IllJllllllllllllilllllillllllllll puBUcI^KSNS

AlllDt Bt2S73

NBSIR 75-933

A Study of the National Humidity

and Moisture Measurement

System

Arnold Wexler

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

August 1975

foo

^ lEPARTMENT OF COMMERCE

vt^ 75- f 33 '^AL BUREAU OF STANDARDS

CO-

NBSIR 75-933

A STUDY OF THE NATIONAL HUMIDITY

AND MOISTURE MEASUREMENT

SYSTEM

Arnold Wexler

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

August 1975

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III, Urtder Secretary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Director

CONTENTS

EXECUTIVE SUMMARY 1 1. INTRODUCTION 3

2. STRUCTURE OF THE MEASUREMENT SYSTEM 3 2.1 Conceptual System 3 2.2 Basic Technical Infrastructure ! ! ! ! 4 2.2.1 Documentary Specification System \ 5 2.2.2 Instrumentation System , . ] . 7 2.2.3 Reference Data ............. g 2.2.4 Reference Materials n

2.2.5 Science and People ...... 12 2.3 Realized Measurement Capabilities ! ! ! ! 12 2.4 Dissemination and Enforcement Network •]3 2.4.1 Central Standards Authorities , ^ 13 2.4.2 State and Local Offices of Weights and Measures | ..,.....,[ 13 2.4.3 Standards and Testing Laboratories and Services ] , 13 2.4.4 Regulatory Agencies , . . . . 15 2.5 Measurements Transaction Matrix . . . . 15 2.5.1 Analysis of Suppliers and Users . . . . 15 2.5.2 Highlights c£ Major Users -ic 3. IMPACT, STATUS AND TRENDS OF MEASUREMENT SYSTEM , ] 15 3.1 Impact of Measurements 15 3.1.1 Functional, Technological and Scientific Applications 15 3.1.2 Economic Impacts--Costs and Benefits , \y

3.1.3 Social, Human, Person-in-the-Street Impacts- 23 3.2 Status and Trends of the System 03

4. SURVEY OF NBS SERVICES . . . 25

4.1 The Past - Historical Background 25 4.2 The Present--Scope of NBS Services •. . . 27 4.2.1 Description of NBS Services 27 4.2.2 Users of NBS Services 31 4.2.3 Alternative Sources 31 4.2.4 Funding Sources for NBS Services .... ..... 3] 4.2.5 Mechanism for Supplying Services ... 3] 4.3 Impact of NBS Services 31 4.3.1 Economic Impact of Major User Classes 32 4.3.2 Technological Impact of Services 32 4.3.3 Pay-off from Changes in Services 32 4.4 Evaluation of NBS Program 33 4.5 The Future 33

5. SUMMARY AND CONCLUSIONS 34 Appendix A. Methodology of the Study 34 Appendix B. Summary of Background Documents .... 35 Appendix C. Manufacturers of Humidity Instruments and Controls 37 Appendix D. Manufacturers of Moisture Instruments and Controls 39 Appendix E. Selected Compilations of Standard Reference Data for

Humidity and Moisture

Appendix F. NBS Interfaces with Users of Humidity Measurement

System over the Past Decade ^"I References 42
LIST OF FIGURES

Figure 1. Interrelationship of humidity units

Figure 2. Hierarchy of humidity standards

Figure 3. Accuracy chart

Figure 4, NBS humidity measurement services

Figure 5. MBS humidity measurement capabilities

LIST OF TABLES

Table 1 .

Table 2. Table 3.

Table 4.

Table 5. Table 6. Table 7. Table 8. Table 9. Table 10 Table 11 Table 12 Table 13

Table 14 Table 15

Table 16

Table 17 Table 18 Table 19 Table 20

Materials covered by ASTM standards with procedures for the measurement

of moisture

Materials covered by ASTM standards for measurement of water vapor transmission

Materials covered by ASTM standards requiring conditioning or control of

cabinets or rooms Organizations having standards, specifications, or procedures involving

humidity or moisture measurement and control

Absolute methods of humidity measurement

Humidity generators

Secondary humidity standards

Fixed humidity points

Classification of humidity measurements

Classification of moisture measurements

Absolute methods of moisture measurement

Direct measurements transactions matrix

Impact of humidity measurement and control on selected disciplines, industries,

and technologies

Industrial statistics on selected manufactured products for 1973 Relative order of occurrence of various types of measurements in the process industries

Relative humidity and temperature requirements for some industrial processes

and products control

Agricultural statistics on selected grain and oilseed crops

riBS calibration ranges and accuracies

Instruments calibrated by NBS over the last ten years

Users of instruments calibrated by NBS over the last ten years

11
A STUDY OF

THE NATIONAL HUMIDITY AND MOISTURE HEASURB-1ENT SYSTS'i

Arnold Wexler

Heat Division

Institute for Basic Standards

August 1975

EXECUTIVE SLiMKARY

Water in the forr: of vapor and liquid

(inoisture) is an ubiouitous substance

that pervades our earth affecting almost every rriaterial , process, device, instrument

and product. Life itself depends on its presence. It plays an important role

in the scientific disciplines, in many

branches of engineering, in medicine,

meteorology, and agriculture, and in such diverse industrial fields as airconditioning, drying, refrigeration,

storage, food processing, electronics

and connunications . Because of the

innate interaction betv,een water and

its surroundings, and the pervasive

effect water has, it is essential to be able to determine or adjust the amount

present, that is, to be able to measure

and control its quantity in a given

environment or material.

Instruments which measure water content

in the vapor phase are classified as hygrorreters; those that measure water

content in the liquid phase, that is,

that measure moisture in liquids and

solids, are classified as moisture

meters. This study delineates the infrastructure of the humidity and

moisture measurement system and the interrelationships that exist between

the fundamental units, the standards,

the calibration procedures, the instruments,

and the users. It examines the impact

that this measurem.enr sysrem has on economic, scientific, social and industrial aspects of our national life.

Finally, it identifies and analyzes certain

deficiencies and needs in the National Measurement System.

The primary responsibility of NBS is to provide the central basis for the National Measurement System, to coordinate

that system nationally and with those

of other nations, and to furnish the

fessential services leading to accurate

and uniform measurements throughout the

USA. The study shov/s that the ','BS base

for the humidity measure.ment system

comprises five primary elem.ent: (1)

measurements research, (2) standards

development, (3) cevelopmient of special

instruments for specific end useS; (4) prototype development and construction

of new instruments to meet the needs for

secondary standards, and (5) issuance of publications, such as monographs, to provide users with infcrr.ation on instruments, methods of measurement,

sources of accuracy, NBS capabilities, etc. Coordination is achieved through the

dissemination of information, data,

techniques, methods, procedures, references

and reprints to Government, industry,

colleges, universities, institutes,

industrial laboratories, foreign

governments and foreign organizations.

One important link in the coordination

chain is the presentation of tutorial

lectures before professional societies,

workshops, seminars, clinics and training

courses. Direct services are offered

through (1) calibration of plant and

laboratory standards, (2) tests for

com.pliance with government procurement

specifications, (3) evaluation and testing

of sensors for special government programs

and (4) tests for the public when comercial,

industrial or university laboratories

cannot meet required needs. This study categorizes and classifies

the instrumentation in current use in terns

of principles of operation, commercial sources, and end uses. At least twentyfour distinct types of humidity instruments

and controls and seventeen distinct types

of moisture meters and controls are knov.r to be made in the USA. These ere available

from-more than 100 manufacturers.

Information gathered so far indicates

that the annual business volume of the

identifiable instrumentation industry

for humidity and moisture measurement

and control is of the order of 35 to

70 million dollars. This instrumentation

impacts on a great diversity of disciplines,

industries and technologies, creating a second order effect that is estimated to

run into the billions.

1
In the process industries such parameters

as temperature, flow, liquid level, pressure,

chemical composition, density, viscosity,

humidity and moisture are monitored and regulated. It is estimated that of the

total number of such measurements, humidity

constitutes 3.5 percent and moisture 0.7

percent. The economic loss resulting

from measurement inaccuracies is substantial.

For example, the uncertainties in the determination of moisture in grain, such

as corn, can result in annual dollar

losses from excess moisture or excess

drying of SI 35 to 375 million.

The amount of water in a material is of

vital commercial concern--in buying, selling,

shipping, etc. It greatly affects the

properties of materials. The relative

humidity of the environment and the moisture

content of a given material must be controlled for many industrial processes

and for the production of a great many

products. Only through such control can such factors as product uniformity, quality,

and process econcmy be achieved. Such

control contributes to the conservation

of fuel and energy in drying processes. In the testing of many materials for strength,

perfonnance , life, etc., humidity control

plays a paramount role. For example, a review of American Society for Testing

and Materials (ASTM) standards has identified at least 45 categories of

materials that must be conditioned in cabinets or rooms prior to test and 84 categories of materials covered by procedures

for the measurement of moisture content. Other organizations having standards,

specifications or procedures involving

humidity or moisture measurement and control

include Air Conditioning and Refrigeration

Institute (ARI), American National Standards

Institute (ANSI), American Petroleum

Institute (API), American Society for

Agricultural Engineers (ASAE), American

Society of Heating, Refrigerating and Air

Conditioning Engineers, Inc. (ASHRAE),

American Society of Mechanical Engineers

(ASME), Association of Official Analytical

Chemists (AOAC), Cooling Tower Institute

(CTI), U. S. Department of Agriculture

(USDA), U. S. Department of Defense (DOG),

Technical Associations of the Pulp and

Paper Industry (TAPPI), Underwriters

Laboratories (UL), International

Organization for Standardization (ISO),

International Electrotechnical Commission

(lEC), U. S. Department of Commerce--

National Oceanographic and Atmospheric

Administration (NOAA), and the World

Meteorological Organization (WMO).

This study has disclosed several

shortcomings and deficiencies in the National Measurement System. As an example,

there are no national standards for moisture

measurements. Various technologies have

established recommended practices or specifications through voluntary documentary

organizations such as The American Society

for Testing and Materials. In the

agricultural field, the U. S. Department of

Agriculture and the Association of Official

Analytical Chemists have established

reference methods for determining moisture

in specific materials, yet none is directly

traceable to NBS.

As a result of this study, and in response to requests from state weight

and measures of^ficials, NBS has initiated a program with the broad goal of providing

the central basis within the USA of a consistent measurement system for moisture

in materials and to provide essential

moisture measurement services throughout

the Nation.

2
1 . INTRODUCTION

Water vapor and moisture are ubiquitous,

pervading our earth and affecting almost

every material , process, device, instrument

and product. Life itself depends on their

presence. They play important roles,

in the scientific disciplines, in many

branches of engineering, in medicine,

meteorology and agriculture, and in such

diverse industrial fields as airconditioning

,

drying, refrigeration, storage, food

processing, electronics and communications.

Because of the innate interaction between water vapor and moisture and their surroundings,

and the effects this has, it is essential

to be able to determine or adjust the amount present, that is to measure or control the quantity in a given environment

or material

.

The amount of water vapor or moisture

associated with other substances, in common

with such other measurable quantities

as mass, length, time, force and pressure,

is a parameter of the National Measurement

System [1-3]. This system is a complex

structure of interrelated scientific,

technological, social and economic components

which has as its essential function the

provision of a measurement basis for

interchangeabi 1 ity and decisions for action

in public affairs, commerce, industry,

science and engineering. This study assesses

the status of the system, that is it determines the current base line of that

segment that is concerned with the measurement

of v;ater vapor and moisture. It focuses

on the physical process of measuring and controlling v/ate-- vapor and moisture.

It describes the nature, extent and economic

dimensions of the system. It indicates

impacts and trends, identifies deficiencies

and shortcomings, and shows what role

NBS plays in the system.

2. STRUCTURE OF THE MEASURET-IENT SYSTEM

2.1 Conceptual System

Humidity in the broadest sense is a term designating the water vapor content

of a gas or the moisture content of a liquid or solid material. In a narrower

context, the term humidity is limited

to denote the water vapor content of a gas, whereas the term moisture content

designates the water associated with a liquid or solid material.

In humidity and moisture measurement,

the basic oroblem is the identification

and quantification of the water (as vapor or liquid) associated with a second

gaseous, liquid or solid substance.

It is usually sufficient to assume that

the substance and its associated v/ater constitute a two-component mixture even though the substance itself may be a mul ti -component mixture as, for example,

atmospheric air. The primary quantity

for designating the amount of one constituent

in a mixture is its mass. Let the mass

of water be m^,^ and the mass of the second

(dry) constituent be m^, then the amount

of water in the binary mixture will

be given by either of two ratios

\ ^ ^d

or

If the mixture is gaseous, then the ratio q is called the specific humidity

and the ratio r is called the mixing

ratio or humidity ratio. If the second

constituent is a liquid or solid then

q X 100 is the percentage moisture content

on a "wet" basis and r x 100 is the percentage moisture content on a "dry"

basis. For gaseous mixtures the amount

of water vapor cresent, that is, the

humidity can also be given in terms

of volume, pressure, mole and density

ratios either on a "wet" or "dry" basis.

The derivation of these expressions

of humidity from the base units of neasurer.ent (mole, mass, length, time) is shewn

in -figure 1. The humidity exoressions

are linked to the base units through

definitions and equations of ohysics. 5y

applying the gas laws any one expression

of humidity can be converted into any other equally valid expression. Futhermore,

because the maximum amount of v/ater vapor that can occupy a given volume

at a fixed temperature is predicted

by the saturation vaoor pressure, it

is often convenient and useful to state

the actual amount of water vapor oresent

with respect to this maximum, leading

to expressions of relative water vapor content.
base units MOLE MASS

water vapor MOLE

content RATIOS

water vapor RELATIVE

content relative MOLE

to saturation RATIOS

MASS

RATIOS

RELATIVE

MASS

RATIOS

LENGTH

AREA

VOLUME

j:

DENSITY

DENSITY

RATIOS

RELATIVE

DENSITY

RATIOS

TIME

VELOCITY

VOLUME

RATIOS

RELATIVE

VOLUME

RATIOS

ACCELERATION

FORCE

zn

PRESSURE

PRESSURE

RATIOS

RELATIVE

PRESSURE

RATIOS

Figure 1. Interrelationship of humidity units

2.2 Basic Technical Infrastructure

The humidity and moisture segment of

the fJational Measurement System has an infrastructure comprising such recognizable

components as (1) a documentary specification

system, (2) an instrumentation system,

(3) reference data, (4) reference materials

and (5) science and people. The documentary

specification system is a collection of

international, legal, mandatory and voluntary agreements which describe the test methods and measurement techniques

for evaluating the behavior, performance

and characteristics of materials, devices,

instruments and products under stipulated

conditions of humidity and moisture.

It establishes humidity criteria for testing

and conditioning, and specifies methods,

procedures and instruments for measuring

humidity and moisture. The instrumentation

system provides calibrated, traceable

humidity and moisture instrumentation

that is consistent and compatible with

the nation's measurement standards.

It is this instrumentation system which

enables a user to make the measurements

that are needed in monitoring or controlling

a manufacturing process, or in determining

the properties or performance of a material

or device, or in studying the phenomena

and lav;s of physics.

Reference data provide the measurement

user with critically evaluated numerical

values of the properties and the characteristics of materials. For example,

the properties of the ordinary water

substance are of paramount importance

to humidity and moisture measurements.

These and similar data simplify the measurement process, allowing a user

to obtain answers, perform experiments,

or design instruments, apparatus, devices

and manufacturing orocesses without making

extensive measurements himself or, at least, allowing him to eliminate part
of a measurement chain. V.'hen a particular

substance, say, water, has been adequately

characterized it r.ay be used as a reference

material. Such a substance, when combined

with suitable techniques for its use,

can be enployed to calibrate instrurents.

The various components of the infra- structure interact with each other, foming

feed-back loops that stimulate the advancenent

and developn^ent of the national "easurenent

System. The interfaces between these

components are people applying science

and technology, operating under economic

and societal constraints, sometimes acting

alone, but more frequently in an organization

as, for examole, in a Governm.ent agency,

in a professional society, or in an industrial or trade association.

2.2.1 Documentary Specification System.

The documentary specification system

is best illustrated by the standards of the American Society of Testing and Materials

(ASTI'I). These standards describe procedures

and instruments for the m.easurement of

humidity and moisture; they specify humidities

for conditioning materials prior to test; they describe test chambers and rooms

for controlling humidity or subjecting

materials to cyclic conditioning; and they specify standard atmospheres which must prevail when certain classes of materials

are to be tested. Table 1 contains a list of materials that are covered by ASTM procedures for m.oisture measurement. Table 2 contains a list of materials covered

by ASTA specifications for the measurement

of water vapor transmission under stipulated

conditions of humidity. Table 3 contains

a list of materials that are covered by ASTM specifications requiring conditioning

in cabinets or room.s under controlled

humidity. Other organizations have

established similar standards, specifications

and procedures involving humidity or moisture measurement and control dealing

with their own areas of interest. Some

of these organizations are tabulated in table 4.

"able 1. Materials covered by ASTM standards with procedures for the measurenent of moisture

1 Linestcne

1 Cyick'.ine Soy protein Xylenols hydroxypropyl methylcellulose Naphthalene

Hydrated line Hydroxyethyl cellulose Pyri dene

GypsiBt and gypsin products Oil-type preservatives Cuinol ine GyDsuD plaster Veneer Fatty nitrogen products Sypsui concrete Plywood

Slued veneer constructions

Soap

Fine aggregate Soap products

mineral aggregate Wood-based fiber and particle Sulfonated and sulfated oils Petrol eiir products panel materials Industrial rnetal clearing

Bitu.'iinous materials Charcoal coTipositions Emulsified asphalts i.'ood Antifreeze

Soil-titLTlnous fixtures Luoricatlng grease Alkyl benzene sulfonates

Asphalt insu:ated sidir.g surfaced Aviation gasolines Chlorine-containing bleaches

wiyi nineral acgreoates Crude oils Activated carbon

Soil Fuel oils Ethylene glycols Hardened concrete Coal Propylene glycols Refractory materials Coke Monobasic organic acids

Cerar.ic wh1te*are clays Coriustion air Liouid chlorine Graphite Gaseous fuels Textile materials

Structural insulating board Lac "^sins Wool Shipping containers Pigments (for paints) Wool products

Paper Volatile solvents 'or paint, varnish. Cotton Paperboard lacouer and related products Cotton products Cellulose acetate prcp'onate Olpentene Nylon Injection molding and extrusion

Cellulose acetate butyrate Pine oil materials

Celljlcse acetate Tall oil TFE-f luorocarbon resin molding and Ethylce! lulcse Pine tar and oine-tar oils extrusion materials

Cellulose Naval stores Urethane foam polyol raw materials

Casein ncsin oils Electrical insulating oils Cresses P'^enol Electrical insulating gases

Table 2. "Materials covered by ASTV standards for ir*isure.Tent of water vapor transmission

Paper Asphalt-treated felts Gycsur products Plastic films Flexible sheets

Wood prooucts Sheet natarials Packages

blaster- products Asphalt-treated papers Organic coating films 'liSt^CS

5
NATIONAL STANDARDS

for BASE UNITS

i

NATIONAL

HUMIDITY STANDARD

STANDARD REFERENCE

MATERIAL

(WATER)

I

PRECISION

GENERATORS

NATIONAL STANDARDS

for other

DERIVED UNITS

FIXED POINTS

(CHEMICAL SYSTEMS)

SECONDARY

STANDARDS

I WORKING

STANDARDS

HYGROMETERS

and

HUMIDISTATS

Figure 2. Hierarchy of humidity standards

6
2.2.2 Instrumentation System.

The hierarchy of humidity standards

is shown in figure 2. There are two routes by v/hich the units of humidity

are prooagated to the ultimate user. Both originate with the national

standards for the base units. One route

leads directly to the primary standards

for humidity and then through precision

generators, secondary standards and fixed points to working standards and,

finally, to working instruments and

controls in industry, science and comjnerce.

The second route leads to the national

standards for derived units, such as pressure, v/hich, in turn, are used to characterize the pure water substance.

The latter then is used as the standard

reference material in precision generators

to produce known (predictable) levels

of humidity in selected test gases. Secondary standards or working standards

can now be calibrated with these cases. Tnere are several absolute methods,

outlined in table 3, v/hich are suitable

for use over parts of the humidity domain

as primary standards. Generators capable

of producing gas streams of known moisture

content are tabulated in table 6. Instruments

suitable for use as secondary standards

are listed in table 7. These instruments

are characterized by good precision,

long term repeatability and oredictable

behavior. Methods for establishing

fixed points are shown in table 8. The calibration and testing of hygrometers

m.ay be approached in either of tv/o ways.

