Humidity Measurement and Instrumentation
General Humidity Measurement Technology
A Technical article on General Humidity - Humidity Definitions, Details on Relative or Absolute Humidity, Practical Requirements of Humidy Measurement, State of the Technology and functional principles - from Vereta.
Notes on Relative Humidity - from the University of Illinois.
Atmospheric Moisture - Sample chapter from the textbook Meteorology Today by C. Donald Ahrens. (PDF 1.5MB 22 pages) - Thanks to www.novalynx.co.
Humidity Sensors for Industrial Applications - This paper reviews various humidity sensor technologies and their typical applications in context of the measurement ranges to which they are best suited. The effects of contamination, highly significant in view of the analytical nature of the measurement, are briefly assessed. In conclusion, it is suggested that, if initial cost is not the prime consideration, the chilled mirror, optical dew point hygrometer offer the most accurate, repeatable and reliable method of humidity measurement with the widest possible range - from Able Instruments and Controls - from Michell Instruments.
Cooled Mirror Sensor Technology - The optical condensation principle of dew point measurement has been established for centuries as the most fundamental method of determining the moisture content of a gas. The dewpoint temperature (that is, the temperature at which water vapour begins to condense to liquid or ice as the gas is cooled) describes precisely the moisture concentration of the gas. The major uncertainties in this measurement are related to the instantaneous detection of the on-set of condensation and the accuracy to which the temperature of the condensing surface can be measured. Early manual dew-point hygrometers suffered inaccuracies due to their cyclical nature, being cooled by an external coolant such as carbon dioxide or by the evaporation of a solvent, and also because of the time taken to produce an observable layer of condensate, often leading to an underestimation of the moisture content. The modern, automatic cooled mirror sensor addresses these deficiencies and also provides an instrument that is rugged and reliable enough to be applied to process control measurement as well as laboratory use - from Michell Instruments.
Moisture Sensor for the Measurement of Absolute Humidity in Process Air and Gases - This latest generation impedance dewpoint sensor combines fast response and high repeatability with long-term stability and resistance to contamination - from Michell Instruments.
Humidity Sensors - Humidity Sensors for Industrial Applications - It could be argued that humidity plays a part in every industrial production process. The very fact that our own atmosphere contains water vapour bears witness to this fact even if it is only that the end product is likely to be stored and eventually used in our environment; therefore, the product’s potential performance under varying conditions of humidity must be known. The extent to which humidity plays a part in any given production process may vary but in many cases it is essential that, at the very least, it is monitored and, in most cases, controlled. It may also be said that humidity is a more difficult property to define and measure than associated parameters such as temperature and pressure. Indeed, it is a truly analytical measurement in which the sensor must contact the process environment, in contrast to pressure and temperature sensors, which are invariably insulated from the process by a thermowell and a diaphragm respectively. This of course has implications for contamination and degradation of the sensor to varying degrees depending on the nature of the environment. This paper reviews various humidity sensor technologies and their typical applications in context of the measurement ranges to which they are best suited. The effects of contamination, highly significant in view of the analytical nature of the measurement, are briefly assessed. In conclusion, it is suggested that, if initial cost is not the prime consideration, the chilled mirror, optical dew point hygrometer offer the most accurate, repeatable and reliable method of humidity measurement with the widest possible range - from Able Instruments and Controls.
Metrology Humidity Technical Papers
The following technical papers are from gesensing:
- An Intercomparison of a Two-Pressure/Two-Temperature Frost Point Generator and Chilled Mirror Condensation Hygrometer
- Humilab Benchtop Humidity calibration system
- The Theory and Operation of Optical Chilled Mirror Hygrometers for Humidity Calibration
- Condensation Hygrometers as Humidity Transfer Standards
- A comparison of chilled mirror hygrometers
- Development of a Bench-Top Time Proportional Humidity Generator with Chilled Mirror Hygrometer Reference Standard
- The State of Pressure Uncertainty by Ken Kolb
- Differential Pressure Primary Standard - Technical Aspects
- Dew Point Measurement in Metal Heat Treatment
- The Effect of Air Laden Soluble Salts on Dew Point Measurement Using Condensation Hygrometers
Humidity Analysers - Theory and information of Condensation Chilled Mirror Hygrometers - from Able Instruments and Controls.
Moisture Analysers and Analysis
The following papers are from gesensing:
- Achieving Reliable Parts-Per-Billion Calibration of Moisture Analyzers
- Care of Grain: Guide to Professional Grainstore Management
- Dampness Measurement in Concrete Floors
- Ventilation, damp, mould & condensation feature article from "Housing Association Building and Maintenance"
- Online Moisture Analysis in Materials Handling - Graeme McGown - Moisture analysis during materials handling and processing presents a number of challenges that can be solved with appropriate use of online techniques - from Intalysis and www.processonline.com.au.
