- slow response time
- long stabilization time
- need frequent calibration
- significant drift
- considerable hysteresis
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Capacitive thin film polymer
Measures the capacitance of an electrode where a polymer acts asthe dielectric portion of the capacitor
The properties of the polymer/dielectric change proportionately withthe change in relative humidity which results in a change of themeasured capacitance
glass substrate
upper electrode
lowerelectrode thin-film polymer
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Capacitive thin film polymer
glass substrate
upper electrode
lowerelectrode thin-film polymer
+ wide measurement range0...100 %RH
+ wide temperature range (up to200C)
+ excellent stability
+ fast response
+ full recovery from condensation
+ highly resistant to contaminants
+ small
+ low cost+ require very little maintenance
- can be limited by distance fromelectronics to sensor
- loss of relative accuracy at lowend (
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Other technologies
Saturated Lithium Chloride
uses hygroscopic salt as a sensing medium, with voltage applied across the salt and measurescurrent; usually displays dewpoint
Spectroscopic measures the light at a specific bandwidth where water vapor absorbs the light, based on the
principle of infrared absorbance.
Color change material such as cobalt chloride will change color based on the amount of water vapor in the air
as it reacts with the chemical
Acoustic transmission of sound in air can indicate humidity
Adiabatic Expansion cooling of air on expansion produces a cloud or fog if the dewpoint temperature is reached
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Which technology gives you the mostaccurate dew point measure?
Resisti
ve
Aluminu
mOxid
e
Chilled
mirror
Noneoft
hese
...
0% 0%0%0%
A. Resistive
B.Aluminum Oxide
C.Chilled mirror
D.None of these isvery accurate
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Thin film polymer sensor is highlyresistant to contamination.
True False
0%0%
A. True
B. False
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Wet bulb temperature is measureddirectly with a ____________.
Wetthum
b
Psychr
omete
r
Chilled
mirror
Swamp
cooler
0% 0%0%0%
A. Wet thumb
B. Psychrometer
C.Chilled mirror
D.Swamp cooler
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Summary
1. Sensor Technologies
Mechanical/Organic
Psychrometers
Chilled mirror
Electronic
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Was the Sensor Technology SectionBeneficial?
Veryb
eneficial
Som
ewhatb
eneficial
Neutral
Mini
mallyb
eneficia
l
Not
atall b
eneficia
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0% 0% 0%0%0%
A. Very beneficial
B. Somewhat beneficial
C. Neutral
D. Minimally beneficial
E. Not at all beneficial
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End of Section 3
Humidity Sensor Technology
Best Practices in HumidityMeasurement
First, you must understand the parameter that you want to measure
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7 General 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
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What is your biggest challenge inmeasuring humidity?
Cantg
et repe
...
Toohigh
uncer...
Toofrequently
...
Cantt
rustsp
...
Educatin
gtech..
.
Other
0% 0% 0%0%0%0%
A. Cant get repeatability
B. Too high uncertainty
C. Too frequently out oftolerance
D. Cant trust specifications
E. Educating technicians
F. Other
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1. Choose the correct instrument
Be aware of what the sensor is measuring and how the
environment could affect it.
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Good Measurement can be- affected by temperature differences?
- affected by pressure differences?
- affected by changes in water vapor content?
Note: Be aware of the possibility of condensation in a sample line
Flow
NO
YES
YES
1. Choose the correct instrument
Condensation Hygrometer
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Measures wet bulb and dry bulb temperatures
Good measurement depends uponAccuracy of the thermometers
Consistency in operation
Contamination of water/sock
Accuracy of the conversion
Volume of the air sample
Psychrometer
1. Choose the correct instrument
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Measures water vapor partial pressure
Good measurement depends upon Keeping the sensor dry
Regular calibration
Accurate pressure measurement
Clean air sample
Generous stabilization time (up to 24 hours)
Aluminum Oxide
1. Choose the correct instrument
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Measures relative humidity
Good measurement depends upon temperature temperature temperature
Polymer capacitor
1. Choose the correct instrument
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How do you decide what instrument topurchase? (choose top 3 in order)
Refe
rral fromac
olle..