An instrument or method that has a firm

theoretical basis and is capable of

giving highly accurate and reproducible

measures of water vapor content is chosen

as a standard. The hygrometer is calibrated

by direct comparison with the standard

when both instruments simultaneously

are exposed or "^nhiected to the same humidities. Alternatively, atmospheres

of known humidity are produced and controlled

by generators which operate predictably

in accordance with known laws of physics.

The hygrometer then is exposed to atmospheres

of knov/n water vapor content or the

gas of known humidity is fed to the instrument under test. Similarly, fixed

points of known humidity are produced

by such chemical systems as saturated

salt solutions, water-glycerin solutions

and water-sulfuric acid solutions. A hygrometer is then exposed to the atmosohere

over the chemical system.

Table 3. i^atsrlals covered by ASTT^ standards requiring conditioning or cortrcl of cabinets or rooms

hydraulic carents Cirboxyr«thyl cellulose Timber

Fiberboard nail-base sheathing

Concrete Hetal preservatives

Soi1-fc1tuminous mixtures Dectrical Insulating materials Coal Fibertoard Veneer Finishes on metal substrates Plywod Paints on wood

GypsuT' products Slued veneer constructions Hoed furniture lacouers Plaster products Adhesive bonds Coatings for plastics

Plastics Dried adhesive solids Fire cords Paper Solid and corrugated fiberboard Cord fabrics Plastic films Wood-based fiber and particle <nit goods Asphalt-treated papers panel materials Industrial filanent yarns AsBhilt-treated felts Wood preservatives Textile products

Flexible sheets '•ood Textiles Paper Products Hood-based materials Textile fibers Shipping containers Structural Insulating roof deck ".ar-i:ade staple fibers Packaoes

Table 4. Organizations having standards, specifications, or procedures Involving hiinidity or moisture measurement and control

A1r Conditioning and Refrigeration Institute 'MI)

A-erican National Standaras Institute (ANSI)

Airerican Petroleum Institute (API) Ar<rican Society for Testing and Materials (ASTM) American Society for Agricultural Engineers (ASA-) American Society of Heating, Refrigerating and Air Conditioning Engineers (^JhRAE) Ar^rican Society of Hethanical Engineers (ASHE) Coding Tower Institute (CTI) General Services Administration (GSA)

U. S. Dept. of Agriculture (USDA)

U. S. Dept. of Defense (OCO/KIL) Technical Associations of the Pulp and Paoer Industry

(TAFP!) Unoerwriters Laboratories (UL)

International Organizatior, for Standardization (ISC) International Electrotechnical Cofmission (lEC)

U. S. Deot. of Comerce (DOC/NCAA) World Meteorological Organization (UMO) British Standards Institute (ESI) Association of Official Analytical Chemists (ACAf) Arwrican Association of Cereal Chenists (AACC)

Ainerlcan Associaticp of Brewing Cher.Uts (AABC) Board of Grain Ccnr.issioners for Canada Com Industries P^esearch Foundation Society of Public Analysts and Other Analytical

Chemists (Britian)

A^ssociation Francaise oe Normalization (AR/OR) International Organization of Legal ^'etrology (OIL")

7
Table 5. Absolute methods of humidity measurement

Name Principle Selected References

Gravimetric^ Measuring the mass of water vapor and volume of gas in a given sample. [4] Volumetric Measuring the chance in volume of a test gas at constant pressure and temperature, after absorption of the water vapor by a deslccant. [5] Pressure Measuring the change In pressure of a test gas at constant volume and temperature, after absorption of the water vapor by a deslccant. [5] Radiochemical Measuring the a-decay In hydrogen tritlde produced by the quantitative

reaction between water vapor and calcium tritlde. [7]

<arl Fischer Titrating moisture, extracted from a test gas by methanol, with a reagent. [8.9]

^Primary (N8S) Standard

Table 6. Humidity generators

Name Principle Selected References

Two-pressure^ Isothermal ly saturating a gas stream at an elevated pressure and then expanding it to a lower fixed pressure. [10-13] Two-temperature^ Isobarically saturating a gas stream at a low temperature and then warming It to a higher fixed temperature. [14-18] Recirculating Two-temperature system with continuous recirculation of the gas stream. [19-21] Combined streams Mixing two gas streams, one dry and the other saturated. [22] Divided-flow Dividing a dry gas stream into a precisely known ratio, saturating one stream while keeping the second dry, then conbining the two. [23-25] Vapor transmission Passing a gas stream on one side of a water vapor permeable membrane, the other

side of the membrane being exposed to liquid water. [26-27] Vapor d1 ffusion Passing a gas stream on one side of a fixed restriction through which water vapor

diffuses frm a liquid source. [28] Catalytic chemical

re act 1 or Analytically reacting oxygen and hydrogen to form water, In the presence of a catalyst. [29]

^ N8S facility

Table 7. Secondary humidity standards

Name Principle Selected References

Dew-point hygrometer Measuring the temperature at which dew or frost forms. [30,31] Pneumatic bridge^ Measuring the pressure drop across a critical flow nozzle bridge. [32.33] Aspirated Psychrometer Measuring the drop In temperature of water due to evaporation in an open system. [34,35] Adiabatic saturation

psychrometer' Measuring the drop in temperature of water due to evaporation In a closedsystem. [36] Coulometrlc hygrometer Measuring the current occuring during the electrolysis of absorbed water. [37-46] Microwave hygraneter^ Measuring the refractive index at microwave frequency. [47-49]

^ NBS development

Table 8. Fixed humidity points

Name Principle Selected References

Saturated salt solutions Establishing an equilibrium humidity over a saturated salt solution. [50] Water-glycerol solutions Establishing an equilibrium humidity over a water-glycerol solution

of known concentration. [51] Water-sulfur1c acid solutions Establishing an equilibrium humidity over a water-sulfuric acid

solution of known concentration. [52.53] Paired-hydrate Establishing an equilibrium humidity over a system of paired salt hydrates. [54]

8
There is a major division between the

instrumentation intended for measuring

humidity and that for measuring moisture.

The instruments and methods utilized for

humidity measurement are designed primarily

for operation in the gas phase; those

utilized for moisture measurement are designed primarily for handling liquids

or solids. Instruments of the first

category are classified as hygrometers,

those of the second category as moisture

meters. Because there is a relationship

between the equilibrium water vapor content

in the atmosphere surrounding a material

and the moisture content of that material,

hygrometers can and often are used to infer the moisture content of materials.

The methods, instruments and procedures that have been used for humidity

and moisture m.easurements encompass a diversity of physical and chemical principles

[55,55]. They range in complexity from

simple mechanical, pneumatic, or electrical

devices to involved, complicated and

sophisticated systems. It is possible,

however, to classify humidity instruments

into six broad groups as shown in table

9. Each of these broad groups contains

a number of general methods that differ

significantly in operating principles.

Each general method, in turn, can have

subcategories and variations.

The essential point to keep in mind

is that there is no one or two universally

accepted methods or instruments that

will suffice for most measurements; rather,

a method or instrument is chosen because

it represents a compromise of performance

characteristics, commercial availability,

cost, etc. that are important for a given

application. Manufacturers of humidity

instruments and controls are listed in Appendix C. Although this apoendix was compiled from several sources it may

not necessarily be complete. There is some overlap since some manufacturers

produce several types of instruments

and controls.

Moisture measuring instruments also

can be classified into six groups based

on broad principles of operation as shown

in table 10. Manufacturers of moisture

meters and controls are given in Appendix

D. Although this appendix was compiled from

several sources it may not be complete.

One critical feature of the moisture measurement system is that nearly all of the continuously indicating devices

are empirical in nature. Not only is each instrument dependent on a calibration,

but each calibration is different for

each material, and varies with the chosen

reference standard. There are four absolute

methods, outlined in table 11 that sometimes

are used as reference standards. These

methods often yield divergent results.

A basic difficulty arises from the vagueness

of the meaning of water content. Water

in a material may be physically adsorbed

on the surface, chemically bonded as

in a hydrate, condensed within the capillaries,

or trapped in interstitial spaces.'

Which forms of water are present and

which forms should be measured depend

on the characteristics, behavior and

use of a given material. The various

methods, procedures and techniques of measurement, including those chosen

as reference standards, do not necessarily

detect all, or even the same kinds and

quantities, of the identifiable forms

of water. Thus there is a lack of uniformity

and consistency in this measuring system.

The typical industrial calibration

orocedure is to remove samples of materials

from a process line under operating

conditions, to forward these to a laboratory,

and to use a reference standard for determining the moisture content. The indication of the moisture meter on the process line is thus related to the moisture content as measured by the reference standard.

Economically, the measurement instrumentation

industry for humidity and moisture is estimated to have an annual sales volume

in the range $35-70 million (see section

3.1.2).

2.2.3 Reference Data.

The physical properties of the pure water substance are utilized as the primary reference data of the measurement

system. There are a large number of

properties of water, alone and as a component of a chemical system, yet

there is no single source of critically

evaluated reference data for use in the humidity and moisture measurement

system; rather, there are a number of

different compilations which do not always agree vnth each other or with

the best available data. Appendix E gives an indication of the types and extent of these data. It shows in which

of several important compilations certain

selected reference data may be found.

It also identifies a limited number

of special data sources. These compilations

are identified by the acronyms given below

and at the bottom of the appendix.
Table 9. Classification of humidity measurements

Generic Name of Method Principle of Operation

1. Removal of water vapor from a moist gas Gravimetric Volumetric

Pressure Coulometric

Pneumatic bridge Diffusion

Weighing water absorbed by a desiccant Measuring decrease in volume at constant pressure Measuring decrease in pressure at constant volume Measuring current from electrolysis of absorbed water Measuring pressure drop across critical flow nozzle bridge Measuring pressure drop across semi -permeable membrane

2. Addition of water vapor to saturate a gas Gravimetric Volumetric

Pressure Psychrometric

Weighing water added to saturate gas Measuring increase In volume at constant pressure Measuring increase in pressure at constant volume Measuring temperature of water due to evaporation

3. Sorption of water vaoor bv a sensor

Electric

^'echanical Weighing Colorimetric

Piezoelectric

Heat of sorption '

Measuring electrical quantity such as resistance, conductance, etc. Measuring dimensional change Measuring change in weight Measuring change in color Measuring frequency change of a quartz crystal Measuring temperature change produced by sorption

4. Measuring physical prooerty of a moist gas Spectroscooic

Refractive

Thermal Conductivity

Measuring attenuation of IR or UV radiation Measuring change in refractive index at RF or microwave frequencies Measuring change in thermal conductivity

5. Vapor-liquid or vaoor-solid equilibrium

Dew (frost) point

Cloud chamber

Saturated salt solution

Measuring temperature at which dew or frost forms Measuring pressure ratio required to produce fog after adiabatic expansion

Measuring equilibrium temperature of saturated salt solution

6. Chemical reactions or procedures

Titration Conversion reactionMethanol extraction of water vapor and titration with Karl Fischer reagent

Reacting water vapor with chemical to produce measurable gas

Table 10. Classification of moisture measurements

Generic Name of Method Principle of Operation

1. Removal of moisture from a material Gravimetric Change in weight after drying in oven, by aspiration, or by vacuum.

2. Measuring physical property of a material Refractive Dielectric

Impedance Spectroscopic '

' Power absorption

Measuring change in refractive index Measuring change in dielectric constant or capacitance at R. F. or microwave frequencies

Measuring change in resistance, impedance or conductance Measuring attenuation of IR radiation Measuring power absorption change

3. Nuclear methods

Neutron scattering Nuclear magnetic resonance Moderation of fast neutrons by hydrogen nuclei Measuring the nuclear magnetic absorption signal of hydrogen nuclei

4. Chemical reactions or procedures Titration

Distillation

Conversion reaction Chromatographic

Methanol extraction of moisture and titration with the Karl Fischer reagent

Solvent extraction followed by distillation

Reacting moisture with chemical to produce measurable gas Solvent extraction followed by chrcmatographic determination

S. Equilibrium vapor pressure

HygrOTietric , Measuring equilibrium humidity in atmosphere surrounding material

6. Thermometric methods

Thermal conductivity

Boiling or freezing point Heat of hydration

Specific heat

Measuring change in thermal conductivity Measuring change in boiling or freezing point Measuring heat production by sorption Measuring change in specific heat

Table 11. Absolute methods of moisture measurement

Name Principle Selected References

Gravimetric Change in weight of a sample after drying in oven, by aspiration, or by vacuum [56] Coulometric Measuring current from electrolysis of absorbed water after removing the water

from a sample by drying and aspiration. [37,39,56-60]

Titration Methanol extraction of moisture and titration with the Karl Fischer reagent [56,61]

I Distillation Solvent extraction followed by distillation and volumetric measurement of moisture [56]

10
The International Critical Tables

(ICT) [62] contain an extensive collection

of data on the properties of water.

These tables were published in 1928 and,

unfortunately, have not been revised

since then. However, because of the

breadth of coverage the tables continue

to be useful. The Landolt-Bornstein

Tabellen (LBT) [66] contain a comparable

coverage that reflect some updating due

to the occassional issuance of revised

editions. The most complete and exhaustive

collection of data, as of 1940, is given

in Dorsey's "Properties of Ordinary WaterSubstance" (D) [72]. Several monographs

[87-89] have been published recently

but these are intended primarily to relate

the properties of water to its structure

rather than present best values. The

Handbook of Chemistry and Physics (HCP)

[65] is a useful source of a wide range

of reference data. New editions are published periodically.

The formulations of Goff and Gratch

(GG) [73-75] yield a consistent set of

evaluated reference data on the low-pressure

properties of water and moist air. These

formulations were adopted in 1947 by the Twelfth Conference of Directors of

the International Meteorological Organization

and by the International Committee on Psychrometric Data in 1949 [75]. Tables

of data based on the Goff and Gratch

formulations are included in the ASHRAE

Guide (AG) [67], in the Smithsonian

Meteorological Tables (SMT) [64] and

in the International Meteorological Tables

(IMT) [63].

Critically evaluated properties of

v/ater are tabulated in great detail in various steam tables (ST) [68-71]. Although

these tables include some values at low pressures, which are of interest in the humidity and moisture field, most of

the data pertain to the high pressure

domain for use in steam power technology.

Hilsenrath (H) [76] has compiled a group

of tables on the thermal properties of

several gases, including steam and air.

2.2.4 Reference Materials.

Pure v/ater is a well characterized

substance with accurately determined

properties of all its phases, of its transitions from phase to phase, and

of its synthesis and dissociation. Water

from naturally occurring sources is categorized as ordinary water and has a reasonably

fixed isotopic composition [90]. Ordinary

water which meets the specifications

of the American Chemical Society (ACS) for reagents [91] is adequately pure

to be used as a standard reference material.

Deionization or distillation or both

often suffices to produce such pure

water. Fortunately, deionization and

distillation are processes that are performed routinely in many laboratories

so that pure ordinary water is readily

available. The essential link between water and its use for calibration of

a measuring device is a technique, procedure,

or apparatus, such as a humidity generator,

that mixes water as vapor or liquid

with a second component to produce a homogeneous mixture of knovm water vapor

or moisture content. Saturated aqueous salt solutions,

water-glycerin solutions, and water-sulfuric

acid solutions when prepared from reagent

grade chemicals meeting ACS specifications

[91], form characterized chemical systems

which can be used for performing humidity

calibrations, that is, they yield fixed

points of humidity. These chemical

systems are prepared by the user. Saturated

salt solutions are prepared and maintained

easily without the need of using analytical

procedures whereas the constituents

for water-glycerin solutions and v/ater-sulfuric

acid solutions must be measured carefully

and monitored frequently to ensure that

the desired concentration is obtained

and remains constant. When proper procedures

are followed these solutions produce

predictable water vapor contents in the ambient atmospheres within closed

and sealed containers.

Manufacturers of several moisture

meters have attempted, with limited

success, to devise artificial standard

reference materials for calibration

purposes. The Agricultural Marketing

Service of the U.S. Department of Agriculture

(USDA) issues grain samples, primarily

to its field offices, licensed inspectors

and repair service facilities, for use

in checking the accuracy of the instrument

officially approved for measuring moisture

in grain. These samples are part of

a measurement assurance program which

determines whether field instruments

are in compliance with USDA specifications,

To avoid bias the operator of the instrument

is kept unaware of the moisture content

of the samples. He reports his measurements

to an issuing office where they are compared to similar measurements on

a part of the same sample.

n
2.2.5 Science and People.

Humidity and moisture measurements

are so diverse and pervasive in science,

technology, industry and commerce that many people are involved in making and

using such measurements. These people

form a diffuse and heterogeneous group

They interact with each other only in narrow technical fields. For example,

instrumentation engineers in the petrochemical

industry vjill exchange information at meetings of the Analysis Instrumentation

Division of the Instrument Society of

America (ISA). Meteorologists v/ill attend

one or more of the numerous conferences

sponsored by the American Meteorological

Society (AMS) at which humidity measurements

and their application to meteorological

problems are discussed. Similarly, air

conditioning engineers seek information

on humidity from their peers at meetings

of the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE).

Those concerned with measurements of moisture

in grain and other agricultural products

attend meetings of the American Society

of Agricul tural Engineers (ASAE). People

in disciplines as unrelated as' these have

little occasion to interact with each

other even though the instrumentation

they use or the problems they mest solve

have common roots

.

These and similar professional societies sponsor meetings, conferences or symposia

at which one or more sessions are sometimes

arranged on humidity and moisture

measurement. Infrequently, there are

mul tidiscipl inary conferences devoted

exclusively to humidity and moisture.

These are so few they can be cited. On November 25, 1921, a meeting on hygrometry

was held at the Imoerial College in London.

The papers were published subsequently

in the Proceedings of the Physical Society

of London [92]. On June 25-27, 1959. the Institut Francais des Combustibles

et de L'Energie held a conference in France

on moisture in gases and materials. During

1961, the International Union of Testing

and Research Laboratories for Materials

and Structures (RILEM) conducted a "Seminar

by Correspondence on Measurement of Moisture

in Materials and Structures." A Russian

conference on humidity was held in Leningrad

in June 1962. In 1953, two U.S. Government

agencies, the National Bureau of Standards

and the Weather Bureau (now the National

Weather Service), and three technical

societies, the American Society of Heating,

Refrigerating and Air Conditioning Engineers,

the Instrument Society of America, and

the American Meteorological Society jointly

sponsored an International Symposium on

Humidity and Moisture which was attended

by over 850 scientists and engineers

from around the v/orld [93]. During 1971,

the International Measurement Confederation

(IMEKO) held a conference on moisture

in Hungary [94].

There is no single discipline which

furnishes the educational base for the

people who provide for or use humidity

and moisture measurements. The general

science or engineering student is exposed

to the humidity and moisture measurement

system during his university career only

peripherally, if at all. Meteorologists

and air conditioning engineers either

during their college training or in the practice of their professions are destined

to be exposed to the concepts of humidity,

particularly psychrometry , but not necessarily

to the measurement process itself, because

the concepts are essential elements of

their disciplines. Chemists and chemical

engineers, similarly, may come into contact

with humidity and moisture because the measurement or control of these quantities

is critical to many manufacturing processes

and to the behavior and performance of most materials, but measurement information

and experience generally is obtained

informally and empirically.

There is an extensive literature on humidity and moisture, but this is scattered

throughout many scientific and technical

journals. Monographs in English, through

few in number, are available [93,95,96].

Monographs have also been published in Germany [97-99], Poland [100], Romania

[101], Russia [102] and Japan [103].

2.3 Realized Measurement Capabilities

Humidity measurement capabilities

run the gamut from parts ner billion

(ppb), that is, essentially bone dry

conditions, to 100 percent water vapor

at ambient temperatures from -100°C to over 100°C and at ambient pressures from

5000 Pa (1/20 atm) to over 10^ Pa (100 atm). Water vapor contents in the ppb range of, say, air at standard atmospheric

pressure correspond to frost points of -1Q0°C.

Smaller trace quantities do not appear

to have any technological , commercial

or scientific importance. When the water

vapor content reaches 100 percent, then,

obviously, we no longer have a mixture

but only the pure phase. The major industrial

importance of pure phase water vapor

is in steam technology. Measurements

of temperature and pressure will specify

steam completely, so that the instrumentation

normally used for humidity is no longer necessary and, in large measure, is not applicable.
Although measurements of the humidity

of atmospheric air are the most frequent,

it must be emphasized that measurements

are also made in such technologically

important gases as argon, helium, neon, nitrogen, oxygen, carbon dioxide, methane,

sulfur dioxide, butane, ethane, refrigerants,

chlorine, propane and natural gas. The ranges

and uncertainties of a number of selected

instruments and methods, in air at standard

atmospheric pressure, are shown in figure

3. These curves represent the upper limits

of accuracy that are currently attainable.

