The Rotronic Humidity Handbook
All you never wanted to know about Humidity and didn’t want to ask!

Rotronic Instrument Corp.
www.rotronic-usa.com
12/2005© 2005 Rotronic Instrument Corp.

Humidity Fundamentals ............................................................. 8
Relative Humidity, Pressure and Temperature ........................................................ 8
Foreword

8

Ideal Gas Laws

8

Mole Fractions and Partial Pressure

10

Effect of a Change In Pressure

10

Real Gases

10

Vapor Pressure Above a Liquid

11

Vapor Pressure of Water

12

Vapor Pressure of Water Mixed with Another Substance

12

Vapor Pressure Above Ice

13Definitions of Humidity

13

Vapor Concentration (Absolute Humidity)

13

Specific Humidity

14

Mixing Ratio

14

Volume Mixing Ratio

15

Relative Humidity

15

Dew Point and Frost Point Temperature

16

Wet Bulb Temperature

16

Effect of Temperature and Total Pressure on Vapor Pressure

16

Effect of Temperature and Pressure on %RH

17

Examples17

Relative Humidity Calibration

19

Method of Calibration

19

Temperature Stability

19

Temperature of Calibration

19

Altitude20

Influence of Temperature Variations on Solutions

20

Are they all the same? Choosing the Right Humidity Instrument....................... 21
Principle of Operation

21

Classification of Errors

22

Linearity Errors

22

Temperature Errors

22

Hysteresis

23

Calibration Errors

23Long Term Stability

24

Choosing a Humidity Instrument

24

Rotronic Instrument Corp.

Page 2

Wet Bulb / Dry Bulb - Description and Limitations................................................ 25
Summary25

Problem Areas in the Wet- and Dry-Bulb Technique25

Non-Observance of Basic Requirements

25Interferences During Measurements

26

Poor Handling and Maintenance26

Typical Accuracy of the Wet- and Dry-Bulb Technique

27

Operational Limitations of the Wet- and Dry-Bulb Technique

27

Technical Information for Rotronic Products......................... 30
Water Activity Instruments: A Comparison of Two Measuring Techniques ....... 30
Water Activity Measuring Techniques

30

Speed of Measurement30

Temperature Stability

30

Accuracy

31

Range of Measurement

32

Maintenance

33

Summary

33

Chemical Resistance of Rotronic Hygromer Humidity Sensors .......................... 34
General34

Uncritical chemicals

34

Critical Chemicals

35

Application Examples

35

Humidity Measurement in Sterilization Chamber (Ethylene oxide)

35

Humidity Measurement in An Ozone Chamber

36

Special Application – Humidity Measurement in Oil

36

Competitor Comparison 2004 ................................................................................. 37
HVAC Transmitters - Wall Mount

37

Humidity Deviation at 1°C

41

Humidity Deviation at 40°C

42Temperature Deviation at 50 %rh

43

Industrial Transmitters with Cable Probes

44

Humidity Deviation at -10°C

47

Humidity Deviation at 23°C

48

Humidity Deviation at 70°C

49

Temperature Deviation at 50 %rh

49Page 3The Rotronic Humidity Handbook

Humidity Deviation From Set Point at 23°C After Different Humidity and Temperature
Conditions

50

HygroClip Performance Over A Range of %RH & Temperature Conditions ....... 53
Evaluation of Competitive Humidity Sensors ........................................................ 55
Temperature Limits

56

Response Time

57

Reset Rate

58

Long Term Accuracy

59

Dew Point Stability

60

Rotronic C-94 Response Time ................................................................................ 61
Long Term Performance of the HygroClip S and C-94 Sensor............................. 62

Application Stories and Tales.................................................. 70
Last Long and Prosper (A water activity tale) ....................................................... 70
Ingredients and Interactions

71

Factors Affecting Stability

72

Stimulating Storage Conditions

73

Speed it Up

74

Precautions and Possibilities

75

Paper & Climate........................................................................................................ 77
Introduction

77

Influence of Moisture Content on Paper

77

Influence of Equilibrium Relative Humidity on Paper

77

Static Electricity

78

Dust Problems in Presses

78

Dimensional Changes of Paper during Printing

78

Deformations of Paper Due to Humidity

79

Deformation of Paper Due to Temperature

79

Curling of Paper Sheets

80

Drying Time of Printing Inks

80

Recommended Values of % ERH

81

Recommended Tolerance of % ERH

81Summary81

Automotive Test Chamber Features Rotronic-Transmitters ................................ 82
Performance Surpasses Expectation!

82

Oresund Bridge Maintenance Cost Slashed .......................................................... 83
The Rotronic Humidity Handbook

Page 4

Jens Olsens’ Worldwatch in Copenhagen ............................................................. 84
Renovation Necessary

84

Munters Dehumidifier Ensures Conditions

84

Munters Leading Dry Air Supplier

85

Cool Application for Rotronic Humidity Technology ............................................ 86
Abbey Library St. Gall.............................................................................................. 87
Rotronic Conquers the Jungfrauhoch.................................................................... 88
The Holy Shroud - The Wounds of the Passion..................................................... 89
Measuring Water Activity at the “Millennium Seed Bank” ................................... 90
The New Treasure Chamber in Cologne’s Cathedral ............................................ 92
Rotronic HygroLog-D: Data Loggers in Church Organs...................................... 93
Now, what happens to an organ when the climate is wrong?

93

Application: Pyramid of Saqquara Egypt ............................................................... 95
A New Discovery

95

Need for Preservation

95

Technology Assists

96

Rotronic Sensors on Kilimanjaro............................................................................ 97
Rotronic Measuring Equipment in Nuclear Research........................................... 98
Analysis of Drilling Mud in Canada ...................................................................... 100
HygoClip S – When Maximum Precision is Required ......................................... 102
What Does Humidity Have to Do with Deep Space Missions? ........................... 103
The European Deep Space Antenna Project in New Norcia (Western Australia)

103

Rotronic Sensors in the Brick Industry................................................................ 105
Humidity Absorption from Munters with Rotronic Humidity Instruments ........ 106
Climate Surveillance in Vienna Palace Liechtenstein ......................................... 108
Use of the Palace over the course of centuries

108

Climate Control

108

Humidity Measurement on the Moving Paper Web ............................................. 110
Web Probe BFC-DIO

111

Testing Water Activity in Seeds Helps the Brazilian Rainforest ........................ 112
Engine Testing at SAAB ........................................................................................ 114
New Ventilated Radiation Shields Co-Developed with MeteoSwiss .................. 115
How Rotronic Helps in the Production of Fine Cheese ...................................... 117

Page 5The Rotronic Humidity Handbook

Protecting Rodin from Japan’s Climate and Earthquakes ................................. 118
How Humidity is used in Fuel Cell Research....................................................... 119
Why the Dew Point is Measured?

119

The Challenge of Measurement in Fuel Cell Testing119

Who are the Customers?

120

HygroClip Probes and the Quality of Plastic Molding......................................... 121
Advantages from the Customer’s Point of View

121

Further Applications for DAS-Systems:

122

Humidity Generators - Examining Uncertainty .................................................... 123

Other Helpful Information....................................................... 128
Temperature Conversion Table............................................................................. 128
Glossary.................................................................................................................. 129

The Rotronic Humidity Handbook

Page 6

Humidity
Fundamentals

Rotronic Instrument Corp.

Page 7

Relative Humidity, Pressure and Temperature

Humidity Fundamentals_____________________________________________________________________

Relative Humidity, Pressure and Temperature
Foreword
This technical note reviews the basic laws of physics that govern relative humidity.
Within a temperature range of -50 to 150°C and at pressures not in excess of 1000 kPa,water vapor practically behaves like an ideal gas. Examples are provided to illustrate theinfluence of temperature and pressure on relative humidity and to show how to convert
relative humidity into dew point and absolute humidity.
This note is largely inspired from the textbook Chemistry by Theodore L. Brown and H.
Eugene LeMay, JR. (Prentice-Hall, 1977).

Ideal Gas Laws
By definition, an ideal gas follows the following laws:
Boyle's Law: this law states that at constant temperature, the product of the volume andpressure of a given amount of gas is a constant.
P x V = constant
The value of the constant depends on how much gas is in the volume.
Charles's Law: this law states that at constant pressure, the volume of a given quantityof gas is proportional to absolute temperature (°K).
V=qxT
where q is a proportionality constant that depends on the quantity of gas.
Charles's law can be stated in another form: at constant volume, the pressure of a given
quantity of gas is proportional to absolute temperature.
P=jxT
where j is a proportionality constant that depends on the particular sample of gas and its
volume.

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Humidity Fundamentals

Note: to convert temperature in °C into absolute temperature in °K, add the constant273.15.
Dalton's Law of Partial Pressures: this law states that that the total pressure of a mixtureof gases is equal to the sum of the pressures that each gas would exert if it were
present alone.
Pt= P1+ P2+ P3+ ...
where P1, P2, etc., are the partial pressures of gases 1, 2, etc.
Avogadro's Hypothesis: this hypothesis states that equal volumes of gases at the same
temperature and pressure contain equal numbers of molecules. For instance, one literof any ideal gas at a temperature of 0°C and a pressure of 101.3 kPa, contains 2.688 x
1022 molecules.
Note: the temperature of 0°C and pressure of 101.3 kPa is the standard temperatureand pressure condition or STP.
Volume of a Mole of Gas at STP:
A mole of any element is defined as the amount of that element that contains the same
number of molecules (or atoms in the case of a mono atomic element) as exactly 12 gof 12C (Carbon 12).
It has been experimentally determined that the number of atoms in this quantity of 12C
is 6.022 x 1023. This number is called Avogadro's number.
As one liter of gas, at STP, contains 2.688 x 1022 molecules (or atoms in the case of amono atomic gas), it follows that a mole of gas (6.022 x 1023 molecules) occupies avolume of 22.4 l, at STP.
Ideal Gas Law: this law states that the product of volume and pressure of a given
amount of gas is proportional to absolute temperature.
PxV=nxRxT
where n is the number of moles of gas and R the molar gas constant.

The constant R is equal to:
0.08206 atm x liter/°K x mole.
Page 9The Rotronic Humidity Handbook

Relative Humidity, Pressure and Temperature

8.30928 Pa x m3/°K x mole
Mole Fractions and Partial Pressure
The composition of one mole of a gas mixture can be expressed in terms of the mole
fractions of its components. The mole fraction of a particular component is defined as
the total number of moles of the component divided by the total number of moles of all
the components. From this definition, it follows that the sum of all mole fractions is equal
to one. Taking dry air near sea level as an example, the mole fractions of the three main
components are as follows:
Nitrogen
OxygenCarbon Dioxide: 0.78084: 0.20948: 0.00954

If Pt is the total pressure of a gas mixture and n1, n2, etc. the mole fractions of its
components, it follows that:
Pt= Pt x (n1+ n2 + ...) and
Pt= Pt x n1+ Pt x n2 + ...
where Pt x n1, Pt x n2, etc. are the partial pressures of components 1, 2, etc.
The above equation is another form of Dalton's law.
Effect of a Change In Pressure
Dalton's law states that the total pressure of a gas mixture is equal to the sum of thepartial pressures of its components. From this, it was derived that the partial pressure of
a component is equal to the product of the total pressure times the mole fraction of thecomponent.
Therefore, a change in the total pressure of a gas mixture, at constant composition,
results in the same change in the partial pressure of each component. For instance,
doubling the total pressure of a gas mixture results in doubling the partial pressure ofeach component.
Real Gases
Real gases fail to obey the laws of ideal gases to greater or lesser degree. The van der
Waals equation corrects the equation established for ideal gases:

The Rotronic Humidity Handbook

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Humidity Fundamentals(P + an2/V2)(V - nb) = nRT
where a and b are constants that depend on the nature of the gas.
From the van der Waals equation, it is apparent that a real gas tends to behave like anideal gas when the volume of gas is large.
The constant b of most common gases is less than. At STP, the number of moles n isequal to one when the volume V equals 22.4 l. Therefore, most real gases behave
almost like ideal gases when placed in a large volume at moderate pressure(1000 kPa or less).
Vapor Pressure Above a Liquid
Molecules in a liquid are closer one to another than they are in a gas. Therefore,
intermolecular forces are stronger than in a gas. For a liquid to vaporize, theintermolecular forces have to be overcome by the kinetic energy of the molecules.
If a liquid is placed in a closed container, the particles entering the vapor phase cannot
escape. In their random motion, many particles strike the liquid and are recaptured byintermolecular forces. Thus two processes occur simultaneously: evaporation andcondensation.
The rate of evaporation increases as temperature increases. This is so because anincrease in temperature corresponds to an increase in the kinetic energy of molecules.
At the same time, the rate of condensation increases as the number of particles in thevapor phase increases: more molecules strike the surface of the liquid. When these twoprocesses become equal, the number of particles and, therefore, the pressure in thevapor phase, becomes stabilized.
The value of the equilibrium vapor pressure depends on the attractive forces between
particles of the liquid and on the temperature of the liquid. Vapor pressure above aliquid increases with increasing temperature.
The presence of gases other than vapor above a liquid does not affect the kinetic
energy of molecules inside or outside the liquid and does not affect the magnitude of theintermolecular forces in the liquid. Therefore, vapor pressure above a liquid does notdepend on the total pressure above the liquid.

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The Rotronic Humidity Handbook

Relative Humidity, Pressure and Temperature

Vapor Pressure of Water
The vapor pressure of water, or saturation vapor pressure, increases strongly withincreasing temperature:
Temperature
(°C)
0
10
20
30
40
50
60
70
80
90
100

Water Vapor
Pressure
(kPa)
0.61
1.23
2.34
4.24
7.37
12.33
19.92
31.18
47.34
70.11
101.33 = 1 atm

Vapor Pressure of Water Mixed with Another Substance
If water is mixed with a non volatile substance to form a non electrolyte solution, thevapor pressure is proportional to the mole fraction of water in the solution (Raoult's law).
Because of the electrostatic attraction between ions, electrolyte solutions do not exactly
follow Raoult's law.
This can be explained as follows:
At a given temperature, the kinetic energy of all particles (molecules, ions) in thesolution is the same. Essentially the same number of particles are at the surface in boththe solution and pure water. However, in the case of the solution, only the watermolecules can escape from the solution. As these represent only a fraction of the total
number of particles present at the surface, vapor pressure is lowered.

The Rotronic Humidity Handbook

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Humidity Fundamentals

The following table provides a few examples of saturated salt solutions (electrolyte
solutions) at a temperature of 25°C:
Solute
LiCL
MgCl
NaCl
KCl

Vapor pressure
(kPa)
0.358
1.039
2.387
2.673

Pressure Ratio
Solution/Pure Water
11.3 %
32.8 %
75.3 %
84.3 %

Vapor Pressure Above Ice
When water freezes, the molecules assume a structure which permits the maximum
number of hydrogen-bonding interactions between molecules. Because this structure
has large hexagonal holes, ice is more open and less dense than liquid water. As
hydrogen-bonding is stronger in ice than in liquid water, it follows that the intermolecular attraction forces are the strongest in ice. For that reason, vapor pressure
above ice is less than the vapor pressure above liquid water.
Temp
(°C)
0
-5
-10
-15
-20
-25
-30

Vapor Pressure
Liquid (kPa)
0.611
0.422
0.287
0.191
0.126
0.081
0.049

Vapor Pressure
Ice (kPa)
0.611
0.402
0.260
0.165
0.103
0.064
0.037

Ratio
Ice/Liq.
1.00
0.95
0.91
0.86
0.82
0.78
0.75

Definitions of Humidity
Vapor Concentration (Absolute Humidity)
The vapor concentration or absolute humidity of a mixture of water vapor and dry air isdefined as the ratio of the mass of water vapor Mw to the volume V occupied by the
mixture.
Dv = Mw / V , expressed in grams/m3 or in grains/cu ft
The value of Dv can be derived as follows from the equation PV = nRTPage 13

The Rotronic Humidity Handbook

Relative Humidity, Pressure and Temperature

Mw = nw x mw, where :nw = number of moles of water vapor present in the volume V
mw = molecular mass of water
Dv = Mw / V = nw x mw / V = mw x p / RT , where:
mw = 18.016 gramp = partial pressure of water vapor [Pa]R = 8.31436 Pa x m3 / °K x moleT = temperature of the gas mixture in °K
Dv = p / 0.4615 x T [g / m3]
1 gr (grain) = 0.0648 g (gram)
1 cu ft = 0.0283168 m3
Dv [gr / cu ft] = 0.437 x Dv [g / m3]
Specific Humidity
Specific humidity is the ratio of the mass Mw of water vapor to the mass (Mw + Ma) ofmoist air.
Q = Mw / (Mw + Ma)
Q = p mw / (p mw + (Pb – p) ma)
Q = 1000 p / (1.6078 Pb – 0.6078 p) [ g / kg]
1 gr (grain) = 0.0648 g (gram)
1 lb = 0.4535923 kg
Q [gr / lb] = 7 x Q [g / kg]
Mixing Ratio
The mixing ratio r of moist air is the ratio of the mass Mw of water vapor to the mass Maof dry air with which the water vapor is associated:
r = Mw / Ma
Mw = nw x mw = mw x p V / RT
Ma = na x ma = ma x pa V / RT = ma x (Pb – p) V / RT, where:
nw = number of moles of water vapor present in the volume V

The Rotronic Humidity Handbook

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Humidity Fundamentals

na = number of moles of dry air present in the volume V
mw = 18.016 gram
ma = 28.966 gramp = partial pressure of water vapor [Pa]pa = partial pressure of dry air [Pa]Pb = total or barometric pressure [Pa]R = 8.31436 Pa x m3 / °K x moleT = temperature of the gas mixture in °K
V = volume occupied by the air – water vapor mixturer = mw p / ma (Pb – p)r = 621.97 x p / (Pb – p) [g / kg]
1 gr (grain) = 0.0648 g (gram)
1 lb = 0.4535923 kg
r [gr / lb] = 7 x r [g / kg]
Volume Mixing Ratio
The volume mixing ratio is the ratio of number of moles of water vapor nw to the numberof moles of dry air na with which the water vapor is associated. This usually expressedin terms of parts per million:
PPMv = 106 x nw / na
nw = p V / RT
na = pa V / RT = ma x (Pb – p) V / RT, where:p = partial pressure of water vapor [Pa]pa = partial pressure of dry air [Pa]Pb = total or barometric pressure [Pa]R = 8.31436 Pa x m3 / °K x moleT = temperature of the gas mixture in °K
V = volume occupied by the air – water vapor mixture
PPMv = 106 x p / (Pb – p)
Relative Humidity
Relative humidity is the ratio of two pressures: %RH = 100 x p/ps
where p is the actual partial pressure of the water vapor present in the ambient and ps
the saturation pressure of water at the temperature of the ambient.

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The Rotronic Humidity Handbook

Relative Humidity, Pressure and Temperature

Relative humidity sensors are usually calibrated at normal room temperature (wellabove freezing). Consequently, it generally accepted that this type of sensor indicates
relative humidity with respect to water at all temperatures (including below freezing).
As already noted, ice produces a lower vapor pressure than liquid water. Therefore,
when ice is present, saturation occurs at a relative humidity of less than 100 %. For
instance, a humidity reading of 75 %RH at a temperature of -30°C, corresponds tosaturation above ice.
Dew Point and Frost Point Temperature
The dew point temperature of moist air at temperature T, pressure Pb and mixing ratio r
is the temperature to which the air must be cooled in order to be saturated with respect
to water (liquid).
The frost point temperature of moist air at temperature T, pressure Pb and mixing ratio r
is the temperature to which the air must be cooled in order to be saturated with respect
to ice.
Wet Bulb Temperature
The wet bulb temperature of moist air at pressure Pb, temperature T and mixing ratio r is
the temperature which the air assumes when water is introduced gradually byinfinitesimal amounts at the current temperature and evaporated into the air by anadiabatic process at constant pressure until saturation is reached.
Effect of Temperature and Total Pressure on Vapor Pressure
When considering the effect of temperature and pressure on the partial pressure ofvapor, it is essential to make a difference between the following situations:• saturation (liquid or ice) vs. no saturation (vapor only);• closed container of fixed volume vs. open space.
Saturation:
The partial pressure of vapor is equal to the saturation pressure and its value depends
only on temperature. There is no difference between the situation in an open
environment and that in a closed container.