.
Web
research
Glob
alSpec,Th
omas...
Vendor w
ebsites
Vendor sale
sperson
0% 0% 0%0%0%
A. Referral from a colleague
B. Web research
C. GlobalSpec, ThomasNet,etc.
D. Vendor websites
E. Vendor salesperson
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2. Follow the Manufacturers Instructions
Read the Manual
Use the Technical Support
Use the Application Engineers
Use the Sales Engineers
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2. Follow the Manufacturers Instructions
Must be mounted in area where air or gas isrepresentative of the process or environment
Air should flow around or past the sensorgood air flow is an advantage; it ensures that the probe
and ambient air are at the same temperature & ensuresthat the measurement is representative of the space
Avoid anomalous sources of heat or cold; i.e.sunlight
Proper installation
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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 preferredto be sealed
to be insulated
Probe installation
2. Follow the Manufacturers Instructions
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3. 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?
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4. Keep records
Record of calibration
Record of adjustments
Record of repairs
Out of tolerance results
Record of any damage to the instrument
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5. Spot-check performance
Check at intervals between calibrations
Check before and after any event that may stressthe instrument
Transportation
Packaging or shipping
Check against one or, even better, two other
instruments
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6. Be knowledgeable about the parameter
Tdppm RHha x Tw
Know what parameter you are measuring and be aware ofthe potential effects of the environment around the point ofmeasure.
sensor type
gas effect
CO2, pure hydrogen, other high concentrations of gas
temperature & pressure effect
is output parameter measured or calculated
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0
200
400
600
800
1000
1200
0 10 20 30 40 50 60 70 80 90 100
Temperature (C)
Pw(mbar) Saturation Curve
PwPws (t)
%RH = 100 x
Note: at 20C a temperature difference of just 1C may add 3% error to the RH measurement
6. Be knowledgeable about the parameter
Polymer & organic sensors measure RH
temperature temperature - temperature - temperature
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Adequate time varies depending on the difference inconditions and the sensor technology
Temperature
Vapor pressure
Sensor type
6. Be knowledgeable about the parameter
Al low adequate time for equil ibrat ion
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Is it measured directly or calculated?
Does the calculation require pressure input?
Is the calculation dependent on temperature?
Dewpoint or Frostpoint? (for example)
Pressure dewpoint or atmospheric dewpoint?
Mixing ratio or ppm calculation require actual pressure input (forexample)
6. Be knowledgeable about the parameter
How is the parameter determined?
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7. Be aware of potential external factors
Do not introduce external factors that will affectthe measurement
direct sunlight
body heat and humidity
non-representative sources of heat
stagnant and/or non representative air samples
temperature leakage
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7. Be aware of potential external factors
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Anomalous Sources of Heat or Cold
7. Be aware of potential external factors
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if the temperature of the process is considerably higherthan that of the environment, the whole probe andpreferably a part of the cable must be in the process
80C70%RH 22C
78
[adds 3.2% error]
Temperature Leakage
7. Be aware of potential external factors
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7. Be aware of potential external factors
28C22C
Temperature leakage Less critical, but enough difference where you want the
whole portion of the metal probe inside the process and thecable sealed.
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7. Be aware of potential external factors
180C 85%RH
Temperature leakage
Very large differencesrequire heavy insulation
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Anomalous Sources of Heat or Cold
7. Be aware of potential external factors
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7. Be aware of potential external factors
70Fambient
temp
Temperature From room to high temperature high humidity chamber
104F60% RH
Testing chamber
You must PRE-HEAT the probe!!
Td = 87F
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7. Be aware of potential external factors
80F @ 35%RH
Water Vapor Pressure
120F
Testing chamber
Td = -76F
ppmv=11
What is Td?
What is ppmv?