The state of the art may be summarized

by stating that the best of the commercial

instruments have uncertainties of the order

of 1 1/2 to 2% of the reading which, under

ideal conditions, may sometimes decrease

to V/c. Most instruments tend to have

uncertainties of the order of 3 to 5%. The highest possible accuracy, (0.1%)

can only be realized by the gravimetric

hygrometer [4].

2.4 Dissemination and Enforcement Network

2.4.1 Central Standards Authorities.

The Organic Act of 1901 (15 United

States Code 271-286) as amended authorizes

the National Bureau of Standards to undertake "the custody, maintenance, and development of the national standards

of measurement, and the provision of means

and methods of making measurements consistent

with those standards, including the comparison

of standards used in scientific investigations, engineering, manufacturing, commerce,

and educational institutions with the standards adopted or recognized by the Government." The Act further authorizes

flBS to undertake a number of specific

activities including "the construction

of physical standards; the testing,

calibration, and certification of standards

and standard measuring apparatus; the

study and improvement of instruments and

methods of measurements"; and "cooperation

v/ith the States in securing uniformity

in weights and measures laws and methods

of inspection."

In pursuance of these legal responsibilities, NBS has provided and disseminated

within the United States the national

standards for the seven base and more

than thirty derived units of measurement,

including humidity. There has been

no comparable NBS involvement with

moisture although several of the States

have requested assistance particularly

in the measurement of moisture in grain.

2.4.2 State and Local Offices of Weights and Measures

.

In recent years several of the grain

producing states have established legal

requirements for the accuracy of moisture

in grain instruments. Maryland and North Carolina have voluntary programs

for checking a field instrument

with a moisture meter in a licensed

laboratory. Virginia in 1956 established

a semi vol untary system for checking

moisture meters. In 1959 Nebraska established

through its State Railway Commission

a system for testing grain moisture

meters using selected moisture meters

as standards and referencing these,

in turn, against the gravimetric (air oven)

method. Indiana, Illinois and Iowa have

adopted similar systems. California is attempting to establish procedures for testing

moisture meters by using artifacts which

check electrical characteristics. Other

states have under consideration legislative

proposals or weights and measures regulations

which will establish accuracy requirements

and test procedures for checking moisture

meters.

2.4.3 Standards and Testing Laboratories

and Services.

Humidity measurement accuracy and

consistency are disseminated to the ultimate

user, either by a direct link with the National Bureau of Standards, by an indirect chain involving one or more

stages of transfer, or by the employment

of standard reference materials. Out of a list of 199 standards laboratories

both in Government and the private sector,

surveyed by the National Conference

of Standards Laboratories [104], 104 resDonded that they had the capability

of performing humidity calibrations.

Of these, 5 offered measurement services

only for primary standards, 74 for secondary

or test instruments and 25 for both. The customers of 49 laboratories were limited to their parent or organizations,

54 provided services to others in snecial cases, and 18 indicated that services

were available on a fee basis. Most of the instrument companies

maintain in-house facilities for calibration

and production line testing and quality

assurance. A few of these will perform

calibrations for a fee on instruments

not of their ov;n manufacture.
UNCERTAINTY. I PART IN _ O

_ o o

_ o o o

o

o

UNCERTAINTY. %

14
Several Government agencies (e.g., U. S. Army Electronics Command, Air Force Cambridge

Research Laboratories, Maval Research

Laboratory, National Weather Service)

have R&D laboratories with humidity

calibration and testing capabilities.

These laboratories provide measurement

services to operational units within their agency (for example, the Air Weather Service)

who make routine observations to fulfill

mission-oriented needs. These laboratories

sometimes design or develop new or improved

instruments which then are procured from

commercial sources.

The U. S. Government has inspection

services and testing laboratories [105]

which have the capability of performing

a broad range of tests on almost every

type of material or device purchased for

official use. The items are procured

under Military or Federal specifications

which sometimes prescribe conditioning

in humidity cabinets or rooms, and measurements

of humidity or moisture content. Facilities

and instrumentation are needed for these

purposes.

2.4.4 Regulatory Agencies.

The U. S. Department of Agriculture

(USDA) under the Grain Standards Act of

1916 as amended has the legal responsibility

for establishing standards covering grain

moving in interstate and foreign commerce;

it also has similar responsibilities for

beans, lentils, peas and rice under the

Agricultural Marketing Act of 1946. Acting

under these legistative mandates, the

USDA, through the Grain Division of the

Agricultural Marketing Service has promulgated

official standards for the moisture determination

in grain and related agricultural products

[106] to be used in verifying the accuracy

of new and modified moisture meters and

for preparing new or verifying old conversion

charts for the USDA official moisture

meter. Measurement accuracy is disseminated

by offically approved moisture meters

through a hierarchical system originating

in a main office, devolving to regional

offices and, finally, to licensed grain

inspectors

.

The USDA does not exercise jurisdiction

at the State level. Since moisture content

is, among other considerations, an essential

ingredient in equity in the selling and

buying of grain and related agricultural

commodities, many States, generally through

their official weights and measures organizations, are involved in checking the accuracy

of moisture meters used in trade and commerce

It is traditional for these organizations

to look to rJBS for traceable standards,

as v/ell as for advice and guidance.

2.5 Measurements Transactions Matrix

2.5.1 Analysis of Suppliers and Users.

The interrelationships between the users and suppliers of the National Measurement System for humidity and moisture are shown in the transactions

matrix of table 12. Every user is also

listed as a supplier of measurement

services even though in some cases this duality of function is questionable

or does not exist. The suppliers have

been identified by Standard Industrial

Classification (SIC) codes. The appearance of only one symbol in any transaction box (that for the primary

magnitude quantity) implies that NBS knowledge is sufficiently limited

that the author prefers not to make

an estimate of the subsidiary information

items. A question mark (?) indicates

NBS has insufficient knowledge on which

to make a judgment. Where estimates

of the magnitude, rate of change,

importance or adequacy of the transaction

have been inserted into a matrix element,

these are coded in accordance with the

key given. It must be emphasized that

these entries are judgments on the part

of the author. It would be prudent to view them with caution, to consider

them primarily as educated guesses.

2.5.2 Highlights re Major Users.

See Sections 2.4 and 3.1 and table 13.

3. IMPACT, STATUS, AND TRENDS OF MEASUREMENT

SYSTEM

3.1 Impact of Measurements

3.1.1 Functional, Technological, and

Scientific Applications.

A few examples may serve to demonstrate

the influence of humidity on man, his environment, and his technology. Atmospheric water vapor affects the probability

and amount of precipitation, the formation

of dew, the prediction of damaging

frosts to agriculture, the potential

danger of forest fires, the development

of thunderstorms, the presence of sharp

refractive index gradients which cause anomalous propagation of electromagnetic

energy at microwave frequencies; it affects evaporation from rivers, lakes,

reservoirs, oceans, and snow and ice surfaces; and it affects the transpiration

of moisture from soils, growing crops,

and forests. Man's comfort and health

15
Table 12. Direct measurements transactions matrix

DIRECT MEASUREMENTS

TRAflSACTIONS MATRIX FOR HUMIDITY Ar;o MOISTURE

SUPPLIERS

U

s

ER

S \

1 1

—- a.

1

Documentary

^

Specification

Org.

Instrumentation

„

Industry N

S

c

4

State

and

Local

Office

Weights

and

Measures

*^ ^

r~

a» 0

aOia.

6

0

S

7

=» 0 1^ {— 0 3- 3 n

r> T

rt> -na.n

8

= 0

-1 at *< n

9

Air

Conditioning

0

Industry

"

Chemical

S

Allied

-

Products

Industry

"

Electrical

Equip.

im

Industry 0 —

1 S

—. 0

n 3

rr n

0.

13

Textile

Hill

^

Products

"

Agriculture

and

m

Food Paper

and

\d

Allied

Products

"

ZZ 3 ra ^

at a. r^ 0

3

ro

fit 3^

17

General

to

Public

' Knowledge

Codinunity

2 1 22 1 2 2 1 2 2 1 2

2

2

? 2 1 2 2 2

I 1 3 2

7 2 3 2 1 1

2 Documentary

Specification

Orqani ?atinns

2 2

2 2 1 3 2 1 2

2 2

1 2 22 3 3 2 2

3

2 1 3 2 1 2 3

2 1

2 ^

2 1 3

3 1 2

*

2 1 4

7 0

3 Instnunentation

Industry SIC 3822.3823.3829

2 1 2 2 1 32 1 2 2 1 23 2 4 42 2 23 1 3

2 1 2

2 1 2

2

2 1 2

3 2

2 *

2

3 1 1

4 NBS

2 3

1 2 33 3 31 2 21 3 3

1

^ 3

' 232 ' 31 2 21 2 , 2 2 1 2 2 , 2 2

T 2 2

2 1

1

1

' 1

^ State and Local Off. Weights and Measures

2 2

1 2 2

2 2

2 3

2

1 2

7 7 1 0 7 7 7 7 7

7 7 0

^ Standards, Calib. and Test Labs. 1

2 2 2 ?

2 2

1 7 2 2 2 2

7 7

7 7 0 0

7 DOD

2 1 2

2 1 22 1 32 1 2 ? 2 7

7 2

7 7

7 7 0

^ Other Federal Agencies

2 1 32 1 32 1 22 1 2 2 1 2 2 3 2

7 37 3 2 2 3

9 Aerospace Industry

SIC 372,376

2 1

1 1

2 1 2N

' 7 7 2 2 2

7 7 ? 7 7 7 7 0

'° A1r Condition

Industry SIC 3535

2

3 2

2 1 2

7 ? 2 3 1 2 1 4

2

2

2 3 4

7 7

2 *

3 4

p

7 7

2 3

Chesn and Allied Prod Industry SIC 28 ? 1 1 7 7 2 2 ? ? 1 2 7 ?

7 7 7 7 0

12 Elect Equipment

Industry

SIC 361 .362 .364

7 1 1 77 7 7

7 7 7 7 ? 7 0

13 Electron and Ccnim Industry SIC 366, 357

2 2 7 7 ^2 2 2 7 7 2

7 7 0

Textile Mill Products SIC 22 7 2

'

1

1 0 7 ? 7 7 7 7 7 7 7 7 0

Agriculture and Food SIC 01 ,20 2 2

2 2

2 2 2

2

2 7 7 2 3 7 7 7 7 7 7 0

Paper and Allied

Products SIC 26 7 2

2

1 2 7 ? ? ? ? 7 7 3

7 7 0

Medicine and Health

SIC 30

2 1

1 1 0 0 7 7 7 1

1 1 2 1

1 7 2 7

3 2

3

2

3 2

3

2 General Public 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

KEY TO MATRIX ENTRIES

C - IMPORTANCE OF TRANSACTIONS

1 = Purely convenience

2 = Strongly desirable

3 = No real alternatives

4 = Essential

B - RATE OF CHANGE

N - Declining

0 = Stable

2 = Growing

4 = Growing explosively

7 " Unknown

- (IN)ADEQUACY OF SERVICES

0 » No improvements needed

1 ' Could be improved

2 - Marginal

3 = Serious deficiencies

4 = Out of Control

- MAGNITUDE OF TRANSACTIONS

0 • Trivial

1 » Minor

2 » Moderate

3 " Important

4 » Major

16
are related to the humidity of his environment.

The water vapor content in sealed aircraft

cabins, pressure suits and space vehicles

must be closely controlled. Certain

lung disorders are alleviated by controlled

atmospheres of humidity.

Fabrics, wood, plastics, grains, processed

foods, dry cereals, and tobacco are subject

to mold, rot and high moisture gain at high humidities. Iron and steel will rust in the presence of moisture. Industrial processes such as heat treating, sintering,

brazing and welding of metals and alloys;

dry cleaning; textile, plastics and paper fabrication; and catalytic operations

in petrochemical industries are seriously

affected by humidity. In fact few quantities

affect so many diverse materials, processes,

and industries as humidity and moisture.

Table 13 contains a list of

selected disciplines, industries

and technologies where humidity measurement

and control exert a significant impact.

The processes, operations or phenomena

affected by humidity or moisture and

the nature of the impact or reasons for measurement are included.

The amount of water in a material

is of vital commercial concern, particularly

in buying, selling and shipping where

costs are related to weight. It has

a pronounced effect on the properties

of materials. It must be controlled

for uniformity in mass production processes,

for achieving formulation and process economies, and for the conservation of

fuels and energy in drying processes.

It greatly influences the quality of many products. Moisture in food products

for example, affects taste, color and preservation.

3.1.2 Economic Impacts--Costs and Benefits.

iio attempt has been made to assess

the overall economic impact that the measurement and control of humidity and

moisture has on the technology, industry

and commerce of the United States. Rather,

v;e have selected examples to illustrate

specific cases of this impact. Where

economic data in dollars are known, they

are included.

VJe examine first, the instrumentation

industry. The annual shipments of the

identifiable humidity and moisture instrumentation are estimated to total about $35

million. This may be conservative because

it does not include data or estimates

from all manufacturers listed in Apoendices

C and D. However, it is unlikely that

the annual shipments exceed $70 million.

(See Appendix A).

This instrumentation, supplemented

by laboratory methods and procedures,

supports the manufacture of a broad range of products. Table 14 contains

a partial list of important products,

together with the appropriate Standard

Industrial Classification (SIC) codes

and the values of the industrial shipments

for 1973. This totals over $150 billion.

It should not be inferred that all these products could not be manufactured

without humidity and moisture measurement

and control. On the other hand, without

such instrumentation, product quality

would be impaired or the cost of production

would increase or both. Let us narrow our focus on one industrial

component of the economy, the process industries, v/here such parameters as temperature, flow, liquid level, pressure,

chemical composition, density, viscosity,

humidity and flow are monitored and regulated. The relative order of occurrence

of various types of measurements in the process industries, as given by

Perry [107] is shown in table 15. It is estimated that of the total number

of such measurements humidity constitutes

3.5 percent and moisture 0.7 percent.

To some extent, these estimates for

humidity and moisture do not entirely

reflect their relative importance for measurements often are not made because

of inadequate instrumentation.

Table 16 outlines some industrial processes where humidity control is important, together with the optimum

relative humidity for the successful

operation of the process.

We turn now from the industrial sector

of the economy to the agricultural

sector and look at grains and oilseeds.

These crops (wheat, corn, soybeans,

oats, barley, etc.) must be dried to

a moisture content of 13 to 15 percent

or lower. This is done, generally,

with artifical heat, involving the consumption of fuel energy (usually

propane). Income and profits depend

on moisture content. Excess moisture

leads to spoilage and loss in quality.

Too much drying is wasteful because

of high fuel costs. Also it contributes

to the National energy crisis. The

price of grain is reduced if the moisture

exceeds a designated value. The farmer

suffers a loss if the moisture content

drops below the designated value because

there is more grain per bushel without

a compensating increase in price.

It is therefore to his disadvantage

if the measurement of the moisture

is not accurate. For example, in 1971 the production of corn was 5.6 billion

bushels for v/hich the average season
Table 13. Impact of humidity measurenent and control on selected disciplines, industries and technologies

Discipline, Industry Process, Operation, or or Technology I Phenomenon

Nature of Impact or Reason for Measurement or Control

Aerospace Operating supersonic wind tunnels.

Controlling capsule environment, life support systems, sealed cabins, and pressure suits.

Simulating high altitude and space conditions in environmental chambers.

Studying planetary atmospheres from orbiters and landers.

Measuring upper air humidity.

Dehydrating contaminated fuel tanks of jet aircraft and detecting moisture in jet fuel

.

Characterizing or controlling environment of test section. Preventing condensation due to pressure changes.

Removing and recovering water vapor from expired breath. Ensuring aviator and astronaut survival and comfort.

At high altitude and space temperatures extreme dryness

is essential to prevent icing and freezing.

Moisture is an indicator of possible life.

Humidity affects aircraft icing, condensation trails, carburetor icing, visibility, fog, clouds, precipitation,

UV transmission, ozone depletion, propagation of electromagnetic energy, and ballistic trajectories.

Moisture can cause freeze-up of fuel lines.

Alp Conditioning Controlling humidity of home, office,

factory, public building, theaters, hospitals, etc.

Controlling environment of libraries, museums, art galleries, archives.

Controlling environment of data processing and computer facilities.

Performance testing of humidifiers, dehumidifiers, heat pumps, cooling towers.

Monitoring a1r to cooling coils.

Controlling humidity of greenhouses.

Ventilating deep mines.

Human comfort and health.

Preservation; high humidity causes mildew and rot; dry atmosphere makes materials brittle and subject to cracking

and dry deterioration.

Computer components, punch cards, etc. are sensitive to humidi ty.

Efficiency and rating depend on humidity.

Freeze-up can occur at high humidity.

High humidity helps plant growth.

Human health and comfort.

Atomic and nuclear Treasuring moisture in high pressure reactor cooling gases.

Operating high temperature nuclear reactors.

Presence of moisture indicates leakage of water into reactor.

Moisture In helium causes graphite corrosion leading to unsafe operation.

Biology and Medicine

Studying environmental stress on human

subjects.

Treating obstructive lung disorders.

Studying water vapor boundary layers 1n biological systems.

Studying plant transpiration.

Studying Insect physiology.

Measuring water potential In plants.

Controlling humidity In hospitals.

Evaporative heat loss is dependent on humidity.

High humidity helps maintain mucous blanket moist which.

In turn, permits It to continuously regenerate and sustain

drainage.

Boundary layer is transition zone for heat and vapor

diffusion.

Transpiration rate affects growth.

Health and growth is related to humidity.

Affects growth.

Required for treatment of certain diseases and ailments;

for care of premature babies; to prevent explosions due

to anesthetic gases.

Ceramics Storing, processing and curing of raw materials and finished products. Moisture affects manufacturing process and quality of finished product.

18
Table 13, cont'd. Impact of humidity measurement and control on selected disciplines. Industries and technologies

Discipline Industryl Process, Operation, or

or Technology 1 Phenomenon

Nature of Imoact or Reason for Measurement or Control

Chemical Manufacturing polyethylene; monitoring

ethylene feed gas.

Manufacturing dry ice.

Manufacturing chlorine.

Manufacturing compressed gas.

Manufacturing aviators breathing oxygen.

Liquefying gases.

Maintaining optimum water content In dry cleaning solvent.

Manufacturing of hygroscopic materials.

Manufacturing of drugs and pharmaceuticals. Manufacturing and storing liquid sulfur

dioxide.

Platinum catalyst used is water soluble.

Too little moisture in gaseous CO^ makes Ice too brittle, fractures too easily, too much moisture causes freeze-up

of valves.

Moisture reacts to form waste acid.

Moisture may condense during compression.

Moisture causes freere-up of valves and components.

Moisture causes freeze-up of valves and components.

Too little water results In poor removal of water-soluble

soil; too much causes wrinkling of fabrics, loss of creases and pleats, shrinking of fabrics.

Dry atmosphere essential for handling.

Moisture affects quality and shelf life.

Moisture, even in small quantities, makes liquid sulfur

dioxide highly coriosive.

Dryi ng Monitoring moisture content of effluent

stream from drying column.

Kiln drying of lumber.

Drying instrument a1r.

Drying plant air for pneumatically

operated valves, tools, equipment.

Columns can be maintained at highest efficiency if regeneration Is initiated just before or at instant of breakthrough of water.

Prevents warping and deterioration.

Necessary for effective operation of pneumatic control instruments In process industries; to prevent condensation, freeze-up, and corrosion.

To prevent condensation, freeze-up and corrosion.

Electrical Assembling lamp bulbs.

Insulating transformers with dielectric

liquids.

Sorption of moisture by electrical

insulating materials.

Electrolytic corrosion.

Assembling motors, colls and transformers.

Moisture 1n inert gas used in filling bulbs decomposes allowing oxygen to oxidize filaments and shorten life.

Moisture causes breakdown, arcing and corrosion.

Causes reduction in resistivity and voltage breakdown.

Causes deterioration.

Low humidity required to prevent moisture sorption.

Electronics and Conmuni cations Manufacturing transistors.

Operating microwave and radar equipment.

Operating infra-red dectlon devices.

Maintaining telephone cables, TV cables.

Monitoring hermetically sealed electronic

modules.

Monitoring radar sites.

Moisture causes decay of semi-conductor material; encapsulation Is accomplished In dry N2, He, or A atmospheres.

Radio propagation 1s affected by atmospheric humidity; moisture in wave guides produces corrosion and reduces power handling capability

Performance of IR detectors is dependent on humidity along

path. Humidity of gas surrounding cables affects operation; must

be dry to prevent electrical shortage from moisture

Infiltration.

High humidity often causes failure of electronic components

and assemblies.

To prevent condensation on components.

Fibrous, Organic

and Plastic Materials

Manufacturing plastic materials.

Manufacturing of textiles.

Moisture affects quality.

Humidity control essential for proper operation

of machinery, regain control, elimination of static electricity, reduction of dust.