No Saturation
Water vapor behaves almost like an ideal gas and the following equation applies
regarding the partial pressure of vapor:

The Rotronic Humidity Handbook

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Humidity Fundamentals

pxV=nxRxTa) In an open space: the volume V occupied by vapor is free to expand. Therefore, thepartial pressure p is not affected by temperature. The partial pressure p can vary only if
n varies (vapor is being added or removed) or if the total pressure varies (Dalton's lawof partial pressures). For instance, total pressure drops with increasing altitude and thisresults in a decrease of the partial pressure of vapor.
b) In a closed container of fixed volume: vapor occupies the entire volume of thecontainer and this volume is constant. Therefore, the partial pressure p can vary only ifthere is a change in absolute temperature (degrees K) or a change in the amount ofvapor. The partial pressure p does not vary with a change in total pressure.
Effect of Temperature and Pressure on %RH
Saturation vapor pressure depends only on temperature. There is no effect of totalpressure and there is no difference between the situation in an open space and that in aclosed container.
From the above it follows that:a) in an open space, at constant moisture level and temperature, %RH is directly
proportional to the total pressure. However, the value of %RH is limited to 100% as pcannot be greater than ps.
b) in an open space, at constant moisture level and pressure, %RH decreases strongly
as temperature increases.
c) in a closed container of fixed volume, %RH decreases as temperature increases,
however not quite as strongly as in the situation of the open space.
Examplesa) Office Building
For practical purposes, an office building can be considered as an open environment. A
localized increase in temperature created by a heater or an office machine, does not
modify the value of the partial pressure of water vapor. Therefore, the local vapor
pressure is the same as elsewhere in the building. However, the saturation vapor
pressure is locally increased. Consequently, relative humidity in the immediate vicinity of
the heat source is lowered.
If we assume that elsewhere in the building temperature is 25°C and relative humidity
50 %, a localized increase of temperature to 30°C lowers relative humidity as follows:

Page 17

The Rotronic Humidity Handbook

Relative Humidity, Pressure and Temperature

ps at 25°C = 3.17 kPa
ps at 30°C = 4.24 kPa
p = 0.5 x 3.17 kPa = 1.585 kPa, corresponding to 50 %RH
Localized %RH = 100 x 1.585/4.24 = 37.4%b) Dew on a Chilled Mirror
If the temperature of a mirror is lowered to precisely the value that makes dew appear at
the surface of the mirror, the value of the mirror temperature is called dew point. Using
the previous example, the dew point corresponding to a condition of 50 %RH and 25°C
can be found as follows:
ps at 25°C = 3.17 kPa
p = 0.5 x 3.17 kPa = 1.585 kPa, corresponding to 50 %RH
If there is equilibrium between the dew on the mirror and the environment, it follows thatps at the temperature of the chilled mirror must be equal to the vapor pressure p. Basedon a simple interpolation of the values of the saturation vapor tables, we find that avalue of ps of 1.585 kPa corresponds to a temperature of 13.8°C. This temperature is
the dew point.
This example shows that converting relative humidity into dew point and vice versa
requires the use of a thermometer and saturation vapor tables.
c) Compression in a Closed Chamber
If the total pressure inside a closed chamber is increased from one to one and a half
atmospheres and temperature is maintained constant, the partial pressure of water
vapor is increased 1.5 times. Because temperature is maintained constant, thesaturation pressure ps is not changed. If we assume that we had a condition of 50 %RH
and 25°C before the compression, the condition after compression is 75 %RH and
25°C.

The Rotronic Humidity Handbook

Page 18

Humidity Fundamentalsd) Injection of a Dry Gas in a Closed Chamber
If, for instance, dry nitrogen is injected in a closed chamber where there is already air at
a condition of 50 %RH and temperature is maintained constant, total pressure in thechamber increases. However, the partial water vapor pressure p remains constantbecause the mole fraction of water vapor in the chamber decreases by an amount thatexactly balances the increase in total pressure (see Dalton's law). Because temperature
is maintained constant, the saturation vapor pressure ps is also unchanged. Therefore,
relative humidity stays at 50 % in spite of the fact that a dry gas was injected in thechamber.

Relative Humidity Calibration
Method of Calibration
A frequent method of calibrating a relative humidity instrument is to place the humidity
sensor in a closed container. By putting a known solution of water and anothersubstance inside the container, a known humidity is established at equilibrium. Thishumidity value is used to provide a reference against which the instrument can be
adjusted or calibrated.
Temperature Stability
Obtaining equilibrium conditions is one of the most critical requirements of the method.
This means that there should be no difference of temperature between the humidity
sensor, the solution and the head space above the solution. Unstable temperatureduring calibration will not permit this. A temperature stability of 0.02°C/min or better isrequired during the calibration process for the method to be accurate.
Temperature of Calibration
The relative humidity values generated by the different solutions used to the purpose ofcalibration, are affected by temperature. Therefore, a correction must be made for thetemperature of calibration. However, no correction is required for the effect oftemperature on the total pressure inside the calibration container.
The temperature of calibration may also be restricted by the design of the instrument.
For instance, an instrument that provides a compensation for the effect of temperatureon the humidity sensor does so by assuming that the temperature of calibration isalways the same. In that case, the manufacturer provides a recommendation as to therange of calibration temperature that result in the best overall accuracy for the
instrument.

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The Rotronic Humidity Handbook

Relative Humidity, Pressure and Temperature

AltitudeBecause vapor pressure above a solution is not affected by total pressure, no correction
is required for altitude.
Influence of Temperature Variations on Solutions
A saturated solution results of the dynamic equilibrium of two processes: formation of asolution and crystallization. If a saturated salt solution is used for calibration, attention
must be paid to this equilibrium. Because solubility depends on temperature, a variationin the temperature of a saturated solution can disturb the dynamic equilibrium process
in the solution. Time must be allowed for equilibrium when the temperature of asaturated solution is changed. This time period is usually significantly longer than thetime required by the temperature of the solution to stabilize at a new value.
Non saturated solutions adapt faster to a change in temperature because they do not
require a dynamic equilibrium between a crystal and a liquid. This is convenient for use
in field calibrations where temperature is not precisely known ahead of time.
Most solutions release or absorb heat during their preparation. For that reason,
solutions should be prepared in advance.

The Rotronic Humidity Handbook

Page 20

Humidity Fundamentals

Are they all the same? Choosing the Right Humidity Instrument
November 2004
Copyrighted material, reprinted with permission from Pharmaceutical Formulation & Quality Magazine

Selecting the right relative humidity instrument for a specific application can be
confusing, largely because most instruments on the market have specifications that arealmost identical. Consider, for example, the accuracy specification. Many instruments,of all cost and quality levels, specify accuracy of ± 2.0% RH or even better, regardlessof the conditions to be measured. Is it possible that instruments that are so widelydifferent both in design and cost are all equally good? Is an accuracy range of 1.0% to
2.0% RH commonplace? What about the long term stability of the humidity
measurement? What role should it play into the decision process when selecting a RH
instrument?
This article will first look at the principle of operation of capacitive humidity sensors, andthen we will examine the source of errors in an RH measurement, and finally discuss
the steps necessary to select the correct instrument.
Principle of Operation
The capacitive humidity sensor consists of a hygroscopic dielectric material placed
between a pair of electrodes which forms a small capacitor. Most capacitive sensors
use a plastic or polymer as the dielectric material, with a typical dielectric constantranging from 2 to 15. When no moisture is present in the sensor, both this constant andthe sensor geometry determine the value of capacitance.
At normal room temperature, the dielectric constant of water vapor has a value of about
80, a value much larger than the constant of the sensor dielectric material. Therefore,
absorption of water vapor by the sensor results in an increase in sensor capacitance.
At equilibrium conditions, the amount of moisture present in a hygroscopic material
depends on both the ambient temperature and the ambient water vapor pressure. Thisis true also for the hygroscopic dielectric material used on the sensor.
By definition, relative humidity is also a function of both the ambient temperature andwater vapor pressure. Therefore there is a relationship between relative humidity, theamount of moisture present in the sensor, and sensor capacitance. This relationship isthe base of the operation of a capacitive humidity instrument.
In a capacitive instrument, as in practically every other type of instrument, humidity ismeasured by a chain process as opposed to being measured directly. Instrument
performance is determined by all of the elements of the chain and not by the sensor
alone. The sensor and associated electronics cannot be considered separately. Any
factor that can disturb the chain process of measurement is bound to have an effect on
the instrument’s performance.

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The Rotronic Humidity Handbook

Are they all the same? Choosing the Right Humidity Instrument

Classification of Errors
For the purpose of analysis, errors of measurement can be divided into two broad
categories: Systematic and Random errors.
Systematic errors are predictable and repeatable, both in magnitude and sign. Errors
resulting from a nonlinearity of the instrument or from temperature effects fall into thisprofile. Systematic errors are instrument specific.
Linearity Errors
The typical response of a relative humidity sensor (between 0 and 100% RH) is nonlinear. Depending on the effectiveness of the correction made by the electronic circuits,
the instrument may have a linearity error. Assuming that both the sensor andassociated electronics have reproducible characteristics, the linearity error is asystematic error.
Generally, the values recommended by the instrument manufacturer for calibration were
determined so as to minimize the linearity error. Calibrating at those values should
produce an even plus and minus distribution of the linearity error. Careless selection of
the calibration values can result in a different distribution of the linearity error and canbe detrimental to instrument accuracy.
Temperature Errors
Temperature can have a major effect on several elements of the chain process ofmeasurement described earlier. In the specific case of a capacitive humidity
instrument, the following effects can produce a temperature error.
Sensor hygroscopic properties vary with temperature. A relative humidity instrument
relies on the assumption that the relationship between the amount of moisture present
in the sensor hygroscopic material and relative humidity is constant. However, in most
hygroscopic materials, this relationship varies with temperature. In addition, thedielectric properties of the water molecule are affected by temperature. At 20°C, thedielectric of water has a value of about 80. This constant increases by more that 8% at
0°C and decreases by 30% at 100°C.
Sensor dielectrics properties also vary with temperature. The dielectric constant of
most dielectric materials decreases as temperature increases. Fortunately, the effect oftemperature on the dielectric properties of most plastics is usually more limited than in
the case of water.
Any length of cable connecting the sensor to the electronic circuits has its own
capacitance and resistance. The electronic circuits can not discriminate between thesensor and its connecting cable. Therefore, since the capacitance of the sensor and

The Rotronic Humidity Handbook

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Humidity Fundamentals

the cable can vary with temperature, the humidity values reported by the electronics
must be compensated for the effects of temperature. Failure to do so can result in large
measurement errors, sometimes as large and 15% to 20% RH.
While systematic errors are predictable and repeatable, random errors are not fully
predictable because they are essentially dependant on factors external to the
instrument. For example, errors resulting from sensor hysteresis, as well as thoseresulting from the calibration procedure are random errors. Usually, random errors are
estimated on the basis of statistical data, experience, and judgment.
Hysteresis
Hysteresis is the maximum difference that can be measured between corresponding
pairs of data, obtained by running an ascending and a descending sequence of humidity
conditions. Hysteresis determines the repeatability of a humidity instrument.
For any given instrument, the value of hysteresis depends on a number of things: thetotal span of the humidity cycle used to measure hysteresis, exposure time of thesensor to each humidity condition, temperature during the measurements, criteria used
to determine sensor equilibrium, and previous sensor history. Usually, sensor
hysteresis increases as the sensor is exposed to high humidity and high temperature
over longer periods of time.
Because of these points, it is not meaningful to state a sensor’s hysteresis values
without providing details on how the tests were performed. In actual measurement
practice, conditions are extremely diverse and hysteresis may or may not reach its
maximum value. Therefore, it is reasonable to consider hysteresis a random value thatcan be neither fully predicted nor compensated. When the accuracy of an instrument is
specified, half the maximum value of hysteresis should be equally distributed as apositive and a negative error. However, instrument repeatability should not be specified
at less than the full value of hysteresis.
Calibration Errors
Calibration consists of adjusting the instrument output to the values provided by two or
more reference humidity conditions. The accuracy to which these conditions are known
is critical. The reference instruments used to provide known humidity and temperature
values for calibration have their own accuracy, repeatability, and hysteresis values
which must be taken into consideration when specifying final instrument accuracy. In
addition, no adjustment made during calibration can perfectly replicate the value seenby the reference instruments. These errors must be considered and treated as random
errors in the calculation of instrument accuracy.

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The Rotronic Humidity Handbook

Are they all the same? Choosing the Right Humidity Instrument

Long Term Stability
Another factor which is crucial, and in fact as important if not more so that instrument
accuracy, is the instrument’s ability to return the same values for RH for a given
humidity condition over a long period of time. This value, usually termed repeatability,
measures an instruments ability to maintain its calibration in spite of shifting
characteristics of the sensor and its associated electronics over long periods of time.
Generally one can split the problem of repeatability into two areas: the ability of thesensor to maintain its response to a given humidity condition at a given temperature andthe stability of the electronics over time.
Long term stability plays a critical role in the frequency of calibration required for ahumidity instrument. In addition, the stability of the instrument also significantly affects
the value of the measurement data received from the instrument between calibration
cycles. Both of these points help determine the overall cost of choosing an instrument.
Choosing a Humidity Instrument
Given all of the difficulties of measuring humidity and the confusing claims of the
majority of suppliers of humidity instrumentation, how can a proper and accurate
instrument be chosen for a particular application? Since specifications for instruments
produce a large range of cost and quality for the same specifications, how can the user
find the correct instrument?
The most important point to understand is there no real physical standard for relative
humidity calibration. As a result, there has probably been more abuse in specifying
humidity instruments than any other type of instrument. This abuse leads tospecifications which are of limited value when comparing instruments from various
manufacturers. Therefore the user finds that he or she must dig deeper into thespecifications and claims of the instrument manufacturer. To achieve this goal, the end
user must carefully examine the supplier’s claims and support documentation in thefollowing areas: sensor linearity, temperature constants, calibration errors, long term
stability of sensor and electronics, and hysteresis.

The Rotronic Humidity Handbook

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Humidity Fundamentals

Wet Bulb / Dry Bulb - Description and Limitations
Summary
Wet- and dry-bulb temperature measurement is a commonly used technique forcontrolling relative humidity in environmental chambers.
ASTM standard E 337-84 reviews in great detail the wet- and dry-bulb technique.
According to this standard, the accuracy which can generally be expected in the case ofa ventilated dry- and wet-bulb device is in the range of 2 to 5 %RH.
This kind of accuracy is acceptable in the case of environmental chambers where bothtemperature stability and uniformity are specified to within 1 degree C. This is so
because an uncertainty of 1 degree C on temperature automatically results in an
uncertainty of 5 to 6 %RH at high humidity. However, some chambers which are
specified to within 0.3 - 0.5 degree C permit and require better humidity control.
Newer humidity measurement techniques such as the HYGROMER C-94 capacitive
humidity sensor have greater accuracy than that of the wet- and dry-bulb technique. Of
equal importance is the fact that the sensor offers superior control characteristics over awide range of temperatures and humidity. Unlike other capacitive sensors, the C-94
sensor performs accurately even at high humidity and temperature. The HYGROMER
C-80 sensor can survive conditions from -50 to +200 C and from 0 to 100 %RH.
Problem Areas in the Wet- and Dry-Bulb Technique
There is no question that the wet- and dry-bulb measurement technique has a soundtheoretical basis. The problem is that this technique is simple only in appearance. And,
it is so widely accepted that many users are not anymore critical or careful. This results
in a number of problems which are reviewed in the following paragraphs.
Non-Observance of Basic Requirements
In practice, there is a tendency to disregard some of the following requirements of thewet- and dry-bulb technique:• Water temperature: the theory of the wet- and dry-bulb technique assumes thatthe temperature of the water used for the wet-bulb is equal to the temperature of
the environment to be measured.

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The Rotronic Humidity Handbook

Wet Bulb / Dry Bulb – Description and Limitation• Psychrometer Coefficient: the psychrometer coefficient is used to establish thepsychrometric chart that converts wet- and dry-bulb temperature readings into
relative humidity. This coefficient has to be determined for each specific design ofpsychrometer and in particular for each design of the wet-bulb.
• Purity of Water: psychrometric charts are established under the assumption thatpure water is being used for the wet-bulb.
• Barometric Pressure: psychrometric charts are usually valid at the "standard"barometric pressure and require a correction at other pressures.
• Matching of the Thermometers: the wet- and dry-bulb thermometers should not
only be accurate, but they should also be matched so as to minimize the error on
the temperature depression readings (or temperature difference).
Interferences During Measurements
In an environmental chamber, errors of measurement can result of a poor choice in themounting location of the wet- and dry-bulb thermometers. This is the case when thethermometers are installed too closely to a source of moisture (water supply for the wetbulb, steam injector, etc.). Errors may also occur when the thermometers are too close
to the walls of the chamber. It is important to mount the thermometers at a location
where conditions are fairly representative of the average conditions inside the chamber.
Poor Handling and Maintenance
Proper handling and frequent maintenance are major requirements of the wet- and drybulb technique. Costly service calls frequently result of the following:• Dirty Wick: the wick should never be directly be touched with fingers. A new wickshould be flooded with distilled water so as to wash away any contamination. In an
environmental chamber, the wick is continuously ventilated and tends to get dirty
after some time. From a maintenance standpoint, this is probably the mostbothering aspect of the dry- and wet-bulb technique.
• Wick Not Properly Pulled: the wick should sufficiently cover the wet-bulb
thermometer so as to minimize errors due to heat conduction along the stem of thethermometer. The wick must also be in close contact with the surface of thethermometer.
• Wick Not Really Wet: a wick which is too old or which has been left to dry out, may
not supply enough water. A properly wetted wick should have a glazed
appearance.

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Humidity Fundamentals

Typical Accuracy of the Wet- and Dry-Bulb Technique
Most of the problems mentioned above have a direct influence on the accuracy of thewet- and dry-bulb technique. Specifically, most errors are on the wet-bulb temperatureand on the temperature depression measurement.
Considering only the uncertainties on temperature measurement and psychrometriccoefficient, ASTM Standard #E 337-84 indicates that the range of errors for ventilated
wet- and dry-bulb devices goes from 2 to 5 %RH:
An error of 2 %RH corresponds to an error of 0.1C on temperature depression and 0.2C
on dry-bulb temperature. An error of 5 %RH corresponds to an error of 0.3C on
temperature depression and 0.6C on dry-bulb temperature. The most important factor
appears to be the accuracy of temperature depression measurement.
Taking into account the many other potential sources of error, it can be assumed thatthe effective accuracy of the wet- and dry-bulb devices installed in most environmental
chambers is not better than 3 to 6 %RH. The error tends to be the largest at low
humidity and at low temperatures. At these conditions, readings are usually too high.
Operational Limitations of the Wet- and Dry-Bulb Technique
In addition to limitations regarding accuracy, the wet- and dry-bulb technique has otherlimitations which may be important in the case of environmental chambers:• No measurement below the freezing point.
• Adds water to the environment (a problem with chambers operating at low
humidity).
• Sluggish response and therefore, poor control characteristics. The wet-bulb
temperature reacts slowly to changes in humidity because of the mass of the wetbulb thermometer and wick. Slow reaction to changes in temperature is due to thetime required by the water supply to adapt.
• Requires a water supply and, therefore, can support the growth of microorganisms.
• Cannot be easily calibrated and trouble-shot.

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The Rotronic Humidity Handbook

The Rotronic Humidity Handbook

Page 28

Technical Information
For
Rotronic Products

Page 29

The Rotronic Humidity Handbook

Water Activity Instruments: A Comparison of Two Measuring Techniques

Technical Information for Rotronic Products_____________________________________________________________________

Water Activity Instruments: A Comparison of Two Measuring
Techniques
June / July 2004
Copyrighted material, reprinted with permission from Food Quality Magazine

A point-by-point comparison shows that there is no real advantage of the chilled mirror
Aw meters over the lower priced instruments that use a relative humidity sensor.
Water Activity Measuring Techniques
Most laboratories measure water activity either with an instrument that uses a relative
humidity sensor or with an instrument that uses a chilled mirror.
Instruments based on a relative humidity sensor are typically less expensive than thechilled mirror instruments. This raises the question of whether the chilled mirror Aw
meters have enough inherent advantages such as speed, accuracy and measuring
range to offset the disadvantage of both a higher price and higher maintenancerequirements.
Speed of Measurement
The measurement of water activity is an indirect measurement. All Aw instruments
measure the amount of water vapor in the air surrounding the product sample. The timerequired for the water vapor in the product sample to equilibrate with the air in thechamber varies significantly with the composition of the product and temperaturestability between the product sample and the air. Typically the full equilibrium timerequires 30 minutes or longer. Using a variety of methods to speed the measurement
most Aw instruments available on the market today provide a reading of Aw inapproximately 5 minutes.
Temperature Stability
Temperature stability always matters during Aw measurements. A temperature
imbalance or the lack of temperature stability between the product sample and thechamber air volume can change the partial pressure of water vapor generated by the
product sample. From this point of view all types of sensors, chilled mirror or relative
humidity, are equally affected by temperature instability. When temperature is notstable, measurements take longer and/or are inaccurate. Therefore the product sample
should always be in equilibrium with the measurement chamber. Since the length oftime required to reach temperature equilibrium depends on the product sample and the

The Rotronic Humidity Handbook

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Technical Information for Rotronic Products

difference in initial temperature of the product sample, be sure the instrument provides
the capability to report temperature instability.
AccuracyWith a chilled mirror instrument, water activity must be computed using both the value ofdew point and the value of temperature. A relative humidity sensor measures the water
vapor directly and then compensates for any temperature variation from 25°C. The
accuracy of this computation or compensation depends on the error made on themeasurement of any of these parameters.
In the food industry, many water activity measurements deal with products in the rangeof 0.800 to 1.000 Aw. At room temperature, a good relative humidity sensor canmeasure a condition of 0.950 Aw with an accuracy of ± 0.01 Aw or better. In terms ofdew point, the equivalent accuracy is ± 0.175°C. The majority of reference chilled
mirror instruments on the market today are specified with a dew point accuracy of ±0.15°C to ±0.2°C. Therefore at high Aw levels, instruments based on a RH sensor are as
accurate as even the best chilled mirror.
Depending both on the model and on the manufacturer, the vast majority of water
activity instruments are specified with an accuracy of ±0.01 aw to ±0.02 aw (±1.0 %RH
to ±2.0 %RH). As opposed to this, water activity instruments that use the combination ofa chilled mirror (dew point) and infrared thermometer are commonly specified with anaccuracy of ±0.003 aw (±0.3 %RH) in the range of 0.10 to 1.00 aw. At first sight, thisappears to make the chilled mirror based water activity instruments much moreaccurate than the other kinds of instruments.
To understand how the accuracy of a chilled mirror instrument is determined it isimportant to remember that water activity (Equilibrium Relative Humidity) has to becomputed from the value of dew point and temperature. During this process, errors
made on both parameters combine to affect the ending accuracy. Therefore, it isimportant to consider the individual accuracies of temperature and dew point:
Generally, infrared thermometry is considered to be more limited in terms of accuracy
than a precision Pt 100 RTD temperature sensor. Even over the narrow temperature
range typical of water activity measurement, it is reasonable to consider thattemperature measurement with an infrared thermometer is no better than ±0.1°C. And
as stated above, top of the line reference grade chilled mirror instruments (dew point)
are typically specified with an accuracy of ±0.15 °C to ±0.2 °C.
How do these errors in temperature and dew point combine to affect Aw accuracies?
Water activity measurements in the range of 0.80 to 1.00 aw, at a temperature close to
25 °C, are fairly common. For these common conditions, combining a ±0.1 °C accuracy
on temperature with a ±0.15°C accuracy on dew point gives the following results:

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The Rotronic Humidity Handbook

Water Activity Instruments: A Comparison of Two Measuring Techniquesa) Actual conditions: 0.800 aw (80.0 %RH), 25.0 °C and Td = 21.3 °C (dew point)
Using the error on dew point and temperature the error band of aw can be calculatedwith commonly available psychometric software. The calculation shows that theaccuracy range on dew point alone results in an error of ±0.007 aw. When this iscombined with the accuracy on temperature, the error on water activity becomes aslarge as ±0.012 awb) Actual conditions: 0.950 aw (95.0 %RH), 25.0 °C and Td = 24.1 °C (dew point)
The accuracy on dew point alone results in an error of ±0.009 aw. When this iscombined with the accuracy on temperature, the error on water activity becomes aslarge as ±0.014 aw
Water activity is not always as high as 0.80 aw ...0.95 aw. For example, pharmaceuticalapplications frequently deal with values below 0.10 aw. When humidity is below 19%RH(0.19 aw) at a temperature of 25 °C, water can condense on a chilled mirror either in theform of liquid or in the form of ice.
At values below 0 °C dew point, the frost point (ice) is always higher than the dew point(liquid). The difference between frost and dew point increases as the humidity
decreases. Good reference chilled mirror instruments are equipped with a microscope
to determine which form of condensation is present on the mirror. For example, at acondition of 25 °C and 5.0 %RH, the frost point is -15.50 °C and the dew point is - 17.25°C ( a difference of 1.75 °C). At a condition of 5.0 %RH (0.050 aw) and 25 °C,
confusing the dew point and the frost point would result in an error of 0.007aw to 0.008
aw. And these errors are additive to the errors caused by the temperature and dew
point measurement.
As can be seen from the examples above, the actual accuracy on water activity using achilled mirror instrument is at best ±0.015 aw. Essentially the same as those achieved
using a RH sensor based system.
Range of Measurement
The ability of chilled mirror instrument to measurement low humidity values depends
both on the power available to cool the mirror and on the evacuation of heat away fromthe mirror. Typical chilled mirror Aw instruments are limited tin these two areas andshould not be used to measure products that are below 0.10 Aw. By contrast, a valueof 0.01 Aw can be measured without problems with a relative humidity sensor.