Natural Gas Moisture Measurement
Hydrocarbon Dew Point Technology - The condensation temperature of heavy hydrocarbon components in gas - commonly known as the hydrocarbon dew point - is a complex and difficult parameter to measure. Traditionally this measurement has been made using a manual optical technique based on the cooling of a mirrored surface in contact with the hydrocarbon gas mixture. Whilst it is possible, with experience and application, to obtain repeatable results with a manual dew-point hygrometer, the subjective nature of this technique yields it ever less applicable in today's de-regulated gas markets where continuous and precise measurement of this critical parameter are demanded - from Michell Instruments.
The following papers are from gesensing:
The War against Water - Ken Soleyn - Water even in small concentrations, poses large problems for the distribution of natural gas. Natural gas is dehydrated and treated prior to transportation and use, at considerable cost to the supplier and consumer. However attempts to reduce dehydration results in a reduction of 'gas quality' and an increase in maintenance costs and transportation, as well as potential safety issues. Consequently, to strike the right balance it is important that the water component of natural gas is measured precisely and reliably. A new instrument that utilises a tuneable diode laser is now available to continuously monitor the water concentration in natural gas and offers considerable advantages over traditional instrument technology.
Moisture Measurement in Natural Gas - Priya Rajesh - This article focuses on the basics of natural gas, why moisture measurement in natural gas is important and the various types of moisture measurement instruments.
The following technical articles are from Michell Instruments:
Moisture Measurement in Natural Gas - Thanks to Rolf Kolass, Michell Instruments GmbH, Friedrichsdorf Germany - Chris Parker, Michell Instruments Ltd, Cambridge, UK.
Hydrocarbon dew point of gas - Redeveloping Instrumentation to reduce the cost of ownership -Thanks to Jon Severn.
Hydrocarbon Dew-point - A Key Natural Gas Quality Parameter.
Pharmaceutical Humidity Measurement
Development of a Bench-Top Time Proportional Humidity Generator with Chilled Mirror Hygrometer Reference Standard - from gesensing.
Ultra High Purity Semiconductor Gases Moisture Measurements
Trace Moisture Measurement in Inert, Reactive and Corrosive Ultra High Purity Semiconductor Gases - from Able Instruments and Controls.
Moisture Behavior in Ultra-High Purity Gas Distribution Systems - The purpose of this Application Note is to familiarise users of CQC systems with the difficulty of making ultra-trace level moisture measurements, to set a practical expectation for moisture analyzer performance and to establish guidelines for the proper use of these analysers in controlling and monitoring moisture in UHP gases - from Delta F.
Detecting Single-Digit parts per billion Levels of Moisture in Ammonia Gas - Andrew O. Wright, Clayton D. Wood, Kimberly J. Reynolds and Mark L. Malczewski - An increasingly important chemical used in the manufacture of electronic devices such as high-intensity light-emitting diodes (LEDs) is ultrahigh-purity (UHP) anhydrous ammonia. However, the presence of residual trace moisture iUHP ammonia is a matter of concern. Especially in blue and white LEDs, there is a strong correlation between device performance and moisture content in the process ammonia used during manufacturing. In addition, increasing chemical consumption is forcing many facilities to use bulk storage tanks as a single supply source instead of cylinders as supply sources for individual tools. In light of these trends, it is imperative to have a robust, continuous process instrument with a single-digit parts-per-billion detection limit that can measure moisture in ammonia.
Humidity Tables - Humidity Charts - Humidity Calculator
Relative Humidity Tables - from the National Weather Forecast Centre.
Humidity Calculator - from the Australian Government Bureau of Meteorology.
Humidity Charts - from the Old Farmers Almanac.
Dew Point Temperature Table (Fahrenheit) - Also includes equations for calculating dew point temperature - from the University of Nebraska-Lincoln.
Humidity Calculator for Conversion of Humidity Measurements - The humidity calculator from E+E Elektronik is used for the rapid conversion of humidity measurements. Uniquely, the humidity calculator also includes measurement uncertainties in the calculation. This is helpful for obtaining realistic and reliable overall uncertainties based on the specification of the measuring device.
Thermal Processes using Electrolytic Hygrometers
Humidity Analysers - Product quality improvement with correct moisture measurement in thermal processes using electrolytic hygrometers - from Able Instruments and Controls.