19
TaOle 13, cont'd. Impact of humidity measurement and control on selected disciplines. Industries and technologies

Discipline, Industry 1 Process, Operation, or

or Technology | Phenomenon

Nature of Impact or Reason for

Measureinent or Control

Food and Agricul ture Drying and storing grain, cereals, rice, flour, starch.

Maintaining moisture control of agricultural

products during harvesting, handling, processing, packaging and transportation. Oistining alcohol, liquor.

Manufacturing and processing food (e.g., bakery products, beer and ale, butter,

candy, chocolate, crakers and biscuits,

macaroni and spaghetti , meat and meat

products, cereals, dehydrated foods).

Manufacturing tobacco products.

Incubating poultry.

High moisture can cause mold and rot, heating. Insect damage, sprouting; sale price affected by moisture content;

improper drying results in loss of quality.

Moisture content can cause deterioration or loss of quality

and quantity, market price affected by moisture content.

Low humidity important where grains are ground.

Humidity affects quality, taste, texture, etc.; high humidity leads to spoilage.

Humidity control necessary for optimum processing.

Proper humidity Insures optimum growth. Marine Mothballing naval vessels.

Storing shipboard cargo.

Drying high pressure air on naval ships, submarines for missile launching, etc.

High humidity causes rust and oxidation of metal structures

instruments components.

High humidity can result in condensation on cargo.

Icing can cause locking and blocking of valves, orifices

and filters.

Metallurgy Welding titanium, stainless steel and other al loys

.

Heat treating, carburlzing, nitriding,

dry cyaniding; polishing, brazing,

sintering, annealing of metals and alloys.

Storage of ferrous metals.

Measuring moisture In sinter mix, coke and Iron ore for blast furnaces.

High water content In A and He causes oxidation of weld.

Water vapor in gases (usually Hj and t>2 ) or furnace atmospheres can decompose yielding oxygen which causes oxidation of metal surfaces; causes decarburization of surface; affects carbon potential.

High humidity causes rust.

Moisture content affects quality and product efficiency

in manufacturing.

| Meteorology Atmospheric monitoring from land stations,

vessels, radiosondes, aircraft.

Stratospheric and mesospheric measurements.

Evaporation from oceans, lakes, reservlors,

rivers, snow surfaces, forests, prairies,

and other land surfaces.

Water vapor turbulence.

Cloud seeding.

Monitoring humidity in forests.

Used for climatology, weather prediction, dynamics of atmosphere, physics of clouds, weather modification.

Weather prediction, atmospheric circulation, IR transmission; climatic Impact from photochemical reactions;

radio propagation.

Affects water budget.

Affects evaporation and transpiration.

Weather modification.

Prediction of forest fires dangers.

Missi les , Munitions , Rockets, Ordnance Monitoring missile tank gas.

Measuring atmospheric humidity.

Monitoring solid propel 1 ent ml xi ng rooms.

Monitoring missile sites.

Controlling humidity around powder type fuses.

Storing liquid rocket propellants.

Too much moisture causes freeze-up bleed valves.

Required for computing trajectories.

Dry atmosphere required for quality control and to prevent corrosion.

Prevention of condensation on components.

RH Is held to 1 percent so that moisture content 1s controlled to 0.1 percent by weight; more moisture

gives slower timing.

Small quantities (few tenths of 1 percent) can cause corrosion rates high enough to cause structural or component failure.

20
Table 13 cont'd. Impact of humidity raeasureinent and control on selected disciplines, industries and technologies

Discipline, Industry

or Technology

Process, Operation, or PhenanencTNature of Impact or Reason for Measurement or Control

Petro-chemical Transporting, transmitting and storing

natural gas and liquified natural gas.

Monitoring moisture level of hydrogen and butane feed lines in butane isororization

process

.

Monitoring water vapor in recycle hydrogen

streams of catalytic reforming processes

for producing high-octane gasoline.

Purging and blanketing operations with

dry gas.

Liquid phase drying of such chemicals as benzine, toluene, zylene, butane, propane, trichlorethylene, refrigerants, methyl chloride.

High moisture content will cause freeze-ups below 0°C

and form hydrates which freeze above 0°C.

Moisture impairs catalyst life and activity.

Provides operational guidance during start-up, normal operation, test run and abnormal conditions. Moisture

poisons catalyst.

Reduces explosive hazards; prevents reaction of chemicals

with moisture.

[ioisture inhibits drying.

Printing and Photography

Color printing and registering.

Letterpress printing, lithography and rotogravure

.

Manufacturing and storage of photographic

film anc paper.

Precise ambient humidity control is essential for controlling paper dimensions to ensure correct registering of successive colors in printing.

Humidity control minimizes problems of static electricity,

ink mist, expanding and contracting of paper with resultant

breaks, swelling or shrinking of composition rollers.

Humidity control to insure optimum manufacturing conditions

and to insure maximum life.

Refrigeration Manufacturing of refrigerant gases.

(tanufacturing and assembly of refrigerating systems.

Moisture will cause freezing-up of expansion valves in compressor.

Moisture will cause operational failures due to freezeup of expansion valves and capillary tubes; formation of ice in evaporators, corrosion, flapper valve failure, damage to insulation.

Research, Development and TestingTesting of materials for water and water

vapor sorption (regain) and permeability

in solid, sheet, granular and powdered

form; includes foods, textiles, grains, ceramics, concrete, building materials,

ruboer, plastics wood, wood products,

tobacco, etc.

Conditioning of materials, products,

instruments, devices in environmental

rooms, chambers, boxes, etc.

Studies of diffusion, viscosity of moist

air, rate of evaporation of water droplets,

sound absorption in gases, germination of mold spores, refractive index of air, etc.

Dry box testing.

Moisture content affects performance, behavior, quality,

and use of materials. Permeability determines effectiveness

as vapor barriers in packaging for moisture

sensitive materials.

Testing for conformance to specifications and standards.

Scientific data.

Materials, devices, coir.ponents , etc. that are affected by moisture are often tested in dry boxes.

Soil Measuring moisture content. Moisture content affects volume changes, which in turn, cause differential movements of structures leading to excessive cracking of floors, walls, and foundations; moisture content important in watershed hydrology; moisture

affects safe current loading of buried cables; and moisture

content affects economic growth of crops.

Storage Kaintaining critical military

inventories, particularly of moisture sensitive materials.

Monitoring dehydrated packaging.

Controlling humidity in warehouses and caves.

Controlling humidity in comercial storage operations 'e.g., beer fermentation

rooms, meat storage, machine tools,

candy, food products, furs, furniture,

paper stock, chemicals).

Many metallic, organic and synthetic materials quickly deteriorate at high humidity due to rot, mildew and fungus growth, particularly in Pacific area and tropics.

Moisture infiltration causes spoilage, corrosion, etc.

Low humidity necessary to prevent deterioration.

To prevent deterioration and loss of product.

1 Structure | (Vjisture content and migration in walls,

1 roofs, etc. Determining origin of moisture (ground moisture

condensation, rain, etc.) necessary to eliminate source.

21
Table 14. Industrial statistics on selected manufactured products for 1973*

r I uuui_ (* Valup n*f T^dt^<^^^\/ M967 basis) Sh i pmen t

s

S Sin-inn^

1925 fiiiidpci rm'^^lps and ^Dar^ vphiclps 3.80

Mpa rkinn nlAnt" nr^di irt"

<

24. 15 2022 Ch6SS6 y ndtural 3nd procssssd 3! 74 2023 Cnnripn^pd snd pvanoratpd milk 1.73

Ti^p i'*p am and "f ynTPn dp< p iH*

c

1 .24

rPI1

1u1 T1 du milt Nil 1 N 9.14

2032 r;innpd WQMilCU qspecial npr* "i a T i ^^ p*; ( 1 . 94 2033 f*annpd frtjit^ vpoptablp nrp^prvp^ iam^ and ipIIip'^ 4.39

tuH 1 Plrtiir" riuui anu Ar\H rt^hpv* uciici ny^ain ^raiii mill tin i i 3(ii|jmic[iuj chinmon^c 3. 10

Dy"Pna)"pH fpoHc ^r\v animalc and ^nu/lc 9.64

uU^ 1 Rfpad and nt'hpf Satinn r{t*r\t\^\rYz 6.24

(*r*ar"tpt*c and /"nnV"ip<i 1 ^83

f*and\/ and rt^'hpv" (*nn ^Pf nn a n»*ndii/"t'c 2.02

Phn/~rt1atp and /"fi^^na n!rndM^'"^c . 72 2095 2.49

21 Tobacco 4.53

2521 31 61 Paopr* and hnard 1 1 .50 ^anitai^v nanpv* nrridiif^c 1 .89 2312 Al kdl i 6S snd chlorlns !77 2813 Industrial aasps .75 2816 Inorgsnic pi gmen ts .78

4 O i o TndllC^r•^a^ rvia n 1 /~ /"h pml ("a 1 < 10.33

2819 Industrial inorganic chemicals sioo

2821 Plastic materials and resins 5.53 2831,33,34 Pharmaceutical preparations 8.62

2841 Soap and detergents 3.33

2851 Paint and allied products 4.15

3011 Tires and inner tubes 6.44

3069 Rubber products 4.25

3585 Air conditioning and cormercial and industrial refrigeration equipment 5.94 TOTAL $150.05

*U. S. Industrial Outlook 1974

Table 15. Relative order of occurrence of various types of measurements in the process industries*

Type of Measurement Estimated Relative Occurrence

Percent Temperature 34.7 Electrical Methods 20.5 Mechanical Methods 12.4 Radiation Methods 1.8 Flow . 17.5 f^chanical Methods 14.6 Electrical Methods

" 2.9 Liquid Level 11.8 Mechanical Methods 10.2

Electrical Methods 1.6 Pressure 11.7 Mechanical Methods 9.8

Electrical Methods 1.9 Chemical Composition 5.6 Electrical Variables (I,E,R, etc.) 4.6 Humidity 3.5 Speed (linear i rotational) 2.1 Density and Specific Gravity 1.8 Moisture 0.7

Others (viscosity, weight, color, etc.) 6.0

*Perry's "Handbook of Chemical Engineering."

22
price paid the farmer was SI. 08 per bushel

(S6.0 billion). The reduction was 2 cents

per bushel for each percent moisture over

15.5 percent. The loss (exclusive of

added drying costs) for each percent moisture

under 15.5 percent was 1.2 cents per bushel.

A spot check in iJovember 1968 in Iowa revealed that ncisture meters commonly

used for moisture measurement of grain

varied as much as 3.4 percent in indicated

moisture on the same samples. If this

same pattern prevailed nationally, farmers

could have suffered a loss of as much

as $341 million from excess moisture

(or moisture indication) or a loss as much as S228 million from excess drying

(or low moisture indication). Reducing

the uncertainty in moisture meters to 0.5 percent could have reduced the possible

loss to $55 million for excess moisture

and to $34 million for excess drying. Similar

calculations can be made for the other

grains. Data on the production and farm

values of important grain and oilseed

crops are given in table 17 for 1971.

It can be seen that moisture measurements

supported agricultural crops in 1971 having a total farm value of at least

$14.9 billion.

3.1.3 Social, Human, Person-in-the-Street

Impacts.

Anyone who has listened to a weather

prediction on radio or TV, or who has read the latest forecast in his nev/spaper, has been exposed to the concept of humidity.

He even may have in his home or office,

a simple instrum.ent which reads or controls

the humidity of his environment. More

likely he has no physical instrument

but his body senses serve as a crude

substitute. High sunmer humidity imparts

a damp or muggy feeling; low winter humidity

imparts a dry and crisp feeling. Physical

effects in and around the home accentuate

the physiological perceptions. When

the humidity is high, drawers stick,

foods become soggy and in winter, condensation

appears on cold window panes. Again,

in the winter, electric shocks from static

charge on rugs or on upholstery in automobiles

are certain signs of low humidity.

Air conditioning, in which humidity

control plays a substantial role, is

a common feature of public buildings,

libraries, museums, art galleries, hospitals,

offices, and with increasing frequency,

private homes. Sometimes when a residence

has no air conditioning, the homeowner

installs a humidifier to increase the humidity for health reasons (usually

bronchial problems) or, perhaps, to improve

the tonal properties of his piano; or

he may install a dehumidifier to reduce

the humidity, particularly in a basement

where mildew and mold have a tendency

to form when the humidity is high.

3.2 Status and Trends of the System

The measurement of very low water

vapor contents is, at best, very crude. Yet there appears to be a need for making

such measurements, particularly in the stratosphere and mesosphere, the oetrochemical

industry, nuclear reactor industry,

com.pressed gases, and in planetary atmospheres.

At the very high water vapor content

end of the humidity domain good methods

of measurement are not available. Instrumentation

that is used over the mid-span of v;ater vapor contents is designed primarily

for ambient pressures of about 0.1 MPa (1 atm)

and for a narrow range of ambient temperatures.

There is a deficiency in the technology

of making humidity measurements at both very low end very high pressures, and

with corrosive gases. In addition,

at high pressures, information is needed

on the enhancement* of water vapor in gases of technological importance.

The assumptions of gas ideality can introduce large errors in the interpretation

of instrument indications.

There is also a need for determining

the frequency response or response time

of instruments and sensors used for

dynamic measurements. Current practice

is to calibrate statically and to assume

that this calibration will hold under

rapidly fluctuating conditions. Within

the measurement system there is only

a limited capability for making response

time studies, yet data of this kind

are vitally needed, particularly for

instruments and sensors used in radiosondes,

rocket sondes and high speed aircraft.

*Erihancement is the ratio of the concentration

of saturated water vapor mixed with

a gas to the concentration of pure phase

saturated water vapor. For example,

at 30=C and 10 MPa there is 34 percent

more vapor present in saturated air

than is predicted solely by the ideal gas 1 av/s

.

23
Table 16. Relative humidity and temperature requirements for some industrial processes and products control

Process or Product Temperature Relative Humidity

or

r Percent Abrasive Manufacture 78 50 Bakery Products Fermentation room 78-82 75 Make-up room 82-84 65 Proof-box 95-98 80-85

Sread cooling 80-85 75 Bread v/rapping 65 65 Brewing Cellar storage 32-35 75 Keg filling and storage 32-35 75 Grain storage 80 70 Ceramics Manufacture

Molding room 80 60-70

Clay storage 50-80 35-65 Decorating 75-80 48 Electrical Products

Coil and transformer winding 72 15 Switchgear 73 50 Conductor wrapping with yarn 75 65-70 Meters-assembling S testing 74-76 60-63

Fur Storage 40-50 55-65 Leather Drying 70-120 75 Matches Manufacture 72-74 50 Pharmaceutical s 75 30-35 Plastics (thermosetting molding) Manufacture 80 25-30 Rubber-dipped Goods Cementing S Dipping 80-90 25-30 Textile Processing

Cotton opening, picking, carding 75 55 Cotton weaving 80 65-70

Linen carding & spinning 75-80 60 Linen weaving 80 80

Wool spinning (worsted) 75-80 50-55

Wool weaving 75-80 50-60

Wool kni tting .

• 76 65 Viscose manufacturing 80 80 Tobacco Products Cigar and cigarette manufacture 70-75 55-65

*ASHRAE Guide and Data Book

Table 17. Agricultural statistics on selected grain and oilseed crops for 1971*

Crop Production Season Average Price Farm Received by Farmer Value

Wheat 1.62 B bu $1.34/bu $2.17 8 Rye 0.05 B bu 0.899/bu 0.04 B Rica 8.58 B lb 0.0534/lb 0.46 B Corn 5.64 B bu 1.08/bu 6.09 B Oats 0.88 B bu 0.520/bu 0.55 B Barl ey 0.46 B bu 0.992/bu 0.45 B Sorghum grain 0.88 B bu 1.03/bu 0.91 B Cottonseed 4.24 M tons 56.81/tcn 0.24 8 Flaxseed 0.02 B bu 2.37/bu 0.04 B Peanuts 3.01 B lb .136/lb 0.41 B Soybeans 1.16 B bu 3.01/bu 3.54 B TOTAL $14.91 B

Agricultural Statistics, 1973. M = millions B = billions

24
Modern meteorological and aerological

research of the atmosphere is moving rapidly

toward the use of passive measurement

technioues. Sensors detect and integrate

signals v/hich travel over long path lengths.

Thus humidity is being detected from satellites, aircraft and balloons by infrared

(IR) and ultraviolet (UV) instruments.

Unfortunately, there are no humidity calibration procedures that can check the accuracy

of these instruments. It is obvious that

as these instruments increase in sensitivity and frequency of use, and

perhaps become synoptic tools, there will

be an urgent need to validate their readings.

Humidity measurement and control for

air conditioning in industrial ooerations,

business establishments, public buildings

and entertainmient centers is an accepted

phenomenon of current American life.

There is an accelerating trend toward

the control of humidity in private homes

for human comfort and health.

\*any industrial processes are dependent

for their successful operation on the drying of materials and products. Agricultural

crops such as grains and oilseeds also

are dried. In the past, with fuel or energy readily available at low cost, empirical

techniques for drying were adequate.

Now, and in the foreseeable future, the

continuous mieasurem.ent and control of Droduct moisture or of the ambient humidity

will be of increasing concern in achieving

optimum mioisture content, high drying

efficiency, and conservation of fuel and energy.

Ccnsum.erism is having an ever increasing

effect on trade and commerce. This is reflected, in part, in regulations issued

at national and local levels, requiring

that product ingredients and even amounts

be specified on the label. It is orobable

that in the future, the inclusion of the

moisture content in specific comj^dities

and products v/ill be required on labels

and that there may also be established

m.andatory limits for m.cisture content. There would, therefore, be a need for

rapid methods of test and inspection.

The field of moisture measurement would

expand into new areas with direct and

imnediate impact on what the person-in-thestreet buys in his local store or supermarket.

4. SURVEY OF UBS SERVICES

4.1 The Past - Historical Background

The history of the involvement of the National Bureau of Standards in the humidity and moisture measurement system

dates back, at least, to the early Twenties,

ihe concern then and over the ensuing years was in the develooment of specialized

instrumentation [10,33,48, 49,108-111,112-129],

humidity cabinets and chambers [15,130-132]

and environmental test room.s [133]. Late in the Thirties, the Bureau developed

a small electrical humidity sensor for

use in radiosondes [116,117] which was adopted by the National Weather Service

(then the Weather Bureau) and by the

U. S. military meteorological services,

and subsequently became an important

industrial device. The evaluation of this sensor presented a new probl em--that

of devising a method and designing a chamber that could be used for calibrations

at temperatures below freezing. This

was the motivation, then, for the development

of the first NES precision humidity generator

[24]. The continued need for better

methods of calibration subsequently led

to the design, development and construction

of other generators [12,19], to an interest

and involvement in the entire field of

humidity measurements, and to the establishment

of facilities and competences that were,

and still are, unique in the country.

As information on the availability

of these facilities became knov/n to other Government agencies, to industry, and

to the scientific community .requests were received with increasing frequency

for calibrations and tests on a variety

of hygrometers. Initially, this work

was restricted to Government agencies.

However, with time it became apparent

that there was a need for humidity standards

and for supplying a calibration service

not only to Government, but also to industry

and other laboratories. This led to the development of a national reference

standard [4] and of lesser order (transfer)

standards [32,36] for use by other laboratories,

to investigating fixed points [50] and

to the acceptance for calibration of instruments suitable for use as laboratory

or plant standards [134],

25
i-3

cn

26
We turn now to the second NBS responsi - bility, the coordination and dissemination of capabilities in the National Measurement

System. In the humidity sector, NBS discharges

this by engaging in three activities:

(a) advice and consultation, (b) participation

in seminars, and (c) hosting foreign guest

v/orkers

.

Information, data, techniques, methods,

procedures, references and reprints are disseminated by telephone, correspondence

and visits. Those who have availed themselves

of this assistance include Government

agencies, industry, colleges and universities,

research institutes, industrial laboratories,

agencies of foreign governments, and foreign

research and commercial organizations.

Many of these interfaces over the past

decade are listed in Appendix F. Tutorial lectures are given before

professional societies, workshops, clinics

and seminars. The following are a few

of these organizations: (a) Moisture

Measurement Clinic, ISA, Rochester, N.

J. 1971 , (b) Symposium on Relative Humidity

and Paper Test F'ethods, TAPPI, Grand Rapids,

Mich., 1960, (c) 14th National Symposium,

Analysis Instrumentation Division, ISA,

Philadelphia, Pa., 1969, (d) Symposium

on Meteorological Observations and Instrumentations, AMS, Washington, D. C.

,

1959, and (e) Industrial Moisture

Measurement Course, Center for Professional

Development, Somerville, N. J., Sept. 1973 and Feb. 1975. Foreign guest workers are welcomed

by NBS in its laboratories. The Humidity

Section has hosted scientists from Japan

and Romania.