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Technical Information for Rotronic Products

Maintenance
Many products contain volatile additives and some products are in the form of a fine
powder. Because the chilled mirror operates at condensation, there is the tendency totrap airborne contaminants on the mirror. Since deposits on the mirror clearly affectaccuracy, frequent mirror cleaning is required. Good relative humidity sensors areunaffected by the vast majority of contaminants typically seen in food andpharmaceutical products. Due to this, calibration and maintenance requirements of an
RH based Aw system is significantly lower than a chilled mirror system.
Summary
Which water activity system is right for you? The majority of instruments on the market
today will provide equally accurate readings. When comparing RH sensor based
systems the most important consideration is the long term stability and repeatability of
the RH sensor. When comparing RH based systems with chilled mirror based systems
there is no accuracy advantage. Therefore, base your decision on all the factors
important to your use. Considerations such as instrument flexibility, ease of use,maintenance requirements, cost, and system software all play an important role.

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The Rotronic Humidity Handbook

Chemical Resistance of Rotronic Hygromer Humidity Sensors

Chemical Resistance of Rotronic Hygromer Humidity Sensors
GeneralCapacitive polymer humidity sensors react to the presence of certain chemicals within
the surrounding gas.
The amount of the influence depends on a lot of parameters:- Type of chemical- Concentration- Length of the influence- Amount of humidity and temperature- Presence of other chemicals
By that it is in principle impossible to make predictions about the deviation and thelifetime of the sensor. Normally it makes no sense to do specific tests in the laboratory,
because they require too much work. It is most convenient to put test probes to thecustomer’s disposal.
Uncritical chemicals
Following gases have no influence on the sensor and the humidity measurement:
Argon
Carbon dioxide
HeliumHydrogen
Neon
Nitrogen
Nitrous oxide (Laughing gas)
Oxygen

Ar
CO2
He
H2
Ne
N2
N2O
O2

Following gases have no or little influence on the sensor and the humidity
measurement:
ButaneEthaneMethaneNatural gas
Propane

The Rotronic Humidity Handbook

C4H10
C2H6
CH4
C3H8

Page 34

Technical Information for Rotronic Products

Critical Chemicals
In the given concentrations the following gases have no or little influence on the sensor
and the humidity measurement. The shown data are only guide values. The resistanceof the sensor depends strongly from the temperature and humidity conditions and thelength of the pollutant influence.
Table: Allowed Fault Caused From Pollutants: ± 2 % RH

PollutantAcetic acid
AcetoneAmmonia
2-Butanone (MEK)
Chlorine
Ethanol
Ethyl acetate
Ethylene glycol
Ethylene oxide
Formaldehyde
Hydrochloric acid
Hydrogen sulfide
Isopropanol
MethanolNitrogen oxides
Ozone
PetrolSulfur dioxide
TolueneXyleneFormula
CH3COOH
CH3COOH3NH3
C2H5COCH3
Cl2
C2H5OH
CH3COOC2H
HOCH2CH2OH
C2H4O
HCHO
HCI
H2S
(CH3)2CHOH
CH3OH
NOX
O3
SO2
C6H5CH3
C6H5(CH3)2

Allowed Concentration
Continuous Operation
ppm
mg/m3
800
2000
3300
8000
5500
4000
3300
8000
0.7
2
3500
6000
4000
15000
1200
3000
3
2400
3000
300
500
350
500
4800
12000
3500
6000
5
9
0.5
1
150000
5
13
1300
5000
1300
5000

Application Examples
Humidity Measurement in Sterilization Chamber (Ethylene oxide)

Customer application:

Sterilization of medical equipment

Sensor:C-94

Concentration Ethylene oxide:
Carbon dioxide

15% by volume
85% by volume

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The Rotronic Humidity Handbook

Chemical Resistance of Rotronic Hygromer Humidity Sensors

Pressure:

0.2 to 2.5 bar absolute

Temperature:app. 40°C

Humidity:

app. 80 %rh

Application experience:
The sensors have a lifetime of approximately 3 months. The chamber is in continuous
operation.
Humidity Measurement in An Ozone Chamber
Sensor:C-94

Concentration Ozone:

app. 500 ppm

Temperature:app. 23°C

Humidity:

app. 50 %rh

Application experience:
The sensors have a lifetime of approximately 1 month at 500 ppm ozone.
Special Application – Humidity Measurement in Oil
Humidity measurement direct in oil is possible in principle. But the lifetime of thesensors depends strongly from the used oil.
Measurements in oil are only possible with a special sensor and tests are inevitable.
If you have an inquiry for such an application, please contact your Rotronic
representative.

The Rotronic Humidity Handbook

Page 36

Technical Information for Rotronic Products

Competitor Comparison 2004
HVAC Transmitters - Wall Mount
E + E Elektronik
Model
OutputPower
Packing

EE10-FT6-D04
Serial No. P19980_00020
4..20 mA = 0...100 %rh, 0...+50°C, 2-wire
15...28 VDC
Cardboard Box
E + E Elektronik HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

80

90

80

90

Humidity (%rh)

Greystone
Model
OutputPower
Packing

RH110A02C2A2Serial No. N/A
4...20 mA = 0...100 %rh, 0...50°C, 3-wire
24 V AC/DC
Plastic Antistatic Bag
Greystone HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

Humidity (%rh)

Page 37

The Rotronic Humidity Handbook

Competitor Comparison 2004

General Eastern
Model
OutputPower
Packing

MRH-2-S-T
Serial No. N/A
4...20 mA = 0...100 %rh, -20...+140°F, 2-wire
12...36 VDC
Cardboard Box
General Eastern HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

40

50

60

70

80

90

Humidity (%rh)

Hycal
Model
OutputPower
Packing

HHT-2SC-TTE
Serial No. 200305530
4...20 mA = 0...100 %rh / 40...90°F, 2-wire
15...30 VDC
Cardboard Box
Hycal HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

80

90

Humidity (%rh)

The Rotronic Humidity Handbook

Page 38

Technical Information for Rotronic Products

Mamac Systems
Model
OutputPower
Packing

HU-225-2-MA
Serial No. 63572
4..20 mA = 0...100 %rh, no temperature, 2-wire
12...40 VDC
Cardboard Box
Mamac HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

80

90

80

90

Humidity (%rh)

Rotronic
Model
OutputPower
Packing

L13SHT2
Serial No. 32621 010
4...20 mA = 0...100 %rh / 0...50°C, 3-wire
10…35 VDC / 24 VDC
Cardboard Box
Rotronic HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

Humidity (%rh)

Page 39

The Rotronic Humidity Handbook

Competitor Comparison 2004

VaisalaModel
OutputPower
Packing

HMW60Y
Serial No. Z0810046
4..20 mA = 0...100 %rh, -5...+55°C, 2-wire
12...35 VDC
Cardboard Box, PCB in plastic antistatic bag with silica gel bag
Vaisala HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

80

90

80

90

Humidity (%rh)

Veris Industries
Model
OutputPower
Packing

HW Series
Serial No. N/A
4...20 mA = 0...100 %rh / 32...122°F, 2-wire
12...24 VDC
Blister
Veris HVAC Transmitter: Humidity deviation from set point
1°C

23°C

40°C

48°C

40

50

60

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

70

Humidity (%rh)

The Rotronic Humidity Handbook

Page 40

Technical Information for Rotronic Products

Humidity Deviation at 1°C
HVAC Transmitters: Humidity deviation from set point at 1°C
E + E Elektronik
Mamac Systems

General Eastern
Rotronic

Greystone
VaisalaHycal
Veris Industries

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

40

50

60

70

80

90

Humidity (%rh)

Humidity Deviation at 23°C
HVAC Transmitters: Humidity deviation from set point at 23°C
E + E Elektronik
Mamac Systems

General Eastern
Rotronic

Greystone
VaisalaHycal
Veris Industries

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

40

50

60

70

80

Humidity (%rh)

Page 41

The Rotronic Humidity Handbook

90Competitor Comparison 2004

Humidity Deviation at 40°C
HVAC Transmitters: Humidity deviation from set point at 40°C
E + E Elektronik
Mamac Systems

General Eastern
Rotronic

Greystone
VaisalaHycal
Veris Industries

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

40

50

60

70

80

90

Humidity (%rh)

Humidity Deviation at 48°C
HVAC Transmitters: Humidity deviation from set point at 48°C
E + E Elektronik
Mamac Systems

General Eastern
Rotronic

Greystone
VaisalaHycal
Veris Industries

Deviation from set point (%rh)

8
6
4
2
0
-2
-4
-6
-8
-10
-12
0

10

20

30

40

50

60

70

80

Humidity (%rh)

The Rotronic Humidity Handbook

Page 4290

Technical Information for Rotronic Products

Temperature Deviation at 50 %rh
HVAC Transmitters: Temperature deviation from set point at 50 %rh
E + E Elektronik

General Eastern
Rotronic

Greystone
VaisalaHycal
Veris Industries

Deviation from set point (°C)

2.5
2
1.5
1.2

1
0.5
0
-0.5
-1
-1.5
-2
-2.5
0

10

20

30

40

Temperature (°C)

- Mamac:- Hycal:Page 43

No temperature output
Temperature range only 40…90°F

The Rotronic Humidity Handbook

50

Competitor Comparison 2004

Industrial Transmitters with Cable Probes
Delta Ohm
Model
OutputPower
Packing

HD2011TC/1
Serial No. Z0930004
4..20 mA = 0...100 %rh, temperature range -30...+140°C, no temperature output
24 VAC
Cardboard box
Delta Ohm Industrial Transmitter: Humidity deviation from set point
-10°C

0°C

23°C

50°C

70°C

50

60

70

Deviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
0

10

20

30

40

80

90

100

Humidity (%rh)

E + E Elektronik
Model
OutputPower
Packing

EE31-PFTD3025D05CA01AB6T5 Serial No. P20511
4..20 mA = 0...100 %rh, -40...+180°C
24 VDC
Cardboard box, calibration certificate, software
E+E Elektronik Industrial Transmitter: Humidity deviation from set point
-10°C

0°C

23°C

50°C

70°C

50

60

70

Deviation from set point (%rh)

3
2
1
0
-1
-2
-3
-4
-5
-6
-7
0

10

20

30

40

80

90

100

Humidity (%rh)

The Rotronic Humidity Handbook

Page 44

Technical Information for Rotronic Products

Rotronic
Model
OutputPower
Packing

Hygroclip IC-1
Serial No. 22112 003
Digital 0…100 %rh, -50…+200°C
9 VDC
N/A
Rotronic Industrial Transmitter: Humidity deviation from set point
-10°C

0°C

23°C

50°C

70°C

50

60

70

Deviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
0

10

20

30

40

80

90

100

Humidity (%rh)

Testo
Model
OutputPower
Packing

Hygrotest 650 PHT - 20/180 Serial No. 35001583/403
4..20 mA = 0...100 %rh, -20...+180°C
24 VDC
Cardboard box, calibration certificate
Testo Industrial Transmitter: Humidity deviation from set point
-10°C

0°C

23°C

50°C

70°C

50

60

70

Deviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
0

10

20

30

40

80

90

100

Humidity (%rh)

Page 45

The Rotronic Humidity Handbook

Competitor Comparison 2004

VaisalaModel
OutputPower
Packing

HMP235 A2A0C2AA12A1A1C Serial No. Z0930004
4..20 mA = 0...100 %rh, -20...+180°C
24 VDC/AC
cardboard box, detailed calibration certificate
Vaisala Industrial Transmitter: Humidity deviation from set point
-10°C

0°C

23°C

50°C

70°C

50

60

70

Deviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
0

10

20

30

40

80

90

100

Humidity (%rh)

The Rotronic Humidity Handbook

Page 46

Technical Information for Rotronic Products

Humidity Deviation at -10°C
Industrial Transmitters: Humidity deviation from set point at -10°C
Delta Ohm

E + E Elektronik

Rotronic

Testo

Vaisala70

80

Deviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
0

10

20

30

40

50

60

90

100

90

100

Humidity (%rh)

Humidity Deviation at 0°C
Industrial Transmitters: Humidity deviation from set point at 0°C
Delta Ohm

E + E Elektronik

Rotronic

Testo

Vaisala70

80

Deviation from set point (%rh)

3
2
1
0
-1
-2
-3
-4
-5
-6
-7
0

10

20

30

40

50

60

Humidity (%rh)

Page 47

The Rotronic Humidity Handbook

Competitor Comparison 2004

Humidity Deviation at 23°C
Industrial Transmitters: Humidity deviation from set point at 23°C
Delta Ohm

E + E Elektronik

Rotronic

Testo

Vaisala70

80

Deviation from set point (%rh)

4
3
2
1
0
-1
-2
-3
-4
-5
-6
0

10

20

30

40

50

60

90

100

90

100

Humidity (%rh)

Humidity Deviation at 50°C
Industrial Transmitters: Humidity deviation from set point at 50°C
Delta Ohm

E + E Elektronik

Rotronic

Testo

Vaisala70

80

Deviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
0

10

20

30

40

50

60

Humidity (%rh)

The Rotronic Humidity Handbook

Page 48

Technical Information for Rotronic Products

Humidity Deviation at 70°C
Industrial Transmitters: Humidity deviation from set point at 70°C
Delta Ohm

E + E Elektronik

Rotronic

Testo

Vaisala70

80

Deviation from set point (%rh)

6
5
4
3
2
1
0
-1
-2
-3
-4
0

10

20

30

40

50

60

90

100

Humidity (%rh)

Temperature Deviation at 50 %rh
Industrial Transmitters: Temperature deviation from set point at 50 %rh
Delta Ohm

E + E Elektronik

Rotronic

Testo

VaisalaDeviation from set point (°C)

0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
-10

0

10

20

30

40

50

60

Temperature (°C)

Page 49

The Rotronic Humidity Handbook

70Competitor Comparison 2004

Humidity Deviation From Set Point at 23°C After Different Humidity andTemperature Conditions
Delta Ohm
Delta Ohm Industrial Transmitter: Humidity Deviation From Set Point @ 23°C
After Different Humidity & Temperature Conditions.
10 %rh

35 %rh

50 %rh

80 %rh

95 %rhDeviation from set point (%rh)

6
5
4
3
2
1
0
-1
-2
-3
-4
Start

1 h after 0.5 h
70°C 95 %rh

18 h after 0.5 h 1 h after 2 h 90°C
70°C 95 %rh
90 %rh18 h after 2 h
90°C 90 %rh

1 h after 2 h
140°C 0.5 %rh

E + E Elektronik
E+E Elektronik Industrial Transmitter: Humidity Deviation From Set Point @23°C After Different Humidity & Temperature Conditions
10 %rh

35 %rh

50 %rh

80 %rh

95 %rhDeviation from set point (%rh)

3
2
1
0
-1
-2
-3
-4
-5
-6
-7
Start

1 h after 0.5 h
70°C 95 %rh

The Rotronic Humidity Handbook

18 h after 0.5 h 1 h after 2 h 90°C
70°C 95 %rh
90 %rh18 h after 2 h
90°C 90 %rh

1 h after 2 h
140°C 0.5 %rh

Page 50

Technical Information for Rotronic Products

Rotronic
Rotronic Industrial Transmitter: Humidity Deviation From Set Point @ 23°C After
Different Humidity & Temperature Conditions
10 %rh

35 %rh

50 %rh

80 %rh

95 %rhDeviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
Start

1 h after 0.5 h
70°C 95 %rh

18 h after 0.5 h 1 h after 2 h 90°C
70°C 95 %rh
90 %rh18 h after 2 h
90°C 90 %rh

1 h after 2 h
140°C 0.5 %rh

Testo
Testo Industrial Transmitter: Humidity Deviation From Set Point @ 23°C After
Different Humidity & Temperature Conditions
10 %rh

35 %rh

50 %rh

80 %rh

95 %rhDeviation from set point (%rh)

5
4
3
2
1
0
-1
-2
-3
-4
-5
Start

Page 51

1 h after 0.5 h
70°C 95 %rh

18 h after 0.5 h 1 h after 2 h 90°C
70°C 95 %rh
90 %rh18 h after 2 h
90°C 90 %rh

1 h after 2 h
140°C 0.5 %rh

The Rotronic Humidity Handbook

Competitor Comparison 2004

VaisalaVaisala Industrial Transmitter: Humidity Deviation From Set Point @ 23°C After
Different Humidity & Temperature Conditions
10 %rh

35 %rh

50 %rh

80 %rh

95 %rhDeviation from set point (%rh)

8
7
6
5
4
3
2
1
0
-1
-2
Start

1 h after 0.5 h
70°C 95 %rh

The Rotronic Humidity Handbook

18 h after 0.5 h 1 h after 2 h 90°C
70°C 95 %rh
90 %rh18 h after 2 h
90°C 90 %rh

1 h after 2 h
140°C 0.5 %rh

Page 52

Technical Information for Rotronic Products

HygroClip Performance Over A Range of %RH & Temperature
Conditions
Reference - MBW –Dew Point
Degree C
% RH
19.97
9.90
20.10
29.80
20.10
49.70
20.00
79.40
20.00
94.30

Page 53

HygroClip S
S/N 12880047% RH Degree C
10.00
19.90
29.90
19.90
50.10
19.90
80.10
19.90
94.60
20.00

%RH
0.10
0.10
0.40
0.70
0.30

C°
-0.07
-0.20
-0.20
-0.10
0.00

HygroClip S
S/N 12880073% RH Degree C
10.00
19.90
29.80
20.00
50.00
20.00
80.00
20.00
94.50
20.00