50F
12,000 ppmv
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7. Be aware of potential external factors
Water Vapor Pressure
ensure a tight seal
be aware of the cable feed through (is itvapor tight)
positive pressure can help prevent ingress
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Page 107/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
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
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Was the Good Measurement Practice
section beneficial?
Veryb
eneficia
...
Som
ewhatb
enef.
..
Neutral
Mini
mallyb
ene..
.
Not
atall b
en...
0% 0% 0%0%0%
A. Very beneficial
B. Somewhat beneficial
C. Neutral
D. Minimally beneficial
E. Not at all beneficial
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End of Section 5
Best Practices in HumidityMeasurement
Calibration of the Hygrometer
In fact, all humidity instruments drift to some extent.
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Why do we calibrate?
Economical Impact
Health, Safety & Environment
Scientific Research Results
Distributed Manufacturing
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Premise for Humidity Calibration
A humidity sensor cannot be protected hermetically: its
active parts are always exposed to the dirt and chemicals
in the ambient air. This may cause the sensor to drift
under some circumstances.
The electronics of a measurement instrument may be
affected by time, temperature changes and mechanical or
electrical shocks.
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Page 113/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
Definitions
Calibration = comparing the output of a measurementinstrument against a reference instrument and reporting theresult
Adjustment = changing the output to correspond to theoutput of a reference instrument
Specification = the performance criteria for aninstrument
Normal service procedure (also called calibration): first calibration + adjustment
then calibration
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Quality Measurement Standards(QMS)
States the minimum requirements and guidance forthe maintenance of measurement equipment
ISO/TS 16949:2002
GLP (good laboratory practice)
ISO 10012
ISO/IEC 17025ANSI/NCSL Z540
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Traceability
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Traceability
a traceable measurement is one which can be related to
appropriate measurement standards, generally national or
international, through an unbroken chain of comparisons
further
humidity parameters may be considered as traceable if they
are derived from actual realized measurements at the national
level along with recognized numerical conversions
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Page 117/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
RH Traceabil ity Chain VaisalaBoston Lab
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Metre Convention May 20, 1875
May 20th
National Metrology Day
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International System of Units (SI Units)
Administered by the BIPM in Paris or International Bureau of
Weights & Measures
Bureau International des Poides et Measures
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Seven basic units of measure
1. Length (meter)
2. Mass (kilogram)
3. Time (second)
4. Current (ampere)
5. Temperature (kelvin)
6. Amount of a substance (mole)
7. Light intensity (candela)
IPK International Prototype Kilogram
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RH Traceabil ity Chain Vaisala
Boston Lab
Compared to average reading oftwo hygrometers
Calibrated every 3 months
Primary standard goes to NIST once ayear for traceable calibration
Calibrated against MBW
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Traceabili ty, by itself, ensures a goodand proper measurement?
True
False
0%0%
A. True
B. False
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Accredited or Non-Accredited
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3rd Party Accrediting Agencies
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Accredited Calibrations
QMS = ISO/IEC 17025 orin some cases ANSI/NCSLZ540
Competence andcompliance are ensured bythird party such as NVLAP or
A2LA
Agency assures that
Measurements carried out tothe highest standards oftechnical competence
Traceable to recognizednational or internationalstandards
Using accepted and agreedmethods
Realistic statements ofuncertainty
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Non-Accredited Calibrations
1. Operate according toother QMS guidelines
2. Competence is notcertified or audited andshould be audited byyou before entrustingyour calibration to anon-accredited lab
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Do you need an accredited calibration?
Yes, if a regulating agency requires it
Yes, if your internal operating rules require it
Yes, if you will have a regular need to defend ordemonstrate proper procedures
No, if your internal guidelines do not specify
No, if you determine that calibration is not critical for
your operation
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The Calibration Process
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Choose your approach...
1. In-house metrology lab Manage your own lab, training, standards, traceability,
documentation, etc.
2. Contract with outside commercial lab Send instruments to an independent lab for calibration,
adjustment, repair, etc.