The third NBS responsibility is to provide essential measurement services.

These are available to the Government,

industry and the public in support of

the National Measurement System. NBS has the humidity measurements facilities shown

in figure 5. A gravimetric hygrometer

serves as the NBS primary reference standard

[4]. This is a device which continuously

and automatically withdrav/s a sample of

moist gas from a constant humidity source,

removes the water vapor in a train of

U-tubes filled with desiccant, and then

determines the volume of the effluent

dry gas by alternately filling and evacuating

calibrated cylinders. The gain in weight

of the absorption tubes and the measured

volume of gas (converted to mass through

pressure, temperature and density) give

a measurement of humidity in units of mass of water vapor per unit mass of dry

gas. Two precision generators are the

main NES facilities for performing calibrations [12,13,18]. Only when the highest order

of accuracy is required is the gravimetric

hygrometer used for calibration of secondary

standards. The NBS two-pressure humidity

generator produces atmospheres of known

humidity by saturating a gas stream at

an elevated pressure and fixed temperature

and expanding it to a lower (usually

ambient atmospheric) pressure. The humidity

is calculated from the pressures and temperatures, or, more precisely, is established and maintained at any desired

value by selecting and then controlling

appropriate temperatures and pressures.

The NBS low frost-point generator operates

on the two-temperature principle, that

is, it produces an atmosphere of known

humidity by saturating a gas stream at

a selected temperature and fixed pressure

and then heating the stream to a higher

temperature at the same pressure. The

frost point of the effluent gas stream

is the same as the saturation temperature.

Fixed points are obtained with selected

saturated salt solutions whose equilibrium

relative humidities have been established

definitively by NBS. NBS humidity calibration

ranges and accuracies are given in detail

in table 18.

PRIMARY STANDARDS

Gravimetric Hygrometer

PRECISION GENERATORS

Two-pr«»ute

Twa-letnperiture

SECONDARY STANDARDS

Dew-point

Aipintad Prychrometer

Adiib. Sat. PsYchrernettt

Coulometrit

Microwsve

Pneumatic Bridge

i

FIXED POINTS

Sfturited Salt Solutions

Figure 5. NBS humidity measurement capabilities
Table 19. Types of instnjments calibrated by NBS over the last ten years

Adiabatic saturation psychraneter

Aspirated psychrometer

Coulometric hygrometer

Dew-(frost-) point hygrometer

Manufacturer

EGSG Thunder Scientific

Sandia

CEC DuPont MEECO

Beckman Vap-AIr

EG4G Trans-Son1cs

C. F. Cassella

Sandia

Bendix Research

Type

Cloud chamber hygrometer

Electric hygrometer

Infra-red hygrometer

Paired-hydrate generator

Manufacturer

Alnor

Hygrodynamics (AMINCO) Honeywell VIZ

Panametrics Thunder Scientific

National Weather Service

Beckman MSA

Union Carbide

Sandia

Table 20. Users of instruments calibrated by NBS over the last ten years

Agency

NOAA, NWS

NBS, Division 232.09

NBS, Division 411.05

N8S, Division 421.03

AF, Aerospace Res. Labs. (W-P AFB) AFCRL

AF, Hq. Electronic Systems Div. Army, Frankford Arsenal

Naval Eastern Standards Laboratory

U. S. Naval Electronics Lab (San Oiego)

Naval Research Laboratory

Interior (Bonneville Power Admin.) USAEC (Fort Monmouth)

USAEC (Fort Monmouth)

NASA, Kennedy Space Center

NASA, Lang ley Res. Center

NASA, Manned Spacecraft Center (Houston)

NASA, Marshall Space Flight Center

NASA, (White Sands)

Governmen t rimediate Purpose

Lab standard

Lab measurements Transfer standard Working instrument

Lab standard

Lab standard

Aircraft Measurements

Lab standard

Lab standard

Lab standard

Field measurements

Lab standard Transfer standard Helicopter measurements

Lab standard

Lab standard

Lab standard

Lab standard

Lab standard

End Use Meteorology

Mass calibrations Interlaboratory tests Thermal engineering tiSts

AF operation Aerology

Air weather research Ordnance

Naval operation

Naval operation

Laser propaaation

Electric power Atmospheric research Air density Aerospace

Aerospace

Aerospace

Aerospace

Aerospace

Industry Company Immediate Purpose End Use Alnor Lab standard Hygrometer manufacturing

Aro Wind tunnel standard Air weather research

Bendix (Kansas City) Lab standard Atomic energy

Bendix (Scintella) Lab standard Aerospace

Bendix (Sidney) Lab standard Nuclear energy

Boeing Company Lab standard Aerospace Curtlss-Wright Lab standard Aerospace

EGJG Lab standard Hygrometer manufacturing

GE (Picayune) Lab standard Oceanography, aerospace

General Dynamics - Convair Lab standard Aerospace

Grunman Aircraft Lab standard Aerospace

Hamilton Standard Lab standard Aerospace

Hewlett-Packard Lab standard Electronics Hygrodynamics Lab standard Hygrometer manufacturing

Lockheed Lab standard Aerospace

LTV Electosystems Lab standard Aerospace

Martin (Denver) Lab standard Aerospace

Monmouth Electric Ub standard Hygrometer manufacturing

North American Rockwell Lab standard Aerospace

Sandi a Lab standard Nuclear energy Thunder Scientific Lab standard Nuclear energy; aerology Tobacco Institute Testing Laboratory Lab standard Tobacco testing Trans-Sonlcs Lab standard Submarines; hygrometer mfg Union Carbide (Oak Ridge) Lab standard Nuclear energy Vap-Air Lab standard Hygrometer manufacturing

30
Concurrent with supplying measurement

services, NBS has also been a user of

the humidity and moisture measurement

system in discharging its responsibilities

and in performing its scientific and technological work. This activity has covered a wide range of investigations

such as studying the effect of humidity

on resistance of standard electrical

resistors [135], paper [136-138], fibers

and textiles [139-U2], plastics [USUS], collagen, hide and leather [147-

151], microchemical balances [152], engines

[153], asphalt [154], air conditioning

[155], ionization measurements [156],

and floor coverings [157]. It has included

studying the effect of moisture on various

materials [158-164], and investigating

water vapor turbulence [165], water vapor

boundary layers [155-167], and evaporation

[168].

The work involving the application

of measurement technology to the solution

of specific problems has been performed

by a number of organizational units within

NBS. The development, maintenance and

dissemination of standards and the provision

of a calibration service, on the other

hand, is under the cognizance of the Humidity

Section in the Institute of Basic Standards.

4.2 The Present - Scope of MBS Services

4.2.1 Description of FIBS Services.

The primary responsibilities of UBS

are to provide the central basis for the

fiational Measurement System, to disseminate measurement capabilities to that system

nationally and coordinate it with those

of other nations, and to furnish essential

services leading to accurate and uniform

measurements throughout the USA. These

responsibilities in the humidity sector

are discharged for NBS by the Humidity

Section. How this is done is depicted

in figure 4. Consider, first, the riBS responsibility

to provide the central basis for the humidity

sector of the National Measurement System.

This is accomplished primarily through

work in five areas: (a) measurement research,

(b) standards development, (c) development

of special instruments, (d) prototype

development and construction of secondary

standards, and (e) publication of monographs. Measurement research involves investigations

of the properties, constants and behavior

of water vapor and water vapor-gas systems

and the development and improvement of

methods of measurement. Examples include

the experimental determination of the enhancement of v;ater vapor in air [169],

the determination of the cross-virial

coefficients for moist air [170], the measurement of the vapor pressure of water at the triple point [171], and

the development of formulations for

the vapor pressure of water [172].

The development of new and improved

standards is a continuing process that

is designed to meet or anticipate the measurement calibration requirements

of commerce, industry, science and technology,

For example, there has been completed

recently a new precision humidity generator

for use in calibrating secondary and transfer standards. This will replace

an apparatus that has been in constant

use for over tv.'enty years [12,13].

Earlier, a low frost-point generator

was constructed capable of generating

trace quantities of water vapor down

to the parts per billion range [18].

The latter apparatus was built to meet

a need of the Viking-Mars lander orogram

for a facility capable of calibrating

sensors under simulated Martian atmospheric

conditions. A small humidity generator

also was designed and fabricated for NASA for use on life support system

studies [173].

The development of instruments for special applications is normally undertaken

at the request of other government agencies

and is usually intended to meet their

mission-oriented needs. Typical of

this type of work are a series of microwave

hygrometers designed for use on a joint

Navy-Forest Service warm air fog research

project [49], a heated-air adiabatic

saturation psychrometer for Air Force meteorological use [108], and a fastresponding humidity sensor for upper

air sounding, cloud physics research

and vapor flux measurements [109-111].

Prototype instruments are developed

to meet the needs for secondary and transfer standards. Such instruments must have accuracy, repeatability and reliability and, preferably, should

produce indications that can be predicted

by the laws of physics. Two examples

of such instruments are a pneumatic

bridge hygrometer [32] and an adiabatic

saturation psychrometer [36].

Publications are issued which provide

users of the measurement system with

information on instruments, methods

of measurement, sources of errors, and

NBS capabilities [55,93,174-176].
Table 13. ;i8S humidity calibration ranges and accuracies

Standard Ambient Conditions

of Test Gas Unit Range

. a Mccuracy

Gravimetric Standard atn. press. Mixing ratio, r,

g water vapor/kg

dry air

0.19 to 20 0.13 percent of value

Standard atm. press. Mixing ratio, r, g water vapor/kg

dry air

0.002 < r < 0.007 0.007 < r < 0.15

0.15 < r < 20

10 percent of value

3 percent of value

0.5 percent of value

Two-pressure

Humidity Generator

Standard atm. press. Dew/frost point,

T,,

d

-70 7 Td< -65 -65 T Td< -55

-55 - Td< -45 -45 r Ta< -30

-30 < Tj? +25

1.2 0.8

0.5 0.2

0.1

Standard atm. press. Volume ratio, V, ppm

2 7 V < 12

12 ? V < 250

250 ^ V 7 30,000

10 percent of value

3 percent of value

C.5 percent of value

Test chamber (gas) temperature, T^., "C -55 ^ T < -40 -40 < Tc < -30 -30 <Ti: t+60

Relative humidity,

percent

10 to 98

10 to 98

10 to 98

2.5

1.0 0.5

Standard atm. press. Mixing ratio, r,

g water vapor/kg

dry air

u . CO X iu '<r< u. 10 X lu 0.16 X 10-'<r< 0.024

0.024 <r< 0.233

< C pcrcfint of vslus

• 3.9 percent of value

< 2.2 percent of value

500 Pa (5 mb) Mixing ratio, r,

g water vapor/kg

dry air

0.0017 <r< 0.33 0.33 <r< 5

5 <r? 51

< 1 .6 percent of value

< 1.0 percent of value

< 0.8 percent of value

Low Frost-point Generator

Standard atm. press. Frost point

T »C

G -ICO to -30 0.05

Standard atm. press. Volume ratio,

V , ppm 0.014- V< 2.62.5 < V< 39 39 7Vr375

< 7.4 percent of value

< 3.9 percent of value

< 2.2 percent of value

500 Pa (5 mb) Volume ratio,

V, ppoi 2.8 < V < 500

500 < V < 8000

8000 < V r 82 ,000

< 1.6 percent of value

< 1 .0 percent of value

< 0.8 percent of value

Test chamber (gas) temperature, T^

,

Relative humidity,

percent

25

0 : -25 -50

-75

0.44 X 10"" to 1 .2 0.23 x 10-' to 6.2 0.22 X 10-2 to 60 0.036 to 53 1.15 to 45

0.5 X lO'^to 0.05

0.3 X 10-''to 0.32

2.9 X 10-Ho 3.6 0.005 to 4.0 0.14 to 4.3

Standard atm. press, and at test chamber

(gas) temperature

T,. 'C

Mixing ratio, r,

g water vapor Ag

dry air

050 0.55 to 3.76 8.3 to 32.7

< ^.9 percent of value

< 1 .4 percent of value

Selected

Saturated

Salt Solutions

Test chamber (gas) temperature , T^, 'c

050

Oew/frost point,

T,. =C -23.8 to -0.1

12.5 to 49 0.20.2

Standard atm. press,

and at test chamber

(gas) temperature,

T , °C

Volume ratio,

V , ppm

c

050 900 to 6,000

14,000 to 133,000

< 1.9 percent of value

< 1 .4 percent of value

Test chamber (gas) temperature, T^

,

Relative humidity, percent

050

15 to 99

11 to 96

< 1.9

< 1.4

^ The accuracy (maximum uncertainty) includes the estimated systematic errors plus three standard deviations

for the random errors.

28
It should be noted that not all users

of the humidity measurement system show

direct traceability to the iJBS primary

humidity standard. Some users establish

their ovm absolute methods of measurement,

use their own humidity generators,

or set up their own fixed points. Others

rely on a secondary standard without

NBS calibration. Some of the reasons

for this may be an ignorance of NBS services

or the cost of NBS calibrations. It

is difficult to estimate the percentage

of the system users who go their own way without tying directly or indirectly

with NBS. The NBS measurement services that

are available may be divided into four

categories: (a) calibration of plant

and laboratory standards, (b) evaluation

and testing of sensors for special government

programs, (c) test for compliance with

government procurement specifications,

and (d) tests for the public.

4.2.2 Users of MBS Services.

Instruments that are submitted for calibration as plant or laboratory standards

include the following: psychrometers , dew-point hygrometers, electric hygrometers,

coulometric hygrometers, infra-red hygrometers,

pneumatic bridges, paired-hydrate generators.

Table 19 is a list for the last ten years

of secondary standards calibrated by NBS and the manufacturers of these instruments.

The principal users of these instruments

are government and industry. The immediate

use of these instruments, for the most

part, is as laboratory standards. The

end purposes are varied, with aerospace,

instrument manufacturing and meteorology

predominating. A detailed breakdown

of users of instruments calibrated by NBS over the last ten years is given

in table 20.

4.2.3 Alternative Sources

The availability of humidity calibration

and testing services from other sources

has been mentioned in Section 2.4.3. Few,

if any, of these organizations have the necessary facilities for performing calibrations at the highest level accuracy. Within

the Federal Government there is equipment

at the U. S. Army Electronic Command

(Fort Monmouth, N. J.) that could be used for calibration purposes. Several

of the instrument manufacturers will

perform calibrations for customers.

The Standards Laboratory of the Sandia

Corporation (Albuquerque, N. H.) provides

services to the atomic energy community.

Calibration services for moisture

meters may be obtained from commercial

testing laboratories. The USDA has facilities

and the capabilities for providing calibrations

of moisture meters for grain and other

agricultural commodities. Several of the States, through their v;eights and measures

offices, can produce calibrations although

the States usually limit their operations

to enforcing compliance of instruments

with State laws and regulations.

flost well -equipped chemical laboratories

usually have the competence to perform

routine moisture measurements on a variety

of materials using oven drying methods,

Karl Fischer titrations and azeotropic

distillation procedures.

4.2.4 Funding Sources for NBS Services.

The establishment and maintenance

of national standards, the supporting

research and the determination of evaluated

data are functions that NBS supports

through funds obtained by direct appropriation

from Congress. The calibration and testing

services, whether to Government agencies

or to the public, are performed on a reimbursable basis. Other measurement activities

for Government agencies are funded by

those agencies requesting the work.

4.2.5 Mechanisms for Supplying Services.

Calibration and testing services are provided to a customer through the

submission by the latter of an acceptable

instrument. After the completion of

the work the instrument, together with

a report of calibration, is returned

to the customer. NBS sets no requirements

for the frequency of calibration.

4,3 Impact of NBS Services

It is difficult to establish the direct and irmediate economic impact

of NBS services on industry, commerce

and Government. It is even more difficult

to assess the indirect leverage that may be exerted on the final users of

the humidity and moisture measurement

system. Perhaps a quantitative picture

of this economic structure will eventually

evolve as more data are accumulated.

31
The first-line users of TIBS calibration

services have been identified in table

20. It is safe to assume that these services

support Government activities and industrial

and technological operations of sizeable

economic proportions. It is also safe

to assume that. IIBS has contributed

significantly to the measurement system

by providing advice, consultation, and

information to Government, industry,

colleges, universities, institutes, industrial

laboratories, and foreign agencies and

organizations (see Appendix F)

.

One instrument manufacturer

has stated: "There is no question in my mind that

NBS has played a very significant

role in the development

of the humidity instrumentation

business. Your facility is the only

one where a full -range, unbiased evaluation of a particular

humidity measuring sensor or system

can be conducted.

The typical $l-million-sales manufacturer

cannot justify the expense of operating

a two-pressure generator or similar

calibration facility. When one considers

that nearly 50 percent of all humidity

instruments are sold to the U. S. Government (either directly, or indirectly through contracts), much

of the industry thusly looks to Government

. users for comments on performance

(or, more specifically, to substantiate

manufacturer's claims--although I realize that this is not the desired

role of MBS), the actual role of NBS

is clearly seen. For example, if

it were not for the NBS facilities

during the space effort of the mid60' s, NASA laboratories all over the country would have had to develop

extensive and expensive facilities

to verify the performance of humidity

sensors employed in the critical life

support systems on the Apollo program. A similar case can be made for

humidity sensors applied on the Poseidon

program, where every submarine has between 32 and 64 optical hygrometers

which carry laboratory certifications

made against an NBS-cal ibrated

reference instrument. I am sure many manufacturers can trace ' NBS-verification

arguments' for the selection of their

sensor in a particular application."

NBS calibrations of a commercial

"dewcel "humidi ty probe for the National

Weather Service (NViS) contributed to the accuracy of the observations that

are and will be used for weather predictions.

NWS has an annual installation and replacement

rate of 100 of these units at a cost

of $400 each. In addition, units will

be installed at 500 airports at $500

each

.

Another case that may be cited is the procurement by DOO and NWS of carbon

sensors, at a cost of about $2 per unit,

for use in radiosonde flights. Approximately

150.000 sensors are flown annually.

Prototype samples are submitted to NBS

by these Government agencies for calibration

and lag tests when the accuracy of the

manufacturer's test facility is in question

or a new company needs to be qualified.

The Mars Viking Mission included

a vehicle which will land on the surface

of flars and seek evidence of life. Because humidity is one indicator of

life as we know it, early plans envisioned

measuring the humidity of the Martian

atmosphere. This atmosphere is essentially

CCo at a pressure of about 500 pascals

and at ambient temperatures as low as -100°C. NASA requested the assistance

of NBS in establishing traceable standards

for calibrating the humidity sensor

to be used for this measurement. NBS designed and built a humidity generator

capable of producing frost points as low as -100°C in a simulated Martian

atmosphere. Because of funding constraints,

NASA deleted the humidity experiment

from the Viking Mission. NBS retained

the generator and subsequently used

it to study and evaluate sensors for stratospheric humidity measurements

for DOT'S Climatic Impact Assessment

Program and for NASA tropopause and stratospheric meteorological investigations.

4.3.1 Economic Impact of Major User

Classes.

See Section 3.1.2.

4.3.2 Technological Impact of Service.

See Section 3.1.1.

4.3.3 Payoff From Changes in NBS Services.

See Section 4.3.

32
4.4 Evaluation of NBS Program

The NBS humidity measurements program

has been reviewed annually by the Evaluation

Panel of the National Academy of Sciences

(NAS) for the flechanics Division. This

Panel periodically has commented favorably

on the quality and content of the humidity

measurements program. However, the Panel

has noted that v^ork in humidity measurements

was somewhat outside of the specific

expertise of its past membership. Therefore,

it did not assess critically the scientific

content of the program. In 1974, NAS appointed to the Panel for the first

time a member with technical expertise

in the humidity measurements area. We can expect that the strengths and weaknesses

of the program will be evaluated in greater

depth and that helpful recommendations

vrill be forthcoming.

Although NBS currently has adequate

facilities and resources to meet most

of the measurement system user needs,

there still are some shortcomings. NBS

can furnish calibrations, through its

generators, over a wide range of humidities

(from ppb to 15 percent) and over ambient

temperatures from +60 to-100°C. Over most of this humidity range the ambient

pressure is restricted at present to atmospheric pressure; over a restricted

humidity range (ppb to 0.2 percent) ambient

pressures as low as 500 Pa (5 mb) can

be achieved. A new facility, which will soon become operational, will extend

the upper (high) end of the humidity

range to about 70 or 80 percent water

vapor content, allow ambient temperatures

as high as 90°C and ambient pressures

as high as 2 x 10^ Pa (2 bars) and as low as 25,000 Pa (1/4 bar). Even after

placing the new facility into use there

v;ill still be some deficiencies. There

will be no capability for performing

calibrations at high temperatures (above

100°C), such as encountered in drying

operations in lumber kilns. Nor will

there be any capability for calibrating

at pressures in excess of 2 x 10^ Pa

(2 bars), such as encountered in high pressure gas operations and process lines.