%RH
0.10
0.00
0.30
0.60
0.20

C°
-0.07
-0.10
-0.10
0.00
0.00

Error

Error

9.98
9.99
10.03
10.02
10.03

9.90
29.60
49.20
78.60
93.20

9.80
29.50
49.60
79.10
93.10

9.80
9.80
9.90
9.90
9.90

-0.10
-0.10
0.40
0.50
-0.10

-0.18
-0.19
-0.13
-0.12
-0.13

9.80
29.30
49.40
79.00
93.00

9.80
9.90
10.00
10.00
10.00

-0.10
-0.30
0.20
0.40
-0.20

-0.18
-0.09
-0.03
-0.02
-0.03

-0.04
0.00
0.00
0.01
0.01

9.90
29.30
48.60
77.60
92.40

9.50
29.00
48.80
77.80
91.50

-0.20
-0.10
-0.20
-0.10
-0.10

-0.40
-0.30
0.20
0.20
-0.90

-0.16
-0.10
-0.20
-0.11
-0.11

9.50
28.80
48.60
77.60
91.30

0.00
0.00
0.00
0.00
0.00

-0.40
-0.50
0.00
0.00
-1.10

0.04
0.00
0.00
-0.01
-0.01

-10.02
-9.95
-9.97
-9.98

9.80
28.50
47.40
75.80

9.10
28.30
47.40
75.40

-10.30-10.20-10.20-10.20

-0.70
-0.20
0.00
-0.40

-0.28
-0.25
-0.23
-0.22

9.00
27.90
47.20
74.90

-10.10-10.10-10.00-10.00

-0.80
-0.60
-0.20
-0.90

-0.08
-0.15
-0.03
-0.02

29.94
29.96
29.97
30.08
30.04

10.00
30.00
50.10
80.00
94.80

10.10
30.20
50.70
80.60
95.20

30.00
30.00
30.00
30.10
30.10

0.10
0.20
0.60
0.60
0.40

0.06
0.04
0.03
0.02
0.06

10.20
30.20
50.60
80.60
95.00

30.00
30.00
30.00
30.10
30.20

0.20
0.20
0.50
0.60
0.20

0.06
0.04
0.03
0.02
0.16

39.89
39.94
39.98
40.01
40.07

10.00
30.10
50.30
80.40
95.40

10.20
30.60
50.90
81.00
95.70

39.90
40.00
40.00
40.10
40.20

0.20
0.50
0.60
0.60
0.30

0.01
0.06
0.02
0.09
0.13

10.40
30.60
50.80
80.90
95.50

40.00
40.00
40.00
40.10
40.20

0.40
0.50
0.50
0.50
0.10

0.11
0.06
0.02
0.09
0.13

49.88
49.91
49.95
50.03
50.11

10.10
30.30
50.50
80.80
95.80

10.50
31.10
51.30
81.40
96.30

50.00
50.10
50.10
50.20
50.30

0.40
0.80
0.80
0.60
0.50

0.12
0.19
0.15
0.17
0.19

10.70
31.20
51.40
81.40
96.20

50.00
50.00
50.00
50.20
50.30

0.60
0.90
0.90
0.60
0.40

0.12
0.09
0.05
0.17
0.19

69.81
69.93
70.01
70.17
70.38

10.20
30.60
51.00
81.30
96.30

10.90
32.20
52.10
82.10
97.30

70.00
70.10
70.20
70.50
70.70

0.70
1.60
1.10
0.80
1.00

0.19
0.17
0.19
0.33
0.32

11.10
32.30
52.20
82.00
97.10

69.90
70.00
70.10
70.30
70.50

0.90
1.70
1.20
0.70
0.80

0.09
0.07
0.09
0.13
0.12

The Rotronic Humidity Handbook

HygroClip Performance Over A Range of %RH & Temperature Conditions

Reference - MBW –Dew Point
Degree C
% RH
20.06
10.00
20.08
30.00
20.09
50.00
20.11
79.90
20.14
94.70

HygroClip S
S/N 13696012% RH Degree C
9.90
20.10
30.10
20.10
50.30
20.10
80.40
20.10
95.00
20.20

%RH
-0.10
0.10
0.30
0.50
0.30

C°
0.04
0.02
0.01
-0.01
0.06

HygroClip S
S/N 13696056% RH Degree C
9.90
20.10
30.10
20.10
50.40
20.10
80.10
20.10
95.00
20.20

%RH
-0.10
0.10
0.40
0.20
0.30

C°
0.04
0.02
0.01
-0.01
0.06

Error

Error

10.17
10.21
10.21
10.22
10.24

10.00
30.00
50.00
80.00
94.90

9.90
30.00
50.20
80.10
94.50

10.10
10.20
10.20
10.20
10.20

-0.10
0.00
0.20
0.10
-0.40

-0.07
-0.01
-0.01
-0.02
-0.04

10.00
30.00
50.40
80.30
94.70

10.10
10.20
10.20
10.20
10.20

0.00
0.00
0.40
0.30
-0.20

-0.07
-0.01
-0.01
-0.02
-0.04

0.29
0.30
0.31
0.32
0.33

10.10
30.00
50.00
80.00
95.00

9.70
29.70
50.00
79.50
93.70

0.20
0.20
0.20
0.30
0.20

-0.40
-0.30
0.00
-0.50
-1.30

-0.09
-0.10
-0.11
-0.02
-0.13

9.80
29.90
50.30
80.00
94.20

0.20
0.20
0.20
0.30
0.20

-0.30
-0.10
0.30
0.00
-0.80

-0.09
-0.10
-0.11
-0.02
-0.13

-9.60
-9.57
-9.57
-9.57

10.30
30.20
50.10
80.00

9.40
29.80
50.00
78.90

-9.70
-9.70
-9.70
-9.60

-0.90
-0.40
-0.10
-1.10

-0.10
-0.13
-0.13
-0.03

9.50
30.00
50.30
79.50

-9.70
-9.70
-9.70
-9.70

-0.80
-0.20
0.20
-0.50

-0.10
-0.13
-0.13
-0.13

29.82
29.88
29.91
29.96
30.00

10.00
30.00
50.00
80.00
94.80

9.70
30.00
50.20
80.40
95.20

29.90
30.00
30.00
30.10
30.10

-0.30
0.00
0.20
0.40
0.40

0.08
0.12
0.09
0.14
0.10

9.70
29.90
50.00
80.20
95.00

29.90
30.00
30.00
30.10
30.10

-0.30
-0.10
0.00
0.20
0.20

0.08
0.12
0.09
0.14
0.10

39.70
39.76
39.79
39.85
39.91

10.00
30.00
50.00
79.80
94.70

9.60
29.90
50.00
80.10
95.10

39.90
40.00
40.00
40.10
40.10

-0.40
-0.10
0.00
0.30
0.40

0.20
0.24
0.21
0.25
0.19

9.50
29.80
49.80
79.80
94.80

39.80
39.90
39.90
40.00
40.10

-0.50
-0.20
-0.20
0.00
0.10

0.10
0.14
0.11
0.15
0.19

49.57
49.63
49.68
49.76
49.82

10.00
29.90
49.90
79.80
94.80

9.40
29.80
50.00
80.00
95.30

49.80
49.80
49.90
50.00
50.10

-0.60
-0.10
0.10
0.20
0.50

0.23
0.17
0.22
0.24
0.28

9.30
29.60
49.60
79.50
95.00

49.70
49.80
49.80
50.00
50.00

-0.70
-0.30
-0.30
-0.30
0.20

0.13
0.17
0.12
0.24
0.18

69.42
69.47
69.56
69.71
69.85

10.00
29.90
49.90
79.80
94.60

9.00
29.90
50.00
79.90
95.20

68.80
69.80
69.90
70.10
70.20

-1.00
0.00
0.10
0.10
0.60

-0.62
0.33
0.34
0.39
0.35

8.90
29.50
49.40
79.10
94.60

69.60
69.60
69.70
69.90
70.10

-1.10
-0.40
-0.50
-0.70
0.00

0.18
0.13
0.14
0.19
0.25

The Rotronic Humidity Handbook

Page 54

Technical Information for Rotronic Products

Evaluation of Competitive Humidity Sensors
This section compares the performance of seven (7) commercial humidity sensor
systems as they were available from key manufacturers in 1997.
Testing procedures were defined by ZURICHSEE – LABOR, an independent researchlaboratory near Zurich, Switzerland. Results may differ from those published by the
manufacturers.
For questions regarding the study please contact Zürichsee-Labor Engineering Officefor Safety and Environment Bahnhofstrasse 5, CH-8820 Wädenswil – Switzerland.
Phone / Fax: +41-1-780 83 30.

Manufacturer /Color CodeModel of Sensor

ROTRONICROTRONIC

Hygromer C-94

VAISALA

Humicap 180

VAISALA

Humicap H

TESTO

600

E+E
PANAMETRIC
S

HC-1000

Hygromer DMS-100

Mini Cap II

Temperature Limits – Response Time – Reset Rate – Long Term Accuracy – Dew Point Stability

April 1998
Zürichsee – Labor
Engineering Office for Safety and Environment Bahnhofstrasse 5
CH-8820 Wädenswil – Switzerland
Phone / Fax: +41-1-780 83 30

Page 55

The Rotronic Humidity Handbook

Evaluation of Competitive Humidity Sensors

Temperature Limits
Most humidity sensors have a defined temperature range where their function is
guaranteed within limits of accuracy. If a humidity sensor is used beyond its
temperature limits, it may display erroneous values or get permanently damaged.
In the following comparison, the sensor ROTRONIC Hygromer C-94 had the widest
temperature limits:

The temperature limits of a sensor device may determine the application areas of theentire gauge consisting of sensor, probe and instrument. A wide temperature range isadvantageous also for accuracy within that range. All sensors tested had the highest
accuracy in the center of their temperature range. They were considerably less accurate
at their lower and upper temperature limits.

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Response TimeThe response time of a humidity sensor is the time it takes to respond to a changing setof humidity conditions, deviating from a standard 50% R.H.
In the comparison below, the sensor VAISALA Humicap 180 took 40 seconds to gofrom 50% R.H. to 70% R.H. The response time for 90% R.H. was 55 seconds. Thus,VAISALA Humicap 180 was the fastest of all evaluated sensors both, on the wet and on
the dry side.

• ROTRONIC Hygromer C.94

O VAISALA Humicap 180▲ ROTRONIC Hygrolyt DMS .100

♦ VAISALA Humicap H* PANAMETRICS Mini Cap ll

X E+E

HC-1000▼TESTO 600

A short response time is advantageous in process control, where it leads to higher
process linearity. In applications where large numbers of humidity measurements mustbe run in sequence, short response times help save time and cost.

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Evaluation of Competitive Humidity Sensors

Reset Rate
The reset rate determines the time (in hours) a humidity sensor takes to reset to 50%
R.H. after it was exposed to 95% R.H. for 24 hours. A drawback of most polymeric
hygroscopic materials used as dielectrics in capacitive humidity sensors is, that theyretain humidity longer than desirable. Thus, polymeric sensors hesitate to reset, andconsequently indicate higher values than they should, for quite long periods of time.
In the comparison below, the sensor ROTRONIC Hygrolyt DMS-100 had the shortest
reset rate. It took ½ hours to reset to 50...51% R.H., a factor 20 faster than any othersensor system.

• ROTRONIC Hygromer C.94

O VAISALA Humicap 180▲ ROTRONIC Hygrolyt DMS .100

♦ VAISALA Humicap H* PANAMETRICS Mini Cap ll

X E+E

HC-1000▼TESTO 600

A quick reset rate is a determining factor in rough climate, when humidity is high andmonitoring of fog, dew point, etc. must be done in short intervals. In non-meteo
applications such as food processing or water adsorption, the reset rate is a key factor
for process control.
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Technical Information for Rotronic ProductsLong Term Accuracy
Long term accuracy differs, of course, from application to application. Under mild
conditions, all sensors may have adequate long term accuracy. This test studied theperformance under adverse conditions, running 3-hour cycles alternating as follows:“high” cycle = +90 °C and 90% R.H. · “low” cycle = –20 °C and 5% R.H. After every 100
cycles, the deviation from the set point at 50% R.H. was recorded.
In the comparison below, the sensor ROTRONIC Hygromer C-94 had the highest longterm accuracy, i.e. deviated least from the set point at any given number of cycles:• ROTRONIC Hygromer C.94

O VAISALA Humicap 180▲ ROTRONIC Hygrolyt DMS .100

♦ VAISALA Humicap H* PANAMETRICS Mini Cap ll

X E+E

HC-1000▼TESTO 600

Long term accuracy determines the reliability of humidity measurements under adverse
conditions. It is equally important if equipment is in remote locations, is difficult toaccess or if service intervals are long.

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Evaluation of Competitive Humidity Sensors

Dew Point Stability
All tested sensors disliked dew point conditions. Because of formation of water dropletson the sensor surface, unreliable readings resulted. Sensors with small surface areas
were particularly sensitive.
In the comparison below, the sensor ROTRONIC C-94 had, relatively, the best dew
point stability:• ROTRONIC Hygromer C.94

O VAISALA Humicap 180▲ ROTRONIC Hygrolyt DMS .100

♦ VAISALA Humicap H* PANAMETRICS Mini Cap ll

X E+E

HC-1000▼TESTO 600

The rate at which a humidity sensor recovers from dew conditions is an equallyimportant consideration in dew point stability. Some sensor electronics may getpermanently damaged (shorted) from dewing. The sensor devices per se do recover,
however, at rates similar to those shown under ‘reset rate’.

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Rotronic C-94 Response Time

Rotronic C-94 Sensor response time
90
80
70
50
40
30
20
10
0

0

0

28

30

0
20

26

0
18

0

0
16

24

0
14

0

0
12

22

0
10

80

60

40

20

0

0
-2
0

% RH

60

Time in Seconds
without filter

wire filter

teflon filter

Response Time in Seconds (1 meter per second airflow)

Page 61

ChangeC-94 Without
Filtert 63
t 90<15 sec<40 sec

C-94 With
Wire Mesh
Filter<20 sec<60 sec

C-94 With
Teflon Filter<20 sec<70 sec

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Evaluation of Competitive Humidity Sensors

Long Term Performance of the HygroClip S and C-94 Sensor

1.1 Long term performance Hygroclip S
Long term performance Hygroclip S with sensor C-94
Conditions: about 23°C and 30 - 60 %RH

Humidity (%rh)

Hygroclip 1

Hygroclip 2

100
90
80
70
60
50
40
30
0

12

24

36

48

60

Month

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Technical Information for Rotronic Products

1.2 Long term performance Hygroclip S
Long term performance Sensor C-94 at 85°C 90 %rh

Humidity (%rh)

probe 1probe 2

95
94
93
92
91
90
89
88
87
86
85
0

20

40

60

80

100

120

140

160

140

160

Time (hours)

1.3 Long term performance Hygroclip S

Long term performance Sensor C-94 at 80°C 95 %rh

Humidity (%rh)

probe 1probe 2

100
99
98
97
96
95
94
93
92
91
90
0

20

40

60

80

100

120

Time (days)

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2. Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point -40°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

80

90

100

80

90

100

Humidity (%rh)

2.1 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point -30°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

Humidity (%rh)

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2.2 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point -20°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

80

90

100

80

90

100

Humidity (%rh)

2.3 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point -10°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

Humidity (%rh)

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2.4 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point 0°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

80

90

100

80

90

100

Humidity (%rh)

2.5 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point +23°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

Humidity (%rh)

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Technical Information for Rotronic Products

2.6 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point +50°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

80

90

100

80

90

100

Humidity (%rh)

2.7 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point +70°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

Humidity (%rh)

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2.8 Performance Hygroclip IC
Hygroclip IC-1 : Humidity deviation from set point +90°C

Deviation from set point (%rh)

Probe 1

Probe 2

Probe 3

Probe 4

3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
0

10

20

30

40

50

60

70

80

90

100

Humidity (%rh)

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Application Stories andTales

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Last Long and Prosper (A Water Activity Tale)

Application Stories and Tales_____________________________________________________________________

Last Long and Prosper (A water activity tale)
By: B. Auerswald
Food Quality Magazine, March/April 2000
(Copyright Carpe Diem Communications, Inc. Reprinted with permission)

Consumer demands and the growth of widespread distribution channels are driving food
manufacturers to constantly devise ways to ensure product stability throughout
extended shelf lives. Temperature and humidity are the key factors that accelerate
physical and chemical changes in foods and thus bring about the end of shelf life.
Manufacturing companies and their ingredient suppliers are increasing their testing
regimens for these factors earlier in the product development cycle in order to anticipate
and ward off storage and distribution conditions that can comprise product.
In an industry where competition is so fierce that a new food product might not make itto the store shelves, let alone into consumers’ homes, food scientist and productdevelopers have to carefully consider a number of attributes deemed desirable by the
consumer. These attributes must work in concert and not compromise the quality orsafety of the product. Further, virtually all organoleptic properties will change over time,making stability and shelf-life testing one of the most important tests conducted by food
manufacturers. These companies need to ensure that when a product is consumed,
say even six months after its manufacture, it is as palatable as the day it was made.
The underlying concept of any effort to extend shelf life is preventing or delaying the
growth of spoilage microorganisms or the onset of chemical change. Along withmicrobial activity, there are a wide range of food deterioration mechanisms, including
enzymatic changes, such as browning, pigment loss, vitamin degradation, chemicalchanges due to packaging, and flavor and aroma changes. These can all contribute insome way to making a product unappetizing to the consumer. Some of these can bealleviated or slowed by techniques such as the addition of organic acids, the use ofadvanced packaging materials or by modifying the environment inside the package.
Perhaps the two factors that have the most profound impact on product shelf life aretemperature and humidity. Higher temperatures and humidity are virtually always
harmful across the spectrum of food products. But it is often more than just a matter oflowering temperatures or reducing humidity; the relationship between these two
conditions is interdependent and must be carefully controlled. For example, if a
product, say a chocolate covered pretzel, is kept in 90% relative humidity (RH), then it
will become stale. By the same token, if it is stored at 95°F, then the chocolate willundoubtedly melt. When the two conditions work together, usually in the presence oflight, the result oxidation can complicate the situation even more.
“For oxidation to occur, you need three primary things: light, moisture and heat,” says
Julie Snarski, Manager of Application and Product Development for David Michael andCO., a flavor manufacturer headquartered in Philadelphia. “If flavors start oxidizing,
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Application Stories and Tales

we’re in trouble. Say you have an orange cookie that you place in a pouch and store ina hot box. If the seal on the pouch is not right and the moisture is too high, and since
you’ve already added the heat, you now have two things that cause oxidation. You’rewell on your way to a cookie that tastes like baby aspirin.”
Ingredients and Interactions
The product development team at David Michael is well aware of oxidation and other ill
effects humidity and temperature can cause, and they test for and guard against themdiligently, whether during prototype design or product development. While the company
does not manufacture flavors for retail sale, it does develop products for companies
using the flavors it manufactures.
“We act as the R&D lab for many of our clients, as is the case with many flavor
companies nowadays,” Snarski says. “At times we develop all of the prototypes and the
product, and other times our customers say, ‘This is our cookie and we need a filling.’”
An important specification for many of these companies is water activity (aw), which isrelated to RH and is the ratio of the vapor pressure of water in equilibrium with a food tothe saturation vapor pressure of water at the same temperature. Aw describes thedegree to which the water is “bound” in the food and hence its availability to act as asolvent and participate in chemical/biochemical reactions and growth of
microorganisms.
“The aw level that we are looking for really depends on the product we’re testing,”
Snarski says, “but we usually want levels in the lower end because of the nature of the
products we test, such as candies, baked foods, fillings, frostings. Protein bars andsnack foods.” For example, a company might approach David Michael with its line ofprotein bars and ask them to develop bits for a new type of bar. The aw levels of the bit
and the bar must be tested. If there’s a coating then test have to be done to see if it
adds moisture and that the unequal moisture levels do not balance out after shipment tostores.
Aw testing is performed while the productis still on the small batch scale, usuallyless than 30 lbs., to allow for formulation
changes, if necessary, Snarski says.
“We use the information gathered fromthe aw testing to take a look at how we
can manipulate the formulas,” she says.
“If the aw level is too high, we can use
gum, starch, glycerin or maybe just add alittle sugars to bind the water, depending on the product. Sometimes the aw readings
will be part of the flavor spec we give to a client, since many times we develop products
for intermediate companies and they need the information for further development or for
use in the QC.”

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Last Long and Prosper (A Water Activity Tale)In the lab, Snarski uses the AwQuickwater activity meter, from Rotronic in
Huntington, NY, which can measureliquids, solids and powders with anaccuracy of ±0.02 aw (aw is measured
over the range 0.0 to 1.0). Price was thedeciding factor for Snarski, throughturnaround time and simplicity of use
were also considered when she began
looking for an aw meter about a year ago.
“We chose Rotronic instruments
because I was familiar with theirproducts and I knew it was easy to use,”
she says. “Usually the analysis time is about five minutes, which is important because
our people handle 10 to 12 products a month and they don’t have the time to wait forresults.”
Factors Affecting Stability
While moisture and humidity are recognized degradants to many types of foods and will
impair shelf life, temperature can have a more widespread and deleterious effect onstability if not properly controlled. Observers say it is far more common for companies
to assess the effects of out-of-range temperatures on their products than the effects ofwater activity. “Smaller companies tend not to test for aw unfortunately, usually because
it’s not understood very well,” says Theodore Labuza, PhD. Professor of Food Scienceand Technology at the University of Minnesota, St. Paul. “This is especially so because
the concept of aw is not taught very well in most undergraduate courses and most small
companies do not have Ph.D working for them. The larger companies do a much betterjob of understanding and testing for aw.
“In the near future there should be more people who understand aw and actually test forit,” says Labuza, who has done extensive research on water activity and shelf-life
testing, and visits large food companies to update their employees on what is occurringin the realm of water activity. “In the 1950’s the big concern with aw was microbes andin the 1960’s it was the stability of dehydrated foods. In the 1980’s and 90’s many
people said that aw is still a very important principle and that combining gas
transmission with aw will create a more stable analysis.
The shelf life of any food is determined by a product’s least stable ingredient. During
shelf-life of any food is determined by a product’s least stable ingredient. During shelflife studies, this limiting attribute is sampled from the product and analyzed at set
intervals. This analysis yields a curve of functionality versus storage time, where thepotency or integrity of the component is shown to degrade over time. Such information
is used to set an end of life date for the product, or to allow product development
scientist to make appropriate adjustments of the target component(s) to stay within
specification up to the end of the product’s life.