3. Field Calibration
Calibrate instruments in the process or in-situ with a portablereference or transfer standard
Use in-house staff or contract for outside service
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1. Lab Calibration example of steps in a lab
1. Instrument equilibrates in the lab for 24 hours2. Conduct visual inspection
3. Calibrator uses saturated salts and 2 referencehygrometers
4. Place probe in each salt for 30 minutes Record as found data for 0%,11%, 33%, 75%
5. Make adjustments (2 point) adjustment is made if out of tolerance more than 50% of nominal
6. Record as left data
7. Print certificate and place calibration sticker
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2. Field Calibrations 1 point or multi-
point
Choose 1 point
Measurement point does not change morethan +/- 20% RH
Conditions are not extreme in RH,temperature or other (i.e. gas composition)
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Field Calibrations 1 point or multi- point
Choose multi-point
RH or temperature varies across wide spectrum (i.e. 5 to 95% RHas in outdoor measurement conditions)
Extreme conditions (i.e. 90% + RH, 300F)
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Field Calibrations choose transferstandard
Generator (multi point) Generator (multi point)
measurement only (one point)
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Field Calibration determine the interval
HUMICAP 180R sensor
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Field Calibration follow your QMS
1. Confirm calibration and check operation of the standard Does the standard meet the specifications of the measurement
Standard should be at least 2x better uncertainty of the unit under calibration
2. Be aware of the conditions around the measurement point Breathing on the probe
Time for equilibration
Non-representative sources of heat or cold
3. Pre-heat and or Purge (if applicable)
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Field Calibration follow your QMS
4. Place probes together and allow equilibrium & takemeasurement
5. Repeat for multiple points
6. Make adjustments as necessary (one point or two point)
7. Record the results, place stickers, etc.
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Note about Adjustment
One Point calibration usually in the ambient environment if an adjustment is necessary:
an OFFSET adjustment is made when RH < 65%
a GAIN adjustment is made when RH > 65%
Multiple Point calibration using two or more referencehumidities:
a salt calibrator or humidity generator is needed
if an adjustment is necessary:
first an OFFSET adjustment is made in the dry point
then a GAIN adjustment in the wet point
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Note about Adjustment
OFFSET adjustment (for RH < 65%): the same correction is made for every point in the measurement
range
Example of an OFFSET adjustment at 20%RH
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Note about Adjustment
GAIN adjustment (for RH > 65%): the correction is in proportion to the measured value
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Note about Adjustment
Point 1 = OFFSET; Point 2 = GAIN
the correction is in proportion to the measured value the same correction is made for every point in the measurement
range
Example of a 2 point adjustment at 11% and 75%RH
Good Calibration Practice
Reference: A Guide to the Measurement of Humidity, National Physical Laboratory
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Good Calibration Practice - general
1. Measure as close as possible to the U.U.C probe/sensor
2. Allow enough time for the instruments/probes to stabilize
temperature & water vapor
anywhere from 5 minutes to 30 minutes depending on the differences
use the graphing feature to see it visually
3. Read the measurement results simultaneously
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Good Calibration Practice - general
4. Choose one point or multi point calibrations andadjustments carefully
5. Follow all manufacturers recommendations and procedures
6. Dont forget to calibrate the analog signal with a calibratedmulti-meter
if separate from the digital reading
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Good Calibration Practice Spot Checking
Use intermediate spot checking not the same as field calibration but similar
use procedures where full calibration is required if spot checking shows out oftolerance by a certain %
Page 146/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
Good Calibration Practice & usingan outside commercial lab
Be familiar with your calibration lab procedures and
equipment
Is the lab going to adjust if out of tolerance? At what point?
What is the traceability chain from NIST to your instrument?
Is the traceability chain documented?
In accordance with which QMS is the lab operating?
Does the service include documenting as found?
Are the lab technicians trained regularly?
Does the lab offer Accredited Services?