In the ppm and ppb regions our procedures

and techniques are constrained by practical

difficulties: low flow rates in the generator, long equilibration times and

high cost of operation.

The gravimetric hygrometer which serves

as the NBS primary standard is limited

in its capability of measuring very low

humidities (in the ppm and pob regions)

and at high humidities (where condensation

can occur). It is likely that another

absolute method will have to be developed

to cover these regions.

The NBS facilities are deficient in their capacity to perform response time

studies on humidity sensors. In providing

calibration and testing services the need often arises for measuring the lag

of a sensor. This can now be done only

partially. What is required is an apparatus

designed specifically to produce discrete

and rapid changes in humidity and having

the capability for adjusting such parameters

as the magnitudes and direction of the humidity change, the temperature, and

the total pressure.

4.5 The Future

There unquestionably will be a need

in the foreseeable future for NBS to continue to develop, improve, maintain

and promulgate standards and calibration

procedures for humidity measurement.

The new precision (two-pressure) humidity

generator that will soon become operational

should be capable of meeting the anticipated

calibration work loads for many years.

Plans have been drafted for coupling

this generator to a minicomputer, thus providing automatic operation as v^ell as automatic acquisition and processing

of data. The schedule for this latter

phase of the work is contingent on funding

and delivery dates. However, it is reasonable

to anticipate completion by 1976. NBS

will continue to provide critically evaluated

data on the pure v«ter substance and

on water vapor-qas systems.

In part as a result of this National Measurement System study, we have identified

serious deficiencies in the measurement

system for moisture, and have initiated

a program to resolve these. The objectives

of the work are (1) the development and promulgation of standards and calibration

procedures directly traceable to NBS;

(2) the evaluation, improvement and development

of methods and instruments for moisture

measurement; and (3) the development

of new principles of moisture measurement,

promulgation of evaluated data, and investigation

of phenomena and behavior of moisture

in materials. The initial effort will

be directed tovard solving several pressing

problems related to grain, particularly

to the grain moisture meter problem of

the State weights and measures comnunity.

Subsequently, moisture measurement problems

in other materials will be addressed.

33
5. SUMiMARY AND CONCLUSIONS

Humidity and moisture are quantities

which affect science, industry, commerce

and trade. Their measurement and control

are vital to our socio-economic system.

A broad spectrum of instrumentation,

from simple inexpensive devices to complex,

sophisticated, costly apparatus, is available. MBS maintains and disseminates

standards for humidity, exerts a leadership

role in advancing the state of the art,

and interacts with the technical community

to support the need of users for measurement

services

.

There are no national standards in moisture measurement directly traceable

to NBS. Although there is a documentary

specification system that includes several

different methods of moisture measurement

as reference standards, there is no general

agreement on which one to use. Because

of the economic impact that errors in measurement have on equity in trade,

conservation of fuel and energy, and

preservation of food and materials, it

is essential that NBS assume the responsibility

for establishing standards and improving

the moisture measurement system.

The humidity and moisture sector of

the National Measurement System supports

large and critical segments of our industry,

technology, agriculture and commerce.

It is essential that this system remain

strong and healthy in order to effectively

meet the continuing and growing measurement

needs of the country.

APPENDIX A. METHODOLOGY OF THE STUDY

The design of this study is given

by the outline of the contents. Basically,

five tasks were undertaken: (a) to describe

the humidity and moisture components

of the National Measurement System; (b) to determine the current status of these

components; (c) to analyze the major

societal impacts of these parts of the

system; (d) to identify important trends;

and (e) to examine how NBS interacts

v;ith the system.

Information and data were sought and

obtained from a variety of sources.

A major source was the expert knowledge

of the state of the art of the technical

staff of the Humidity Section. This

was augmented by data abstracted from

correspondence, calibration reports,

internal memoranda, visitor log books

and other documents in Section files.

The catalogs and technical literature

of instrument manufacturers were searched.

A compilation was made of manufacturers

who produce and sell humidity and moisture

instruments using internal catalog files,

and lists published in trade and technical

journals, and books. One hundred and

ninety manufacturers were then surveyed

for economic and marketing information.

Of these, 59 replied, 22 supplied sales

data and 19 supplied other marketing

information. These data were then augumented

by a limited number of Dun and Bradstreet

reports. Social and Economic Administration

Reports on Selected Instruments and Related Products, and data from the

U. S. Industrial Outlook for 1974 issued

by the Domestic and International Business

Administration. Selected agricultural

data were obtained fron Agricultural

Statistics 1974 issued by the U. S. Department of Agriculture.

The Section maintains in its files

a comprehensive bibliography and an - extensive collection of papers, reports,

publications, reprints, patents and

documents on the humidity and moisture.

This collection was searched to obtain

pertinent data on significant elements

of the measurement infrastructure and

for information on other aspects of

this study.

A workshop on moisture in grain, and one on the application of nuclear magnetic

resonance to moisture measurement were

held under NBS sponsorship. These provided

useful inputs from representatives from

trade associations, State weights and measures officials, industry and Government

on the status and problems of the moisture measurement technology. Numerous contacts in person and by

telephone and correspondence, both prior

to and during this study, were made

with calibration clientele. Government

agency sponsors of humidity work at

NBS and instrument manufacturers. Over

a period of many years. Section personnel

have provided advice, consultation,

and information to government, industry,

colleges and universities, institutes,

industrial laboratories, agencies and

other organizations of foreign countries.

These contacts have contributed to the store of wisdom in the staff which was tapped for this study.

Due to the constraints of time, manpower

and funding, the data base for this

study is heavily weighted with material

from accessible sources: staff wisdom,

Section files, technical and scientific

literature. Trends and forecasts represent

educated view-points of NBS staff members

and are not the result of a Delphi or more in-depth study.
APPENDIX 3. SUM:-1ARY OF BACKGROUND DOCUMENTS

1. Correspondence Files of Humidity

Section. These files contain letters

to and from Government agencies, industry,

colleges and universities, institutes,

industrial laboratories, agencies of foreign

governments and foreign research and commercial

organizations requesting information,

data, techniques, methods, procedures,

references and reprints on the measurement

system.

2. Calibration Reports. In addition

to calibration data, these reports contain

the names of the manufacturers of the

instruments submitted, data on the operating

principles of the instruments tested,

and the names of the users of the calibrated

instruments.

3. Visitors' Register. The name, affiliation

and purpose of each visitor is recorded.

4. Catalogs of Instrument Manufacturers.

The section maintains a file of catalogs

and other manufacturer's literature on humidity and moisture instrur.entation.

These v/ere used as a source cn the Instrumsenta- tion System.

5. Thomas Register. This publication

contains an extensive classified list

of manufacturers, their products, and

the magnitude of their tangible assets.

5. ISA Transducer Compendium. The chapter

on humidity lists manufacturers of humidity

sensors, together v/ith descriptions of

the performance characteristics of the

devices.

7. Survey of Instruments for Microneteorology

by J. L. ronteith, Blackwell Scientific

Publications, Oxford, 1972. This is a guide to the choice of comercial instrumentation.

It includes specifications and costs on hygrometers and moisture meters.

8. Moisture and Humidity, a staff survey

appearing in Measurements and Data, Jar-Feb

1S73. This article lists commercial instruments,

operating ranges, and costs.

9. Guide zo Scientific Instruments,

Science 182A, 27 November 1973. This

is a classified listing of instrument

manufacturers

.

10. Buyers' Guide 1974, Instruments and

Control Systems. This is a classified

listing of instrument manufacturers.

n. Current Industrial Reoorts. Selected

Instruments and Related Products 1971. Series: riA-3SB(71 -1 ) , March 1973, Bureau

of the Census. This publication contains

data on the auantity and value of shipr.ents

of selected instruments and related

products

.

12. U. S. Industrial Outlook 1974,

U. S. Dept. Comerce, Domestic and International

Business Administration. Assessments

are made of future trends for major

industrial manufactured orcducts , Data

are given on values of shipments.

13. U. S. Grain Standards Act As A.mended,

August 15, 1968. This is the enabling

legislation giving the L'SDA the legal

authority for promulgating regulations

and standards for grain crops entering

interstate and foreign commierce.

14. Grain Standards, Formal and Informal

Procedures, Rules and Peculations, Federal

Register, Monday, July S', 1974, Vol.

39_, :;o. 131, Part II. Amendments to tne U.S. Grain Standards Act.

15. Oven Methods for Moisture Determination,

GR Notice 1211, issued by USDA, Consumer

and Marketing Service, Grain Division,

11/15/71. Official USDA methods for

determining moisture in grain by oven drying methods.

16. USDA, Af-:S, Service and Regulatory Announcement No. 147, Revised March

1959, Method of Determining Moisture

Content as Specified in the Official

Grain Standards of the United States

and in the United States Standards for Beans, Peas, Lentils and Rice. Tr.is document specifies oven drying methods.

17. Agricultural Statistics 1973,

USDA, U. S. Government Printing Office,

Washington. This publication includes

data on the annual production, season average price received by farmer and

annual farm value of agricultural croos.

18. Dun and Bradstreet Reoorts . These

reports include marketing information

on a selected number of instrument manufacturers.

19. Partial List of Rapid Mois-u'-e-'esting

Devices for Grain and Related Commodities,

issued by the Grain Division, Consumer

and Marketina Service, USDA, January

1967.

20. A Partial List of Moisture "ester

Users, C. W. Brabender Instruments.

This is a list of companies, classified

35
by industry and product, who use the Brabender

oven drying tester for determining moisture

content.

21. How to Grade Grain, issued by Burrows Equipment Co. This publication contains

a condensed version of the procedures

and specification for grading grain condensed

from the Grain Grading Primer of the USDA.

22. Checks on Moisture Testers Urged,

by Tom Patrick, Des Moines, Iowa Register,

December 22 , 1968. A nev/spaper story

on wide range in readings obtained with

different moisture meters testing the

same samples of grain.

23. r.oisture and Its Measurement by I. Hlynka and A. D. Robinson in the Storage

of Cereal Grains and Their Products (J. A. Anderson and A. W. Alcock), American

Association of Cereal Chemistry, St. Paul,

1954. This chapter deals with the interrelationships between moisture and grain and the

methods used to measure moisture.

24. What Designers Should Know About

Humidity by A. P. Harris and E. W. Parrott,

Electronics, October 30, 1959. This article

discusses problems which designers of

ground and space electronic equipment

face with regard to humidity and moisture.

25. ASHRAE Guide and D:ita Book, American

Society of Heating Refrigerating and Air

Conditioning Engineers. This handbook

contains chapters on humidi fi cation ; sorption

dehumidi fication and pressure drying

equipment; process and product air conditioning;

printing plants; textile processing; factory

dehydrating, charging and testing; and moisture in refrigerant systems.

26. Handbook of Air Conditioning, Heating

and Ventilating by Strock and Koral . Industrial

Press, 1965. Data are given on the temperature

and humidity conditions for industrial

plants which manufacture or process a wide assortment of products. There are also included air conditioning design

criteria for commercial buildings and

transportation equipment.

27. Selected ASTt-1 Standards:

(a) E41-63 (Reapproved 1971), Standard

Definitions of Terms Relating to Conditioning.

These terms pertain to the conditioning

of materials for test purposes.

(b) E95-66, Standard Methods of Test

for Water Vapor Transmission of Materials

in Sheet Form. These methods cover determinations

of the rate of water vapor of materials

in sheet form. The methods are applicable

to materials such as paper, plastic films,

and sheet materials in general.

(c) E104-51 (Reapproved 1971), Recommended

Practice for Maintaining Constant Relative

Humidity by Means of Aqueous Solutions.

The methods use aqueous glycerin solutions,

aqueous sulfuric acid solutions and aqueous salt solutions.

(d) E171-63 (Reapproved 1972), Standard

Specification for Standard Atmospheres

for Conditioning and Testing f!aterials. This standard lists three acceptable

standard atmospheres of humidity and

temperature. It also lists conditioning

requirements for specific materials.

(e) E392-69T, Tentative Recommended

Practice for Equipment for Conditioned

Atmospheres: Temperature and Relative

Humidity. This recommended practice

covers performance and construction

requirements for equipment to be used

in obtaining conditioning atmospheres

of temperature and humidity in a space volume of 0.14 cm^ (5 ft^).

(f) E398-70, Standard Recommended Practice

1^or Dynamic Measurement of Water Vapor

Transfer. This recommended practice

covers dynamic evaluation of the rate

of transfer of v;ater vapor through a barrier material

.

28. Moisture in Grain Workshop. Internal NBS document of Mechanics Division summarizing

results of a meeting held on June 13,

1974, at NBS. Workshop was attended

by respresentati ves from Government,

industry, trade associations and weights

and measures officials. The workshop

drafted specific recommendations regarding

actions NBS should take concerning critical

problems in measuring and providing

standards for moisture in grain.

36
APPENDIX C. KANUFACTURERS OF HUfllDITY INSTRL'MEKTS AND CONTROLS

Dew "oint

Chandler Engineering Co'^ipany General Eastern Corporation Robbins Aviation, Inc. Comoustion Engineering Hankison Corporation Technology/Versatronico , Inc. Comp'jdyne Corporation Heavy-Duty Heating Equipment Co. Trans-Sonics , Inc. EG&G, Envi ronr-ental Ep. Div. Ipsen Industries, Inc. Tri-Met Associates, Inc.

Envi ronfTrental Tectonics Corp., Leone Engineering Company Vao-Air Division of Vapor Comercial Products Division Panametrics Corporation (Singer Co.) Foxboro Weiohina and Controls. Inc. Color Chanqe

0. C. Cooper Company Humidial Company Jacoby-Tarbox , Inc. Henry Valve Comsany Industrial Packaging Kahl Scientific Instrument

Products Company Corporation

Robbins Aviation, Inc. Electric

American Instrument Co. (Hygrodynamics) Gulton Industries, Inc., Thunder Scientific Corporation

Atlantic Instrument J Electronics, Inc. Rustrak Instr'jnent Div. Veskay Limited Baroer-Coleran Co., Industrial Instr. Div. Honeywell Victoreen Instrument Co. Beckman (Cedar Grove) Jelrus Technical Products Corp. VIZ Manufacturing

3ry-Air, Inc. Lab-Line Instruments, Inc. Waynco Inc. General Eastern Corporation Panametrics Cosa Corporation

Phys-Chemical Res. Corp.

mcnanical

Abbeon Climet Instrurents, Inc. Meteorology Research Inc. Airgu'ide Instrurnent Company D. C. Cooper Company New Jersey Safety Eq. Cu. American Moistening Co. Edroy Products Co., Inc. Pacific Transducer Corp.

Ai?stro Corporation Environmental Tectonics Corp. Philadelphia Scientific

Atkins Technical Company Commercial Products Div. Controls, Inc. Bacnaracn Instrument Company Epic, Inc. Phys-Chemical Res. Corp. Bahnscn Company Foxboro Powers Regulator Company

Earoer-Colem^n Co., Industrial Henry J. Green, Inc. Science Associates Inc. Instruments Div. E. Vernon Hill , Inc. Scientific Systems Corporation

Bel fort Instrument Company Honeywel

1

Taylor Instruments, Process Bendix Corporation, Environmental Impact Register, Inc. Control Div., Sybon Corporation

Science Division Johnson Service Company Testlab Civ. of GDI Inc. Bristol Div. of American Chain and Kahl Scientific Instrument Corp. Testing Machines, Inc. Cable Company Kent Cambridge Instrument Corp. Texas Electronics, Inc. Brooklyn Thermometer Co. Luft Instruments, Inc. Watrous and Company, Inc. CUmatronics Corporation Lux Scientific Instrument Corp. Weathermeasure Corporation Weksler Instrument Corporation Fsychrometric

Abbeon Environmental Tectonics Corp., Moeller Instrument Company

Airguide Instrument Company Corrmercial Products Div. Pacific Transducer Corporation

Al nor Epic, Inc. Partlow Corporation American Instrument Co. (Hygrodynamics) Esterline Angus Div., Esterline Corp. Phys-Chemical Research Corp. American ^;oistening Company Fischer and Porter Precision Themoneter anc American Standard, Inc . -Advanced Foxboro Instrument Com.pany Technical Products Division Gas Drying Princo Instruments, Inc. '^stro Corporation General Eastern Corporation Science Associates, Inc. Atkins Technical Company G. M. Hfg . and Instrument Corp. Scientific Systems Corp. Sacharach Instrument Company Henry J. Green, Inc. Sigma Instruments Inc. selfprt mstrir^nt Company Harrel , Inc. Taylor Instruments, Taylor Instruments, Process

Bsndi X ^.orpcr at i 0 n , Environmental H-B Instrument Company, Inc. Control Div.,Sybron Corp. Science Division E. Vernon Hill , Inc. Testing Machines, Inc. Blue ^ Electric Company Honeywel

1

Thunder Scientific Corporation

Bristol Div. of American Chain Integrated Development and Mfg. Co. H. 0. Trecice Company

and Cable Company Kahl Scientific Instrument Corp. U.G.C. Industries, Inc- Brooklyn Thermometer Company Leeds and Northrop Weathermeasure Corpora cion Cooling Tov/er Institute Leone Engineering Company Weksler Instrument Corp. Doric .Scientific Corporation Manning, Maxwell and Koore, Inc. Westronics, Inc. (subsidary of Environmental Technology Corp. Marshalltown Mfg., Inc. Tracer, Inc.) Mee Industries, Inc. Wilkerson Corporation

Yellow Sorinas Instruments Co. Coulometric 1

American Standard, Inc., General Eastern Corporation 01 in Corporation

Advanced Technical Products D1v. Kahn and Company, Inc. Process Analyzers, Inc. Beck.Tan, Scientific and Process Ilanufacturers ' Eng. and Eq. Corp. Science Associates, Inc. Instruments Division

E. I. DuPont de Nemours & Co.,

Instrur-»nt Prndii'ts Div. Diffusion

Lux Scientific Instrument Corporation

37
APPENDIX C (CONTINUED)

Saturation Salt Solutions (Dewcels and Ceworobes)

Atkins Technical Comoany

Bristol Oiv. of American Chain

and Cable Conpany Climatronics Corporation

Davis Instruments Hfg. Co., Inc. Thomas A. Edison Industries Foxboro

General Eastern Corporation

Honeywel

1

Science Associates, Inc. Weathermeasurs Corporation Yellow Springs Instrument Co.

Cloud Chamber

1

Alnor Instrunent Corporation

Block Associates , Inc

.

Spectroscopic (IP and UV)

Electromagnetic Research Corp. (Lyman a ) miks Scientific Corp. !

Piezoelectric Crystal

E. I. Uupont de Nemours S Co., Instrument Products Oiv.

Heat of Sorption

Mine Safety Appliances Conpany

38
;?PE'1DIX D. VANUFACTURErlS Or rCIST'JP.i "iTERS ANj COMROLS

Sravinatric

Central Scientific Company

Harry W. Dietert Company

Dynatronic Instrument Corporation

Greiner Scientific Corporation

Lab-Line Instrurents, Inc. Chaus Scale Corporation

Bracender Coroo'ation

C. W. Brabender Instruments, Inc. Scientific Supply Division

Kettronics, Inc. OAL Associates

'-ecision Scientific

A.msrican Crop Drying Ec. Co. Seedburo Equipment Company

Phipps S Bird, Inc. American Farm. Equipment It. Buhler Corporation

Dcoka, Tra'jcr.-^n J S^'r-.'-s, In,

Neutron Back Scatter

Kaiser Aerospace 4 Electronics Corp.

Seaiiian Nuclear Corporation

iCay-Ray, Inc. Testlab Civisicn cf GDI, Inc. Nuclear Chicago Corporation

E. I. DuFont de Hemours 4 Co. Instrjnent Products Division Newport of Mortn Anerica The Praxis Corporation

1 Karl Fischer

Sreiner Scientific Corporation

Technicon Corporation

Luft Instruments, Inc. Beckman Ins^rLinenis , Inc. 'recision Scientific Comoany

Centra" Scientific Company

Microwave

Acurex Corporation

.Rank Precision Industries, Inc. Anacon, Inc. Caltron industries. Inc. Microwave :nstrum,ents Comoan;

Mi seel 1 aneous

Mason-Neilan Division, <«orthington Corporation (pressure)

lietaMTiatic Co-c. (expandable cartridge)

Seicor Division Seismograon Science

Corp. (for ionizable solids' Taylor Instruments, ProcessControl Div. Syoron Co"-?. (radioisotcpes ]

Dielectric Constant

American ?1eter Controls, Inc. Brubaker Electronics

Burrows Eauiptnent Co. Fischer and Porter roxboro Cotnpany

Paul tl. Gardner Company Greiner Scientific Corp. Hallikainen Instruments

Honeywel

1

Hygrotester, Inc.