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Stimulating Storage Conditions
Excessive temperatures will accelerate a range of chemical and biochemical reactions
and thus bring on the end of shelf life. At David Michael, the effects of temperature are
analyzed in both real-time and accelerated conditions, using a large incubator for
accelerated storage, as well as a refrigerator for real-time studies. Typically, room
temperatures samples are placed in their packages and stored for set periods of time,Snarski says. The timeframe for testing at David Michael depends on the customer
specifications or on the type of product. Usually, the company performs stability test forsix to 12 months, but has completed tests that lasted 18 months due to customer
specifications.
“One type of testing we do is what we call our ‘Texas warehouse test,’ where webasically set up the test for the same conditions the product would encounter in thattype of climate: lots of heat and humidity,” Snarski says. “Since it often happens that a
product will be manufactured and shipped to all types of climates and conditions, it isvery important we test for extreme conditions because it affects the acceptability of the
product as well as the packaging.
“Testing for temperature is definitely critical, but as with everything else, it depends on
the product,” she continues. “Take hard candy for example, if the candy has a low aw
as it should and is packaged well, temperature really doesn’t play a role. As long as
there is no humidity to make the candy stick together, the temperature won’t make itmelt – it’s already been cooked to about 300°F. But if you hold cookies or mayonnaise
at 150°F, you will definitely have issues with oxidation and even rancidity. That’s where
the Texas warehouse test comes in.”Since temperature ranges are product specific the temperature range and the type of
testing performed is dependent on the sample, says Mike Grob, Lab Manager
Minnesota Valley Testing Laboratory in New Ulm, MN which performs shelf life testing
mostly on raw meats and perishable fruits and vegetables. “If you have a raw meatproduct that is not brined or vacuum-packed and you store it at ambient temperature it
will have a very short life,” he says. “It’s almost unrealistic to test meat at ambient oreven accelerated temperatures because it goes rancid so fast. However, products likefruits, vegetables and some cheeses can withstand these temperatures.

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Speed it Up
While product stability is tested throughout the development process and extended withthe application of various processing techniques, product integrity is most subject tocompromise in the storage and distribution system. Food companies commonly use
elevated temperatures to conduct accelerated shelf life testing since it is generally theleast complicated type of test method available and can often relate to actual
temperature variations encountered during product distribution and storage.
Accelerated shelf life testing is also often driven by marketing departments which arerequiring product with extended shelf lives of a year or more to be developed in shortertime frames of perhaps only a few months. In order to meet the timetable, a means ofestimating the product’s end of shelf life must be utilized.
Generally, an initial step in shelf life testing is to identify potential modes of deteriorationin the product based on an assessment of the factors that will influence product stability,
such as product composition, packaging and environmental factors. Potential modes ofdegradation might include chemical changes, physical separation, color or flavorchange, or nutrient loss. It is then important for the food technologist to select test
methods that can accurately measure the degradative changes so that useful data isgathered.
Grob and his colleagues at MVTL conduct accelerated shelf life testing, in which
storage temperatures are raised so that aging processes are accelerated. For example,
storage at 30 to 33°C can give a two-to three-fold increase for many flavor changes; inparticular, while storage at 35 to 40°C can accelerate oil or water separation four-fold
and four to six weeks of storage at 55°C can cause pickle and sauce products tobecome unstable. Storage defects in frozen projects can be accelerated by storage at
higher than normal temperatures, thus more rapid changes will occur at 18°C comparedto the normal long term storage temperature of below -25°C, and still faster changes will
occur at 10°C. Certain forms of deterioration, such as crystal growth and freezer burn,will also be accelerated if the storage temperature is made to fluctuate while the foodstill remains frozen.
For both real time and accelerated testing, MVTL’s clients select the type of testing andthe interval the samples are tested at. “Usually, we will be contacted by a plant
manager, the head of the QC department or even a lab manager to perform the testingfor their company, depending on their needs, Grob says. “We provide them with thedates, times-say one day, five days, two months-and temperatures we tested at, as wellas the results of aerobic plate count or coli form testes that we may have performed.
The results we present help our clients in a number of ways, including determining shelf
life dates for the product.

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Precautions and Possibilities
Some note that many people conducting accelerated shelf life studies don’t fully utilize
the data they collect, or don’t collect the right kind of data. Different foods and theirchemical components will react differently when subjected to different storage
temperatures, so a universal acceleration factor cannot be used for all foods at any one
storage temperature. Also some reactions that would not normally occur at standard
distribution and storage conditions may be initiated at higher temperatures, resulting ininaccurate predictions for the shelf life of the product.
One problem that can occur when dealing with shelf life is the tendency to project thetesting results and stability of one product onto another, especially when working withaccelerated testing. Nancy Tregunno, applied Research Scientist at the Guelph Foodtechnology Centre in Guelph, Ontario, has encountered this scenario. “One rule ofthumb for shelf stable products is a two to three times acceleration at 33°C,” she says.
“Sometimes companies know what their acceleration factor is for a product line becauseof past verification studies. However, if significant changes are made to a formulation,
or a new product is being studied, testing may be required to determine a new
acceleration factor.” This requires storing the products at both ambient and abusive
conditions, and dividing real time shelf life by that obtained at high temperature/highhumidity to get an acceleration factor; that is 12 months real time divided by four months
accelerated equals three times acceleration factor.
If products are very similar in nature, perhaps only a few ingredients are changed that
do not affect the stability of the product, then it is likely that the acceleration factor of thefirst product can be applied to the second one, Tregunno says. But if ingredient areadded that make it more complicated, then the product needs to be re-evaluated for theacceleration factor.
At GFTC, which conducts contract research for food and packaging companies, shelf
life testing is performed for manufacturers of a range of products, such as beverages,sauces and dressings, dry snack foods and condiments. High temperature andhumidity are used where appropriate, but often it is oxidation that is expected to limit a
product’s shelf life.
Another problem that can arise during shelf life testing, especially when working withunrealistically high temperatures, is a change in chemical pathways, Tregunno says,
whereby two compounds react to form another unexpected compound. To combat this,
GFTC often sues high oxygen levels instead of high temperature to perform testing,especially when working with new packaging. “Often, our customers want to know what
the shelf life of an existing product will be in new packaging, for example, whenchanging from glass to plastic which is increasingly common,” Tregunno says. “We put
the samples in a high-oxygen environment, usually around 85%. That gives us aboutfour times the acceleration factor. Comparing the samples to a control allows us to
identify a point in time when the sample will be considered different or unacceptable.”

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Last Long and Prosper (A Water Activity Tale)

Whether testing a product in real time or at high oxygen acceleration, the trend istoward maintaining the safety stability and quality of product over longer periods of time,often with reduced usage of preservatives. “The need to extend shelf lives without
using preservative definitely presents a challenge, but with the use of sound science,
safe an effective processes can be developed, “Tregunno says. “If oxidation is
occurring, we can add anti-oxidants and if necessary, we can add certain gums forstability. When we are dealing with different considerations and stabilizers, and evenvarious conditions such as temperature, we work with different modifications of theformulation or recipe. There is mostly a scientific basis when it comes to the formulationof food, but there is definitely the element of art.”

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Paper & Climate
Introduction
Modern machines for printing paper or cardboard,coating paper with aluminum and other types of
unique applications are both fast and sophisticated.
They are also quite sensitive, not only to theproperties of the product to be transformed, but also
to any variation of some physical phenomena. Oneof the parameters long recognized as influencing
the properties of paper and cardboard has beenmoisture content. Equilibrium Relative Humidity is,
together with the relative humidity of storage and work areas, responsible for any
change which may occur in the moisture content of the product.
A recent study has demonstrated in the importance of Equilibrium Relative Humidity(%ERH), and some guidelines have been proposed. The narrow tolerances which arerecommended exceed the capabilities of conventional hygrometers. A new generationof electronic hygrometers has been developed to meet these requirements.
Influence of Moisture Content on Paper
Moisture content influences a great number of physical properties of paper. The weight
per surface unit, thickness and volume increase with moisture content. Changes inmoisture content result in swelling or shrinking of paper fibers, while humidity cycles
result impermanent dimensional changes as internal tensions in paper are released.
Similarly, mechanical properties of paper, as well as printing properties, are influenced
by the moisture content. Moisture content is therefore an importance production
parameter which is normally monitored and controlled directly on paper machines.
However, this production parameter has relatively little practical significance for paper
converting industries. As shown in the following paragraphs, many problems can be
avoided if paper has the correct % ERH and if humidity does not differ from the ambient
humidity. Moisture content must, of course, conform to the specified values; however,moisture content cannot be used to define the climatic conditions necessary to insure
good conditions during paper printing.
Influence of Equilibrium Relative Humidity on Paper
Any difference which may exist between the %ERH of paper and the room relative
humidity (%RH), results in changes in the moisture content of paper. These changes
must be avoided or else problems will occur during the paper conversion or printing
process. It is difficult to eliminate any difference between the ambient % RH and the%ERH, however, controls or limits can be established. A % ERH of 50% is ideal forPage 77

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Paper & Climate

paper since any changes, say from 40-60% will have little effect on the moisture
content, (for cardboard converters 80% may be considered ideal). It has been
determined that a large difference between a nominal 50% in paper and ambient air willcause a number of problems.
Static Electricity
From time to time, screen printers will experience difficulties due to static electricity
phenomena, such as paper sheets sticking together. This happens mostly when the air
is too dry and the paper is too dry. It has been found that when both the paper and air
are in the 40-45% range this problem seldom occurs.
Dust Problems in Presses
Dry paper, more than moist, tends to generate dust. Sever dust problems in offset
printing machines are due to the fact that the brittle fibers at the surface of the dry pager
are easily detached. The result is the appearance of a dust layer on intermediary rollscausing poor printing.
Dimensional Changes of Paper during Printing
Vegetable fibers, which constitute the vase of paper absorb or desorbs water dependingon the ambient relative humidity value. This water exchange results I n a swelling or
shrinking of paper fibers, which affects the diameter of these fibers run parallel to therunning direction of the paper machine. Accordingly, dimensional changes which are
the results of moisture variations are more important along the axis that is perpendicular
to the running direction of the paper machine, than along the axis parallel to it. At
approximately 50% ERH a humidity change of 10% ERH results in a change of typically
0.1-0.2% in the length of the paper. Such a humidity difference gives a dimensionalvariation of 1 to 2mm on a 1x1 meter paper and therefore probabilities of poor,
inaccurate printing due to positioning problems are high.
Paper running through an offset press usually gains water as it is moistened in theprocess. The change in the moisture content depends not only on the % ERH of thepaper (40-60%), but also on the ambient %RH. An institute which has made a study ofproperties of paper and printing in Europe ran a test on two different offset presses and,based on results, have determined that the difference between % RH should not be
more than 10%. Within this range the dimensional changes will remain at a constantlevel because the moisture of the paper will not change by more than 1%.
The same indication has been observed when using other types of presses, such as inscreen printing, where the paper is not moistened and tends to lose water as it
experiences heat.

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It must be pointed out that all difficulties experienced with poor paper positioning are notentirely due to incorrect humidities.
Deformations of Paper Due to Humidity
Paper in stacks or rolls shows deformation if too much moisture is exchanged with thesurrounding air through the edges of the stack or roll. This is due to the uneven
distribution of this moisture as it is exchanged with the ambient air during storage ortransport. Water-vapor-tight packaging protects the paper and it should not be removed
without first checking % ERH of paper and % RH in the ambient environment.
Differences up to ±5% RH will not cause problems, while a difference of 8-10% RH now
becomes critical.
When difficulties are expected due to a large difference between % ERH and % RH
then certain measures should be taken either to adjust the %RH to a correct value, as
by air conditioning, or to progressively condition the paper to the ambient RH. In thecase of paper stacks, individual sheets may be eventually conditioned by full exposure.
It has often been commented
that the printer or paper
converter does not have the time
to condition the paper to theroom environments. The paper
must come in and get out. But,
is this really the way? Paper
stored at a mill or distributor is at
a specific level, then duringtransport it goes throughdifferent climatic changes.
When the printer gets the paper
he assumes it is exactly as it
was when leaving the paper mill.
With the quality control
procedures of the mill, very
careful attention is paid to the correct moisture content of the paper that is ordered. In
many mills the %ERH is also carefully monitored before the protective wrapping isplaced on the roll or stack. However, it is not possible to have final control until itreaches the printer. For this reason, many mills will have their technical service people
go out to the printer and try to assist him in determining where the problem exists, i.e.,
paper, room, storage area, etc. Many technical reps also have a sword probe or similar
unit which allows them to test the paper and the room for differences in humidities.
Obviously, if it is a condition to be checked by the technical a representative, it also is apoint which must be considered by the printer.
Deformation of Paper Due to Temperature

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Paper & Climate

Temperature exerts a minimal influence on paper; however, any large temperature
difference between the paper an the ambient air will have almost the same results as ahumidity difference. This is due to the fact the % RH in the air layer in the immediatesurroundings of the paper stack or roll is modified by the paper temperature. Assuming
an ambient air of approximately 50% RH, a temperature difference of ±1°C will result ina humidity variation of ±3% RH. Thus, it can be seen that when temperature
differences approach 3-4°C, problems can occur.
Once again we have the differentiation of moisture content and % ERH. The
temperature will have little effect on the moisture content, even at values which are
20°C, yet the humidity changes at lower values and problems occur. Perhaps theprinter or paper converter doe not take this into consideration either.
Large temperature differences between paper and storage or work areas easily occur inwinter or summer due to transportation of the product. Without air conditioning, thetemperature variation between storage and work areas may be 10-20°C on a summerday. A stack or roll of paper can adapt to this variation, but very slowly. At 45% RH, adifference of 5°C between the paper and air creates a % RH of 60%, thus exceeding therecommendations of 10% without even getting to the press!
Paper should be kept in its vapor-tight packaging as long as a temperature difference
exists. An equilibrium time of 24 hours for each 10°C temperature difference and cubic
meter of paper is recommended.
Curling of Paper Sheets
Paper fibers does not all run
exactly in the same direction
across the thickness of a sheetof paper. Very large moisturevariations will result in unequal
dimensional changes on bothsides of the paper sheet,
therefore curling occurs. Thisis more prominent problem
with coated stock, since bothsides of the paper are notsimilar. When working withsuch paper, minimal effects
can occur with humidity
variations of less than 10%
RH.
Drying Time of Printing Inks

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High values of %ERH as well as low temperatures result I n long drying times after
printing. Experiments on offset presses have shown that a % ERH of 60% and atemperature of 20°C are practical limits for acceptable drying times.
Recommended Values of % ERH
There is no optimum value of %ERH which would be valid for all paper and cardboard
converts and printers. The printing industry normally requires % ERH in the range of
50-60%, while cardboard converters require an ERH of about 80% which allows them toform their product easier. The packaging industry, on the other hand, will require
another value of ERH.
Since paper and cardboard mills cannot deliver their products at an exact ERH, a
compromise must be established. A nominal value of 52% ERH for paper and 80%
ERH for cardboard seem to be the general rule to live with.
Recommended Tolerance of % ERH
Again we have to make a compromise. Here a ±6°RH seems to be accepted by milland user. Also this value is recommended by the European institute previously
mentioned.
Summary
FOGRA (The German Research Institute for Printing and Reproduction Techniques),
from which most of these figures and facts have been obtained, has done testes on
many machines and instruments. Based on these tests their recommendations havebeen developed.
Now that the numbers have been established, how do the printer and paper converter
put them to use? Obviously, suitable instruments must be made available to performthese measurements and at the same time not cost larger amounts of investment. The
unit must be easily handled and should provide quick measurements so that the user
will not be waiting for hours to determine suitability of the roll or stack.
The old fashioned saber probe was too difficult to handle, required calibration often and
was also very slow in response. Modern technology has created a new probe which is
inexpensive, light in weight, provides quick and accurate readings and is simple to use.

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Automotive Test Chamber Features Rotronic Transmitters

Automotive Test Chamber Features Rotronic-Transmitters
Rotronic Humidity News - Issue: 1/2000
Performance Surpasses Expectation!
Clive Hurley Environmental Engineering is one of the world’s leading manufacturers ofenvironmental test chambers. A recent installation at the UK’s leading independent
automotive development center, LTC, featured a Rotronic I-2000 industrial humidity andtemperature transmitter.
Traditionally, Clive Hurley’s has employed
wet an dry bulb psychometery for humidity
Measurement duties, due to the wide
operating range of LTC chamber, aRotronic I-2000 transmitter was installed.
Andrew Hurley, director commented,“Obviously above 100°C and below 0°C,
wet and dry bulb humidity measurement is
not practical, and our customer needed toknow the humidity value over thechambers full working range. The Rotronic
I-2000 offered the widest available
temperature range so it naturally became our preferred choice. Once installed, we werereally impressed with the accuracy stability and response times it provided.”
The LTC test chamber is designed to cope with vehicles up to the size of a truck tractor
unit, with internal dimensions of 3.3 x 4.3 x 6.3 length and a load capacity of 8 tons!
The temperature range is –40…+120°C, with a humidity capability of up to 99% RH over
the temperature range of 10…70°C. In addition, full solar capabilities are incorporated
so that an extensive range of real world conditions can be reproduced. One company
who has already made use of the LTC chamber is
sports car manufacturer TVR.
The Rotronic I-2000 transmitters are available in awide range of configurations to suit almost any
application. Maximum measurement ranges for the
I-2000 are 0…100% RH and 50…+200°C, with
operational exposure to –75°C not affecting thesensors.

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Oresund Bridge Maintenance Cost SlashedRotronic Humidity News - Issue: 1/2000
Rotronic humidity instruments haveslashed corrosion protection costs
on one of Europe’s largest civilengineering projects.
The Oresund Bridge will physicallylink Denmark and Sweden for the
first time. Most of the major
construction has not been
completed. The bridge’s weightbearing support structure,comprised of steel girders, willfeature a corrosion protection
system that will be monitored by
Rotronic humidity instruments.
With an internal volume of over
120,000 cubic meters cost effective corrosion protection was critical within the hollow
girders. Nine Munters’ air dryers have been installed to keep relative humidity below alevel where corrosion of the steel can occur. The dryers are controlled by a series of
Rotronic MP400 probes, whose wide operating range and excellent long-term stability
are essential for the correct operation of the system.
Stig Fristad, project leader at Munters, says, “Experience from a similar project(Hogakusten Bridge in Sweden) showed that over several years the cost of running the
air dryers is approximately 1% of the cost of traditional corrosion protection schemes.
The accuracy and stability of the Rotronic sensors is an important factor in keeping
humidity levels, and therefore energy consumption under control.
There are in total 18 MP400 installed in this application, 16 are used for the control of
the air dryers, 2 are used purely for monitoring purposes, the measurement data can beviewed by both the Danish and Swedish authorities.

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Jens Olsen’s Worldwatch in Copenhagen

Jens Olsens’ Worldwatch in Copenhagen
Rotronic Humidity News - Issue: 1/2000
Jens Olsens’ Worldwatch on Copenhagen’s city hall is known by most Danish people
and internationally as a unique astrological clock. The clock consists of 15,448 parts in
12 mechanisms. Apart from the time around the world, the clock shows the time ofeach sun rise and sun set, the year, the weekday, the date, the month, the sun & moon
rotations, and the planets movements.
Renovation NecessaryJens Olsens’ Worldwatch was started in 1955
and was functional until 1995, when the clock
was disassembled. It was stated that themechanisms had become inaccurate andrenovations were necessary. The display casethat held the clock partially protects the works
against dirt and environmental conditions. But it
was obvious that this protection was inadequate.
Several of the mechanisms were affected bycorrosion, which prevented correctly operation.
After two years of intense work, renovations were
finished in 1997.
Munters Dehumidifier Ensures Conditions
It was examined how you could best protect thisvaluable work from the air’s destructive effects.
Since the main problem was corrosion, caused byhigh humidity, the choice was dry air preservationby the means of an absorption dehumidifier from
Munters. A dehumidifier type ML 180 was built inwith the room’s ventilation system to ensure theair condition in the showcase is kept constant.
The showcase receives a constant 25 m³/h
volume of air at 18°C and a relative humidity of
40% RH. The dehumidifier is controlled with theventilation system through a CTS system. To prevent air from the outside from entering
the showcase an elevated pressure is maintained in the showcase. The showcase isequipped with Rotronic humidity and temperature sensors in each side of the clock box.
By keeping the relative humidity at only 40% RH corrosion is prevented. The clocks
stable operation after the renovation is expected to continue for many years since thedelicate mechanism is no longer affected by the surrounding air.

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Munters Leading Dry Air Supplier
Munters is a leading international supplier of dry
air solutions. They have delivered dehumidifiersystems for many similar conservation purposes
and are a well known name within and among
others and museums around the world. Manystorage rooms, depots and warehouses today are
equipped with Munters absorption dehumidifiers.
At low temperatures these absorption
dehumidifiers assure good and dry storage
conditions for valuable items. Munters in addition
supplies to the process industry where production
environments are dependent on a constant andlow humidity year around.

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Cool Application for Rotronic Humidity Technology

Cool Application for Rotronic Humidity Technology
Rotronic Humidity News - Issue: 2/2000
The CTS Company is concerned with the design, manufacture and the distribution ofhigh quality devices and systems for environmental simulation, as well as refrigeration
and air conditioning. Under the management of three partners with many years ofexperience in environmental simulation and climate technology, CTS employs around50 staff and continues to expand, and now operates world wide with a reputation forhigh quality products.
The CTS Climatic C-20-200/S provides very high accuracy over a wide temperature
range and uses a Rotronic I-2000 Industrial Humidity and Temperature transmitter,
which has an operational range of 0 to 100%RH and –50 to +200°C.
The system’s optimized CTS control unit, combined with precise measurements
provided by the Rotronic I-2000, provides a very large performance range which does
not stop at the simulation of polar climate. “Previously, that was a problem.”, says Sales
Director, Dipl. Ing Helmut Maute, who further states, “In the range below the freezing
point, many measuring methods are completely useless, or very inaccurate. Our
customers include, amongst others, well known manufacturers in the automobile
industry, where reliable and exact measured values offer the entire range are especiallyindispensable. With the Rotronic industrial transmitter (I-2000) we have found a productmatching our high demands for measurement accuracy and long term stability. The I2000 perfectly covers the working range of our climatic cabinets and has additional
reserves.”
The climatic cabinet C-20/200/S has a temperature range of –20°C to +120°C and ahumidity range of 10% to 98% RH. Thus all of the world’s climate zones are fully
covered taking account of the seasons and can also be simulated over long periods.