Is the lab able to calculate the uncertainty or just providing accuracy
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Common Sources of Error
1. Temperature fluctuations in the calibration environment
2. Temperature difference between reference and unit undercalibration
3. Temperature leakage into sensor environment
4. Not enough stabilization time
5. Accuracy of reference
6. Calibration methodology
Calibrating with Saturated Salts
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Saturated Salt Solutions
An aqueous salt solution generates a certain equilibrium relative
humidity in the air above it; different salts generate differentrelative humidity
equilibrium relative humidityin the air
saturated salt solution10...20 %
undissolved salt80...90 %
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Saturated Salt Solutions
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Page 151/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
Saturated Salt Solutions
Good choices for common salts (at 20C)LiCl (lithium chloride) 11.3 %RH
MgCl2 (magnesium chloride) 33.1 %RH
NaCl (sodium chloride) 75.5 %RH
K2SO4 (potassium sulphate) 97.6 %RH
Page 152/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
Uncertainty of Saturated Salts
Reference: Vaisala HMK15 User Guide
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Uncertainty of Saturated Salts
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Uncertainty of Saturated Salts
For NaCl at 25C;
1.4% + .1% = +/-1.5%
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Traceabili ty & Saturated Salts
ASTM E104-02 (2007), JIS Z 8806, DIN 50 008Standards
Batch Traceability
NaCl
Page 156/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity
Traceabili ty & Saturated Salts
For NIST traceability use areference hygrometer
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Summary
1. Approaches to calibration in-house lab, outside lab, field
2. Good Calibration Practices
3. Reference Equipment
4. Saturated Salts as a humidity reference
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Was the Calibration section beneficial?
Veryb
eneficia
...
Som
ewhatb
enef.
..
Neutral
Mini
mallyb
ene..
.
Not
atall b
en...
0% 0% 0%0%0%
A. Very beneficial
B. Somewhat beneficial
C. Neutral
D. Minimally beneficial
E. Not at all beneficial
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End of Section 5
Calibration
Before we conclude
1. A few final evaluation slides
2. Raffle HM34F
3. Distribute Request Info & Comments sheet
Satisfaction Survey
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How well did the online registrationand confirmation process work?
A.Excellent
B.Veryg
ood
C.Ok
D.Fair
E.Poor
0% 0% 0%0%0%
A. Excellent
B. Very good
C. Ok
D. Fair
E. Poor
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Was the information on the web siterepresentative of the actual seminar?
A.Yes,veryc
omplet
e
B.Couldha
vebeen
...
C.Sufficien
t
D.Not
enough
E.Did
notu
sethew
e...
0% 0% 0%0%0%
A. Yes, very complete
B. Could have been more info
C. Sufficient
D. Not enough
E. Did not use the website
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How do you rate the instructorsknowledge of the subject?
A.Excellent
B.Veryg
ood
C.Ok
D.Fair
E.Poor
0% 0% 0%0%0%
A. Excellent
B. Very good
C. Ok
D. Fair
E. Poor
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How do you rate the instructorspresentation skills?
A.Excellent
B.Veryg
ood
C.Ok
D.Fair
E.Poor
0% 0% 0%0%0%
A. Excellent
B. Very good
C. Ok
D. Fair
E. Poor
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How do you rate the PowerPointslides and handout materials?
A.Excellent
B.Veryg
ood
C.Ok
D.Fair
E.Poor
0% 0% 0%0%0%
A. Excellent
B. Very good
C. Ok
D. Fair
E. Poor
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Would you recommend this seminarto a colleague?
A.Definitel
y
B.Mostlikely
C.Maybe
D.Probably
not
E.Not
atall
0% 0% 0%0%0%
A. Definitely
B. Most likely
C. Maybe
D. Probably not
E. Not at all
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What did you think about the pollingsystem as a feature of the seminar?
A.Great
feature B.Ok
C.Ok,buttoo
much
D.A
little
annoying
E.A
distractio
n,no...
0% 0% 0%0%0%
A. Great feature
B. Ok
C. Ok, but too much
D. A little annoying
E. A distraction, no value
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Wrap up
Theory, terms & definitions
Psychrometrics
Best practices
Calibration
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End of Humidity 201 SeminarWhat you need to know about humidity
Thank you