Moisture Register Company

^totomco Inc. Westpn Instrument

Laucks Laboratories, Inc.

F. H. Peavey and Companv

1

]

Infra-red

1

Anacon, Inc. Block Associates, Inc. Carle Instrun^erts , Inc.

General Electric Co., Instrument Dept. Moisture Register Company

Nucleonic Data Sys-ems, Inc.

Taylor Instruments, Rrtcess

Control Div., SyPron Corp. Testlab Division of GDI, Inc

1

1

i

Impedance and Resistance 'Conduction)

1

AAA Plastic Equipment, Inc. Agtronics Manufacturing Co.

Curtiss-'>*right Corp. Delcmorst Instrur'ent Co. Harry W. Dietert Company

Electronic Autoriaticn Systems, Inc. Epic, Inc. Hart Moisture .".eie's , Inc.

Henry Francis Parks Laboratory

Strandbe rg Engineeri ng La cs . , Inc. Security Engineering Weston Instruments

Tnwing-Al Pert Instrument Co. Chathan International Corp. Selco Electronics

Burrows Eouipment Company

Honeywell Kettronics, Inc.

H. T. HcGill , Inc. Marconi Instrument, Inc. National Instrument Comipany Skuttle .''anufacturing Co. Seedburo Equipment Co. 'ayior Enterprises, Inc. Chemalloy Electronics Corp.

[

1

Chroma tporaphy Hi

I aendix Corporation, Cincinnati Civ. Carle Instruments, Inc. Lpckwood S '^cLor-e, Inc.

Distillation

Seedburo Equipment Co. California Laooratory Eo. Co. Burrows Equipment Co. Gerber Sheet Metal , >c.

Coulometric

E. I. OuPont de Nemours 1 Co. Chemical Reaction 1

Heyl and Patterson, Inc. Alpha-Lux Company i

Power Less

Boor.ton Polytechnic Company

39
APPENDIX Z. SELECTEO COMPLIATIONS OF STANDARO REFERENCE DATA FOR HUMIDITY AND MOISTURE

SELECTED

DATA

1 COMPLIATIONS

ICT [62]IMT

[63] SMT[64]

1 HCP 1 LBT

1 [65] ; [55]

AG

i ST

[61] |[68-71]

D [72]

1 GG

i[73-75]

H [76] OTHER

GENERAL

Conversion factors 1

i

1 O • ! • 1 • 1 9 |r77.78T

Furda-ental constants 1 1 O 1 • . • 1 • ! 1 1781 LIQUID WATER

Oensi tv • • 1 • 9 1 9 1 [791 Oie'ectric constant •

1

1 • 9 ; 9

Electr-cal conductivity 1 Latent neat of vaoorization • —i 9 i *

1 9 ' 9 ! 1 [ao.aiT

Refractive index • ! Entnal Dv 19 19 9 1 9 ; 9 —reo.sii Soecific neat • • • 'sol 5cec:fic volume • 9 ' 9 9 9 9 9 7S Tho'"a! conductivitv • • 9 1 9 I •

Viscositv 1 • 1 _9 1_ 9 . [ 9

ICE Density • 1

! 1 Dielectric constant • 1 T82I

Electrical conductivity •

Latent heat of fusion • • [83,34]

Latent neat of suolimation • • Hi

Refractive index 1

. Enthalov • 1 e 9 ' 9

Soecific heat r—

C • 9 e

Soecific volume -.1^

Thenral conductivitv • «

1 9 1 DILATED (UNSATURATED) WATER VAPOP

Comoressibi 1 1 tv factor 9

Densi tv . • 1 . — 9

Dielectric constant •

Idea] qas thermo. functions 9 9 9 ^861 Enthal DV • 9 9 9

Soecific heat • 9 9 9

, ^ ...

Soecific volume 1 9. _ 9

Thermal conductivitv • • 1 • r-lViscositv • 9 9 9

Virial coefficients 9 1 « 9 9

SATURATED WATER VAPOR Compressibi 1 i tv factor 9 1 1 Critical data 9

Censitv • 9 * • •

Electrical conuuctivity

Enthalov • 9 9 9 9 9 rao.sn

Soecific heat • * • 9 9 9

Soecific volume 9 9 9 9 9 9 [80

1

Vaoor cressure of water e 9 9 9 9 9 9 •

Vapor pressure of sunorr-nlpd watpr • • 9 9 9 9

Vapor pressure of ice • 0 9 9 9 9 9

AIR Compos i ti on • 1 9 J ._• _ _

Coi:ipr9SSi bi 1 i ty factor 9

Dens i ty • « 9 9 9 9

Dielectric constant • 9

Ideal qas therto. functions 9 9

Refractive index • 9 9 9

Enthalpy 9 9 e

Specific heat • 9 9

Soecific volume 9 9 9

Thermal conductivity 9 9 9

Virial coefficients 9 9 9 «

Viscositv • 9 9 9

UATFR VAPOR AIR

Comoressibility factor 9 . 1 Density 9

Dielectric constant 1 :i77] Ennancenent factor * 9 9

Interaction [cross) virial coef f i ci ent 9 9

Mixina ratio at saturation • 9 9 9

Psvchrometric tables • 9 9

Refractive index 9 1771 1 Saturation -^nthalov 9 9 9 1 Saturation volume 9 9 1 ICT International Critical Tables AG ASHRAE Guide

IMT International Meteorological Tables ST Steam Tables

SMT Smithsonian Meteorological Tables D Properties of Ordinary Water-Substance by Dorsey

HCP Handbook of Chemistry and Physics GG Goff and Gratch Formulation

LBT Landolt-Bornstein Tabellen H Tables of Thermal Properties of Gases by HUsenrath

40
TtSFACES WITH USERS OF KL'CIDITY MEASURETIENTS SYSTEMS OVER THE PAST SECADE

(ADVICE, CONSULTATION, DISSE-IIHATION OF INFORMATION)

Forest Service NQJA

NCAA, Research Labs.

Nationa'! Weather Service

Air Force Camsridge Res. Labs. W-P Air Force Sase Army, At."cs:heric Research Labs. Anny, Aberdeen Proving Grounds Amy, HQ Desert Test Center Amv, NADIC Laboratories

GovemTOnt

Army, Night Vision Lab. (Fort Belvoir] Amy, White Sands >!issile Range

Naval Air Station

Naval Research Lab. Navy, Metrology Engineering Center (Panona) Office of Naval Research

U. S. Naval Acader.y

U. S. Naval Avionics Facility

L'. S. Naval Weapons Ouality

Assurance Office

Marine Engineering Lab. AEC Bureau of Mines Geological Survey

Dept. of Transportation

Federal Aviation Agency

EFA, SE Water Lab. Federal Trade Coroiission NASA, Anes Research Center

NASA, Goddard

NASA, Lang lev

Autonetics Helpar

Hughes Aircraft

Geotronics

Franklin GNO Hygrodynanics Martin-Marietta Harley

Plessy

Belolt

Pen Products Atonic Power Developnent Associates

Borg-Warner Trane

Enviroanental Technology Corporation

Ranco

Kellog

Deluihorst Instruments

Northpjp Carolina Factory Mutual Engineering

Boeing

Halley Carburetor

Industry

Bedonan Instruments

Honeywel

1

Technology /Versatronics

Ca.nbridge Syster.s Bendix, Aerospace Division TRW

Thunder Scientific

DuPont

Bendix, Research Labs. GE

Smith, Kline and French VIZ Nuclear-Chicago

Lennox Industries

Atkins Technical

General Dynamics, Electronics Div.

H. E. Sostran

Control Data

Gl (West Lynn) Motorola, Semiconductor Prod. Stackpole Carbon Minnesota Instrument

Vap-Air

IRC Bendix, Environmental Divison Transcontinental Gas Pipeline

Fairchild Hiller

Dow Chemical Panapetrics

Yellow Springs Instruments

Perr.a Pure Products

LTV Electrosystems

B. F. Goodrich Chemical Hankison Corporation

Gulf Energy 4 Environmental Systems

Haddan Mfg. Mee Industries Union Carbide, Linde Division

Wing Sperry Rand Wagner- Insul

L. S. & A. Electronics

Basic Inc. Sylvani a

Columbia University

Lehigp University

Lousiana State MIT

New Mexico State University

New York Unive-sity

Oregon State university

Penr State university

Co'leces and Universities

San Diego State College

San Jose State College

Soutn Dakota School of Mines

S Technology

Starford University University of Alaska University of California University of Connecticut

University University

University

Univer.';i ty University

University University

University

Utah State

of Hawaii

of Maryland

of Michigan

of Missouri

of Virginia

of Washington

of Wisconsin

of Wyoming University

Applied Physics Lab. AVCC Everett Research Lab.

Bell Teleshcne Labs. Bouser-Momer

Institutes, InCLStrial Labs. Etc. Esso Researcn Moore Business Foms-Res. Div. NCAR

Regional Science Res. Institute

Underwriter's Labs. Westinghouse Research Labs. Wylie Labs.

Australian National University

CSIRO, Oiv. rood Preservation

(Australia)

CSIRO. Div. Mech. Eng. (Australia) CSIRC. National Standard Lab. (Australia) London College of Printing University of Melbourne

(Austral ia) University of Western Australia

Canadian Meteorology Service

Mobil on Company, Ltd. (Canada)

NRC. Building Res. Div. (Canada) University of Guelph (Canada) Technical University (Czecnoslovakia)

Central Electrical Generating

Board (England)

Imperial Tobacco (England)

Foreign Meteorological Office (England) Hetrolocical Office (England) National Physical Laboratory (England) Radio and Space Res. Station (England)

Sira Institute, Ltd. (England) University of Reading (England) Centre Technique des Industries Aerauliques et Thermioues (France) Institut de Mecanioue Statistique

de la Turpulence (France) Laboratoire National C'Essais (France) Institut fur landwertschaftliche

Bauforschung (Germany) Kom S Berg (W. Germany)

Institute of Medical Physics

(Holland) Electrochemical Lab. (Japan) Japan Meteorology

National Res. Lab. of Metrology

(Japan)

Shizuoi.a University (Japan) Laboratory of Low Temp. (Netherlands)

CSIRC, Chem. Div. (New Zealand)

Det Norske Veritos (Norway) Polish CaniTiittee for Standization

and Measures

The National Institute for Materials

Testing (Sweden) Nestle Products Technical Assistance Co. (Switzerland)

Sina Limited (Switzerland) Instrument and Repair Calibration Center (Thailand)

The Scientific and Technical Research Council of Turkey

41
REFERENCES

Huntoon, R. D., Concept of a national measurement system, Science 1 58 , 67-71 (Oct. 1967).

Huntoon, R. D., The measurement

system of the United States, Proc. 1955 Standards Laboratory Conference,

Misc. Pub. 291, National Bureau

of Standards, 89-98 (Washington,

U. S. Gov. Print. Off., 1967).

Silverman, Shirleigh, The national measurement system, Mat. Res. Stds,

9, No. 10, 11-14 (1969).

Wexler, Arnold and Hyland, R. W. , The NBS standard hygrometer, NBS Monograph 73, May 1 , 1954 (U. S. Govt. Print. Off., Washington, D. C. 20402 )

.

Bongards , H. , Feuchtigkeitsmessung , 53-54 (Munchen, Oldenbourg, 1926.

Ibid, 64-75. Yates, John T. Jr. and Madey, T. E., NBS, Informal communication.

Mitchell, J., Jr., and Smith, D. M., Aquametry , p. 168-172 (Interscience,

New York, 1948).

Thuman, W. C. and Robinson, E., A technique for the determination

of water in air at temperatures

below freezing, J. Meteor. 1_1_, 214-219 (1954).

Weaver, E. R. and Riley, R. , Measurement

of mter in gases by electrical

conduction in a film of hygroscopic

material and the use of pressure

changes in calibration,

J. Res. NBS 40, 169-214 (1948).

Amdur, Eli as Jr., and White, Robert

W. , Two-pressure relative humidity

standards. Humidity and Moisture,

Editor-in-chief Arnold Wexler Vol

.

Ill, 445-454 (Reinhold Publishing

Corp. , New York, 1955)

.

Wexler, Arnold and Daniels, R. D.,

Jr., Pressure-humidity apparatus,

J. Res. NBS 48, 269-274 (1952).

Hasegav/a, S. , Hyland, R. W. and Rhodes, S. W., A comparison betv;een the National Bureau of Standards

two-pressure humidity generator

and the National Bureau of

Standards standard hygrometer.

Humidity and Moisture , loc. cit.

Vol . Ill, 455-459.

Shaw, W. N., Report on hygrometric

methods. Trans. Roy. Soc. London

179A , 73 (1888).

Wiegerink, J., G. , Equipment for conditioning materials at constant

humidities and at elevated temperature.

J. Res. NBS 24, 639 (1940).

[16] Burcham, J. N., A variable temperature and humidity oven, J. Sci. Instr. 30, 335 (1953). ~

[17] Edney, E. B., Construction and calibration of an electrical hygrometer

suitable for microclimatic measurements.

Bull. Entomol. Res. 44, 333 (1953).

[18] Greenspan, Lewis, Low frost-point

humidity generator, J. Res. NBS 77A , 571-677 (1973).

[19] Wexler, Arnold, Recirculating apparatus

for testing hygrometers, J. Res. NBS 45_, 357-362 (1950).

[20] Till, C. E. and Handegord, G. 0., New humidity standard. Trans. ASHRAE,

288 (1960).

[21] Wentzel , J. 0., An atmosphere producer

for laboratory use. Humidity and Moisture , loc. cit.. Vol. Ill, 461-466.

[22] Walker, A. C, Supplying atmospheres of known

humidity, Bell Lab. Record VII, 169 (1933).

[23] Gluckauf, E., Investigation on absorption hygrometers at low temperatures,

rJroc. Phys. Soc. London 59, 344 (1947).

[24] Wexler, Arnold, Divided fTow, low-temperature

humidity test apparatus, J. Res. NBS 40, 479-486 (1948).

[25] SmitFT P. R. , A new apparatus for the study of moisture sorption

by starches and other foodstuffs

in humidified atmospheres. Humidity

and Moisture, loc. cit, Vol . Ill

,

487-454.

[26] O'Keefe, A. E. and Ortman, G. C,

Anal. Chem. 38, 760 (1966).

[27] Kertzman, J., A new humidity generator.

Trans. Inst, Soc. /mer. 7_, 373-376 (1968).

[28] McKelvey, J. M. and Hoelscher,

H. E. , Apparatus for the preparation

of very dilute mixtures. Anal.

Chem. 29, 123 (1957).

[29] Gamache, L. D., A water vapor generator

for use in hygrometer calibration

and related fields. Analysis Instrumentation

3, 167-176 (1965).

[30] Wexler, Arnold Dew-point hygrometry.

Humidity and Moisture , loc. cit..

Vol . 1 , Section II, 125-2^,5.

[31] Sonntag , D., Hyorometrie , Chap.

6, p. 547-656, (Akademi e-Verl ag

,

Berlin, 1955-1958).

[32] Greenspan, Lewis, A pneumatic bridge

hygrometer for use as a working

humidity standard. Humidity and Moisture

loc. cit.. Vol. Ill, 433-443:

[33] Wildhack, W. A., Perls, T. A.,

et al , Continuous-absorption hygrometry

with a pneumatic bridge utilizing

critical flow. Humidity and floisture , loc. cit., Vol. 1 , 552-570.
[34] Wexler, Arnold,Psychronietry , Humidity

and Moisture , loc. eft., Vol . I

,

Section 1 , 3-121

.

[35] Sonntag, D. , Hygrometrie . , Chap.

4, 119-410. (Akademie-Verlag, Berlin,

1966-1958).

[36] Greenspan, Lewis and Wexler, Arnold,

An adiabatic saturation psychrometer

,

J. Res. NBS 72C. 33-47 (1968).

[37] Keidel, F. A., Determination of

v/ater by direct amperometric measurement,

Anal. Chem. 31_, 2043 (1959).

[38] Crawshaw, J. K. and Davidson, F. G., Electrolytic hygrometer for

the measurement of moisture in gases

down to a few parts per million,

J. Sci. Instr. 36, 121 (1959).

[39] Cole, L. G., CzuFa, M. , et al .

,

Continuous coulometric determination

of parts per million moisture in organic liouids. Anal. Chem. 31,

2048 (1959).

[40] Czuha, Michael, Jr., Adaptation

of the electrolytic moisture detector

to atmospheric humidity measurement.

Humidity and Moisture , loc. cit..

Vol. I, 522-528.

[41] Czuha, M. , Gardiner, K. W. , and

Sawyer, D. T. , The electrochemical

behavior and analytical applications

of the Pt -P2O5- H2O system, ' J. Electroanal. Chem. 4, 51 (1952).

[42] Jones, R. H., Additional performance

data on a new electrolytic hygrometer

cell. Humidity and Moisture , loc. cit., Vol. I, 507-511.

[43] Walker, J. A. J., and Campion, P.,

The use of electrolytic hygrometers

for the determination of H2O and

H2, Analyst 90, 199 (1965).

[44] Goldsmith, P. and Cox, L. C. , An improved electrolytic hygrometer,

J. Sci . Instr. 29-36 (1967).

[45] Bourke, P. J., and Dawson, R. W. , Investigation of the accuracy of the Goldsmith-Cox electrolytic hygrometer

at the lO'^atm level, J. Sci. Instr.

44, 87-89 (1967).

[45] Gray, P. S. and Gordon, I., A pressurized

Goldsmith-Cox hygrometer for plant

use at ultra-low humidities, J. Sci. Instr. 44, 84-36 (1967).

[47] Magee, J. B. and Grain, C. M. , Recording

microwave hygrometer, Rev. Sci. Instr. 29_, 51 (1958).

[48] Sargent, J., Recording microwave

hygrometer. Rev. Sci. Instr. 30, 348 (1959).

[49] Hasegawa, S. and Stokesberry, D.

,

Microwave hygrometer, fiBS Report

10 334, Sept. 1970.

[50] Wexler, Arnold and Hasegawa, Saburo,

Relative humidity-temperature relationships

of some saturated salt solutions

in the temperature range 0° to 50°C, J. Res. NBS 53, 19-25 (1954).

[51] Grover, D. W., and Nicol, J. M.,

The vapor pressure of glycerin

solutions at 20°, J. Soc. Chem.

Ind. 59, 175 (1940).

[52] Wilson, R. E., Humidity control

by means of sulfuric acid solutions

with a critical compilation of vapor pressure data, Ind. Eng. Chem. 1_3, 326 (1921 ). [53] Collins, E. M., The partial pressure

of water in equilibrium with aqueous solutions of sulfuric acid, J. Phys. Chem. 37, 1191 (1933).

[54] Montgomery, U7D., Googin, J. M. and Phillips, L. R., Moisture monitor

testing and calibration, Humidity and

Moisture, loc. cit.. Vol. Ill,

457-472.

[55] Wexler, Arnold, Measurement of

humidity in the free atmosphere

near the surface of the earth. Meteor. F'lonographs 11 , 262-282

(1970).

[55] Luck, Winfried, Feuchtigkeit , Chapter

9, (Oldenbourgh, Munchen, 1954).

[57] Shaffer, J. and Finley, C. M., Design

criteria of a new moisture monitor

for solids, Proc. Inst. Soc. Amer. 15_ (2) (1960).

[58] Czuha, M. and Gardener, K. W.,

Analysis of water in jet fuels,

Inst, and Control Syst. 34_, 2074

(1951 ). [59] Leibee, J. B. Electrolytic determination

of moisture in rubber and textiles,

Rubber Age 94, 924 (1964)

.

[60] Finley, C. M. and Shaffer, John,

The detection of parts per million

moisture in refrigerants,

Humidity and Moisture , loc. cit..

Vol. 1, 529-535.

[61] Mitchell, Jr., John and Smith,

Donald M. , Aquametry (Interscience

Publishers, Inc. New York, 194S).

[62] Washburn, E. W., (Editor),

International Critical Tables (McGraw-Hill

Book Co., New York, 1928 J. [63] Letestu, S. (Editor), International

Meteorological Tables , WM0-No.l88.

TP. 94 (World Meteorological Organization,

Geneva, Switzerland, 1965).

[64] List, Robert (Editor), Smithsonian

Meteorological Tables , Sixth Revised

Edition, (Smithsonian Institution,

Washington, D. C. 1951 ). [65] Weast, Robert C, Handbook of Chemistry

and Physics (The Chemical Rubber

Co. , Cleveland, Ohio).
[65] Landolt-Bornstein, Tabellen , Zuhlwerte

und Functonen, 5. Auflage, II (SpringeVerlag, Berlin, 1960).

[57] ASHRAE Guide and Data Book , (American

Society of Heating, Refrigerating

and Air Conditioning Engineers, 1972).