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Abbey Library St. Gall
Rotronic Humidity News - Issue: 2/2000
The Abbey Library of St. Gall is the oldest
library in Switzerland and one of the oldest
and most important monastic libraries in
the world. Constant humidity andtemperature conditions are essential forthe storage of books. Thanks to its
reliability and its easy application the
Abbey Library St. Gall uses the HygroLog
Humidity Temperature Data Logger of
Rotronic. HygroLog stores humidity andtemperature values in user definedintervals, data is easily downloaded to a
PC via a RS-232 interface.
Its unique collection of books reveals thedevelopment of European culture anddocuments the cultural achievements ofthe monastery of St. Gall from the eight-century to the dissolution of the abbey in 1805.
Numerous works, fundamental to the history of European thought,
have been transcribed in these manuscripts and are wellpreserved within the library. The Abbey Library along with theentire abbey precinct of St. Gall was included in the UNESCO listof global cultural heritage site in 1983. At the core of the library’s
collection is the largely indigenous corpus of Carolingian andOttonian manuscripts from the eight to the eleventh centuries.
Today the Abbey Library is partof the Catholic Administration of
the State of St. Gallen. A
modern scholars library,specializing in the medieval
period, it is also one of the leading museums in
Switzerland. Every year some 100,000 visitors fromall over the world view the exhibition in the renowned
baroque hall; considered one of the most beautiful
library rooms in the world.

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Rotronic Conquers the Jungfrauhoch

Rotronic Conquers the Jungfrauhoch
Rotronic Humidity News - Issue: 2/2000
The Jungfrauhoch in
Switzerland is one of
the most popular andattractive excursion
destinations andAlpine vantage points.
At the beginning of the20th Century, theJungfraubahn project– a railway between
the famous
Wengernalp and theJungfrauhoch at 3454
m (11’333 ft) above
sea level, was finishedand officially opened
to the public. Thus it became possible to install a scientific laboratory, where since1931 astronomers, astrophysicists, geologist, meteorologists, hydrologists andphysicians work under the high alpine conditions in very clean air. Avalanche research,general weather information, as well as other data has been collected here. There’s
even a solar laboratory.
Instruments for measuring relative humidity andtemperature must be able to withstand the harshest
imaginable environmental conditions: direct sun
and high UV radiation in the daytime, fierce andbitter cold at night and during winter,
thunderstorms, blizzards and heavy snow, and last
but not least very high wind speeds.
The reliability of the Rotronic sensors installed on
Jungfrauhoch is assured, with the exception ofoccasional calibration (recommended once a year),
there is almost no maintenance required.

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The Holy Shroud - The Wounds of the Passion
Rotronic Humidity News - Issue: 2/2000
A century ago the Shroud generated excitement when it was photographed in 1898 forthe first time by Secondo Pia. The negative of that photograph revealed in detail andwith even greater clarity than the positive image all the wounds that the shroudpreserved. How was the image of the Shroud formed? Science has not yet come up
with any plausible explanations.
Since 1998 the Shroud has laid horizontally on a sliding support inside a ballistic steel
shrine with safety glass. Inside the shrine the inert atmosphere (Argon with 0.5%
oxygen) prevents the generation of anaerobic organisms. What is important is that theflax fibers are kept under the same conditions, which they have been for centuries. The
humidity and temperature is measured with the I-1000 device by Rotronic. Humidity
values are controlled between 50…60% RH at 20°C.
The man whose image appears on the
Shroud was crucified in the same way
as Jesus and details of the wounds
which appear on the Shroud
correspond to those described in theGospels. The Shroud is an image to belooked at and contemplated.
For believers it is an “Icon of the
Passion” as defined by Pope Paul VI.
The wounds of the Passion of Jesus
are the reason for so much interest in
the shroud, and explained its
veneration since ancient times.
A Difficult Piece
The Shroud is a linen sheet, 4.36 meters long by 1.10 meters wide. Two dark parallellines with the white triangles, burn marks (from the Chambery fire in 1532) and theimprint of an image of the front and back of a man who died from crucifixion are clearlyvisible.
The Public Shroud
The shroud is shown only on special occasions. From 12th to 22nd October 2000, theShroud can be seen in Turin. It is the longest exhibition time for the shroud in history,
and only the sixth time it has been displayed in the last 100 years.

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Measuring Water Activity at the “Millennium Seed Bank”

Measuring Water Activity at the “Millennium Seed Bank”
By: Chris Birch
Rotronic Humidity News - Issue: 1/2001
The Royal Botanic Gardens are using a range of Rotronic Instruments to monitor thefree or available moisture (water activity) of seeds stored at the Millennium Seed Bank,
Wakehurst Place in the South of England.
Sponsored by theMillennium Commission,
Orange PLC and theWellcome trust, theMillennium Seed Bank is an
important conservation andresearch facility storing live
seeds in suspended
animation for possibly
thousands of years, acting
as a safe depository for theworld’s wild plant species.
Due to the ever increasing
spread of humanity, thefocus is being directed
toward those wild plants
most in need ofconservation, mainly in tropical dry lands. The seed bank hopes to preserve around
25,000 plant species by the year 2010.
Scientific information obtained from the many rare seeds will be registered on acomprehensive data base, which will be made available to universities, agricultural
bodies and organizations in the developing world, thus publishing the contents of theseed bank.
For this ambitious project to be successful the seeds have to remain viable, they are
required to germinate after the significant periods of storage involved. Seeds arecollected in collaboration with Kew’s overseas partners. The seeds are rapidly shippedback to the Seed Bank, where they are separated from their seed casing and dried to
15% Equilibrium Relative Humidity (ERH). They are then frozen and placed in air tightcontainers for storage at -20°C. Because of the very low temperature and moisture
contents the seed’s ability to germinate is suspended. To ensure that seed remain inthis state, the artificial environment is monitored very carefully, and a sample of eachseed is taken periodically and tested for germination, confirming they are still alive. By
caring for the seed in this way, their life span is increased dramatically they are
expected to survive for hundreds and some times thousands of years!

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Rotronic Instruments provide an exact measure of the Equilibrium Relative Humidity ofthe seeds before and during storage they have a high accuracy of ±1.5%rh, ±0.3°C at
23°C. They are specially designed to be fast and easy to use and with a very low drift
specification all Rotronic Instruments remain accurate over long periods of time.

Keith Manger, the Laboratory Manager for Kew’s Seed Conservation Department said,“The seed bank routinely uses a range of Rotronic Instruments for research and generalseed sample measurement. We have worked closely with Rotronic to develop our
measurement technique”.
Products used include the AWVC measurement head with BT-RS and the new
HygroLab display unit.

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The New Treasure Chamber in Cologne’s Cathedral

The New Treasure Chamber in Cologne’s Cathedral
By: Roland Scheurich
Rotronic Humidity News - Issue: 1/2001
After six years of planning and construction, a new treasure “chamber” exhibition in
Cologne cathedral sacristy opened in autumn 2000. The exhibition area now extends
onto three levels and stretches over 500 square meters. Just entering this unique
historical area with a view of the original Roman town wall is well worth a visit.
The treasures belonging to the church include shrines, relics, and many types ofaccessories used in holy service such as chalices, monstrance’s, crosses, censers,
bowls for chrism and many more. Examples of the crosier, chest crosses, and otherinsignia of the Archbishop of Cologne, as well as chasubles, are also included in thecathedral’s treasures. Discoveries from the Franconian graves and examples of thecathedral’s high quality sculptures from the middle ages are shown for the first time in
the new exhibition.
The concept of the exhibition was developed by the directors of the cathedral’s buildingarchives, Dr. Rolf Lauer and Dr. Leonie Becks, in cooperation with the exhibition’sorganizer, Ingrid Bussenius.
In order for the valuable displays to be
sufficiently protected, the Kieler
Company “Glas + Spiegel Schulz” hasbeen entrusted with the design andmanufacture of high quality andtechnically complex display cases.
For humidity and temperature
measurement, the HygroClip from
Rotronic was selected. Its compact
construction, interchangeable service
concept, modular design, combinedwith high accuracy and excellent longterm stability made it the natural
choice. The religious and historicalimportance of the treasures meant that only high quality products are specified for use
in the exhibition.
The objects are superbly presented through non-reflective glass and the display cases
feature customer lighting by specialist designer Daniel Zerlang-Roesch. The costs forthe construction of the treasure chamber amounted to around 15 million German Marks,
not including the costs for building renovations.

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Rotronic HygroLog-D: Data Loggers in Church Organs
By: Peter Muller
Rotronic Humidity News - Issue: 2/2001
The protection of cultural-assets is a much discussed topic. Various environmental
pollutants damage irreplaceable cultural possessions. Humidity is certainly one of thefactors which can irreversibly damage these precision made objects. Obviously, it is ofgreat importance to avoid such damage. However, the people responsible for such
instruments often don’t know the climate conditions of their premise. Rotronic dataloggers help to obtain the data needed to preserve these ancient treasures.
Within the area of preserving church organs, the Swiss company, Christoph Metzler
Orgelbau, also known as “The Flying Registers”, have been doing pioneer work since1995. Christoph Metzler is a 4th generation organ builder. His company is located in
Dietikon, a suburb of Zurich, and works together with 5 partner companies of the “IG
Orgel”, covering all Europe as well as the United States. It is their common goal topreserve old organs and to restore damaged ones. Their objective is to preserve theinstrument(s) in its original condition, as best as possible. Unfortunately, as time
passes by, many organs are altered and partly reconstructed; some of them over andover again. Chritoph Metzler says, “With every change, an organ loses some of its
character.” The changes were usually made when the spirit of the times changed, often
also with the change of an organist. Many organs had to be replaced due to failed
reconstructions.
Now, what happens to an organ when the climate is wrong?
If the moisture content becomes too high, the wood
starts to swell; if it’s too low, it shrinks. These
actions may easily destroy the glued junctions andin extreme cases even lead to the ripping of thewood itself. If the wood swells, the organ is nolonger easy to play. The reaction time of the various
components is not correct anymore; the organ does
not sound good. Obviously, this effect results in aloss of value, and it seems rather logical, that many
alterations and reconstructions of old instruments
have been done for that reason.
So the goal is to prevent the instruments from being
damaged or even destroyed. Obviously, it is mucheasier to prevent than to repair. The humidity
should always be in a range of 50…60%RH. Using
the HygroLog data logger the conditions are easily
recorded.
Since the beginning of 2001, Christoph Metzler has

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Rotronic HygroLog – D: Data Loggers in Church Organs

used Rotronic HygroLog D data logger, which is placed inside the organ and records
the climate data autonomously for long periods of time. Humidity and temperature data
provides information which correlates to the reasons of eventual damages. Even if
there is no damage, the data recorded give us information on the climate; thus showing
whether or not the premises should be heated, ventilated or air conditioned. Once thedata is known, it is also easy to determine whether or not a claim for warranty isjustified. And of course, this is a simple task for a Rotronic HygroLog.

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Application Stories and Tales

Application: Pyramid of Saqquara Egypt
By: Irmina Sibilska, President B&L International
Rotronic Humidity News - Issue: 2/2001
The Great Pyramid at Saqquara, on a desert plateau some 30 km south of Cairo, is thesite where the Egyptians first tried to put into practice, on a massive scale, their attempt
to defeat time and death by building tombs and temples in stone. It is here theEgyptians built the world’s first pyramid, part of an extensive funerary complex for the
Pharaoh Zoser. The Step Pyramid, (a stairway to heaven for the departing Pharaoh),some 62m high, is central to the complex and was constructed 4500 years ago. It isolder than the more famous pyramids at Gizeh and the Sphinx, and had already beenstanding for over a thousand years when Tutankhamen came to the throne around
1500BC.
A New Discovery
Archaeologists have been excavating the site for over 150 years. But up until 1987 noone has explored the desert area on the complex’s western side, as archeologists
believed there was little to be found there. However, an archaeological mission led byProfessor Karol Mysliwiec, working on behalf of the Centre of Mediterranean
Archaeology at Warsaw University, discovered burials spanning nearly 4,000 years, oneof which was the well preserved and colorful tomb of a powerful Egyptian politician, apreviously obscure vizier name Fefi.
A Vizier was the right hand man of the pharaoh. Fefi seems to have been a colorful
character that lived in the 24th century BC. The tomb’s walls inscriptions portray him
cavorting with woman known as “The One Who Loves Life”. His five wives apparently
were stuck at home. He lived late in the reign of King Teti, first ruler of the Sixth
Dynasty, a time of turbulence. Fefi controlled much of the nation’s financial andadministrative affairs. The 1987 excavation found deep shafts hewn in the rock, many
mummies and a wall running parallel to the pyramid, which seemed to be part of amonumental tomb. The team returned to Egypt in 1996, as part of a joint PolishEgyptian expedition with the Supreme Council for Egyptian Antiquities.
It unearthed the courtyard of the tomb, discovering a leveled rock surface covered witha thick layer of mud. When this mud-brick rubble was finally removed, the team foundcolorful relief’s decorating the entrance to a funerary chapel showing the tomb’s ownerin the company of a lady.
Need for Preservation
The extremely fragile structure of the local limestone causes salts to concentrate on thepaintings. This poses challenge to conservators from the National Museums in Warsaw
and Krakow. Conservation will take years of hard work. The work depends greatly on
climate conditions inside the tomb. Of particular importance is monitoring changes inPage 95

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Applicaton: Pyramid of Saqquara Egypt

humidity conditions over time, between successive archaeological digs. To achieve thisaccurate and stable data acquisition equipment was needed to collect as muchtemperature and humidity data as possible.
Technology Assists
In desert conditions humidity and temperature
can vary widely over a 24 hr period, including
excursions to high humidity and hightemperature the worst type of environment forelectronic instrumentation. The product ofchoice for this demanding application is the
Rotronic HygroLog, supplied through Rotronic’s
Polish distributor – B&L International Warsaw.
HygroLog is a self contained modular logger
featuring the interchangeable HygroClip sensor
module. When calibration or maintenance ofthe measurement hardware is required the site
personnel can simply fit a pre-calibrated newmodule within seconds. Continuous collection ofvaluable climatic data is therefore guaranteed
and the conservation team is able to precisely
record the conditions to which the reliefs are
exposed. From this data decisions can bemade as to how the paintings need to betreated to prevent further deterioration, andtherefore preserve this priceless record of thepast for future generations.

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Application Stories and Tales

Rotronic Sensors on Kilimanjaro
By: Gary Moliver
Rotronic Humidity News - Issue: 2/2001
The first European sighting of Kilimanjaro occurred 62 years after the ascent of Mon
Blanc. Yet, reports of snow and ice high on the mountain were viewed for many years
as an apparition. We now know that the massive equatorial volcano in Tanzania, with asummit elevation of 5895 m (19,341 ft), supported ~20 km² of glaciers until late in the
19th century. By last year, the ice-covered area that Johannes Rebmann described as“dazzling whiteness” in 1848 had decreased by ~90%, to 2.2km².
Today researchers are actively investigating themeteorological conditions of Kilimanjaro to better
understand the relationship between the mountain’s
climate and the demise of its beautiful tropicalglaciers. An automated weather station wasestablished near the summit in February 2000,
employing Rotronic MP101A probes to measurehumidity and temperature. Data are stored on-site
and transmitted via Argos telemetry to the Universityof Massachusetts. Rotronic probes continue toprovide accurate measurements despite severe
conditions including perpetually sub-freezing
temperature and solar radiation often in excess of1200 W m-2.
Further details on the weather station and Kilimanjaro climate research are available at:www.gejo.umass.edu/climate/kibo.html

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Rotronic Measuring Equipment in Nuclear Research

Rotronic Measuring Equipment in Nuclear Research
By: Carl Welinder
Rotronic Humidity News - Issue: 1/2002
Radioactive waste from nuclear power stations needs to be stored for 100,000 years
before radiation levels reach that of naturally occurring Uranium. After 1000 years, thedirect radiation will have declined to a harmless level. According to Thomas Karlsson at
SKB (Swedish Nuclear Fuel and Waste Management) time is the most critical factor in
our project to develop a storage method for highly radioactive waste.
The Adpo Hard Rock Laboratory is a center for research on the storage of nuclear
waste. Its construction began in 1991 with a shaft 480m down into the hard rockoutside Oskarshamn on the east coast of Sweden. At this depth, 8m x 1.75m diameterholes were drilled into the solid rock each contains one canister (4.83m x 1.05m
diameter, 27 tons). Instead of waste, a 1800 W heater is installed inside the canister toincrease the temperature in order to stimulate the presence of nuclear waste.
The waste itself is very non-reactive and is unlikely to contaminate ground water, but aseries of additional barriers are used to prevent leakage. First level of encapsulationconsists of cast iron, which is then enclosed within a 5cm thick copper container. Filling
the gap between the metal canister and the hard rock is a layer of clay.
To explain the thinking behind the method, it is necessary to consider evidence from
historic natural occurrences (man-made radioactive waste has only been produced in
the last 60 years). Two billion years ago in West Africa nuclear reactions occurredunderground and produced several tons of radioactive waste. Investigations haveshown that radioactive isotopes permeated only a short distance through the rock
structure, which shows that certain rock can be a good containment material.
One factor of high interest is the clay’s ability to absorb water from the surrounding rock.
When clay absorbs water it expands, which in this application causes an increase inpressure around the canister. The fully saturated clay seals the canister from oxygenthat might cause corrosion. The research required a measurement of the moisture level
present within the clay between the hard rock and the canister. By recommendationfrom international researchers Rotronic sensors were specified as being accurate inlong cable high pressure and high temperature applications. In addition custom filtersand seals were designed. In September 2001 measurement started.
So far, the Swedish nuclear power industry has produced 5000 tons of highly
radioactive waste. According to a plebiscite, the nuclear power plants in Sweden will all
be shut down and 4000 canisters with two tons of waste each will need to be buried andsealed, with completion by 2050. In case a future generation would like to recover thewaste and reuse it a concurrent project is running to test canister retrieval methods. For
each kWh of energy produced in the 12 Swedish nuclear power plants, 0.001-0.002
Euro is allocated to pay for the future storage of radioactive waste. This fund is alsofinancing the research at SKB, as well as other projects in Germany, United Kingdom,

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Finland, France, Japan, and Spain who also run their own projects at Aspo Hard RockLaboratory. For instance Spanish scientists are monitoring possible movements of thecanisters as the clay expands.
The picture to the left is taken at a depth of 480m,
and shows from left to right, Carl Welinder from
Rotronic’s distributor in Sweden Swema,
electronic engineers Thomas Karlsson, from SKB,
and Sten Johansson from the site’s electricalcontractor, JL Elektronik. In the middleRotronic’s cabinet for electronics of the 95m
cable, 10 bar pressure resistant humidity andtemperature probes. At the top, drilled holes forthe sensor cables are shown, these lead to a clay
and rock filled tunnel. In the tunnel, holes for canisters are drilled in the tunnel floor.
Inside the clay around each canister the Rotronic humidity and temperature probes are
installed.

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Analysis of Drilling Mud in Canada

Analysis of Drilling Mud in Canada
By: Gary Moliver
Rotronic Humidity News - Issue: 1/2002
Newpark Drilling Fluids (Canada) a division of Newpark Resources (USA) is a company
operating within North America that supplies water and oil based fluids to thehydrocarbon drilling industry.
Most of the chemicals used in water and oil based fluids are designed to carry out
different functions in the course of drilling a well. Some of these tasks include: holecleaning, i.e. lifting the rock and dirt from the drill bit (bottom of the well) to the surface,penetration through and protection of the rock formations being drilled, providing
strength to the rock walls of the hole being drilled, drill string cooling, lubrication,
corrosion resistance and buoyancy. Sub-surface pressures are also controlled.
In September 2001 Newpark introduced a new oil-based invert called New-100. An
invert is best described as a stable salad dressing; it is water and oil emulsified together
in different ratios. (An oil-based invert has a higher percentage of oil (>50%, typically90%) (external phase), with the water (internal phase) emulsified within the oil).
Oil Inverts are used primarily to add additional protection to water sensitive rockformations, but, the water within the invert has to be modified with salts such as calcium
chloride to further reduce the activity of the water phase. The New-100 invert (which
can’t be titrated) replaces the calcium with a water-soluble liquid. This has two major
effects, first it reduces the amount of water in the whole fluid system and secondly it
replaces the salt with an environmentally friendly liquid. New-100 is 100%
biodegradable and non-bioaccumulative (i.e. no salt build up in drilling wastes disposedof at approved sites).
So how does Rotronic fit into this?
The water sensitive shale (rock) canvary in different parts of the world; but
within North America the water
activity (aw) ranges from 0.7 – 0.8.
The internal phase of an invert isadjusted to be slightly less than the awof the rock to prevent water fromflowing from the drilling fluid into therock resulting in borehole stability
problems. With the activity less than
the surrounding shale’s water flows
from the rock to the drilling mud. Thishas the effect of increasing the watercontent of the drilling fluid.

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If drilling with a calcium chloride invert an increase in water concentration wascountered with additions of calcium chloride to maintain the desired salt concentration
and water activity. With a New-100 internal phase, an increase in water concentration
cannot be easily measured by titration of the internal phase. Newpark knows that theconcentration is falling but how to quantify it? We solved this problem using the
Rotronic water activity system. An increase in water content should increase the aw of
the entire invert. After preparing a number of inverts with different aw internal phases, acorrelation were made between the whole mud aw and the amount of water added.
After five months and more than a dozen New –100 wells drilled in Western Canada,
the Rotronic water activity analyzer has proven to be an invaluable tool for this type of
application.

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HygroClip S – When Maximum Precision is Required

HygoClip S – When Maximum Precision is Required
By: Christophe Thubert
Rotronic Humidity News - Issue: 1/2002
The Danube International Company, world leader in the cleaning of industrial clothing,has been recognized due to its innovative technology in the area of cleaning,decontamination, drying and pressing of the most diverse textiles. Both hotels andclinics – Danube’s main target groups – have to fulfill the most stringent hygiene andsafety requirements.
The technology in the machines manufactured and exported by Danube must therefore
offer the utmost reliability. Several years ago, in the course of the continuous
development of its range of products, the Danube International Company applied for apatent for the fully automated dry pressing of textiles. The cloth is transported by aroller of variable length that is heated to about 100°C over long periods. The first(competitor) humidity and temperature sensor to be tried out produced bad results,
showed effects of saturation and had to be exchanged frequently. Then the HygroClip-S
from Rotronic was tested over a period of nine months – with success!
The HygroClip S in combination withan MOK-02-XX cable ensures reliable
humidity measurement, even in longterm operation. The sensor’s
resistance to saturation, its longevity,
and the long-term stable precision ofits measurements has contributed
significantly to this success. The
exchangeability that the HygroClip S
technology permits is much valued byusers with regard to the ease ofmachine maintenance. In addition,
each HygroClip S is calibrated andsupplied with temperaturecompensation, which has the advantage that it can be exchanged without alternations
having to be made to the machine controls.

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What Does Humidity Have to Do with Deep Space Missions?
Rotronic Humidity News - Issue: 1/2003
The European Deep Space Antenna Project in New Norcia (Western Australia)
The European Space Agency operates and maintains a network of ground stations,which consists of several stations using 15m antennas in the short wave band fortelemetry, command and tracking in support of spacecraft operations. A 35m DeepSpace Ground Station at New Norcia (Western Australia) now augments this network,
and was ready for operational use as of autumn 2002.
The facilities feature three (3) Rotronic HygroFlex 2
temperature and humidity transmitters which transmit
climatic humidity and temperature data, via an RS-232
interface, directly to the European Space Operations
Centre (ESOC) in Darmstadt (Germany). Sensors aremounted within Rotronic VHTS2 ventilated radiation
shields on a collapsible aerial mast, with the HygroFlex
transmitters installed in an enclosure underneath, and are
powered by a solar panel and battery. The weather data
is used to improve the directional accuracy required fordeep space missions especially in the X-Band (ca.8Ghz).
Directional errors caused by, for example, weather
dependent atmospheric refraction that can be correctedby the refraction model. The refraction index is a functionof temperature, humidity, atmospheric pressure andantenna elevation. The antenna is calibrated using stars
as signal sources and positional references, provided
there is no wind load on the mechanical structure. Wind
speed information is used to disable the correction
process when certain speeds are exceeded.
The New Norcia antenna is one of the largest in
the world used for Telemetry, Tracking andCommand (TT&C) applications and represents
the jewel in the network of ground stations
operated by the ESOC. This exceptional antenna
is required for high performance communications
with deep space and high elliptical orbit missions,in particular for the European Space Agencies(ESA) science missions Rosetta and Mars
express. Reliable long distance communications
between the New Norcia ground station and theRosetta spacecraft are essential to acquirescientific data collected by the instruments onboard the spacecraft. It also allows the

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What Does Humidity Have to Do with Deep Space Missions?

operations centre to remotely control the spacecraft and its instruments over distancesof up to 900 million kilometers away from Earth, more than six times the distance from
Earth to the sun. As with all other ESA ground stations the New Norcia antenna will beremotely controlled and operated from ESOC at Darmstadt.
The ESA is planning to enlarge the network by a second antenna of the same size in
Europe. This represents a further step in the enhancement of the European DeepSpace network in the Ka band, and is core to the future of the Aurora project.

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Rotronic Sensors in the Brick Industry
By: Rainer Hofmann
Rotronic Humidity News - 1/2003
The history of brick manufacturers can be traced back to at least the 3rd millennium BC.
We know that the ancient Egyptians used bricks when building the Temples of Karnak,
and the Romans were prolific in their use. Today, the brick industry has to deal with thechallenge of manufacturing a quality brick in immense quantities. This means that the
manufacturing process is becoming more and more automated, and that better andbetter process control is required. In parallel, reduction in energy consumption is a highpriority. Before the bricks are fired, they are placed in a drying chamber for about 44
hours where the moisture is extracted.
The company Olfry has been producing bricks and tiles in all their possible forms for thelast one hundred years. For the last 15 years they have been using Rotronic humidity
and temperature transmitters to control the drying process. The benefits of humidity
control are clear; bricks which are fired with too much moisture within their structure
crack or explode. If the brick is over dried, unnecessary amounts of energy isexpended.
The exact measurement of humidity in the brick and tile industry has often created aproblem: As the brick enter the drying chambers with a very high moisture content,
condensations often forms on the surfaces of the drying chamber, and moresignificantly, on the measurement probe. This causes corrosion of metals including theconnections of the humidity and temperature sensors. Depending on the levels ofcondensation formed, and the control strategy, the life of the sensors could be anythingfrom a few weeks to a few years. When sensors fail, they of course, have to be
replaced. This could prove costly for the customer. Perhaps more significantly,
incorrect measurements cause failures of the process control, leading to higher scrap
rates and less profit for the brick manufacturer. It is clear that other solutions have beensought, but at that time there was simply no alternative.
Solution: By working closely with the company Olfry, Rotronic has made a start intackling the problem. Whenever the relative humidity is above 85%RH, the sensors areheated. As soon as the humidity falls below this threshold, the heating is switched off
and the measurement is performed in the usual way. Thanks to this technology, thecondensation of water vapor is avoided and the life time of the sensors has been
multiplied. The new probes have been in use for the last two years. According to theacting Deputy Manager, Mr. Viefhues, “They have functioned correctly for the past two
years without causing us any problems. This has led to us replacing the existing probeswith the new type. It has completely solved our problems”.

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Humidity Absorption from Munters with Rotronic Humidity Instruments

Humidity Absorption from Munters with Rotronic Humidity
Instruments
By: Joseph Farcher
Rotronic Humidity News - 1/2003
Munters is a company renowned
throughout the world for air
dehumidifying systems. The new
Munters Ice Dry system for cold rooms
and refrigerated storage has been tested
and is available for sales in the USA andEngland. It is now available acrossEurope. It dehumidified the air thatpenetrates into cold areas, especiallythrough open doors and conveyor belt
openings. The dry air eliminates the riskof accidents caused by slippery ice, andsignificantly reduces the need for
deicing. This system will also improve
working conditions in a cool room; dryfloors, less humidity in the air and theelimination of icing improves safety andprofitability. Munters cooperates with
Rotronic in many countries. For
example the bridge over the Oresund
between Sweden and Denmark was
furnished with dehumidifying systems
from Munters. The humidity measuring
instruments were naturally from
Rotronic. Munters (Switzerland) AG
puts Rotronic transmitters before allothers. Josef Facher, project manager
of Munters (Switzerland) AG explains:
We use Rotronic instruments for allprocess-controlled installations because
they have a superior standard of quality.
The humidity sensors are extremely long
lasting and accurate. The instruments of
the M3 series are capable to calculate
psychometric parameters. But what is
especially important is theinterchangeability of the probes which
has reduced our service cost immensely.
A Rotronic HygroClip sensor can beexchanged in seconds. Also the transmitter doesn’t need to be switched off. A
diagnosis or system validation by computer is no problem with the new M series devices

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thanks to a service interface. It means that there is no downtime. And of course thecompetitive prices of Rotronic instruments are a convincing argument.
The build-up of the ice in cold rooms and refrigerated warehouses is a well establishedproblem. The humidity in the air condenses and forms ice on countless surfaces, forexample, the floor. Every time more humid air enters the room the pockets of ice getlarger so that after a certain period of time the room must be defrosted.
The humidity measuring instruments from Rotronic M series are used to control thedehumidifier and make it possible to obtain precise control within narrow margins, andtherefore contribute significantly to energy optimization. They can, depending on theapplication, provide measurement of relative humidity, or psychometric calculations plus
the temperature.
The life cycle of machines and facilities is increased when there is less humidity
servicing intervals are reduced because of the lower levels of corrosion. Manual
cleaning becomes a thing of the past. The advantage of this system will become
especially clear in summer and autumn. With IceDry the build up of ice almost
completely fails to appear even in summer. The necessity to defrost the plant becomesless and less frequent and cold rooms can be kept dry with the new Ice Dry system from
Munters.
Rotronic instruments contribute through their high level of precision and the possibility of
performing psychometric calculations to a plant which optimizes energy use andoperates at a favorable cost. The dry air prevents the growth of mold and other microorganism, which is clearly important in cold rooms especially where groceries and otherperishable products are stored.

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Climate Surveillance in Vienna Palace Liechtenstein

Climate Surveillance in Vienna Palace Liechtenstein
Ernest Aringer
Rotronic Humidity News - 1/2003
The construction of Liechtenstein Palace was completed in 1705. Many famous artists
worked on this impressive building designed to be the summer residence of Prince
Johann Adam Andreas of Liechtenstein (1657-1712). The art loving prince insisted on
the magnificent furnishing of his summer property and commissioned some of the mostrespected artists of his time.
Use of the Palace over the course of centuries
In the 18th Century the garden palace was used as the summer residence of the
Liechtenstein family and to celebrate various festivals. At the beginning of the 19th
century Prince Johann Josef of Liechtenstein (1760-1836) decided to concentrate thefamily’s extensive art collection from various palaces and castles at the Liechtenstein
Palace. It remained there between 1944 and 1948, when it was moved to Vaduz as aresult of the war. The building, including the ceiling works, were subject to a basic
restoration in 1978/79.
The collection of the Prince of Liechtenstein will return to the Danube metropolis in early
2004. One of the largest collections of Rubens, important works of Van Dyck, Lucas
Cranach and Rafael are just as wonderful as those of Rembrandt, van Ruysdael and
Hamilton.
Climate Control
It is clear that all of these works of art are extremely valuable and correspondingly must
be protected, preserved and stored correctly. Control of the climate surrounding thevarious works is the most important factor. Of course the climate of the exhibition
rooms was considered in the course of the renovation. Because the palace is a
protected building, conventional air conditioning with ventilation ducts could not be used.
Fan coils, which are mounted behind the wood of the sills, were chosen. To control the
relative humidity of the exhibition rooms, over 50 Rotronic transmitters of the FH series
were installed. Thanks to these, the aesthetic demands of the architecture can befulfilled. The transmitters have been mounted next to the hidden fan coils. The
HygroClip S probes were sunk into the wall by special flanges so that only the probe
tips are visible. The connecting cables run under the plaster to the measuring sensor.

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An important factor in the purchasing decision was the simple interchangeability of the
HygroClip sensor, which is of great importance for such applications. Since theinstallation is concealed, it is especially important that the probes can be easily replaced
without particular expense. A welcome side effect is that service costs are also reducedin this way. Rotronic has miniature sensors for use in museums of 4mm and 5mm
diameter respectively which can be installed practically anywhere and are virtuallyinvisible.

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Humidity Measurement on the Moving Paper Web

Humidity Measurement on the Moving Paper Web
By: Roland Scheurich
Rotronic Humidity News - 1/2003
Bayropa Jung GmbH, situated in Wertingen, Germany, celebrated its 25th anniversary inthe year 2000. The paper tiger, as Bayropa is known, not only have extensive printing
experience, but also possesses state of the art roll-offset printing machinery with paperwidths up to 100cm and DIN A4 production lines for pre-printed laser paper with athroughput of 6600 sheets per minute. Of course, Bayropa is also using state of the art
technology for their humidity measurement.
Humidity is a very important parameter in the paper and printing industry. Humidity
influences the characteristics of a printing process, especially in high volume laser
printers. When the paper humidity is not correct, the paper tends to curl, and hence is
unacceptable to customers.
Problem: Statistical data alone is not enough to maintain high quality. Paper
manufacturers only provide average humidity values for paper webs of more than 10m
in width. Therefore, single paper rolls may be well out of tolerance. This is the result of
the paper production process, which delivers paper webs of 10 m width that are cut into
smaller webs only at the end of the manufacturing process.
The solution is online measurement ofequilibrium relative humidity (ERH) andtemperature on the web running at 500m
per minute. It serves to detect and rejectrolls that are out of tolerance.
The online measurement at Bayropa Jungis achieved with one Rotronic BFC-DIO
web probe at the machine, with themeasurement data managed with
HygroFlex transmitters. On-line
measurement offers the following
advantages:••••

Uninterrupted measurement of ERH and temperature on the moving web, andhence the possibility to control the process.
Avoidance of finish problems by customers.
Simple logging of the measurement values with validated Rotronic HW3 windows
software.
Alarm function when exceeding threshold values.

A consistent and defined humidity is of great importance when paper is being printed inorder to achieve good printing results.

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The measurement principle grants a practical and low priced measurement ofequilibrium humidity and temperature on the moving paper web.
Web Probe BFC-DIO
The web probe BFC-DIO is
installed directly under or above
the moving web, but without directcontact. The humidity andtemperature of the paper creates a
microclimate in the confined spacein and around the measurement
chamber that is directly measured.
With this simple and well-priced
instrument, paper quality can bemonitored without interruption, andimportant conclusions can bemade in order to increase theproductivity and profitability.

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Testing Water Activity in Seeds Helps the Brazilian Rainforest

Testing Water Activity in Seeds Helps the Brazilian Rainforest
By: Niek Jan Bink,
Rotronic Humidity News - Issue: 1/2004
Jose Marcio Faria, from Brazi,l is doing a PhD thesis in the Netherlands on storage
protocols for seed drying. In this research water activity plays a major role. His
supervisor, Dr. Henk Hilhorst, saw the water activity measurement system of Rotronic
for the first time with colleagues in the USA. There he became convinced of thecapabilities of the Rotronic HygroLab system. He insisted on having one himself, andnow they are using it enthusiastically in this project on desiccation sensitivity in legume
seeds. Both Dr. Hilhorst and Jose are very satisfied with the Rotronic system. Jose
hopes to finish his dissertation next year.
Riparian forests are those that grow along side rivers and they are tightly associatedwith water, helping in the maintenance of water quality and quantity. In Brazil, these
forests belong to the most threatened ecosystems, mainly because of agriculture,grazing and flooding due to formation of lakes for hydroelectric power generation. In aworld where the decreased of water supply is of great concern, the importance of theecological restoration of such kind of forest becomes even more evident. In Brazil,
several programs of reforestation with native species have been carried out, attempting
to diminish the problem, and seeds are, in practice, the basis of these programs. Thus
the importance of storing in seed banks for use in the future to restore these damaged
or destroyed environments is obvious.
One of the main tree species
used in ecological restorationof riparian forests in southeastern Brazil is Inga vera
(Leguminosae), whose
seedlings can withstand up to
3 months of total submersion.
Its seeds are shed with highmoisture content (MC) around
60% (fresh weight basis) andthey are recalcitrant, i.e. theydie if dried to MCs low enoughto allow storage. Fresh Inga
vera seeds attain 100% of
germination, but upon
desiccation they quickly lose
viability. If MC drops to 30% they cannot germinate anymore (Faria et al., 2002).
Intolerance to desiccations is a serious problem with regard to the long term storage ofseeds of this species, as well as other recalcitrant species.

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The main objective of this study is to better understand what causes the death of theseeds during drying. This is the first step towards the development of storage protocols
for seeds of this species and other recalcitrant seeds.
Traditionally, most of the work on seed desiccation deals with water in seed byassessing only MC, but as shown by Vertucci and Roos (1990) and others water activity(aw) of seeds provides a much better measure of their physiological level since it relates
to the energy status of the water, i.e. the availability of the water to participate inchemical and physical processes. Thus in these studies aw is measured as it is a much
more relevant parameter than MC to assess when desiccation damages start to appear.
Another advantage of working with aw is the possibility of comparing different species,
since a number of physiological processes that are relevant to desiccation tolerance or
damage have been shown to occur within a narrow range of aw values (Sun 2002).
Moreover, determining the aw in single seeds or populations is essentially nondestructive. This is a great advantage when dealing with rare species of which only
small numbers of seeds are available.

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Engine Testing at SAAB

Engine Testing at SAAB
By: Martin Slatis
Rotronic Humidity News - 1/2004
Saab Automobile Powertrain AB is a part of Fiat-GM Powertrain, working on thedevelopment and testing of the highly advanced engines used within the Saab range.
At its engine test facility in Trollhattan, Sweden, Rotronic HygroFlex Industrial
transmitters are used to measure the test conditions.
Engine Power Test
Engines are mounted in test cells where the power output is measured. Engine power
is influenced by environmental conditions, so to make sure that the power output iscorrectly stated, the dew point and temperature of the engine’s inlet air is measured.
Testing is supervised by an external accredited company, such as TNO in the
Netherlands, or AVL from Austria.
Emissions Testing
Car exhaust emissions must be tested to according to different test cycles for different
markets. Examples include the FTP75 (FTP-Federal Test Procedure) for the US
market, and EUDC (Extra Urban Driving Cycle) for the European market. Cars are run
on a dynamometer simulating highway conditions, and the environment is controlled tomaintain air temperatures of 20…30°C and dew points of 10…15°C using humidification
systems. Humidity measurement transmitters are part of the control system which
maintains the correct throughout the testing cycles.
Rotronic Transmitters
Saab recently selected Rotronic HygroFlex transmitters with
HygroCLip IM-1 probes to replace another manufacturer’s
equipment.
The HygroFlex was chosen because of Rotronic reputation formeasurement accuracy and long term stability in industrial
applications. Another advantage of this instrument is theinterchangeable probe which could be calibrated in Saab’s
calibration facility where a Thunder Scientific two-pressure
generator is used. This means that the probes can be quickly
and easily removed and calibrated whenever required and tomeet validation requirements.
As the test specifications define the humidity in units of dew point, the HygroFlex
HTM32D unit was specified. This unit has three analogue outputs which can be freely
configured to give %RH, dew point and temperature signals simultaneously.

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New Ventilated Radiation Shields Co-Developed with MeteoSwiss
By: Leonhard Low
Rotronic Humidity News - 1/2004
The measurement of climatic humidity and temperature for environmental research,weather forecasting and pollution control is essential. Improvements in the precisionand reliability of measurement data will continue to be in demand, especially as ourknowledge of the climate and our need to forecast its behavior continues to grow.
Rotronic meteorological probes have been one of the mainstays of climatic humidity
measurement for over 20 years. In all applications their precision and long-term stability
are well respected. Of course it is the case that in some circumstances even the bestequipment doesn’t always provide the results that the user needs.In these situations it isessential that further development work is carried out to improve the product. An
example of this is the recent development of a new series of ventilated radiation shields
to improve measurement performance in some of the harshest conditions.
The new RS ventilated shield has
been developed in close
cooperation with the Swiss
National Meteorological Service(Meteoswiss). It is a highly
advanced product, designed tominimize the influence of thermalradiation on humidity andtemperature measurements, while
maximizing protection from thevery worst weather conditions,
including horizontally driving windand rain. The performance of the
RS shield in combination with thelatest Rotronic meteorologicalprobes is such that in comparative test, measurement performance was practically
identical to chilled mirror condensation hygrometers which are used by many National
Meteorological Organizations as a reference.
Ventilation of measurement sensors is not a new concept, but it is worth mentioning
why this may be useful feature. At high %RH values or saturation, measurement
becomes difficult. Small changes or differences in temperature can cause largechanges in actual or measured relative humidity. The thermal mass of the humidity
probe and its mounting hardware is quite large, and as a result its response totemperature change is slow and condensation may form as a result. This doesn’t
present a problem for Rotronic probes, as they recover well from periods of saturation,
but for a period of time, maximum %RH values may be measured by the probe and thedata recorded incorrect. In situations where the condensation takes many hours toevaporate, this can mean incorrect measurements are given for a significant period ofPage 115

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New Ventilated Radiation Shields Co-Developed with MeteoSwisstime. By actively ventilating the measurement sensors, the measurement part of theinstallation will return to actual %RH more rapidly.
Ventilation can also be useful where ambient temperatures are higher. The effects ofsolar gain are minimized bycareful shield design andspecialist paints, but incombination with active
ventilation; measurement
performance can certainly besuperior to naturally ventilated
designs.
The new shields are detailed in
our new catalog together withthe full range of compatible
Meteorological probes.