[63] Meyer, C. A,, McClintock, R. 3. Silvestri, G. J., and Spencer, Jr.,

R. C, ASME Steam Tables , (The American

Society of Mechanical Engi neers , flew York, M. Y., 1967).

[69] Keenan, J. H., Keyes , F. G., Hill,

P. G. and Moore, J. G., Steam Tables,

(John Wiley and Sons, Inc., New

York, M. Y., 1959).

[70] Bain, R. W. , MEL Steam Tables (Her

Majesty's Stationary Office, Edinburgh,

1964).

[71] Schmidt, Ernst, VDI-Wasserdamptabeln , (Springer-Verl ag , Berlin, 1968).

[72] Dorsey, N. E. , Properties of Ordinary

Water-Substance , (Reinhold Publishing

Corp. , Hew York, N. Y, 1940),

[73] Goff, John A. and Gratch, S., Low-pressure

properties of water from -160 to 212 F, ASHVE Trans. 52, 95 (1946).

[74] Goff, John A. and Gratch, S., Thermodynamic

properties of moist air. Heating,

Piping and Air Conditioning (ASHVE

Journal Section) 17, 334-348 (1945).

[75] Goff, John A., Fina'l Report of the

Working Subcommittee of the International

Joint Committee on Psychrometric

Data, ASME Trans. 71, 903-913 (1949).

[76] Hilsenrath, J. et aT. , Tables of

Thermal Properties of Gases , National Bureau of Standards Circular 564 , ^J. S. Govt. Print. Off., Washington,

D. C, 1955).

[77] Mechtly, E. A., The International

System of Units, Physical Constants

and Conversion Factors , NASA Sp-7012

(National Aeronautics and Space

Administration, U. S. Govt. Print.

Off., Washington, D. C, 1964).

[78] Cohen, E. Richard and Taylor, B. M., The 1973 least-squares adjustment

of the fundamental constants, J. Phys. Chem. Ref. Data 2, 663-734

(1973).

[79] Kel 1, G. S., Precise representation

of volume properties of water at one atmosphere, J. Chem. Eng. Data

12, 66 (1967).

[80] Osborne, U. S., Stimson, H. F. , and Ginnings, D. C. , Measurements

of heat capacity and heat of vaporization

of water in the range 0" to 100°C,

J. Res. NBS 23, 197-260 (1939).

[81] Osborne, N. S., Stimson, H. F.

,

and Ginnings, 0. C, Thermal properties

of saturated water and steam, J. Res. NBS 23, 261-270 (1939).

[82] Ginnings ,~!J. C. and Corruccini,

R. J., An improved ice calorimeter--the

determination of its calibration

factor and the density of ice at

0°C, J. Res. NBS 38, 583 (1947).

[83] Osborne, N. S., Heat of fusion

of ice, A revision, J. Res. NBS

23, 643 (1939).

[84] Dickinson, H. C. and Osborne, N. S., Specific heat and latent heat

of fusion of ice. Bull. Bur. Stds. 12, 49 (1915).

[85] Giauque, W. F, and Stout, J. W.,

The entropy and third law of thermodynamics.

The heat capacity of ice from 15

to 273°K, J. Amer. Chem. Soc. 58,

1144 (1936). "~

[86] Friedman, A. S. and Haar, L. , High-speed

machine computation of ideal gas thermodynamic functions. I. Isotopic water molecules, J. Chem. Phys.

22, 2051 (1934).

[87] FFanks, F. , Water, A Comprehensive Treatise , Vol. 1 (Plenum Press, New York,

1972).

[88] Glen, John W. , The Physics of Ice . Cold Regions Science and Engineering

Monograph II-C2a (Corps, of Engineers,

U. S. Army, Cold Regions Research

and Engineering Laboratory, Hanover).

[89] Riehl, N. , Bullemer, B. and Engelhardt,

H. , Physics of Ice (Plenum Press,

New York 1969).

[90] Shatenshtein , A. I., Yakaleva,

E. A., Zvyagintseva , E. N. , Varshavskii,

Ya. M. , Israilevich, E. J., and Dykhno, N. M., Isoptopic Water Analysis , U. S. Atomic Energy Commission

translation AEC-tr-4136, 2nd Edition

(1960).

[91] American Chemical Society Specifications,

Reagent Chemicals , 4th Edition

(Am. Chem. Soc, Washington, D. C,

r , 1968).

[92] Physical Society of London, Discussion on hygrometry (South Kensington, Nov.

25, 1921), Proc. Phys. Soc. Lond.

34, p. i-xcv (1921/1922).

[93] Wexler, Arnold (Editor-in-chief),

Humidity and Moisture , Volumes 1-4,

(Reinhold Publishing Corp., New York,

1965).

[94] International Measurement Confederation,

Proceedings of the IMEKO-Symposium

on Moisture Measurement, 5-8 October

1971, Esztergom, Hungary.

44
[95] Gregory, H. Spencer and Rourke, E. , Hyqrometry (Crosby Lockwood & Son,

Ltd., London, 1957).

[95] Pande, A., Modern Hyqrometry (Somaiya

Publications Pvt. Ltd., Bombay, 1970).

[97] Bongards, H. , Feuchti gkei tsmessung

^

( Oldenbourg, Munchen, 1925),

[98] Luck, Winfried, Feuchti gkei

t

(Oldenbourg,

Munchen, 1964).

[99] Sonntag, Dietrich, Hygrometrie (AkademieVerlag, Berlin, 1965-1968).

[100] Lapinski, M. , Kostyrko, K. , and Wlodarski,

W. , Nowoczesne Metody Pomiaru I Regulacji_ Wilj^otnosci (Wydawnictwa

fiaukowo-Techmczne , Warszawa, 1968).

[101] Steru, Mar i us, Masurarea A Electrica

Umidi tatu Materialelor (Editura

Tehnica, Bucuresti , 1957 )

.

[102] Berliner, M. A., Humidity Measurements

(Energy, Moscow, 1973). (In Russian),

[103] Ikeda, fiagayoshi , Humidity and Moisture Measurement , 1 955 (In Japanese).

[104] National Conference of Standard Laboratories

A Directory of Standard Laboratories , (National Bureau of Standards, 1967 Edition)

.

[105] U. S. Federal Supply Service, Directory

of U. S. Government Inspection Services

and iesting Laboratories , (U. S . ^ Govt. Print. Off., Washington D, C, 1967).

[106] GR Instruction 916-6 Equipment Manual,

Chapter XII, Oven methods for determining

moisture content of grain and related

agricultural commodities (U.S. Dept.

of Agriculture, Consumer and Marketing

Division 1971 ).

; [107] Perry, Chemical Engineer's Handbo ok,

i (5th Mc6raw-Hi I I , fiew York, 19/3).

; [108] Greenspan, Lewis, Heated air adiabatic

' saturation psychrometer , J. Res. NBS 75C 69-78 (1971 ). [109] Wexler, Arnold et al . , A fast responding

electric hygrometer, J. Res. NBS

55, 71-78 (1955).

[110] Jones, Frank E. and Wexler, Arnold,

A barium fluoride film hygrometer

element, J. Geophys. Res. 65, 2087-2095

(1960). ~

[111] Jones, Frank, Evaporated-film electric

hygrometer elements, J. Res. NBS

66C , 209-216 (1962).

I [112] Weaver, E, R., and Ledig, P. G. , Detector

j of water vapor in closed pipes,

i* Tech. Papers Bur. Stds . 17, 637,

(1 922-24); Ind. Eng. Chem. 1_5, 931

[ (1923).

[113] Weaver, E. R., Electrical measurement

of water vapor with a hygroscopic

film. Anal. Chem. 23, 1073 (1951).

[114] Weaver, E. R., Hughes, E. E., and Diniak,

A. W. , Determination of water

vapor from the change in electrical

resistance of a hygroscopic film,

J. Res. NBS 60, 489-508, (1958).

[115] Diamond, H.jTTimman, Jr., W. S. and Dunmore, F. W. , A method for the investigation of upper-air

phenomena and its application

to radio meteorography, J. Res. NBS 20, 369-392 (1938).

[116] Dunmore, F. W., An electric hygrometer

and its application to radio neteorograohy

,

J. Res. NBS 20, 723-744 (1933).

[117] Dunmore, F. 177, An im.proved electric

hygrometer, J. Res. NBS 23_, 701-714

(1939).

[118] Diamond, H. and Hinman, Jr., W.

S. , An automatic weather station,

J. Res. NBS 25, 133-148 (1940).

[119] Diamond, H. , Hinman, Jr., W. S., Dunmore,

F. W. and Lapham, E. G., An improved

radiosonde and its performance,

J. Res. NBS 25, 327-368 (1940).

[120] Weaver, E. R., Colorimetric determination

of acetylene and its applications

to the determination of water.

Bull . Bur. Stds. 13_ (1916-17).

[121] Kennedy, R. J., A method of determining

the dew points of fuel -air mixtures,

Bull. Bur. Stds. 20 (1924-26).

[122] Tryon, M. , An improved apparatus

for determining moisture in rubber

by distillation with toluene,

NBS J. Res. 45_, 362-365 (1 950).

[123] Weise, E. L., Burke, R. W. and Taylor, J. K. , Gas chromatograohi

c

determination of the moisture

content of grain, Humidity and Moist ure , loc. cit. , Vol . 4,

[124] Carson, F. T. and Worthington,

v.. Apparatus for determining

v;ater-vapor permeability

of moisture barriers, NBS Circular

453, (Nov. 8, 1946).

[125] Ziegler, C. A., and Schwebel , A., Techniques for monitoring

tritiated-water vapor in air. Nucleonics 1_5. '"^o- ^ > (1957).

[126] Wolfe, W. C, Differential dielectric

apparatus for determining water

added to solvents. Anal. Chem.

35, 1884-1887 (Nov. 1963).

[127] UFnes, F. E., Performance of the barium fluoride film hygrometer

element on radiosonde flights,

J. Geophys. Res. 68, 2735-2751

(1963).
[128] Jones, F. E. , Study of the storage

stability of the barium fluoride

film electric hygrometer element,

J. Res. , riBS 7K, 199 (1967).

[129] Cause, R. and Tucker, Jr., J.,

Method for determining the moisture

condition of hardened concrete.

J. Res. NBS 25_, 403-416 (1940).

[130] Carson, F. T. , Control of relative

humidity in a small enclosed space.

Paper Trade J. 93, 71 (1931 ). [131] Carson, F. T. , and Uorthington

,

F. v., Hygrometry in paper testing,

Paper Trade Jour. 94, No. 2, 34-42

(1932). "~

[132] Hasegawa, S., Garfinkel , S. B.

,

and Wexler, A., Simple humidity

lag apparatus, Rev. Sci . Instr.

26, 1196 (1955).

[133] Roth, F. L. and Stiehler, R. D. , Control of relative humidity and

temperature in rubber laboratory

of National Bureau of Standards,

Humidity and Moisture, loc. cit.,

Vol . 2, 287-292.

[134] Wexler, Arnold, Calibration of

humidity-measuring instruments

at the National Bureau

of Standards, Trans. Inst. Soc. Amer.

7, 356-362 (1968).

[135] Rosa. E. B. and Babcock, H. D. , On the variation of resistances with atmospheric

humidity. Bull. NBS 4, (1907-8).

[136] Weber, C. G. and Snyder, L. W. , Reactions of lithographic papers

to variations in humidity and

temperature, J. Res. NBS 12, 53-66

(1934). ~

[137] Carson, F. T. , Permeability of membranes

to water vapor with special reference

to packaging materials, NBS Miscellaneous

Publication 127 (1937).

[138] Carson, F. T., Effect of humidity

on physical properties of paper. , NBS Circular 445 (Jan. 31, 1944).

[139] McGowan, F. R. and Schoffstall , C. W., Tentative standard test methods

and percentages of oil and moisture

In hair and press cloths, Tech. Papers of the Bur. Stds. 17,

(1922-24). ~"

[140] Wiegerink, J. G. , Moisture relations

of textile fibers at elevated temperatures,

J. Res. NBS 24, 645-564 (1940).

[141] Schenke, E. M. , and Shearer, H.

E. , Strength and elongation of silk yarns as affected by humidity, NBS

J. Res. 25_, 783-790 (1940).

[142] Schenke, E. M. and Shearer, H. E. , Moisture content of thrown silk

affected by threads and twist. Southern

Knitter (Jan. 1940).

[143] Wier, J. E., Pons, D. C. and Axil rod,

B. M. , Effects of humidity during

fabrication of polyester laminates,

SPE J. 8, No. 9, 8 (1952)

.

[144] Scheiber, D. J. and Mead, D. J.,

Effect of absorbed water upon

the dielectric properties

of certain acrylic ester polymers,

J. Chem. Phys. 37, No. 1 , 81-84

(July 1962). ~

[145] Scott, A. H. and Harris, W. P.,

Long-time effects of humidity

change on the dielectric

properties of certain polymers,

(Proc. 1962 Annual Rept. Conf. Electrical Insul ation ,Hershey

,

Pa., Oct. 15-17, 1962), Nat'l.

Acad. Sci-Nat'l. Res. Council

Publ. 1080, 41-44 (1963).

[146] Scott, A. H., and Kinard, Jr.,

J. R., Polymeric materials for

dielectric reference specimens,

J. Res. NBS 71_C, 119-125 (1967).

[147] Kanagy, J. P., Effect of oxygen

and moisture on the stability of

leather at elevated temperatures,

J. Res. NBS 25, 149-160 (1940),

[148] Kanagy, J. R. , Adsorption of v/ater vapor by untanned hide and various

leathers at lOCF, NBS J. Res.

38, 119-128 (1947).

[149] Kanagy, J. R., Influence of temperature

on the adsorption of water vapor

by collagen and leather, J. Res, NBS 44, 31-46 (1950),

[150] Kanagy, J. R. , Influence of temperature

on the adsorption of water vapor

by collagen and leather, J. Amer. Leather Chemists Assn., 45, 12 (1950).

[151] Kanagy, J. R., and Vickers, R, A,, Factors affecting the water

vapor permeability of leather,

J, Amer, Leather Chemists Assoc,

45, 211 (1950).

[152] ATmer, H, E,, Response of microchemical

balances to changes in relative

humidity, J. Res, NBS 64C, 281 (1960),

[153] Brooks, Donald B., Correcting engine

tests for humidity, J. Res. NBS

3, 795-806 (1929).

[154] Wright, J. R. and Bowman, P. B.,

The effect of temperature and humidity

on the oxidation of air-blown asphalts.

Mater. Res, Std, 2, No, 12, 988-995

(Dec, 1962),

[155] Davis, J, C, and Achenbach, P. R,, An investigation of psychrometric measurement technique in air conditioning

calorimetry. Humidity and Moisture

loc, cit, , Vol , 2, 303-313,

46
[156] Loftus, i. P., Weaver, J. T., and Petrie, 3., Effect of humidity

on ionization neasurenents using

cavity and free-air chanfcers , Radiolocy

85, No. 1, 149 (Can. 1965).

[157] Sigler, P. A., Martens, R. I., and Koerner, E. A., Dimensional

changes of floor coverings with

changes in relative hunidity and temperature, N3S Building Materials

and Structures Report 85 (July

15, 1942).

[158] Weir, C. E., Kiqh-pressure apparatus

for conpressibility studies and

its application to measurenents

on leather and collacen, J. Res.

;JBS 45, 458-475 (1950).

[159] Weir, C. E., The influence of tenperature

and moisture on the electrical

properties of leather, J. Res. NBS 48, 349-359 (1952).

[160] Weir, C. E. , Effect of raisture

on compressibility of natural high

polvmers ,:oS J. Res. ^9, 135-139

(1952). —

[161] Hebert, R. L., and M.cDonell, A.

E. , Note on the Kubela method of

measuring water absorption of leather,

J. Ar.er. Leather Chemists Assoc.

57, No. % 451-469 (Sept. 1952),

[162] Kanagy, J. R. , Moisture permeation

of leatner and plastics used in shoes, J. Aner. Leather Chen. Assoc.

Tech. Note LXII, No. 2, 115-122

(Feb. 1967).

[153] Pitts, J. W. , and f-toore, D. G.

,

Apparatus for studying the e-fects

of atmospheric pollution and cyclic

dew formation on the deterioration

of materials. Mater. Res.

Std. 6, No. 7, 328-333 (July 1956).

[164] Diniak, A. W. , Hughes, E. E. , and Fujii , M. , Determination of water content in Freon-12 circulating

in a refrigeration system, Refrig.

Eng. 52, No. 2, 55 (1954).

[155] Bean, B. R. , and McGavin, R. E., The use of the radio refractometer

to measure water vapor turbulence.

Humidity and "oisture , loc. cit..

Vol . 2 , 561 -558

.

[156] Gates, D. M. , Vetter, J. and Thompson,

Ml. C, Measurement of moisture,

boundary layers and leaf transpiration

with a microwave refractometer.

Nature 197, 1070-1072 (Mar. 1953).

[167] Gates, D. M. , The measurement of

v<ater vapor boundary layers in biological systems with a radio

refractometer, Hum.idity and '-'oisture , loc.cit.. Vol. 2, 33-38. [158] Goltz, S. M. , Tanner, C. B., Thurtell

,

G. W. and Jones, F. E., Evaporation measurements by an eddy correlation

method. Water Resources 5, No.

2, 440-445 (1970).

[159] Hyland, Richard W. and Wexler,

Arnold, The enhancement of water

in carbon dioxide-free air at

30, 40 and 50°C. , J. Res. NBS

77A, 115-131 (1973).

[170] HyTand, Richard W. and Wexler,

Arnold, The second interaction

(cross) virial coefficient

for moist air. J. Res. NBS 77A , 133-147 (1973).

[171] Johnson, D. P., Guildner, L. A.,

and Jones, F. E., Vapor pressure

of water at its triple ooint (oresented

at the 8th International Conference

on the Properties of Water and Steam, Hveres-Gi ens , France, September

23-27, 1974).

[172] Wexler, Arnold and Greenspan,

Lewis, Vapor pressure equation

for water in the ranee

0 to 100°C, J. Res.^|ES 75A,

213-230 (1971).

[173] Little, J. W., and Hasegawa, S., A small continuous-flow humidity

generator, NBS Report 10 856 (1972).

[174] Wexler, Arnold end Brombacher,

W. G., Methods of measuring humidity

and testing hygrometers, NBS Circular 512, (U. S. Govt. Print.

Off., 'Washington, D. C, Sept.

28, 1951 , Price 20 cents).

[175] Wexler, Arnold, Electric hygrometers,

NBS Circular 585, U. S. Govt. Print. Off., Washinaton,

D. C, Sept. 3, 1 957 , Price 20 cents )

.

[176] Wexler, Arnold, Humidity standards,

TAPPI 44, 1S0A-191A, (1961).

[177] Smith, E. K. and Weintraub, S. , The constants in the equation for atmospheric

refractive index at radio freauencies,

Proc. I.R.E.,£1_, 1035-1037 (1953).

jSCCiVm .BS C

NBS-n4A (REV. 7-73)

U.S. DEPT. OF COMM.

QID( ir^/^DADUil^ DATA

SHEET

1. PUBLICATION OR RHl^ORT NO.

NBSIR 75-933

2. Gov't -Accession 3. Recipient's Accession No.

4. TITLE .\N'D SUBTITLE

A Study Of The National Hiimidity And Moisture Measurement

55v«! t em

—

5. Publication Date Aueust 1975

6. Performing Organization C^ode ^gx^ 221.06

7. AUTHORISE

Arnold Wexler

0. Performing Organ. Kopori No.

9. PERFOR.MLNG ORGANIZATION NA.ME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/I'ork Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

(Same as No. 9)

13. Type of Report & Period

Covered

Final

1 4 . bpons oring Agency Code

15. SUPPLE.MENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

This Study analyzes and assesses the status of the National Measurement System

for humidity and moisture. It focuses on the physical process of measuring and

controlling water vapor and moisture. It describes the nature, extent and

economic dimensions of the system. It indicates impacts and trends, identifies

deficiencies and shortcaaings and shows the role NBS plays in the system. The

study presents an overview of the complex structure of interrelated scientific,

technological, social and economic components that form the basis of this system.

17. KEY ^'ORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Humidity; humidity measurement system ;measurement of humidity; measurement of

moisture; moisture; moisture measurement system; water vapor.

18. AVAILABILITY [x^ Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

, For Official Distribution. Do Not Release to NTIS

UNCL ASSIFIED 51

1

' Order From Sup. of Doc, U.S. Government

Washington, D.C. 20402. SD Cat. No. C13

Printing Office 20. SECURITY CLASS

' THIS PAGE)

22. Price

1 T ' Order From National Technical Information

Springfield, Virginia 22151

Service (NTIS)

UNCLASSIFIED $ 4.50

USCOMM-DC 29042-F74