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How Rotronic Helps in the Production of Fine Cheese
By: Thomas Ryan
Rotronic Humidity News - 1/2004
The Courlaoux Cheese Dairy has been part of the Unicopa
group since 1996. Unicopa is a large organization with over
5000 employees active in a diverse range of high quality foodactivities such as poultry, pork butcheries, saltings, as well as
dairy products such as cheese from the Jura Courlaoux. Under
the management of Messieurs Bouchet and Duchaux, the plant
managers/directors, the Jura Courlaoux transforms 17 million
liters of milk into 1600 tons of cheese! The final product is
90% Comte and the remainder Emmental, sold under the
Rippoz brand.
Milk is skimmed on arrival, and then stands for 32 minutes while curds form before
being heated to 55°C in 30 minutes. The curd is then extracted, and over the next 24hours is pressed and formed into the familiar shape. The cheese is put in pre-maturing
cellars for two months, and then spend another two to six further week in maturing
cellars before being put into final storage.
The conditions during the maturing process play an essential role in the quality andweight of the cheese. The pre-maturing cellars are controlled to 92 - 93 % RH at 10 12 °C. It is imperative that the cheese remain within an environment of 85…95% RH to
ensure optimal maturation, so control systems using Rotronic humidity and temperaturetransmitters are used.
For many years the factory has used Rotronic FT transmitters, and recently
these have been upgraded to the latest M2 series with HygroClip-S
interchangeable probes. Their improved performance provides a bettermeasurement accuracy of ±0.3°C, and an improved IP65 enclosure gives
better protection to the electronics in extreme conditions.
Of even more benefit in this application is the flexibility of maintenanceoptions that the M2 series provides. Interchangeable probes and digital technology
allow the Jura Courlaoux to carry out a more rigorous maintenance schedule to achieve
best possible measurement results, but without increased costs. A HygroPalm 3
handheld instrument is used to carry out calibration checks, and when necessary used
to make adjustments at one or multiple points of temperature and humidity.
The HygroPalm 3 handheld instrument/calibrator is also used by Mr..Duchaux to spot
check the absolute humidity. This information allows him to make sure that theconditions in each area are comparable. The combination of M2 series and the
HygroPalm gives Mr. Duchaux the tools to ensure that humidity control can have thebest possible impact on the quality of the cheese.

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Protecting Rodin for Japan’s Climate and Earthquakes

Protecting Rodin from Japan’s Climate and Earthquakes
By: Masaru Kawanishi
Rotronic Humidity News - 1/2004
The National Museum of Western Art (www.nmwa.go.jp) in Tokyo has recently installed
a number of Rotronic HygroClip IC05 mini probes for use in the conservation of theRodins statues Adam and Eve.
Masaru Kawanishi, of Rotronic’s distributor inJapan, Shinyei Kaisha worked closely with thestaff of the museum to provide ameasurement solution which would integratewith very specialized measurement andprotection technology used to preserve theRodin statues. To further complicate theapplication, the statues were also mounted
onto a seismic isolator to protect them fromthe frequent earthquakes in the region. The
complexity of this mounting platform meantthat the humidity probes used needed to be of the highest quality and smallest
dimension. The 5mm diameter probe and cable of the HygroClip IC05 was therefore
ideal.
HygroClip IC05 probes are connected to HygroFlex transmitters, which takes the digital
measurement information from the probe, and converts it to an analog signal for NWMA
monitoring requirements.
The NWMA curator commented, “The HygroClip IC05
works very well, especially during the summer months
when humidity can be very high. Its very small sizemeans it can fit into the limited space inside the statues
without a problem. Humidity is very important to theconservation of works of art, especially paintings, and in
the future I want to use the HygroClip IC05 to measure
between the canvas and backboard.”
The HygroClip IC05 is one of a range of different probe
types that are available to connect to the HygroFlex. The
digital electronics retain the probe calibration data so they
can be interchanged without loss of measurement
performance.

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Application Stories and Tales

How Humidity is used in Fuel Cell Research
By: S. Ikawa
Rotronic Humidity News - 1/2005
A fuel cell is a power generating device using materials such as natural gas, methanol,
petroleum, coal, gas or biomass.
Since the fuel cell is based on the reverse reaction of electrolysis of water, it does not
require the combustion of fuel like typical thermal power generation methods.
Therefore, it has attracted considerable attention as a high efficiency power generator
with low environmental impact. In addition, since heat is produced by the chemical
reaction, the fuel cell can supply both electricity ad heat simultaneously. Fuel cells areintended not only for large scale power plants, but also as a power source for homes,
office buildings hospitals, cars and buses etc. The power output can be from tens totens of thousands of kW.
Why the Dew Point is Measured?
A fuel cell requires high temperature and high dew point values for efficient power
generation. When testing fuel cells, monitoring of temperature and dew point isrequired to determine the best atmosphere for power generation. Usually, dew point ismeasured at the inlet and outlet of hydrogen rich gas and air circuits. Measurements
are generally performed at four points on each testing machine.
The Challenge of Measurement in Fuel Cell Testing
Fuel cell testing machines are operated between
80…150°C and 90…100% relative humidity. The dew
point can reach almost 90°C! The atmosphere isdemanding for humidity sensors. During testing, thehumidity sensors are exposed to extreme conditions,where condensation may easily occur.
Additionally, the sensors must withstand pressure.
Fuel cell testing machines supply minute moleculargases like hydrogen. Therefore, it is very importantthat the probes are pressure tight. The leakage ofhydrogen will result in pressure changes, which in turnaffect the test results of the fuel cells. Which
Instrument is Suitable?
As mentioned above, the atmosphere of the fuel cell
testing machine sometimes reaches 150°C. The
product of choice is a HygroFlex 3 transmitter with an analog output of the calculated

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How Humidity is Used in Fuel Cell Researchdew point signal to the control systemof the fuel cell testing equipment. The
recommended probe is a customized
HygroClip IE-X/M screw-in pressureprobe with an operating range of 50…200°C. This probe can withstandboth high temperature and pressure up
to 50 bar. To ensure that theapplication is successfully measured, it
is recommended that the probe isheated to prevent condensation. In
case condensation occurs, a special
filter has been designed to allow the condensate to flow away. The high tolerance ofRotronic hygromer series to high humidity, high temperature and saturation conditions,means that it is one of the available methods for measurement in this application.
Who are the Customers?
Around the world, car manufacturers, electric power, gas, fuel companies anduniversities are rushing into the development of fuel cells. Many manufacturers of
testing machinery are approaching the fuel cell developers with different testing designs
and a variety of measurement requirements. One of Rotronic strengths is our flexibility
to customize products exactly to the customer’s needs and in this complex anddemanding application, we are often specified as the product of choice.

The Rotronic Humidity Handbook

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Application Stories and Tales

HygroClip Probes and the Quality of Plastic Molding
By: Ernst Aringer
Rotronic Humidity News - 1/2005
For maximum output and reliable quality, injection molding machinery must be
constantly cooled. If condensation occurs on the surface of the cooled molds, thisaffects the quality of both product and molds.
Eisbaer Trockentechnik GmbH in Goetzis (Austria) operates in the building drying andplant construction sector of the plastics industry. They are specialists in air drying
systems that are used with injection molding machines, and for film cooling in extrusion
plants. The common requirement of these machines is their constant need for very dry
air to maintain high standards of quality and productivity. In order to avoid condensationon the molds, the dry air of the DAs-devices (Dry Sir System) is blown into the portioned
tool section of the machines in exactly the right volume. To ensure that condensation
does not occur, temperature and humidity in the tooling section are constantly
measured. This allows adjustment of the dryer performance and optimizes energy
consumption.
The second point of humidity measurement is at the process of air outlet of the dryer
system. It provides for permanent control of dryer performance which brings additional
benefit for the customer in terms of simplified support and maintenance.
The interaction of these two measurements guarantees
condensation free tools with minimal energy
consumption, and ensures continuously high surface
quality of the products with maximum productivity. In
combination with a customized version of an M23 duct
mount transmitter, the Rotronic HygroClip probes aremounted directly in the output duct of the DAS system
and into the tool section of the injection molding
machine. The interchangeability of the probes ensures
practically uninterrupted operation even during
maintenance, whilst the probe key features of accuracy
and stability helps to ensure consistent air quality.
Advantages from the Customer’s Point of View
The competitiveness in the plastics industry, andespecially in the PET industry, is determined by the socalled cycle time. This describes the time elapsing from closing the tools, injection ofliquid plastic, cooling down and hardening of the molded part, opening of the tools andejection of the part. The major part of the cycle time is usually taken by cooling andhardening of the molded part. It is therefore obvious that the industry tries to reduce
this time to a minimum. Reducing the cycle time can be achieved by cooling the tools(usually with water). In extreme cases the cooling can be close to nearly freezing, andPage 121

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HygroClip Probes and the Quality of Plastic Molding

this results in condensation of the humidity from the surrounding air on the tools (bycorrosion) and product’s surface by water marks.
The Eisbar DAS-System helps prevent this by drying the supply air. Due to a slightoverpressure in the tool section, humid ambient air cannot reach the tools section. In
short, injection molding is possible with the best possible capacity and quality anywherein the world, regardless of the actual ambient conditions thanks to Eisbar systems andRotronic probes.
Further Applications for DAS-Systems:••••

Drying of plastic granulate
Drying of material such as fertilizers
Food drying in silos, of sweets, dry vegetables
Corrosion prevention in power stations, military facilities, water works, etc.

The Rotronic Humidity Handbook

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Application Stories and Tales

Humidity Generators - Examining Uncertainty
David P. Love
VP – Sales & Marketing
Rotronic Instrument Corp
Reprinted with permission from Pharmaceutical Formulation & Quality – November 05, 2005

From saturated salt solutions to humidity generators there are many different ways togenerate a humidity value for calibration. In order to define a method for your humidity
calibrations and also to properly evaluate the number of commercial solutions available
on the market today, there are several key areas requiring close examination. In order
to simplify the discussion this article will broadly review the issues presented whenusing a commercial humidity generator. These are available from a variety of
manufacturers. The principles used to generate the precise humidity environment vary;
two pressure generators, two temperature generators, and split flow are the mostcommon. Within each group the instruments may appear similar; there are however
vast differences in the accuracy and quality of the instruments available in eachcategory. The critical question is how to tell the difference between a good and a poor
instrument. Are the lower cost generators really as good as the more expensive
generators? This brief review will provide a framework for facilitating the decision
process required to decide which humidity generator is right for your requirements.
Let’s look initially at the problems associated with the humidity generator itself. In orderto properly calibrate a humidity sensor, the reference generator must provide a very
stabile and uniform humidity and temperature environment. This is critical for two very
basic reasons. First, small temperature gradients throughout the chamber can result insignificant errors in the measured relative humidity values. A temperature gradientinside the calibration chamber of as little as ±0.1°C can cause errors of more than
±0.5% RH at higher humidity levels. While temperature differences within the chamber
will lead to problems with the humidity level, the design of the instrument can also leadto gradients in the actual humidity in the chamber. Therefore, it is also critical toexamine the homogeneity of the humidity values in the chamber. Poor airflow design,
the previously mentioned temperature effects, and inefficient chamber design can leadto uneven humidity values.
The second reason a uniform and stabile chamber is critical is the response time of the
instrument under test to real changes in humidity and temperature. These instruments
move rather slowly in response to environmental changes (primarily due to their
physical mass). Therefore if the environment never truly stabilizes, then the instrument
will never come to equilibrium with the environment. In this situation, an accurate
calibration is close to impossible.
Well, if the stability and uniformity of both humidity and temperature inside the chamber
are critical to proper calibration then it also makes sense to review the contribution of
the instruments that measure these parameters to the overall uncertainty of thecalibration.

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Humidity Generators – Examining Uncertainty

When you are serious about the quality of the calibrations you are performing you will
want to use reference instruments separate from the humidity generator control
instruments to provide the reference values. This is due to that fact that laboratory
grade temperature and RH reference instruments will provide better levels of
uncertainty than the control instruments used on most if not all humidity generators.
On the temperature side, a high quality reference PRT co-located with the instruments
under test will help minimize any errors. The manufacturer of the temperature reference
should provide you with all of the uncertainty data needed to calculate the uncertainty ofyour calibrations. To maintain consistency of your calibrations over time, it is criticalthat the reference thermometer is always exact same location. If the reference
thermometer is not in the same location the changes in the temperature reading may besmall; however the focus is to minimize all uncertainties, no matter how small.
Which instrument to use for the reference humidity value is a more confusing choice.
There are several different types of methods used as a humidity control instrument:
chilled mirrors, pressure and temperature measurements, and capacitive humidity
sensor to mention the main types. Which instrument is used to control humidity is lessimportant than which instrument is used as the reference humidity instrument. It is
generally accepted that that a reference chilled mirror will provide an excellent level of
uncertainty in a humidity calibration. As with the temperature reading, the manufacturerof the chilled mirror should be able to provide you with all the data necessary to
calculate the uncertainty of the reference instrument. If the accuracy of yourcalibrations is a bit looser, say ±2.0% or higher, the use of a high quality RH instrument
based on a capacitive sensor can be used. But, it is critical to note here that thesensors should be specialized for calibrations at one point only. This is due to thenegative effect sensor hysteresis has on the accuracy of the capacitive sensor.
Chamber stability, chamber uniformity,
and reference instruments uncertainty
have all been discussed regarding theirimpact on your instrument choice. But
what can be done with all thisinformation? It must be pulled together ina total study of the uncertainty of thecalibration system. A summary exampleof this is shown in Table One. Eachcolumn of data has a specific uncertainty
analysis which generated the values
shown in the table. For example, for thecolumn titled HygroGen, data was developed on the stability and uniformity shown in
the HygroGen for both temperature and humidity. This data was then summarized into
one standard uncertainty using common statistical methods.
In order to properly evaluate a calibration instrument for use in your calibration lab it isvery important to review the data provided by the instrument manufacturer. ThisThe Rotronic Humidity Handbook

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Application Stories and Tales

information must include specifications addressing the stability and uniformity of thecalibration chamber. The specifications must also address both temperature andhumidity variables. This data should include analysis at the actual temperatures andhumidity values you plan to use. Due to mechanical design, controller performance,
temperature control, and the humidification system, performance of the various
generators on the market today can vary widely over the stated operating range of theunit.
Look at all the facts, compare the key uncertainty data, address your individual
calibration needs, and then decide which instrument is right for your calibrationlaboratory.
Table One
Uncertainty of % RH inside the Hygrogen (at 20 °C)

Humidity

Reference
Temperature
uncertainty σ% RH

ChilledMirror
Uncertaintyσ% RH

Dew Point
to RH
conversion
algorithm
σ%RH

HygroGenσ% RH

Expanded
Uncertainty
95%
confidence
(k=2)
%RH

80%
50%
35%
10%
5%

0.190
0.107
0.071
0.027
0.017

0.367
0.244
0.177
0.088
0.048

0.001
0.001
0.002
0.014
0.007

0.073
0.125
0.036
0.048
0.044

0.84
0.59
0.39
0.21
0.14

Instruments included in the chilled mirror uncertainty analysis include the following:-Temperature indicator Chub-E4, mod. 1529-R (Hart Scientific)-Platinum Resistance Thermometer (PRT), mod. 5614
(Burns Engineering)-Dew point indicator, mod. M1 (General Eastern)-Chilled mirror sensor mod. 1311DR-SR (General Eastern)
The Rotronic document "HygroGen 2 – Stability and Uniformity Analysis" is available at www.rotronic-usa.com for detailed
information on the analysis. Modifications reserved.
The development of this data follows ANSI/NCSL Z540-2-1997 (R2002) standard regarding the expression of uncertainty inmeasurement. Please refer to this standard for a more detailed discussion on uncertainty analysis if needed.

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The Rotronic Humidity Handbook

Page 126

Other Helpful Information‘

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The Rotronic Humidity Handbook

Temperature Conversion Table

Other Helpful Information
Temperature Conversion TableºC-45.56-45.00-44.44-43.89-43.33-42.78-42.22-41.67-41.11-40.56-40.00-39.44-38.89-38.33-37.78-37.22-36.67-36.11-35.56-35.00-34.44-33.89-33.33-32.78-32.22-31.67-31.11-30.56-30.00-29.44-28.89-28.33-27.78-27.22-26.67-26.11-25.56-25.00-24.44-23.89-23.33-22.78-22.22-21.67-21.11-20.56-20.00-19.44-18.89-18.33-17.78-17.22-16.67

To ConvertºF or ºC
-50
-49
-48
-47
-46
-45
-44
-43
-42
-41
-40
-39
-38
-37
-36
-35
-34
-33
-32
-31
-30
-29
-28
-27
-26
-25
-24
-23
-22
-21
-20
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2

ºF
-58.0
-56.2
-54.4
-52.6
-50.8
-49.0
-47.2
-45.4
-43.6
-41.8
-40.0
-38.2
-36.4
-34.6
-32.8
-31.0
-29.2
-27.4
-25.6
-23.8
-22.0
-20.2
-18.4
-16.6
-14.8
-13.0
-11.2
-9.4
-7.6
-5.8
-4.0
-2.2
-0.4
1.4
3.2
5.0
6.8
8.6
10.4
12.2
14.0
15.8
17.6
19.4
21.2
23.0
24.8
26.6
28.4
30.2
32.0
33.8
35.6

ºC
-16.11-15.56-15.00-14.44-13.89-13.33-12.78-12.22-11.67-11.11-10.56-10.00
-9.44
-8.89
-8.33
-7.78
-7.22
-6.67
-6.11
-5.56
-5.00
-4.44
-3.89
-3.33
-2.78
-2.22
-1.67
-1.11
-0.56
0.00
0.56
1.11
1.67
2.22
2.78
3.33
3.89
4.44
5.00
5.56
6.11
6.67
7.22
7.78
8.33
8.89
9.44
10.00
10.56
11.11
11.67
12.22
12.78

The Rotronic Humidity Handbook

To ConvertºF or ºC
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55

ºF
37.4
39.2
41.0
42.8
44.6
46.4
48.2
50.0
51.8
53.6
55.4
57.2
59.0
60.8
62.6
64.4
66.2
68.0
69.8
71.6
73.4
75.2
77.0
78.8
80.6
82.4
84.2
86.0
87.8
89.6
91.4
93.2
95.0
96.8
98.6
100.4
102.2
104.0
105.8
107.6
109.4
111.2
113.0
114.8
116.6
118.4
120.2
122.0
123.8
125.6
127.4
129.2
131.0

ºC
13.33
13.89
14.44
15.00
15.56
16.11
16.67
17.22
17.78
18.33
18.89
19.44
20.00
20.56
21.11
21.67
22.22
22.78
23.33
23.89
24.44
25.00
25.56
26.11
26.67
27.22
27.78
28.33
28.89
29.44
30.00
30.56
31.11
31.67
32.22
32.78
33.33
33.89
34.44
35.00
35.56
36.11
36.67
37.22
37.78
38.33
38.89
39.44
40.00
40.56
41.11
41.67
42.22

To ConvertºF or ºC
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108

ºF
132.8
134.6
136.4
138.2
140.0
141.8
143.6
145.4
147.2
149.0
150.8
152.6
154.4
156.2
158.0
159.8
161.6
163.4
165.2
167.0
168.8
170.6
172.4
174.2
176.0
177.8
179.6
181.4
183.2
185.0
186.8
188.6
190.4
192.2
194.0
195.8
197.6
199.4
201.2
203.0
204.8
206.6
208.4
210.2
212.0
213.8
215.6
217.4
219.2
221.0
222.8
224.6
226.4

ºC
42.78
43.33
43.89
44.44
45.00
45.56
46.11
46.67
47.22
47.78
48.33
48.89
49.44
50.00
50.56
51.11
51.67
52.22
52.78
53.33
53.89
54.44
55.00
55.56
56.11
56.67
57.22
57.78
58.33
58.89
59.44
60.00
60.56
61.11
61.67
62.22
62.78
63.33
63.89
64.44
65.00
65.56
66.11
66.67
67.22
67.78
68.33
68.89
69.44
70.00
70.56
71.11
71.67

To ConvertºF or ºC
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161

ºF
228.2
230.0
231.8
233.6
235.4
237.2
239.0
240.8
242.6
244.4
246.2
248.0
249.8
251.6
253.4
255.2
257.0
258.8
260.6
262.4
264.2
266.0
267.8
269.6
271.4
273.2
275.0
276.8
278.6
280.4
282.2
284.0
285.8
287.6
289.4
291.2
293.0
294.8
296.6
298.4
300.2
302.0
303.8
305.6
307.4
309.2
311.0
312.8
314.6
316.4
318.2
320.0
321.8

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Other Helpful Information

Glossary
Accuracy – The nearness of agreement between a measured value and a known
standard.
Calibration – The comparison of an instrument’s performance to a known standard. Can
be used to verify an instrument’s accuracy or used to adjust the accuracy of an
instrument through a given set of instructions.
Capacitive Humidity Sensor – A sensor consisting of a hygroscopic dielectric material
placed between a pair of electrodes forming a small capacitor.
Condensation – The change in phase of a gas to a liquid state.
Dew Point – The temperature to which a gas must be cooled in order for condensation
to form.
Frost Point – The temperature at which frost forms upon cooling a gas.
Linearity – The variation between a know standard and the instrument’s reading acrossthe low and high end of the measuring range.
Mixing Ratio – The mass of water vapor within an area divided by the mass of dry air
within the same area.
Repeatability – The closeness between multiple readings performed under the sametest conditions.
Resolution – The smallest change in a reading that an instrument is capable ofdisplaying. Typically governed by the instrument’s display.
Response Time – How long an instrument takes to react to changes in a given
condition.
Traceability –The property of the result of a measurement or the value of a standard
whereby it can be related to stated references, usually national or international
standards, through an unbroken chain of comparisons, all having stated uncertainties.
Uncertainty of Measurement – Any measurement, has components which effect results
given. These can include systematic (instrument) and random (human) errors. The
combined amount of these errors form the uncertainty of measurement.
Water Activity – The relative humidity reached in a sealed container where ahygroscopic product has been placed. Water activity (aw) is expressed on a scale of 0 to
1.

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